Structural control of mixed ionic and electronic transport in conducting polymers

DOE PAGES

Rivnay, Jonathan; Inal, Sahika; Collins, Brian A.; ...

2016-04-19

Poly(3,4-ethylenedioxythiophene) doped with poly(styrenesulfonate), PEDOT:PSS, has been utilized for over two decades as a stable, solution-processable hole conductor. While its hole transport properties have been the subject of intense investigation, recent work has turned to PEDOT:PSS as a mixed ionic/electronic conductor in applications including bioelectronics, energy storage and management, and soft robotics. Conducting polymers can efficiently transport both holes and ions when sufficiently hydrated, however, little is known about the role of morphology on mixed conduction. Here, we show that bulk ionic and electronic mobilities are simultaneously affected by processing-induced changes in nano- and meso-scale structure in PEDOT:PSS films. Wemore » quantify domain composition, and find that domain purification on addition of dispersion co-solvents limits ion mobility, even while electronic conductivity improves. We show that an optimal morphology allows for the balanced ionic and electronic transport that is critical for prototypical mixed conductor devices. As a result, these findings may pave the way for the rational design of polymeric materials and processing routes to enhance devices reliant on mixed conduction.« less

Magnetospheric electrons

NASA Technical Reports Server (NTRS)

Coroniti, F. V.; Thorne, R. M.

1972-01-01

Coupling of source, transport, and sink processes produces a fairly accurate model for the macroscopic structure and dynamics of magnetospheric electrons. Auroral electrons are controlled by convective transport from a plasma sheet source coupled with a precipitation loss due to whistler and electrostatic plasma turbulence. Outer and inner zone electrons are governed by radial diffusion transport from convection and acceleration sources external to the plasmapause and by parasitic precipitation losses arising from cyclotron and Landau interactions with whistler and ion cyclotron turbulence.

The Electron Transport Chain: An Interactive Simulation

ERIC Educational Resources Information Center

Romero, Chris; Choun, James

2014-01-01

This activity provides students an interactive demonstration of the electron transport chain and chemiosmosis during aerobic respiration. Students use simple, everyday objects as hydrogen ions and electrons and play the roles of the various proteins embedded in the inner mitochondrial membrane to show how this specific process in cellular…

A solution-processed binary cathode interfacial layer facilitates electron extraction for inverted polymer solar cells.

PubMed

Zhang, Xinyuan; Li, Zhiqi; Liu, Chunyu; Guo, Jiaxin; Shen, Liang; Guo, Wenbin

2018-03-15

The charge transfer and separation are significantly affected by the electron properties of the interface between the electron-donor layer and the carrier-transporting layer in polymer solar cells (PSCs). In this study, we investigate the electron extraction mechanism of PSCs with a low temperature solution-processed ZnO/PEI as electron transport layer. The incorporation of PEI layer can decrease the work function of ZnO and reduce interfacial barrier, which facilitates electron extraction and suppresses bimolecular recombination, leading to a significant performance enhancement. Furthermore, PEI layer can induce phase separation and passivite inorganic surface trap states as well as shift the interfacial energy offset between metal oxide and organic materials. This work offers a simple and effective way to improve the charge transporting property of organic photovoltaic devices. Copyright © 2017 Elsevier Inc. All rights reserved.

Benchmark solution for the Spencer-Lewis equation of electron transport theory

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ganapol, B.D.

As integrated circuits become smaller, the shielding of these sensitive components against penetrating electrons becomes extremely critical. Monte Carlo methods have traditionally been the method of choice in shielding evaluations primarily because they can incorporate a wide variety of relevant physical processes. Recently, however, as a result of a more accurate numerical representation of the highly forward peaked scattering process, S/sub n/ methods for one-dimensional problems have been shown to be at least as cost-effective in comparison with Monte Carlo methods. With the development of these deterministic methods for electron transport, a need has arisen to assess the accuracy ofmore » proposed numerical algorithms and to ensure their proper coding. It is the purpose of this presentation to develop a benchmark to the Spencer-Lewis equation describing the transport of energetic electrons in solids. The solution will take advantage of the correspondence between the Spencer-Lewis equation and the transport equation describing one-group time-dependent neutron transport.« less

Microscopic dynamics research on the "mature" process of dye-sensitized solar cells after injection of highly concentrated electrolyte.

PubMed

Liang, Zhongguan; Liu, Weiqing; Chen, Jun; Hu, Linhua; Dai, Songyuan

2015-01-21

After injection of electrolyte, the internal three-dimensional solid-liquid penetration system of dye-sensitized solar cells (DSCs) can take a period of time to reach "mature" state. This paper studies the changes of microscopic processes of DSCs including TiO2 energy-level movement, localized state distribution, charge accumulation, electron transport, and recombination dynamics, from the beginning of electrolyte injection to the time of reached mature state. The results show that the microscopic dynamics process of DSCs exhibited a time-dependent behavior and achieved maturity ∼12 h after injecting the electrolyte into DSCs. Within 0-12 h, several results were observed: (1) the conduction band edge of TiO2 moved slightly toward negative potential direction; (2) the localized states in the band gap of TiO2 was reduced according to the same distribution law; (3) the transport resistance in TiO2 film increased, and electron transport time was prolonged as the time of maturity went on, which indicated that the electron transport process is impeded gradually; (4) the recombination resistance at the TiO2/electrolyte (EL) interface increases, and electron lifetime gradually extends, therefore, the recombination process is continuously suppressed. Furthermore, results suggest that the parameters of EL/Pt-transparent conductive oxide (TCO) interface including the interfacial capacitance, electron-transfer resistance, and transfer time constant would change with time of maturity, indicating that the EL/Pt-TCO interface is a potential factor affecting the mature process of DSCs.

Electron and hole transport in the organic small molecule α-NPD

NASA Astrophysics Data System (ADS)

Rohloff, R.; Kotadiya, N. B.; Crǎciun, N. I.; Blom, P. W. M.; Wetzelaer, G. A. H.

2017-02-01

Electron and hole transport properties of the organic small molecule N,N'-Di(1-naphthyl)-N,N'-diphenyl-(1,1'-biphenyl)-4,4'-diamine are investigated by space-charge-limited current measurements. The hole transport shows trap-free behavior with a mobility of 2.3 × 10-8 m2/Vs at vanishing carrier density and electric field. The electron transport, on the other hand, shows heavily trap-limited behavior, which leads to highly unbalanced transport. A trap concentration of 1.3 × 1024 m-3 was found by modeling the electron currents, similar to the universal trap concentration found in conjugated polymers. This indicates that electron trapping is a generic property of organic semiconductors, ranging from vacuum-deposited small-molecules to solution-processed conjugated polymers.

Magnetic-flutter-induced pedestal plasma transport

NASA Astrophysics Data System (ADS)

Callen, J. D.; Hegna, C. C.; Cole, A. J.

2013-11-01

Plasma toroidal rotation can limit reconnection of externally applied resonant magnetic perturbation (RMP) fields δB on rational magnetic flux surfaces. Hence it causes the induced radial perturbations δBρ to be small there, thereby inhibiting magnetic island formation and stochasticity at the top of pedestals in high (H-mode) confinement tokamak plasmas. However, the δBρs induced by RMPs increase away from rational surfaces and are shown to induce significant sinusoidal radial motion (flutter) of magnetic field lines with a radial extent that varies linearly with δBρ and inversely with distance from the rational surface because of the magnetic shear. This produces a radial electron thermal diffusivity that is (1/2)(δBρ/B0)2 times a kinetically derived, electron-collision-induced, magnetic-shear-reduced, effective parallel electron thermal diffusivity in the absence of magnetic stochasticity. These low collisionality flutter-induced transport processes and thin magnetic island effects are shown to be highly peaked in the vicinity of rational surfaces at the top of low collisionality pedestals. However, the smaller but finite level of magnetic-flutter-induced electron heat transport midway between rational surfaces is the primary factor that determines the electron temperature difference between rational surfaces at the pedestal top. The magnetic-flutter-induced non-ambipolar electron density transport can be large enough to push the plasma toward an electron density transport root. Requiring ambipolar density transport is shown to determine the radial electric field, the plasma toroidal rotation (via radial force balance), a reduced electron thermal diffusivity and increased ambipolar density transport in the pedestal. At high collisionality the various flutter effects are less strongly peaked at rational surfaces and generally less significant. They are thus less likely to exhibit flutter-induced resonant behaviour and transition toward an electron transport root. Magnetic-flutter-induced plasma transport processes provide a new paradigm for developing an understanding of how RMPs modify the pedestal structure to stabilize peeling-ballooning modes and thereby suppress edge localized modes in low collisionality tokamak H-mode plasmas.

Observational evidence of competing source, loss, and transport processes for relativistic electrons in Earth's outer radiation belt

NASA Astrophysics Data System (ADS)

Turner, Drew; Mann, Ian; Usanova, Maria; Rodriguez, Juan; Henderson, Mike; Angelopoulos, Vassilis; Morley, Steven; Claudepierre, Seth; Li, Wen; Kellerman, Adam; Boyd, Alexander; Kim, Kyung-Chan

Earth’s outer electron radiation belt is a region of extreme variability, with relativistic electron intensities changing by orders of magnitude over time scales ranging from minutes to years. Extreme variations of outer belt electrons ultimately result from the relative impacts of various competing source (and acceleration), loss, and transport processes. Most of these processes involve wave-particle interactions between outer belt electrons and different types of plasma waves in the inner magnetosphere, and in turn, the activity of these waves depends on different solar wind and magnetospheric driving conditions and thus can vary drastically from event to event. Using multipoint analysis with data from NASA’s Van Allen Probes, THEMIS, and SAMPEX missions, NOAA’s GOES and POES constellations, and ground-based observatories, we present results from case studies revealing how different source/acceleration and loss mechanisms compete during active periods to result in drastically different distributions of outer belt electrons. By using a combination of low-Earth orbiting and high-altitude-equatorial orbiting satellites, we briefly review how it is possible to get a much more complete picture of certain wave activity and electron losses over the full range of MLTs and L-shells throughout the radiation belt. We then show example cases highlighting the importance of particular mechanisms, including: substorm injections and whistler-mode chorus waves for the source and acceleration of relativistic electrons; magnetopause shadowing and wave-particle interactions with EMIC waves for sudden losses; and ULF wave activity for driving radial transport, a process which is important for redistributing relativistic electrons, contributing both to acceleration and loss processes. We show how relativistic electron enhancement events involve local acceleration that is consistent with wave-particle interactions between a seed population of 10s to 100s of keV electrons, with a source in the plasma sheet, and chorus waves. We show how sudden losses during outer belt dropout events are dominated at higher L-shells (L>~4) by magnetopause shadowing and outward radial transport, which is effective over the full ranges of energy and equatorial pitch angle of outer belt electrons, but at lower L-shells near the plasmapause, energy and pitch angle dependent losses can also occur and are consistent with rapid scattering by interactions between relativistic electrons and EMIC waves. We show cases demonstrating how these different processes occur simultaneously during active periods, with relative effects that vary as a function of L-shell and electron energy and pitch angle. Ultimately, our results highlight the complexity of competing source/acceleration, loss, and transport processes in Earth’s outer radiation belt and the necessity of using multipoint observations to disambiguate between them for future studies.

A Deterministic Computational Procedure for Space Environment Electron Transport

NASA Technical Reports Server (NTRS)

Nealy, John E.; Chang, C. K.; Norman, Ryan B.; Blattnig, Steve R.; Badavi, Francis F.; Adamcyk, Anne M.

2010-01-01

A deterministic computational procedure for describing the transport of electrons in condensed media is formulated to simulate the effects and exposures from spectral distributions typical of electrons trapped in planetary magnetic fields. The primary purpose for developing the procedure is to provide a means of rapidly performing numerous repetitive transport calculations essential for electron radiation exposure assessments for complex space structures. The present code utilizes well-established theoretical representations to describe the relevant interactions and transport processes. A combined mean free path and average trajectory approach is used in the transport formalism. For typical space environment spectra, several favorable comparisons with Monte Carlo calculations are made which have indicated that accuracy is not compromised at the expense of the computational speed.

Alcohol-Soluble Electron-Transport Materials for Fully Solution-Processed Green PhOLEDs.

PubMed

Chen, Fudong; Wang, Shirong; Xiao, Yin; Peng, Feng; Zhou, Nonglin; Ying, Lei; Li, Xianggao

2018-05-18

Two alcohol-soluble electron-transport materials (ETMs), diphenyl(4-(1-phenyl-1H-benzo[d]imidazol-2-yl)phenyl)phosphine oxide (pPBIPO) and (3,5-bis(1-phenyl-1H-benzo[d]imidazol-2-yl)phenyl)diphenylphosphine oxide (mBPBIPO), have been synthesized. The physical properties of these ETMs were investigated and they both exhibited high electron-transport mobilities (1.67×10 -4 and 2.15×10 -4  cm 2  V -1  s -1 ), high glass-transition temperatures (81 and 110 °C), and low LUMO energy levels (-2.87 and -2.82 eV, respectively). The solubility of PBIPO in n-butyl alcohol was more than 20 mg mL -1 , which meets the requirement for fully solution-processed organic light-emitting diodes (OLEDs). Fully solution-processed green-phosphorescent OLEDs were fabricated by using alcohol-soluble PBIPO as electron-transport layers (ETLs), and they exhibited high current efficiencies, power efficiencies, and external quantum efficiencies of up to 38.43 cd A -1 , 26.64 lm W -1 , and 10.87 %, respectively. Compared with devices that did not contain PBIPO as an ETM, the performance of these devices was much improved, which indicated the excellent electron-transport properties of PBIPO. © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Stepping stones in the electron transport from cells to electrodes in Geobacter sulfurreducens biofilms.

PubMed

Bonanni, Pablo Sebastián; Massazza, Diego; Busalmen, Juan Pablo

2013-07-07

Geobacter sulfurreducens bacteria grow on biofilms and have the particular ability of using polarized electrodes as the final electron acceptor of their respiratory chain. In these biofilms, electrons are transported through distances of more than 50 μm before reaching the electrode. The way in which electrons are transported across the biofilm matrix through such large distances remains under intense discussion. None of the two mechanisms proposed for explaining the process, electron hopping through outer membrane cytochromes and metallic like conduction through conductive PilA filaments, can account for all the experimental evidence collected so far. Aiming at providing new elements for understanding the basis for electron transport, in this perspective article we present a modelled structure of Geobacter pilus. Its analysis in combination with already existing experimental evidence gives support to the proposal of the "stepping stone" mechanism, in which the combined action of pili and cytochromes allows long range electron transport through the biofilm.

Solution processed metal oxide thin film hole transport layers for high performance organic solar cells

DOE Office of Scientific and Technical Information (OSTI.GOV)

Steirer, K. Xerxes; Berry, Joseph J.; Chesin, Jordan P.

2017-01-10

A method for the application of solution processed metal oxide hole transport layers in organic photovoltaic devices and related organic electronics devices is disclosed. The metal oxide may be derived from a metal-organic precursor enabling solution processing of an amorphous, p-type metal oxide. An organic photovoltaic device having solution processed, metal oxide, thin-film hole transport layer.

Coulomb Blockade and Multiple Andreev Reflection in a Superconducting Single-Electron Transistor

NASA Astrophysics Data System (ADS)

Lorenz, Thomas; Sprenger, Susanne; Scheer, Elke

2018-06-01

In superconducting quantum point contacts, multiple Andreev reflection (MAR), which describes the coherent transport of m quasiparticles each carrying an electron charge with m≥3, sets in at voltage thresholds eV = 2Δ /m. In single-electron transistors, Coulomb blockade, however, suppresses the current at low voltage. The required voltage for charge transport increases with the square of the effective charge eV∝ ( me) ^2. Thus, studying the charge transport in all-superconducting single-electron transistors (SSETs) sets these two phenomena into competition. In this article, we present the fabrication as well as a measurement scheme and transport data for a SSET with one junction in which the transmission and thereby the MAR contributions can be continuously tuned. All regimes from weak to strong coupling are addressed. We extend the Orthodox theory by incorporating MAR processes to describe the observed data qualitatively. We detect a new transport process the nature of which is unclear at present. Furthermore, we observe a renormalization of the charging energy when approaching the strong coupling regime.

Antiresonance and decoupling in electronic transport through parallel-coupled quantum-dot structures with laterally-coupled Majorana zero modes

NASA Astrophysics Data System (ADS)

Zhang, Ya-Jing; Zhang, Lian-Lian; Jiang, Cui; Gong, Wei-Jiang

2018-02-01

We theoretically investigate the electronic transport through a parallel-coupled multi-quantum-dot system, in which the terminal dots of a one-dimensional quantum-dot chain are embodied in the two arms of an Aharonov-Bohm interferometer. It is found that in the structures of odd(even) dots, all their even(odd) molecular states have opportunities to decouple from the leads, and in this process antiresonance occurs which are accordant with the odd(even)-numbered eigenenergies of the sub-molecule without terminal dots. Next when Majorana zero modes are introduced to couple laterally to the terminal dots, the antiresonance and decoupling phenomena still co-exist in the quantum transport process. Such a result can be helpful in understanding the special influence of Majorana zero mode on the electronic transport through quantum-dot systems.

Regulation of Photosynthetic Electron Transport and Photoinhibition

PubMed Central

Roach, Thomas; Krieger-Liszkay, Anja Krieger

2014-01-01

Photosynthetic organisms and isolated photosystems are of interest for technical applications. In nature, photosynthetic electron transport has to work efficiently in contrasting environments such as shade and full sunlight at noon. Photosynthetic electron transport is regulated on many levels, starting with the energy transfer processes in antenna and ending with how reducing power is ultimately partitioned. This review starts by explaining how light energy can be dissipated or distributed by the various mechanisms of non-photochemical quenching, including thermal dissipation and state transitions, and how these processes influence photoinhibition of photosystem II (PSII). Furthermore, we will highlight the importance of the various alternative electron transport pathways, including the use of oxygen as the terminal electron acceptor and cyclic flow around photosystem I (PSI), the latter which seem particularly relevant to preventing photoinhibition of photosystem I. The control of excitation pressure in combination with the partitioning of reducing power influences the light-dependent formation of reactive oxygen species in PSII and in PSI, which may be a very important consideration to any artificial photosynthetic system or technical device using photosynthetic organisms. PMID:24678670

METHES: A Monte Carlo collision code for the simulation of electron transport in low temperature plasmas

NASA Astrophysics Data System (ADS)

Rabie, M.; Franck, C. M.

2016-06-01

We present a freely available MATLAB code for the simulation of electron transport in arbitrary gas mixtures in the presence of uniform electric fields. For steady-state electron transport, the program provides the transport coefficients, reaction rates and the electron energy distribution function. The program uses established Monte Carlo techniques and is compatible with the electron scattering cross section files from the open-access Plasma Data Exchange Project LXCat. The code is written in object-oriented design, allowing the tracing and visualization of the spatiotemporal evolution of electron swarms and the temporal development of the mean energy and the electron number due to attachment and/or ionization processes. We benchmark our code with well-known model gases as well as the real gases argon, N2, O2, CF4, SF6 and mixtures of N2 and O2.

A Deterministic Transport Code for Space Environment Electrons

NASA Technical Reports Server (NTRS)

Nealy, John E.; Chang, C. K.; Norman, Ryan B.; Blattnig, Steve R.; Badavi, Francis F.; Adamczyk, Anne M.

2010-01-01

A deterministic computational procedure has been developed to describe transport of space environment electrons in various shield media. This code is an upgrade and extension of an earlier electron code. Whereas the former code was formulated on the basis of parametric functions derived from limited laboratory data, the present code utilizes well established theoretical representations to describe the relevant interactions and transport processes. The shield material specification has been made more general, as have the pertinent cross sections. A combined mean free path and average trajectory approach has been used in the transport formalism. Comparisons with Monte Carlo calculations are presented.

Effect of electron-electron scattering on the conductance of a quantum wire studied with the Boltzman transport equation

NASA Astrophysics Data System (ADS)

Lyo, S. K.; Huang, Danhong

2006-05-01

Electron-electron scattering conserves total momentum and does not dissipate momentum directly in a low-density system where the umklapp process is forbidden. However, it can still affect the conductance through the energy relaxation of the electrons. We show here that this effect can be studied with arbitrary accuracy in a multisublevel one-dimensional (1D) single quantum wire system in the presence of roughness and phonon scattering using a formally exact solution of the Boltzmann transport equation. The intrasubband electron-electron scattering is found to yield no net effect on the transport of electrons in 1D with only one sublevel occupied. For a system with a multilevel occupation, however, we find a significant effect of intersublevel electron-electron scattering on the temperature and density dependence of the resistance at low temperatures.

Breaking the barriers of all-polymer solar cells: Solving electron transporter and morphology problems

NASA Astrophysics Data System (ADS)

Gavvalapalli, Nagarjuna

All-polymer solar cells (APSC) are a class of organic solar cells in which hole and electron transporting phases are made of conjugated polymers. Unlike polymer/fullerene solar cell, photoactive material of APSC can be designed to have hole and electron transporting polymers with complementary absorption range and proper frontier energy level offset. However, the highest reported PCE of APSC is 5 times less than that of polymer/fullerene solar cell. The low PCE of APSC is mainly due to: i) low charge separation efficiency; and ii) lack of optimal morphology to facilitate charge transfer and transport; and iii) lack of control over the exciton and charge transport in each phase. My research work is focused towards addressing these issues. The charge separation efficiency of APSC can be enhanced by designing novel electron transporting polymers with: i) broad absorption range; ii) high electron mobility; and iii) high dielectric constant. In addition to with the above parameters chemical and electronic structure of the repeating unit of conjugated polymer also plays a role in charge separation efficiency. So far only three classes of electron transporting polymers, CN substituted PPV, 2,1,3-benzothiadiazole derived polymers and rylene diimide derived polymers, are used in APSC. Thus to enhance the charge separation efficiency new classes of electron transporting polymers with the above characteristics need to be synthesized. I have developed a new straightforward synthetic strategy to rapidly generate new classes of electron transporting polymers with different chemical and electronic structure, broad absorption range, and high electron mobility from readily available electron deficient monomers. In APSCs due to low entropy of mixing, polymers tend to micro-phase segregate rather than forming the more useful nano-phase segregation. Optimizing the polymer blend morphology to obtain nano-phase segregation is specific to the system under study, time consuming, and not trivial. Thus to avoid micro-phase segregation, nanoparticles of hole and electron transporters are synthesized and blended. But the PCE of nanoparticle blends are far less than those of polymer blends. This is mainly due to the: i) lack of optimal assembly of nanoparticles to facilitate charge transfer and transport processes; and ii) lack of control over the exciton and charge transport properties within the nanoparticles. Polymer packing within the nanoparticle controls the optoelectronic and charge transport properties of the nanoparticle. In this work I have shown that the solvent used to synthesize nanoparticles plays a crucial role in determining the assembly of polymer chains inside the nanoparticle there by affecting its exciton and charge transport processes. To obtain the optimal morphology for better charge transfer and transport, we have also synthesized nanoparticles of different radius with surfactants of opposite charge. We propose that depending on the radius and/or Coulombic interactions these nanoparticles can be assembled into mineral structure-types that are useful for photovoltaic devices.

49 CFR 272.105 - Requirement to file critical incident stress plan electronically.

Code of Federal Regulations, 2014 CFR

2014-10-01

... 49 Transportation 4 2014-10-01 2014-10-01 false Requirement to file critical incident stress plan...) FEDERAL RAILROAD ADMINISTRATION, DEPARTMENT OF TRANSPORTATION CRITICAL INCIDENT STRESS PLANS Plan Components and Approval Process § 272.105 Requirement to file critical incident stress plan electronically...

Electron transfer across a thermal gradient

PubMed Central

Craven, Galen T.

2016-01-01

Charge transfer is a fundamental process that underlies a multitude of phenomena in chemistry and biology. Recent advances in observing and manipulating charge and heat transport at the nanoscale, and recently developed techniques for monitoring temperature at high temporal and spatial resolution, imply the need for considering electron transfer across thermal gradients. Here, a theory is developed for the rate of electron transfer and the associated heat transport between donor–acceptor pairs located at sites of different temperatures. To this end, through application of a generalized multidimensional transition state theory, the traditional Arrhenius picture of activation energy as a single point on a free energy surface is replaced with a bithermal property that is derived from statistical weighting over all configurations where the reactant and product states are equienergetic. The flow of energy associated with the electron transfer process is also examined, leading to relations between the rate of heat exchange among the donor and acceptor sites as functions of the temperature difference and the electronic driving bias. In particular, we find that an open electron transfer channel contributes to enhanced heat transport between sites even when they are in electronic equilibrium. The presented results provide a unified theory for charge transport and the associated heat conduction between sites at different temperatures. PMID:27450086

Electron transport in single molecules: from benzene to graphene.

PubMed

Chen, F; Tao, N J

2009-03-17

Electron movement within and between molecules--that is, electron transfer--is important in many chemical, electrochemical, and biological processes. Recent advances, particularly in scanning electrochemical microscopy (SECM), scanning-tunneling microscopy (STM), and atomic force microscopy (AFM), permit the study of electron movement within single molecules. In this Account, we describe electron transport at the single-molecule level. We begin by examining the distinction between electron transport (from semiconductor physics) and electron transfer (a more general term referring to electron movement between donor and acceptor). The relation between these phenomena allows us to apply our understanding of single-molecule electron transport between electrodes to a broad range of other electron transfer processes. Electron transport is most efficient when the electron transmission probability via a molecule reaches 100%; the corresponding conductance is then 2e(2)/h (e is the charge of the electron and h is the Planck constant). This ideal conduction has been observed in a single metal atom and a string of metal atoms connected between two electrodes. However, the conductance of a molecule connected to two electrodes is often orders of magnitude less than the ideal and strongly depends on both the intrinsic properties of the molecule and its local environment. Molecular length, means of coupling to the electrodes, the presence of conjugated double bonds, and the inclusion of possible redox centers (for example, ferrocene) within the molecular wire have a pronounced effect on the conductance. This complex behavior is responsible for diverse chemical and biological phenomena and is potentially useful for device applications. Polycyclic aromatic hydrocarbons (PAHs) afford unique insight into electron transport in single molecules. The simplest one, benzene, has a conductance much less than 2e(2)/h due to its large LUMO-HOMO gap. At the other end of the spectrum, graphene sheets and carbon nanotubes--consisting of infinite numbers of aromatic rings--have small or even zero energy gaps between the conduction and valence bands. Between these two limits are intermediate molecules with rich properties, such as perylene derivatives made of seven aromatic rings; the properties of these types of molecules have yet to be fully explored. Studying PAHs is important not only in answering fundamental questions about electron transport but also in the ongoing quest for molecular-scale electronic devices. This line of research also helps bridge the gap between electron transfer phenomena in small redox molecules and electron transport properties in nanostructures.

Transport of secondary electrons and reactive species in ion tracks

NASA Astrophysics Data System (ADS)

Surdutovich, Eugene; Solov'yov, Andrey V.

2015-08-01

The transport of reactive species brought about by ions traversing tissue-like medium is analysed analytically. Secondary electrons ejected by ions are capable of ionizing other molecules; the transport of these generations of electrons is studied using the random walk approximation until these electrons remain ballistic. Then, the distribution of solvated electrons produced as a result of interaction of low-energy electrons with water molecules is obtained. The radial distribution of energy loss by ions and secondary electrons to the medium yields the initial radial dose distribution, which can be used as initial conditions for the predicted shock waves. The formation, diffusion, and chemical evolution of hydroxyl radicals in liquid water are studied as well. COST Action Nano-IBCT: Nano-scale Processes Behind Ion-Beam Cancer Therapy.

Intelligent Transportation System Strategic Plan For Las Vegas Valley

DOT National Transportation Integrated Search

1996-11-01

"INTELLIGENT TRANSPORTATION SYSTEMS" (ITS) IS A COLLECTIVE TERM FOR MEASURES TARGETING THE EFFICIENT OPERATIONS AND MANAGEMENT OF TRANSPORTATION FACILITIES AND SERVICES, USUALLY INVOLVING THE USE OF ELECTRONIC EQUIPMENT FOR COLLECTING,. PROCESSING, R...

Crossing Over: Nanostructures that Move Electrons and Ions Across Cellular Membranes

DOE PAGES

Ajo-Franklin, C. M.; Noy, A.

2015-04-27

Critical biological processes such as energy generation and signal transduction are driven by the flow of electrons and ions across the membranes of living cells. As a result, there is substantial interest in creating nanostructured materials that control transport of these charged species across biomembranes. The recent advances in the synthesis of de novo and protein nanostructures for transmembrane ion and electron transport and the mechanistic understanding underlying this transport are described. Moreover, this body of work highlights the promise such nanostructures hold for directing transmembrane transport of charged species as well as challenges that must be overcome to realizemore » that potential.« less

DOE Office of Scientific and Technical Information (OSTI.GOV)

Woo, Sung Oh; Teizer, Winfried; WPI-Advanced Institute for Materials Research, Tohoku University, Sendai

We report a deterioration of the electrical transport properties of a graphene field effect transistor due to energetic electron irradiation on a stack of Poly Methyl Methacrylate (PMMA) on graphene (PMMA/graphene bilayer). Prior to electron irradiation, we observed that the PMMA layer on graphene does not deteriorate the carrier transport of graphene but improves its electrical properties instead. As a result of the electron irradiation on the PMMA/graphene bilayer, the Raman “D” band appears after removal of PMMA. We argue that the degradation of the transport behavior originates from the binding of hydrogen generated during the PMMA backbone secession process.

Distribution of tunnelling times for quantum electron transport.

PubMed

Rudge, Samuel L; Kosov, Daniel S

2016-03-28

In electron transport, the tunnelling time is the time taken for an electron to tunnel out of a system after it has tunnelled in. We define the tunnelling time distribution for quantum processes in a dissipative environment and develop a practical approach for calculating it, where the environment is described by the general Markovian master equation. We illustrate the theory by using the rate equation to compute the tunnelling time distribution for electron transport through a molecular junction. The tunnelling time distribution is exponential, which indicates that Markovian quantum tunnelling is a Poissonian statistical process. The tunnelling time distribution is used not only to study the quantum statistics of tunnelling along the average electric current but also to analyse extreme quantum events where an electron jumps against the applied voltage bias. The average tunnelling time shows distinctly different temperature dependence for p- and n-type molecular junctions and therefore provides a sensitive tool to probe the alignment of molecular orbitals relative to the electrode Fermi energy.

Ultrahigh-efficiency solution-processed simplified small-molecule organic light-emitting diodes using universal host materials

PubMed Central

Han, Tae-Hee; Choi, Mi-Ri; Jeon, Chan-Woo; Kim, Yun-Hi; Kwon, Soon-Ki; Lee, Tae-Woo

2016-01-01

Although solution processing of small-molecule organic light-emitting diodes (OLEDs) has been considered as a promising alternative to standard vacuum deposition requiring high material and processing cost, the devices have suffered from low luminous efficiency and difficulty of multilayer solution processing. Therefore, high efficiency should be achieved in simple-structured small-molecule OLEDs fabricated using a solution process. We report very efficient solution-processed simple-structured small-molecule OLEDs that use novel universal electron-transporting host materials based on tetraphenylsilane with pyridine moieties. These materials have wide band gaps, high triplet energy levels, and good solution processabilities; they provide balanced charge transport in a mixed-host emitting layer. Orange-red (~97.5 cd/A, ~35.5% photons per electron), green (~101.5 cd/A, ~29.0% photons per electron), and white (~74.2 cd/A, ~28.5% photons per electron) phosphorescent OLEDs exhibited the highest recorded electroluminescent efficiencies of solution-processed OLEDs reported to date. We also demonstrate a solution-processed flexible solid-state lighting device as a potential application of our devices. PMID:27819053

One-dimension modeling on the parallel-plate ion extraction process based on a non-electron-equilibrium fluid model

NASA Astrophysics Data System (ADS)

Li, He-Ping; Chen, Jian; Guo, Heng; Jiang, Dong-Jun; Zhou, Ming-Sheng; Department of Engineering Physics Team

2017-10-01

Ion extraction from a plasma under an externally applied electric field involve multi-particle and multi-field interactions, and has wide applications in the fields of materials processing, etching, chemical analysis, etc. In order to develop the high-efficiency ion extraction methods, it is indispensable to establish a feasible model to understand the non-equilibrium transportation processes of the charged particles and the evolutions of the space charge sheath during the extraction process. Most of the previous studies on the ion extraction process are mainly based on the electron-equilibrium fluid model, which assumed that the electrons are in the thermodynamic equilibrium state. However, it may lead to some confusions with neglecting the electron movement during the sheath formation process. In this study, a non-electron-equilibrium model is established to describe the transportation of the charged particles in a parallel-plate ion extraction process. The numerical results show that the formation of the Child-Langmuir sheath is mainly caused by the charge separation. And thus, the sheath shielding effect will be significantly weakened if the charge separation is suppressed during the extraction process of the charged particles.

Study of certain features of the electronic structure of the ternary alloys Ni2(Mn, Fe) and Ni3(Mn, Co)

NASA Technical Reports Server (NTRS)

Zhukova, V. M.; Fadin, V. P.

1981-01-01

The changes in electronic structure related to transport processes occurring during the alloying of he alloy Ni3Mn with iron and cobalt, and the ordering of the ternary alloys thus formed are presented. The Hall effect, the absolute thermal emf, the internal saturation induction, the Nernst-Ettingshausen constant, and the electrical resistivity were measured. Results show a decrease in the contribution of hole sections of the Fermi surface to the transport process occurs together with a considerable increase in the contribution of electron sections. In this case, the mobility of 3 dimensional holes decreases and the mobility of 4s electrons increases considerably.

Short-term regulation and alternative pathways of photosynthetic electron transport in Hibiscus rosa-sinensis leaves.

PubMed

Trubitsin, Boris V; Vershubskii, Alexey V; Priklonskii, Vladimir I; Tikhonov, Alexander N

2015-11-01

In this work, using the EPR and PAM-fluorometry methods, we have studied induction events of photosynthetic electron transport in Hibiscus rosa-sinensis leaves. The methods used are complementary, providing efficient tools for in situ monitoring of P700 redox transients and photochemical activity of photosystem II (PSII). The induction of P700(+) in dark-adapted leaves is characterized by the multiphase kinetics with a lag-phase, which duration elongates with the dark-adaptation time. Analyzing effects of the uncoupler monensin and artificial electron carrier methylviologen (MV) on photooxidation of P700 and slow induction of chlorophyll a fluorescence (SIF), we could ascribe different phases of transient kinetics of electron transport processes in dark-adapted leaves to the following regulatory mechanisms: (i) acceleration of electron transfer on the acceptor side of PSI, (ii) pH-dependent modulation of the intersystem electron flow, and (iii) re-distribution of electron fluxes between alternative (linear, cyclic, and pseudocyclic) pathways. Monensin significantly decreases a level of P700(+) and inhibits SIF. MV, which mediates electron flow from PSI to O2 with consequent formation of H2O2, promotes a rapid photooxidation of P700 without any lag-phase peculiar to untreated leaves. MV-mediated water-water cycle (H2O→PSII→PSI→MV→O2→H2O2→H2O) is accompanied by generation of ascorbate free radicals. This suggests that the ascorbate peroxidase system of defense against reactive oxygen species is active in chloroplasts of H. rosa-sinensis leaves. In DCMU-treated chloroplasts with inhibited PSII, the contribution of cyclic electron flow is insignificant as compared to linear electron flow. For analysis of induction events, we have simulated electron transport processes within the framework of our generalized mathematical model of oxygenic photosynthesis, which takes into account pH-dependent mechanisms of electron transport control and re-distribution of electron fluxes between alternative pathways. The model adequately describes the main peculiarities of P700(+) induction and dynamics of the intersystem electron transport. Copyright © 2015 Elsevier B.V. All rights reserved.

Simulation of electron transport during electron-beam-induced deposition of nanostructures

PubMed Central

Jeschke, Harald O; Valentí, Roser

2013-01-01

Summary We present a numerical investigation of energy and charge distributions during electron-beam-induced growth of tungsten nanostructures on SiO2 substrates by using a Monte Carlo simulation of the electron transport. This study gives a quantitative insight into the deposition of energy and charge in the substrate and in the already existing metallic nanostructures in the presence of the electron beam. We analyze electron trajectories, inelastic mean free paths, and the distribution of backscattered electrons in different compositions and at different depths of the deposit. We find that, while in the early stages of the nanostructure growth a significant fraction of electron trajectories still interacts with the substrate, when the nanostructure becomes thicker the transport takes place almost exclusively in the nanostructure. In particular, a larger deposit density leads to enhanced electron backscattering. This work shows how mesoscopic radiation-transport techniques can contribute to a model that addresses the multi-scale nature of the electron-beam-induced deposition (EBID) process. Furthermore, similar simulations can help to understand the role that is played by backscattered electrons and emitted secondary electrons in the change of structural properties of nanostructured materials during post-growth electron-beam treatments. PMID:24367747

Interface Energetics and Chemical Doping of Organic Electronic Materials

NASA Astrophysics Data System (ADS)

Kahn, Antoine

2014-03-01

The energetics of organic semiconductors and their interfaces are central to the performance of organic thin film devices. The relative positions of charge transport states across the many interfaces of multi-layer OLEDs, OPV cells and OFETs determine in great part the efficiency and lifetime of these devices. New experiments are presented here, that look in detail at the position of these transport states and associated gap states and electronic traps that tail into the energy gap of organic molecular (e.g. pentacene) or polymer (P3HT, PBDTTT-C) semiconductors, and which directly affect carrier mobility in these materials. Disorder, sometime caused by simple exposure to an inert gas, impurities and defects are at the origin of these electronic gap states. Recent efforts in chemical doping in organic semiconductors aimed at mitigating the impact of electronic gap states are described. An overview of the reducing or oxidizing power of several n- and p-type dopants for vacuum- or solution-processed films, and their effect on the electronic structure and conductivity of both vacuum- and solution-processed organic semiconductor films is given. Finally, the filling (compensation) of active gap states via doping is investigated on the electron-transport materials C60 and P(NDI2OD-T2) , and the hole-transport polymer PBDTTT-C.

Electron Fluid Description of Wave-Particle Interactions in Strong Buneman Turbulence

NASA Astrophysics Data System (ADS)

Che, Haihong

2013-10-01

To understand the nature of anomalous resistivity in magnetic reconnection, we investigate turbulence-induced momentum transport and energy dissipation associated with electron heating in Buneman instability. Using 3D particle-in-cell simulations, we find that the macroscopic effects generated by wave-particle interactions can be described by a set of electron fluid equations. These equations show that the energy dissipation and momentum transports in Buneman instability are locally quasi-static but globally non-static and irreversible. Turbulence drag dissipates both the bulk energy of electron streams and the associated magnetic energy. The decrease of magnetic field maintains an inductive electric field that re-accelerates electrons. The net loss of streaming energy is converted into electron heat and increases the electron Boltzmann entropy. The growth of self-sustained Buneman waves satisfies a Bernoulli-like equation which relates the turbulence-induced convective momentum transport and thermal momentum transport. Electron trapping and de-trapping drives local momentum transports, while phase mixing converts convective momentum into thermal momentum.These two local momentum transports sustain the Buneman waves and act as the micro-macro link in the anomalous heating process. This research is supported by the NASA Postdoctoral Program at NASA/GSFC administered by Oak Ridge Associated Universities through a contract with NASA.

Insights into electron and ion acceleration and transport from x-ray and gamma-ray imaging spectroscopy

NASA Astrophysics Data System (ADS)

Hurford, Gordon J.; Krucker, Samuel

The previous solar maximum has featured high resolution imaging/spectroscopy observations at hard x-ray and gamma-ray energies by the Reuven Ramaty High Energy Solar/Spectroscopic Imager (RHESSI). Highlights of these observations will be reviewed, along with their impli-cations for our understanding of ion and electron acceleration and transport processes. The results to date have included new insights into the location of the acceleration region and the thick target model, a new appreciation of the significance of x-ray albedo, observation of coronal gamma-ray sources and their implications for electron trapping, and indications of differences in the acceleration and transport between electrons and ions. The role of RHESSI's observational strengths and weaknesses in determining the character of its scientific results will also be discussed and used to identify what aspects of the acceleration and transport processes must await the next generation of instrumentation. The extent to which new instrumentation now under development, such as Solar Orbiter/STIX, GRIPS, and FOXSI, can address these open issues will be outlined.

Crossing Over: Nanostructures that Move Electrons and Ions across Cellular Membranes.

PubMed

Ajo-Franklin, Caroline M; Noy, Aleksandr

2015-10-14

Critical biological processes such as energy generation and signal transduction are driven by the flow of electrons and ions across the membranes of living cells. As a result, there is substantial interest in creating nanostructured materials that control transport of these charged species across biomembranes. Recent advances in the synthesis of de novo and protein nanostructures for transmembrane ion and electron transport and the mechanistic understanding underlying this transport are described. This body of work highlights the promise such nanostructures hold for directing transmembrane transport of charged species as well as challenges that must be overcome to realize that potential. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Low-temperature solution-processed hydrogen molybdenum and vanadium bronzes for an efficient hole-transport layer in organic electronics.

PubMed

Xie, Fengxian; Choy, Wallace C H; Wang, Chuandao; Li, Xinchen; Zhang, Shaoqing; Hou, Jianhui

2013-04-11

A simple one-step method is reported to synthesize low-temperature solution-processed transition metal oxides (TMOs) of molybdenum oxide and vanadium oxide with oxygen vacancies for a good hole-transport layer (HTL). The oxygen vacancy plays an essential role for TMOs when they are employed as HTLs: TMO films with excess oxygen are highly undesirable for their application in organic electronics. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Two-fluid description of wave-particle interactions in strong Buneman turbulence

NASA Astrophysics Data System (ADS)

Che, H.

2014-06-01

To understand the nature of anomalous resistivity in magnetic reconnection, we investigate turbulence-induced momentum transport and energy dissipation while a plasma is unstable to the Buneman instability in force-free current sheets. Using 3D particle-in-cell simulations, we find that the macroscopic effects generated by wave-particle interactions in Buneman instability can be approximately described by a set of electron fluid equations. We show that both energy dissipation and momentum transport along electric current in the current layer are locally quasi-static, but globally dynamic and irreversible. Turbulent drag dissipates both the streaming energy of the current sheet and the associated magnetic energy. The net loss of streaming energy is converted into the electron component heat conduction parallel to the magnetic field and increases the electron Boltzmann entropy. The growth of self-sustained Buneman waves satisfies a Bernoulli-like equation that relates the turbulence-induced convective momentum transport and thermal momentum transport. Electron trapping and de-trapping drive local momentum transports, while phase mixing converts convective momentum into thermal momentum. The drag acts like a micro-macro link in the anomalous heating processes. The decrease of magnetic field maintains an inductive electric field that re-accelerates electrons, but most of the magnetic energy is dissipated and converted into the component heat of electrons perpendicular to the magnetic field. This heating process is decoupled from the heating of Buneman instability in the current sheets. Ion heating is weak but ions play an important role in assisting energy exchanges between waves and electrons. Cold ion fluid equations together with our electron fluid equations form a complete set of equations that describes the occurrence, growth, saturation and decay of the Buneman instability.

The best thermoelectric.

PubMed Central

Mahan, G D; Sofo, J O

1996-01-01

What electronic structure provides the largest figure of merit for thermoelectric materials? To answer that question, we write the electrical conductivity, thermopower, and thermal conductivity as integrals of a single function, the transport distribution. Then we derive the mathematical function for the transport distribution, which gives the largest figure of merit. A delta-shaped transport distribution is found to maximize the thermoelectric properties. This result indicates that a narrow distribution of the energy of the electrons participating in the transport process is needed for maximum thermoelectric efficiency. Some possible realizations of this idea are discussed. PMID:11607692

Transport of Space Environment Electrons: A Simplified Rapid-Analysis Computational Procedure

NASA Technical Reports Server (NTRS)

Nealy, John E.; Anderson, Brooke M.; Cucinotta, Francis A.; Wilson, John W.; Katz, Robert; Chang, C. K.

2002-01-01

A computational procedure for describing transport of electrons in condensed media has been formulated for application to effects and exposures from spectral distributions typical of electrons trapped in planetary magnetic fields. The procedure is based on earlier parameterizations established from numerous electron beam experiments. New parameterizations have been derived that logically extend the domain of application to low molecular weight (high hydrogen content) materials and higher energies (approximately 50 MeV). The production and transport of high energy photons (bremsstrahlung) generated in the electron transport processes have also been modeled using tabulated values of photon production cross sections. A primary purpose for developing the procedure has been to provide a means for rapidly performing numerous repetitive calculations essential for electron radiation exposure assessments for complex space structures. Several favorable comparisons have been made with previous calculations for typical space environment spectra, which have indicated that accuracy has not been substantially compromised at the expense of computational speed.

Observation of multi-channel non-local transport in J-TEXT plasmas

NASA Astrophysics Data System (ADS)

Shi, Yuejiang; Chen, Zhongyong; Yang, Zhoujun; Shi, Peng; Zhao, Kaijun; Diamond, Patrick H.; Kwon, JaeMin; Yan, Wei; Zhou, Hao; Pan, Xiaoming; Cheng, Zhifeng; Chen, Zhiping; Yang, SeongMoo; Zhang, Chi; Li, Da; Dong, Yunbo; Wang, Lu; Ding, YongHua; Liang, Yunfeng; Hahn, SangHee; Jhang, HoGun; Na, Yong-Su

2018-04-01

In cold pulse experiments in J-TEXT, not only are rapid electron temperature increases in the core observed, but also steep rises in the inner density are found. Moreover, some evidence of acceleration of the core toroidal rotation is also observed during the non-local transport process of electron temperature. These new findings of cold pulse experiments in J-TEXT suggest that turbulence spreading is a possible mechanism for the non-local transport dynamics.

Secondary electron generation, emission and transport: Effects on spacecraft charging and NASCAP models

NASA Technical Reports Server (NTRS)

Katz, Ira; Mandell, Myron; Roche, James C.; Purvis, Carolyn

1987-01-01

Secondary electrons control a spacecraft's response to a plasma environment. To accurately simulate spacecraft charging, the NASA Charging Analyzer Program (NASCAP) has mathematical models of the generation, emission and transport of secondary electrons. The importance of each of the processes and the physical basis for each of the NASCAP models are discussed. Calculations are presented which show that the NASCAP formulations are in good agreement with both laboratory and space experiments.

Improved electron transport properties of n-type naphthalenediimide polymers through refined molecular ordering and orientation induced by processing solvents.

PubMed

An, Yujin; Long, Dang Xuan; Kim, Yiho; Noh, Yong-Young; Yang, Changduk

2016-05-14

To determine the role played by the choice of processing solvents in governing the photophysics, microstructure, and charge carrier transport in naphthalenediimide (NDI)-based polymers, we have prepared two new NDI-bithiophene (T2)- and NDI-thienothiophene (TTh)-containing polymers with hybrid siloxane pentyl chains (SiC5) (P(NDI2SiC5-T2) and P(NDI2SiC5-TTh)). Among the various processing solvents studied here, the films prepared using chloroform exhibited far better electron mobilities (0.16 ± 0.1-0.21 ± 0.05 cm(2) V(-1) s(-1)) than the corresponding samples prepared from different solvents, exceeding one order of magnitude higher, indicating the significant influence of the processing solvent on the charge transport. Upon thin-film analysis using atomic force microscopy and grazing incidence X-ray diffraction, we discovered that molecular ordering and orientation are affected by the choice of the processing solvent, which is responsible for the change in the transport characteristics of this class of polymers.

Computational study of hot electron generation and energy transport in intense laser produced hot dense matter

NASA Astrophysics Data System (ADS)

Mishra, Rohini

Present ultra high power lasers are capable of producing high energy density (HED) plasmas, in controlled way, with a density greater than solid density and at a high temperature of keV (1 keV ˜ 11,000,000° K). Matter in such extreme states is particularly interesting for (HED) physics such as laboratory studies of planetary and stellar astrophysics, laser fusion research, pulsed neutron source etc. To date however, the physics in HED plasma, especially, the energy transport, which is crucial to realize applications, has not been understood well. Intense laser produced plasmas are complex systems involving two widely distinct temperature distributions and are difficult to model by a single approach. Both kinetic and collisional process are equally important to understand an entire process of laser-solid interaction. By implementing atomic physics models, such as collision, ionization, and radiation damping, self consistently, in state-of-the-art particle-in-cell code (PICLS) has enabled to explore the physics involved in the HED plasmas. Laser absorption, hot electron transport, and isochoric heating physics in laser produced hot dense plasmas are studied with a help of PICLS simulations. In particular, a novel mode of electron acceleration, namely DC-ponderomotive acceleration, is identified in the super intense laser regime which plays an important role in the coupling of laser energy to a dense plasma. Geometric effects on hot electron transport and target heating processes are examined in the reduced mass target experiments. Further, pertinent to fast ignition, laser accelerated fast electron divergence and transport in the experiments using warm dense matter (low temperature plasma) is characterized and explained.

Beyond Orbital-Motion-Limited theory effects for dust transport in tokamaks

DOE Office of Scientific and Technical Information (OSTI.GOV)

Delzanno, Gian Luca; Tang, Xianzhu

Dust transport in tokamaks is very important for ITER. Can many kilograms of dust really accumulate in the device? Can the dust survive? The conventional dust transport model is based on Orbital-Motion-Limited theory (OML). But OML can break in the limit where the dust grain becomes positively charged due to electron emission processes because it overestimates the dust collected power. An OML + approximation of the emitted electrons trapped/passing boundary is shown to be in good agreement with PIC simulations.

Development and fabrication of a solar cell junction processing system

NASA Technical Reports Server (NTRS)

Banker, S.

1982-01-01

Development of a pulsed electron beam subsystem, wafer transport system, and ion implanter are discussed. A junction processing system integration and cost analysis are reviewed. Maintenance of the electron beam processor and the experimental test unit of the non-mass analyzed ion implanter is reviewed.

Using Adobe Flash animations of electron transport chain to teach and learn biochemistry.

PubMed

Teplá, Milada; Klímová, Helena

2015-01-01

Teaching the subject of the electron transport chain is one of the most challenging aspects of the chemistry curriculum at the high school level. This article presents an educational program called "Electron Transport Chain" which consists of 14 visual animations including a biochemistry quiz. The program was created in the Adobe Flash CS3 Professional animation program and is designed for high school chemistry students. Our goal is to develop educational materials that facilitate the comprehension of this complex subject through dynamic animations which show the course of the electron transport chain and simultaneously explain its nature. We record the process of the electron transport chain, including connections with oxidative phosphorylation, in such a way as to minimize the occurrence of discrepancies in interpretation. The educational program was evaluated in high schools through the administration of a questionnaire, which contained 12 opened-ended items and which required participants to evaluate the graphics of the animations, chemical content, student preferences, and its suitability for high school biochemistry teaching. © 2015 The International Union of Biochemistry and Molecular Biology.

Charge transport and electron-hole asymmetry in low-mobility graphene/hexagonal boron nitride heterostructures

NASA Astrophysics Data System (ADS)

Li, Jiayu; Lin, Li; Huang, Guang-Yao; Kang, N.; Zhang, Jincan; Peng, Hailin; Liu, Zhongfan; Xu, H. Q.

2018-02-01

Graphene/hexagonal boron nitride (G/h-BN) heterostructures offer an excellent platform for developing nanoelectronic devices and for exploring correlated states in graphene under modulation by a periodic superlattice potential. Here, we report on transport measurements of nearly 0 ° -twisted G/h-BN heterostructures. The heterostructures investigated are prepared by dry transfer and thermally annealing processes and are in the low mobility regime (approximately 3000 cm2 V-1 s-1 at 1.9 K). The replica Dirac spectra and Hofstadter butterfly spectra are observed on the hole transport side, but not on the electron transport side, of the heterostructures. We associate the observed electron-hole asymmetry with the presence of a large difference between the opened gaps in the conduction and valence bands and a strong enhancement in the interband contribution to the conductivity on the electron transport side in the low-mobility G/h-BN heterostructures. We also show that the gaps opened at the central Dirac point and the hole-branch secondary Dirac point are large, suggesting the presence of strong graphene-substrate interaction and electron-electron interaction in our G/h-BN heterostructures. Our results provide additional helpful insight into the transport mechanism in G/h-BN heterostructures.

Ionospheric chemical releases

NASA Technical Reports Server (NTRS)

Bernhardt, Paul A.; Scales, W. A.

1990-01-01

Ionospheric plasma density irregularities can be produced by chemical releases into the upper atmosphere. F-region plasma modification occurs by: (1) chemically enhancing the electron number density; (2) chemically reducing the electron population; or (3) physically convecting the plasma from one region to another. The three processes (production, loss, and transport) determine the effectiveness of ionospheric chemical releases in subtle and surprising ways. Initially, a chemical release produces a localized change in plasma density. Subsequent processes, however, can lead to enhanced transport in chemically modified regions. Ionospheric modifications by chemical releases excites artificial enhancements in airglow intensities by exothermic chemical reactions between the newly created plasma species. Numerical models were developed to describe the creation and evolution of large scale density irregularities and airglow clouds generated by artificial means. Experimental data compares favorably with theses models. It was found that chemical releases produce transient, large amplitude perturbations in electron density which can evolve into fine scale irregularities via nonlinear transport properties.

Out-of-plane electron transport in finite layer MoS2

NASA Astrophysics Data System (ADS)

Holzapfel, R.; Weber, J.; Lukashev, P. V.; Stollenwerk, A. J.

2018-05-01

Ballistic electron emission microscopy (BEEM) has been used to study the processes affecting electron transport along the [0001] direction of finite layer MoS2 flakes deposited onto the surface of Au/Si(001) Schottky diodes. Prominent features present in the differential spectra from the MoS2 flakes are consistent with the density of states of finite layer MoS2 calculated using density functional theory. The ability to observe the electronic structure of the MoS2 appears to be due to the relatively smooth density of states of Si in this energy range and a substantial amount of elastic or quasi-elastic scattering along the MoS2/Au/Si(001) path. Demonstration of these measurements using BEEM suggests that this technique could potentially be used to study electron transport through van der Waals heterostructures, with applications in a number of electronic devices.

Lane Blockage Effects on Freeway Traffic Flow

DOT National Transportation Integrated Search

1996-09-01

Intelligent Transportation Systems (ITS) apply advanced and emerging technologies in such fields as information processing, communications, control, and electronics to surface transportation needs. ITS encompasses a number of diverse program areas in...

An easily accessible carbon material derived from carbonization of polyacrylonitrile ultrathin films: ambipolar transport properties and application in a CMOS-like inverter.

PubMed

Jiao, Fei; Zhang, Fengjiao; Zang, Yaping; Zou, Ye; Di, Chong'an; Xu, Wei; Zhu, Daoben

2014-03-04

Ultrathin carbon films were prepared by carbonization of a solution processed polyacrylonitrile (PAN) film in a moderate temperature range (500-700 °C). The films displayed balanced hole (0.50 cm(2) V(-1) s(-1)) and electron mobilities (0.20 cm(2) V(-1) s(-1)) under ambient conditions. Spectral characterization revealed that the electrical transport is due to the formation of sp(2) hybridized carbon during the carbonization process. A CMOS-like inverter demonstrated the potential application of this material in the area of carbon electronics, considering its processability and low-cost.

Control of electron transport routes through redox-regulated redistribution of respiratory complexes

PubMed Central

Liu, Lu-Ning; Bryan, Samantha J.; Huang, Fang; Yu, Jianfeng; Nixon, Peter J.; Rich, Peter R.; Mullineaux, Conrad W.

2012-01-01

In cyanobacteria, respiratory electron transport takes place in close proximity to photosynthetic electron transport, because the complexes required for both processes are located within the thylakoid membranes. The balance of electron transport routes is crucial for cell physiology, yet the factors that control the predominance of particular pathways are poorly understood. Here we use a combination of tagging with green fluorescent protein and confocal fluorescence microscopy in live cells of the cyanobacterium Synechococcus elongatus PCC 7942 to investigate the distribution on submicron scales of two key respiratory electron donors, type-I NAD(P)H dehydrogenase (NDH-1) and succinate dehydrogenase (SDH). When cells are grown under low light, both complexes are concentrated in discrete patches in the thylakoid membranes, about 100–300 nm in diameter and containing tens to hundreds of complexes. Exposure to moderate light leads to redistribution of both NDH-1 and SDH such that they become evenly distributed within the thylakoid membranes. The effects of electron transport inhibitors indicate that redistribution of respiratory complexes is triggered by changes in the redox state of an electron carrier close to plastoquinone. Redistribution does not depend on de novo protein synthesis, and it is accompanied by a major increase in the probability that respiratory electrons are transferred to photosystem I rather than to a terminal oxidase. These results indicate that the distribution of complexes on the scale of 100–300 nm controls the partitioning of reducing power and that redistribution of electron transport complexes on these scales is a physiological mechanism to regulate the pathways of electron flow. PMID:22733774

Connection between the membrane electron transport system and Hyn hydrogenase in the purple sulfur bacterium, Thiocapsa roseopersicina BBS.

PubMed

Tengölics, Roland; Mészáros, Lívia; Győri, E; Doffkay, Zsolt; Kovács, Kornél L; Rákhely, Gábor

2014-10-01

Thiocapsa. roseopersicina BBS has four active [NiFe] hydrogenases, providing an excellent opportunity to examine their metabolic linkages to the cellular redox processes. Hyn is a periplasmic membrane-associated hydrogenase harboring two additional electron transfer subunits: Isp1 is a transmembrane protein, while Isp2 is located on the cytoplasmic side of the membrane. In this work, the connection of HynSL to various electron transport pathways is studied. During photoautotrophic growth, electrons, generated from the oxidation of thiosulfate and sulfur, are donated to the photosynthetic electron transport chain via cytochromes. Electrons formed from thiosulfate and sulfur oxidation might also be also used for Hyn-dependent hydrogen evolution which was shown to be light and proton motive force driven. Hyn-linked hydrogen uptake can be promoted by both sulfur and nitrate. The electron flow from/to HynSL requires the presence of Isp2 in both directions. Hydrogenase-linked sulfur reduction could be inhibited by a QB site competitive inhibitor, terbutryne, suggesting a redox coupling between the Hyn hydrogenase and the photosynthetic electron transport chain. Based on these findings, redox linkages of Hyn hydrogenase are modeled. Copyright © 2014 Elsevier B.V. All rights reserved.

Theoretical Discussion of Electron Transport Rate Constant at TCNQ / Ge and TiO2 System

NASA Astrophysics Data System (ADS)

Al-agealy, Hadi J. M.; Alshafaay, B.; Hassooni, Mohsin A.; Ashwiekh, Ahmed M.; Sadoon, Abbas K.; Majeed, Raad H.; Ghadhban, Rawnaq Q.; Mahdi, Shatha H.

2018-05-01

We have been studying and estimation the electronic transport constant at TCNQ / Ge and Tio2 interface by means of tunneling potential (TP), transport energy reorientation (TER), driving transition energy DTE and coupling coefficient constant. A simple quantum model for the transition processes was adapted to estimation and analysis depending on the quantum state for donor state |α D > and acceptor stated |α A > and assuming continuum levels of the system. Evaluation results were performed for the surfaces of Ge and Tio2 as best as for multilayer TCNQ. The results show an electronic transfer feature for electronic TCNQ density of states and a semiconductor behavior. The electronic rate constant result for both systems shows a good tool to election system in applied devices. All these results indicate the

Influence of the electron-cation interaction on electron mobility in dye-sensitized ZnO and TiO2 nanocrystals: a study using ultrafast terahertz spectroscopy.

PubMed

Nemec, H; Rochford, J; Taratula, O; Galoppini, E; Kuzel, P; Polívka, T; Yartsev, A; Sundström, V

2010-05-14

Charge transport and recombination in nanostructured semiconductors are poorly understood key processes in dye-sensitized solar cells. We have employed time-resolved spectroscopies in the terahertz and visible spectral regions supplemented with Monte Carlo simulations to obtain unique information on these processes. Our results show that charge transport in the active solar cell material can be very different from that in nonsensitized semiconductors, due to strong electrostatic interaction between injected electrons and dye cations at the surface of the semiconductor nanoparticle. For ZnO, this leads to formation of an electron-cation complex which causes fast charge recombination and dramatically decreases the electron mobility even after the dissociation of the complex. Sensitized TiO2 does not suffer from this problem due to its high permittivity efficiently screening the charges.

Stable High-Performance Perovskite Solar Cells Based on Inorganic Electron Transporting Bi-layers.

PubMed

Gu, Hao; Zhao, Chen; Zhang, Yiqiang; Shao, Guosheng

2018-06-27

As one of the significant electron transporting materials (ETM) in efficient planar heterojunction perovskite solar cells (PSCs), SnO₂ can collect/transfer photo-generated carriers produced in perovskite active absorbers and suppress the carrier recombination at interfaces. In this study, we demonstrate that mild solution-processed SnO₂ compact layer can be an eminent ETM for planar heterojunction PSCs. Here, the device based on chemical-bath-deposited SnO₂ electron transporting layer (ETL) exhibits a power conversion efficiency (PCE) of 16.10% and with obvious hysteresis effect (hysteresis index=19.5%), owing to the accumulation and recombination of charge carriers at SnO₂/perovskite interface. In order to improve the carrier dissociation and transport process, an ultrathin TiO₂ film was deposited on the top of SnO₂ ETL passivating nonradiative recombination center. The corresponding device based on TiO₂@SnO₂ electron transporting bi-layer (ETBL) exhibited a high PCE (17.45%) and a negligible hysteresis effect (hysteresis index=1.5%). These findings indicate that this facile solution-processed TiO₂@SnO₂ ETBL paves a scalable and inexpensive way for fabricating hysteresis-less and high-performance PSCs. © 2018 IOP Publishing Ltd.

Development and fabrication of a solar cell junction processing system

NASA Technical Reports Server (NTRS)

1984-01-01

A processing system capable of producing solar cell junctions by ion implantation followed by pulsed electron beam annealing was developed and constructed. The machine was to be capable of processing 4-inch diameter single-crystal wafers at a rate of 10(7) wafers per year. A microcomputer-controlled pulsed electron beam annealer with a vacuum interlocked wafer transport system was designed, built and demonstrated to produce solar cell junctions on 4-inch wafers with an AMI efficiency of 12%. Experiments showed that a non-mass-analyzed (NMA) ion beam could implant 10 keV phosphorous dopant to form solar cell junctions which were equivalent to mass-analyzed implants. A NMA ion implanter, compatible with the pulsed electron beam annealer and wafer transport system was designed in detail but was not built because of program termination.

Diffusive vs. impulsive energetic electron transport during radiation belt storms

NASA Astrophysics Data System (ADS)

Vassiliadis, D.; Koepke, M.; Tornquist, M.

2008-12-01

Earth's electron radiation belts are continually replenished by inward particle transport (as well as other, local acceleration processes) taking place during radiation belt storms. For some storms the radial transport is primarily diffusive while for others it is impulsive, or characterized by injections. To distinguish between these types of inward transport, we first use a dynamic model of the phase-space density as measured by POLAR/HIST and expressed in terms of adiabatic invariants [Green and Kivelson, 2004]. In a review of storms from 1997 to 2004 the coefficients of the model are peaked at characteristic temporal and phase- space (mu, k, L*) scales during specific storms. The transport is quantified in terms of those invariants which are violated and identified with peaks of the electron distribution in invariant space. Second, we run guiding- center simulations in wave fields fitted to in situ measurements complemented at low and high L by ground ULF pulsations. The modes of response identified in earlier studies from SAMPEX and POLAR electron flux measurements are now associated with primarily diffusive transport in the central range of the outer belt, L=4-8, and primarily impulsive transport near the plasmapause boundary, L=3-4.

Veritable electronic characteristics in ZnO nanowire circuits uncovered by the four-terminal method at a low temperature

NASA Astrophysics Data System (ADS)

Li, Xin; Zhang, Qi

2017-04-01

Understanding the natural electrical properties in semiconductor channels and the carrier transport across the metal-semiconductor contact is essential to improve the performance of nanowire devices. This work presents the true electronic characteristics of ZnO nanowire devices measured by a four-electrode method at a low-temperature environment. The temperature rise leads to the decrease in near-band-gap emission, which is attributed to two non-radiative recombination processes. For ZnO circuits, thermionic emission carrier transport mechanism plays a dominant role at Ti-Au/ZnO interface and the transport mechanism in ZnO nanowires is governed by two competitive thermal activation conduction processes: optical or acoustic phonons assisting hopping.

Induced Infiltration of Hole-Transporting Polymer into Photocatalyst for Staunch Polymer-Metal Oxide Hybrid Solar Cells.

PubMed

Park, Jong Hwan; Jung, Youngsuk; Yang, Yooseong; Shin, Hyun Suk; Kwon, Soonchul

2016-10-05

For efficient solar cells based on organic semiconductors, a good mixture of photoactive materials in the bulk heterojunction on the length scale of several tens of nanometers is an important requirement to prevent exciton recombination. Herein, we demonstrate that nanoporous titanium dioxide inverse opal structures fabricated using a self-assembled monolayer method and with enhanced infiltration of electron-donating polymers is an efficient electron-extracting layer, which enhances the photovoltaic performance. A calcination process generates an inverse opal structure of titanium dioxide (<70 nm of pore diameters) providing three-dimensional (3D) electron transport pathways. Hole-transporting polymers was successfully infiltrated into the pores of the surface-modified titanium dioxide under vacuum conditions at 200 °C. The resulting geometry expands the interfacial area between hole- and electron-transport materials, increasing the thickness of the active layer. The controlled polymer-coating process over titanium dioxide materials enhanced photocurrent of the solar cell device. Density functional theory calculations show improved interfacial adhesion between the self-assembled monolayer-modified surface and polymer molecules, supporting the experimental result of enhanced polymer infiltration into the voids. These results suggest that the 3D inverse opal structure of the surface-modified titanium dioxide can serve as a favorable electron-extracting layer in further enhancing optoelectronic performance based on organic or organic-inorganic hybrid solar cell.

Charge transport in metal oxide nanocrystal-based materials

NASA Astrophysics Data System (ADS)

Runnerstrom, Evan Lars

There is probably no class of materials more varied, more widely used, or more ubiquitous than metal oxides. Depending on their composition, metal oxides can exhibit almost any number of properties. Of particular interest are the ways in which charge is transported in metal oxides: devices such as displays, touch screens, and smart windows rely on the ability of certain metal oxides to conduct electricity while maintaining visible transparency. Smart windows, fuel cells, and other electrochemical devices additionally rely on efficient transport of ionic charge in and around metal oxides. Colloidal synthesis has enabled metal oxide nanocrystals to emerge as a relatively new but highly tunable class of materials. Certain metal oxide nanocrystals, particularly highly doped metal oxides, have been enjoying rapid development in the last decade. As in myriad other materials systems, structure dictates the properties of metal oxide nanocrystals, but a full understanding of how nanocrystal synthesis, the processing of nanocrystal-based materials, and the structure of nanocrystals relate to the resulting properties of nanocrystal-based materials is still nascent. Gaining a fundamental understanding of and control over these structure-property relationships is crucial to developing a holistic understanding of metal oxide nanocrystals. The unique ability to tune metal oxide nanocrystals by changing composition through the introduction of dopants or by changing size and shape affords a way to study the interplay between structure, processing, and properties. This overall goal of this work is to chemically synthesize colloidal metal oxide nanocrystals, process them into useful materials, characterize charge transport in materials based on colloidal metal oxide nanocrystals, and develop ways to manipulate charge transport. In particular, this dissertation characterizes how the charge transport properties of metal oxide nanocrystal-based materials depend on their processing and structure. Charge transport can obviously be taken to mean the conduction of electrons, but it also refers to the motion of ions, such as lithium ions and protons. In many cases, the transport of ions is married to the motion of electrons as well, either through an external electrical circuit, or within the same material in the case of mixed ionic electronic conductors. The collective motion of electrons over short length scales, that is, within single nanocrystals, is also a subject of study as it pertains to plasmonic nanocrystals. Finally, charge transport can also be coupled to or result from the formation of defects in metal oxides. All of these modes of charge transport in metal oxides gain further complexity when considered in nanocrystalline systems, where the introduction of numerous surfaces can change the character of charge transport relative to bulk systems, providing opportunities to exploit new physical phenomena. Part I of this dissertation explores the combination of electronic and ionic transport in electrochromic devices based on nanocrystals. Colloidal chemistry and solution processing are used to fabricate nanocomposites based on electrochromic tin-doped indium oxide (ITO) nanocrystals. The nanocomposites, which are completely synthesized using solution processing, consist of ITO nanocrystals and lithium bis(trifluoromethylsulfonyl)amide (LiTFSI) salt dispersed in a lithium ion-conducting polymer matrix of either poly(ethylene oxide) (PEO) or poly(methyl methacrylate) (PMMA). ITO nanocrystals are prepared by colloidal synthetic methods and the nanocrystal surface chemistry is modified to achieve favorable nanocrystal-polymer interactions. Homogeneous solutions containing polymer, ITO nanocrystals, and lithium salt are thus prepared and deposited by spin casting. Characterization by DC electronic measurements, microscopy, and x-ray scattering techniques show that the ITO nanocrystals form a complete, connected electrode within a polymer electrolyte matrix, and that the morphology and properties of the nanocomposites can be manipulated by changing the chemical composition of the deposition solution. Careful application of AC impedance spectroscopy techniques and DC measurements are used to show that the nanocomposites exhibit mixed ionic and electronic conductivity, where electronic charge is transported through the ITO nanocrystal phase, and ionic charge is transported through the polymer matrix phase. The synthetic methods developed here and understanding of charge transport ultimately lead to the fabrication of a solid state nanocomposite electrochromic device based on nanocrystals of ITO and cerium oxide. Part II of this dissertation considers electron transport within individual metal oxide nanocrystals themselves. It primarily examines relationships between synthetic chemistry, doping mechanisms in metal oxides, and the accompanying physics of free carrier scattering within the interior of highly doped metal oxide nanocrystals, with particular mind paid to ITO nanocrystals. Additionally, synthetic methods as well as metal oxide defect chemistry influences the balance between activation and compensation of dopants, which limits the nanocrystals' free carrier concentration. Furthermore, because of ionized impurity scattering of the oscillating electrons by dopant ions, scattering must be treated in a fundamentally different way in semiconductor metal oxide materials when compared with conventional metals. (Abstract shortened by ProQuest.).

Nanopipettes for Metal Transport

NASA Astrophysics Data System (ADS)

Svensson, K.; Olin, H.; Olsson, E.

2004-09-01

Here we demonstrate, for the first time experimentally, a nanopipette action for metals using multiwalled carbon nanotubes. The process relies on electromigration forces, created at high electron current densities, enabling the transport of material inside the hollow core of carbon nanotubes. In this way nanoparticles of iron were transported to and from electrically conducting substrates.

Nanopipettes for metal transport.

PubMed

Svensson, K; Olin, H; Olsson, E

2004-10-01

Here we demonstrate, for the first time experimentally, a nanopipette action for metals using multiwalled carbon nanotubes. The process relies on electromigration forces, created at high electron current densities, enabling the transport of material inside the hollow core of carbon nanotubes. In this way nanoparticles of iron were transported to and from electrically conducting substrates.

Solar energetic particle transport and the possibility of wave generation by streaming electrons

NASA Astrophysics Data System (ADS)

Strauss, R. D. T.; le Roux, J. A.

2017-12-01

After being accelerated close to the Sun, solar energetic particles (SEPs) are transported (mainly) along the turbulent interplanetary magnetic field. In this study, we simulate the propagation of 100 keV electrons as they are scattered in the interplanetary medium. A consequence of these wave-particle interactions is the possible modification (either growth or damping) of the background turbulence by anisotropic SEP electron beams. This process was thought to be negligible, and therefore neglected in past modeling approaches. However, recent observations and modeling by Agueda and Lario (2016) suggest that wave generation may be significant and is therefore included and evaluated in our present model. Our results suggest that wave amplification by streaming SEP electrons is indeed possible and may even significantly alter the background turbulent field. However, the simulations show that this process is much too weak to produce observable effects at Earth's orbit, but such effects may well be observed in future by spacecraft closer to the Sun, presenting an intriguing observational opportunity for either the Solar Orbiter or the Parker Solar Probe spacecraft. Lastly, we note that the level of perpendicular diffusion may also play an important role in determining the effectiveness of the wave growth process. Reference: Agueda, N. and Lario, D. Release History and Transport Parameters of Relativistic Solar Electrons Inferred From Near-the-Sun In Situ Observations, ApJ, 829, 131, 2016.

Electron energetics in the inner coma of Comet Halley

NASA Astrophysics Data System (ADS)

Gan, L.; Cravens, T. E.

1990-05-01

A quasi-two-dimensional model of the spatial and energy distribution of electrons in the inner coma of Comet Halley has been constructed from a spherically symmetric ion density profile based on Giotto measurements, using the two-stream electron transport method and the time-dependent electron energy equation. A sharp jump in the electron temperature was found to be present at a cometocentric distance of about 15,000 km. This thermal boundary separates an inner region where cooling processes are dominant from an outer region where heat transport is more important. Both thermal and suprathermal electron populations exist inside the thermal boundary with comparable kinetic pressures. Outside the thermal boundary, a cloud electron population does not exist, and the electrons are almost isothermal along the magnetic field lines.

Theoretical investigations of molecular wires: Electronic spectra and electron transport

NASA Astrophysics Data System (ADS)

Palma, Julio Leopoldo

The results of theoretical and computational research are presented for two promising molecular wires, the Nanostar dendrimer, and a series of substituted azobenzene derivatives connected to aluminum electrodes. The electronic absorption spectra of the Nanostar (a phenylene-ethynylene dendrimer attached to an ethynylperylene chromophore) were calculated using a sequential Molecular Dynamics/Quantum Mechanics (MD/QM) method to perform an analysis of the temperature dependence of the electronic absorption process. We modeled the Nanostar as a series of connected units, and performed MD simulations for each chromophore at 10 K and 300 K to study how the temperature affected the structures and, consequently, the spectra. The absorption spectra of the Nanostar were computed using an ensemble of 8000 structures for each chromophore. Quantum Mechanical (QM) ZINDO/S calculations were performed for each conformation in the ensemble, including 16 excited states, for a total of 128,000 excitation energies. The spectral intensity was then scaled linearly with the number of conjugated units. Our calculations for both the individual chromophores and the Nanostar, are in good agreement with experiments. We explain in detail the effects of temperature and the consequences for the absorption process. The second part of this thesis presents a study of the effects of chemical substituents on the electron transport properties of the azobenzene molecule, which has been proposed recently as a component of a light-driven molecular switch. This molecule has two stable conformations (cis and trans) in its electronic ground state, with considerable differences in their conductance. The electron transport properties were calculated using first-principles methods combining non-equilibrium Green's function (NEGF) techniques with density functional theory (DFT). For the azobenzene studies, we included electron-donating groups and electron-withdrawing groups in meta- and ortho-positions with respect to the azo group. The results showed that the molecular structure is crucial in optimizing the electron transport properties of chemical structures, and that the transport properties in electronic devices at the molecular level can be manipulated, enhanced or suppressed by a careful consideration of the effects of chemical modification.

Drift-resonant, relativistic electron acceleration at the outer planets: Insights from the response of Saturn's radiation belts to magnetospheric storms

NASA Astrophysics Data System (ADS)

Roussos, E.; Kollmann, P.; Krupp, N.; Paranicas, C.; Dialynas, K.; Sergis, N.; Mitchell, D. G.; Hamilton, D. C.; Krimigis, S. M.

2018-05-01

The short, 7.2-day orbital period of Cassini's Ring Grazing Orbits (RGO) provided an opportunity to monitor how fast the effects of an intense magnetospheric storm-time period (days 336-343/2016) propagated into Saturn's electron radiation belts. Following the storms, Cassini's MIMI/LEMMS instrument detected a transient extension of the electron radiation belts that in subsequent orbits moved towards the inner belts, intensifying them in the process. This intensification was followed by an equally fast decay, possibly due to the rapid absorption of MeV electrons by the planet's main rings. Surprisingly, all this cycle was completed within four RGOs, effectively in less than a month. That is considerably faster than the year-long time scales of Saturn's proton radiation belt evolution. In order to explain this difference, we propose that electron radial transport is partly controlled by the variability of global scale electric fields which have a fixed local time pointing. Such electric fields may distort significantly the orbits of a particular class of energetic electrons that cancel out magnetospheric corotation due to their westward gradient and curvature drifts (termed "corotation-resonant" or "local-time stationary" electrons) and transport them radially between the ring current and the radiation belts within several days and few weeks. The significance of the proposed process is highlighted by the fact that corotation resonance at Saturn occurs for electrons of few hundred keV to several MeV. These are the characteristic energies of seed electrons from the ring current that sustain the radiation belts of the planet. Our model's feasibility is demonstrated through the use of a simple test-particle simulation, where we estimate that uniform but variable electric fields with magnitudes lower that 1.0 mV/m can lead to a very efficient transport of corotation resonant electrons. Such electric fields have been consistently measured in the magnetosphere, and here we provide additional evidence showing that they may be constantly present all the way down to the outer edge of Saturn's main rings, further supporting our model. The implications of our findings are not limited to Saturn. Corotation resonance at Jupiter occurs for electrons with energies above about 10 MeV throughout the quasi-dipolar, energetic particle-trapping region of the magnetosphere. The proposed process could in principle then lead to rapid transport and adiabatic acceleration electrons into ultra-relativistic energies. The observation by Galileo's EPD/LEMMS instrument of an intense Jovian acceleration event at the orbital distance of Ganymede during the mission's C22 orbit, when > 11 MeV electron fluxes were preferentially enhanced, provides additional support to our transport model and insights on the origin of that orbit's extreme energetic electron environment. Finally, if the mode of radial transport that we describe here is a dominant one, radial diffusion coefficients (DLL) would be subject to strong energy, pitch angle and species dependencies.

Charge-transport anisotropy in black phosphorus: critical dependence on the number of layers.

PubMed

Banerjee, Swastika; Pati, Swapan K

2016-06-28

Phosphorene is a promising candidate for modern electronics because of the anisotropy associated with high electron-hole mobility. Additionally, superior mechanical flexibility allows the strain-engineering of various properties including the transport of charge carriers in phosphorene. In this work, we have shown the criticality of the number of layers to dictate the transport properties of black phosphorus. Trilayer black phosphorus (TBP) has been proposed as an excellent anisotropic material, based on the transport parameters using Boltzmann transport formalisms coupled with density functional theory. The mobilities of both the electron and the hole are found to be higher along the zigzag direction (∼10(4) cm(2) V(-1) s(-1) at 300 K) compared to the armchair direction (∼10(2) cm(2) V(-1) s(-1)), resulting in the intrinsic directional anisotropy. Application of strain leads to additional electron-hole anisotropy with 10(3) fold higher mobility for the electron compared to the hole. Critical strain for maximum anisotropic response has also been determined. Whether the transport anisotropy is due to the spatial or charge-carrier has been determined through analyses of the scattering process of electrons and holes, and their recombination as well as relaxation dynamics. In this context, we have derived two descriptors (S and F(k)), which are general enough for any 2D or quasi-2D systems. Information on the scattering involving purely the carrier states also helps to understand the layer-dependent photoluminescence and electron (hole) relaxation in black phosphorus. Finally, we justify trilayer black phosphorus (TBP) as the material of interest with excellent transport properties.

Spatiotemporal Monte Carlo transport methods in x-ray semiconductor detectors: application to pulse-height spectroscopy in a-Se.

PubMed

Fang, Yuan; Badal, Andreu; Allec, Nicholas; Karim, Karim S; Badano, Aldo

2012-01-01

The authors describe a detailed Monte Carlo (MC) method for the coupled transport of ionizing particles and charge carriers in amorphous selenium (a-Se) semiconductor x-ray detectors, and model the effect of statistical variations on the detected signal. A detailed transport code was developed for modeling the signal formation process in semiconductor x-ray detectors. The charge transport routines include three-dimensional spatial and temporal models of electron-hole pair transport taking into account recombination and trapping. Many electron-hole pairs are created simultaneously in bursts from energy deposition events. Carrier transport processes include drift due to external field and Coulombic interactions, and diffusion due to Brownian motion. Pulse-height spectra (PHS) have been simulated with different transport conditions for a range of monoenergetic incident x-ray energies and mammography radiation beam qualities. Two methods for calculating Swank factors from simulated PHS are shown, one using the entire PHS distribution, and the other using the photopeak. The latter ignores contributions from Compton scattering and K-fluorescence. Comparisons differ by approximately 2% between experimental measurements and simulations. The a-Se x-ray detector PHS responses simulated in this work include three-dimensional spatial and temporal transport of electron-hole pairs. These PHS were used to calculate the Swank factor and compare it with experimental measurements. The Swank factor was shown to be a function of x-ray energy and applied electric field. Trapping and recombination models are all shown to affect the Swank factor.

On the Monte Carlo simulation of electron transport in the sub-1 keV energy range.

PubMed

Thomson, Rowan M; Kawrakow, Iwan

2011-08-01

The validity of "classic" Monte Carlo (MC) simulations of electron and positron transport at sub-1 keV energies is investigated in the context of quantum theory. Quantum theory dictates that uncertainties on the position and energy-momentum four-vectors of radiation quanta obey Heisenberg's uncertainty relation; however, these uncertainties are neglected in "classical" MC simulations of radiation transport in which position and momentum are known precisely. Using the quantum uncertainty relation and electron mean free path, the magnitudes of uncertainties on electron position and momentum are calculated for different kinetic energies; a validity bound on the classical simulation of electron transport is derived. In order to satisfy the Heisenberg uncertainty principle, uncertainties of 5% must be assigned to position and momentum for 1 keV electrons in water; at 100 eV, these uncertainties are 17 to 20% and are even larger at lower energies. In gaseous media such as air, these uncertainties are much smaller (less than 1% for electrons with energy 20 eV or greater). The classical Monte Carlo transport treatment is questionable for sub-1 keV electrons in condensed water as uncertainties on position and momentum must be large (relative to electron momentum and mean free path) to satisfy the quantum uncertainty principle. Simulations which do not account for these uncertainties are not faithful representations of the physical processes, calling into question the results of MC track structure codes simulating sub-1 keV electron transport. Further, the large difference in the scale at which quantum effects are important in gaseous and condensed media suggests that track structure measurements in gases are not necessarily representative of track structure in condensed materials on a micrometer or a nanometer scale.

Vibronic coupling effect on the electron transport through molecules

NASA Astrophysics Data System (ADS)

Tsukada, Masaru; Mitsutake, Kunihiro

2007-03-01

Electron transport through molecular bridges or molecular layers connected to nano-electrodes is determined by the combination of coherent and dissipative processes, controlled by the electron-vibron coupling, transfer integrals between the molecular orbitals, applied electric field and temperature. We propose a novel theoretical approach, which combines ab initio molecular orbital method with analytical many-boson model. As a case study, the long chain model of the thiophene oligomer is solved by a variation approach. Mixed states of moderately extended molecular orbital states mediated and localised by dress of vibron cloud are found as eigen-states. All the excited states accompanied by multiple quanta of vibration can be solved, and the overall carrier transport properties including the conductance, mobility, dissipation spectra are analyzed by solving the master equation with the transition rates estimated by the golden rule. We clarify obtained in a uniform systematic way, how the transport mode changes from a dominantly coherent transport to the dissipative hopping transport.

An electron transporting unit linked multifunctional Ir(III) complex: a promising strategy to improve the performance of solution-processed phosphorescent organic light-emitting diodes.

PubMed

Giridhar, Thota; Saravanan, Chinnusamy; Cho, Woosum; Park, Young Geun; Lee, Jin Yong; Jin, Sung-Ho

2014-04-18

An oxadiazole based electron transporting (ET) unit was glued to the heteroleptic Ir(III) complex (TPQIr-ET) and used as a dopant for phosphorescent organic light-emitting diodes (PhOLEDs). It shows superior device performance than the dopant without the ET unit (TPQIr) due to the balanced charge carrier injection by the ET unit.

Photovoltaic devices based on quantum dot functionalized nanowire arrays embedded in an organic matrix

NASA Astrophysics Data System (ADS)

Kung, Patrick; Harris, Nicholas; Shen, Gang; Wilbert, David S.; Baughman, William; Balci, Soner; Dawahre, Nabil; Butler, Lee; Rivera, Elmer; Nikles, David; Kim, Seongsin M.

2012-01-01

Quantum dot (QD) functionalized nanowire arrays are attractive structures for low cost high efficiency solar cells. QDs have the potential for higher quantum efficiency, increased stability and lifetime compared to traditional dyes, as well as the potential for multiple electron generation per photon. Nanowire array scaffolds constitute efficient, low resistance electron transport pathways which minimize the hopping mechanism in the charge transport process of quantum dot solar cells. However, the use of liquid electrolytes as a hole transport medium within such scaffold device structures have led to significant degradation of the QDs. In this work, we first present the synthesis uniform single crystalline ZnO nanowire arrays and their functionalization with InP/ZnS core-shell quantum dots. The structures are characterized using electron microscopy, optical absorption, photoluminescence and Raman spectroscopy. Complementing photoluminescence, transmission electron microanalysis is used to reveal the successful QD attachment process and the atomistic interface between the ZnO and the QD. Energy dispersive spectroscopy reveals the co-localized presence of indium, phosphorus, and sulphur, suggestive of the core-shell nature of the QDs. The functionalized nanowire arrays are subsequently embedded in a poly-3(hexylthiophene) hole transport matrix with a high degree of polymer infiltration to complete the device structure prior to measurement.

Flow-Directed Crystallization for Printed Electronics.

PubMed

Qu, Ge; Kwok, Justin J; Diao, Ying

2016-12-20

The solution printability of organic semiconductors (OSCs) represents a distinct advantage for materials processing, enabling low-cost, high-throughput, and energy-efficient manufacturing with new form factors that are flexible, stretchable, and transparent. While the electronic performance of OSCs is not comparable to that of crystalline silicon, the solution processability of OSCs allows them to complement silicon by tackling challenging aspects for conventional photolithography, such as large-area electronics manufacturing. Despite this, controlling the highly nonequilibrium morphology evolution during OSC printing remains a challenge, hindering the achievement of high electronic device performance and the elucidation of structure-property relationships. Many elegant morphological control methodologies have been developed in recent years including molecular design and novel processing approaches, but few have utilized fluid flow to control morphology in OSC thin films. In this Account, we discuss flow-directed crystallization as an effective strategy for controlling the crystallization kinetics during printing of small molecule and polymer semiconductors. Introducing the concept of flow-directed crystallization to the field of printed electronics is inspired by recent advances in pharmaceutical manufacturing and flow processing of flexible-chain polymers. Although flow-induced crystallization is well studied in these areas, previous findings may not apply directly to the field of printed electronics where the molecular structures (i.e., rigid π-conjugated backbone decorated with flexible side chains) and the intermolecular interactions (i.e., π-π interactions, quadrupole interactions) of OSCs differ substantially from those of pharmaceuticals or flexible-chain polymers. Another critical difference is the important role of solvent evaporation in open systems, which defines the flow characteristics and determines the crystallization kinetics and pathways. In other words, flow-induced crystallization is intimately coupled with the mass transport processes driven by solvent evaporation during printing. In this Account, we will highlight these distinctions of flow-directed crystallization for printed electronics. In the context of solution printing of OSCs, the key issue that flow-directed crystallization addresses is the kinetics mismatch between crystallization and various transport processes during printing. We show that engineering fluid flows can tune the kinetics of OSC crystallization by expediting the nucleation and crystal growth processes, significantly enhancing thin film morphology and device performance. For small molecule semiconductors, nucleation can be enhanced and patterned by directing the evaporative flux via contact line engineering, and defective crystal growth can be alleviated by enhancing mass transport to yield significantly improved coherence length and reduced grain boundaries. For conjugated polymers, extensional and shear flow can expedite nucleation through flow-induced conformation change, facilitating the control of microphase separation, degree of crystallinity, domain alignment, and percolation. Although the nascent concept of flow-directed solution printing has not yet been widely adopted in the field of printed electronics, we anticipate that it can serve as a platform technology in the near future for improving device performance and for systematically tuning thin film morphology to construct structure-property relationships. From a fundamental perspective, it is imperative to develop a better understanding of the effects of fluid flow and mass transport on OSC crystallization as these processes are ubiquitous across all solution processing techniques and can critically impact charge transport properties.

Measurement of brightness temperature of two-dimensional electron gas in channel of a high electron mobility transistor at ultralow dissipation power

NASA Astrophysics Data System (ADS)

Korolev, A. M.; Shulga, V. M.; Turutanov, O. G.; Shnyrkov, V. I.

2016-07-01

A technically simple and physically clear method is suggested for direct measurement of the brightness temperature of two-dimensional electron gas (2DEG) in the channel of a high electron mobility transistor (HEMT). The usage of the method was demonstrated with the pseudomorphic HEMT as a specimen. The optimal HEMT dc regime, from the point of view of the "back action" problem, was found to belong to the unsaturated area of the static characteristics possibly corresponding to the ballistic electron transport mode. The proposed method is believed to be a convenient tool to explore the ballistic transport, electron diffusion, 2DEG properties and other electrophysical processes in heterostructures.

Electron Waiting Times of a Cooper Pair Splitter

NASA Astrophysics Data System (ADS)

Walldorf, Nicklas; Padurariu, Ciprian; Jauho, Antti-Pekka; Flindt, Christian

2018-02-01

Electron waiting times are an important concept in the analysis of quantum transport in nanoscale conductors. Here we show that the statistics of electron waiting times can be used to characterize Cooper pair splitters that create spatially separated spin-entangled electrons. A short waiting time between electrons tunneling into different leads is associated with the fast emission of a split Cooper pair, while long waiting times are governed by the slow injection of Cooper pairs from a superconductor. Experimentally, the waiting time distributions can be measured using real-time single-electron detectors in the regime of slow tunneling, where conventional current measurements are demanding. Our work is important for understanding the fundamental transport processes in Cooper pair splitters and the predictions may be verified using current technology.

Charge transport in organic semiconductors.

PubMed

Bässler, Heinz; Köhler, Anna

2012-01-01

Modern optoelectronic devices, such as light-emitting diodes, field-effect transistors and organic solar cells require well controlled motion of charges for their efficient operation. The understanding of the processes that determine charge transport is therefore of paramount importance for designing materials with improved structure-property relationships. Before discussing different regimes of charge transport in organic semiconductors, we present a brief introduction into the conceptual framework in which we interpret the relevant photophysical processes. That is, we compare a molecular picture of electronic excitations against the Su-Schrieffer-Heeger semiconductor band model. After a brief description of experimental techniques needed to measure charge mobilities, we then elaborate on the parameters controlling charge transport in technologically relevant materials. Thus, we consider the influences of electronic coupling between molecular units, disorder, polaronic effects and space charge. A particular focus is given to the recent progress made in understanding charge transport on short time scales and short length scales. The mechanism for charge injection is briefly addressed towards the end of this chapter.

Advanced electronic displays and their potential in future transport aircraft

NASA Technical Reports Server (NTRS)

Hatfield, J. J.

1981-01-01

It is pointed out that electronic displays represent one of the keys to continued integration and improvement of the effectiveness of avionic systems in future transport aircraft. An employment of modern electronic display media and generation has become vital in connection with the increases in modes and functions of modern aircraft. Requirements for electronic systems of future transports are examined, and a description is provided of the tools which are available for cockpit integration, taking into account trends in information processing and presentation, trends in integrated display devices, and trends concerning input/output devices. Developments related to display media, display generation, and I/O devices are considered, giving attention to a comparison of CRT and flat-panel display technology, advanced HUD technology and multifunction controls. Integrated display formats are discussed along with integrated systems and cockpit configurations.

Pivotal Role of Iron in the Regulation of Cyanobacterial Electron Transport.

PubMed

González, A; Sevilla, E; Bes, M T; Peleato, M L; Fillat, M F

2016-01-01

Iron-containing metalloproteins are the main cornerstones for efficient electron transport in biological systems. The abundance and diversity of iron-dependent proteins in cyanobacteria makes those organisms highly dependent of this micronutrient. To cope with iron imbalance, cyanobacteria have developed a survey of adaptation strategies that are strongly related to the regulation of photosynthesis, nitrogen metabolism and other central electron transfer pathways. Furthermore, either in its ferrous form or as a component of the haem group, iron plays a crucial role as regulatory signalling molecule that directly or indirectly modulates the composition and efficiency of cyanobacterial redox reactions. We present here the major mechanism used by cyanobacteria to couple iron homeostasis to the regulation of electron transport, making special emphasis in processes specific in those organisms. © 2016 Elsevier Ltd. All rights reserved.

What controls deposition rate in electron-beam chemical vapor deposition?

PubMed

White, William B; Rykaczewski, Konrad; Fedorov, Andrei G

2006-08-25

The key physical processes governing electron-beam-assisted chemical vapor deposition are analyzed via a combination of theoretical modeling and supporting experiments. The scaling laws that define growth of the nanoscale deposits are developed and verified using carefully designed experiments of carbon deposition from methane onto a silicon substrate. The results suggest that the chamber-scale continuous transport of the precursor gas is the rate controlling process in electron-beam chemical vapor deposition.

Mixed ionic and electronic conducting membranes for hydrogen generation and separation

NASA Astrophysics Data System (ADS)

Cui, Hengdong

Dense mixed ionic and electronic conducting (MIEC) membranes are receiving increasing attention due to their potential for application as gas separation membranes to separate oxygen from air. The objective of this work is to study a novel, chemically-assisted separation process that utilizes oxygen-ion and electron-conducting MIECs for generating and separating hydrogen from steam. This research aims at exploring new routes and materials for high-purity hydrogen production for use in fuel cells and hydrogen-based internal combustion (IC) engines. In this approach, hydrocarbon fuel such as methane is fed to one side of the membrane, while steam is fed to the other side. The MIEC membrane separation process involves steam dissociation and oxidation of the fuel. The oxygen ions formed as a result of steam dissociation are transported across the membrane in a coupled transport process with electrons being transported in the opposite direction. Upon reaching the fuel side of the membrane, the oxygen ions oxidize the hydrocarbon. This process results in hydrogen production on the steam side of the membrane. The oxygen partial pressure gradient across the membrane is the driving force for this process. In this work, a novel, dual-phase composite MIEC membrane system comprising of rare-earth doped ceria with high oxygen ion conductivity and donor-doped strontium titanate with high electronic conductivity were investigated. The chemical diffusion coefficient and surface exchange coefficient have been measured using the electrical conductivity relaxation (ECR) technique. These two parameters control the rate of oxygen permeation across the membrane. The permeation data have been fit with a kinetic model that incorporates oxygen surface exchange on two sides of the membrane and bulk transport of oxygen through the membrane. This material has higher bulk diffusion coefficient and surface exchange reaction rate compared to other known MIEC conductors under the process conditions of interest. Over 10 mumol·cm-2·s-1 (micromoles per square cm per second) of area specific hydrogen flux has been achieved employing a membrane of this material with thickness of 0.2 mm. This flux is several orders of magnitude higher than the hydrogen generation rates reported using other MIEC materials under similar operating conditions.

Power Electronics and Electric Machines Facilities | Transportation

Science.gov Websites

current processes. Photo by Dennis Schroeder, NREL A photo of a researcher in safety glasses using a large focus in NREL's power electronics and electric machines labs. Photo by Dennis Schroeder, NREL Heat

Shot noise generated by graphene p–n junctions in the quantum Hall effect regime

PubMed Central

Kumada, N.; Parmentier, F. D.; Hibino, H.; Glattli, D. C.; Roulleau, P.

2015-01-01

Graphene offers a unique system to investigate transport of Dirac Fermions at p–n junctions. In a magnetic field, combination of quantum Hall physics and the characteristic transport across p–n junctions leads to a fractionally quantized conductance associated with the mixing of electron-like and hole-like modes and their subsequent partitioning. The mixing and partitioning suggest that a p–n junction could be used as an electronic beam splitter. Here we report the shot noise study of the mode-mixing process and demonstrate the crucial role of the p–n junction length. For short p–n junctions, the amplitude of the noise is consistent with an electronic beam-splitter behaviour, whereas, for longer p–n junctions, it is reduced by the energy relaxation. Remarkably, the relaxation length is much larger than typical size of mesoscopic devices, encouraging using graphene for electron quantum optics and quantum information processing. PMID:26337067

Respiratory processes in non-photosynthetic plastids

PubMed Central

Renato, Marta; Boronat, Albert; Azcón-Bieto, Joaquín

2015-01-01

Chlororespiration is a respiratory process located in chloroplast thylakoids which consists in an electron transport chain from NAD(P)H to oxygen. This respiratory chain involves the NAD(P)H dehydrogenase complex, the plastoquinone pool and the plastid terminal oxidase (PTOX), and it probably acts as a safety valve to prevent the over-reduction of the photosynthetic machinery in stress conditions. The existence of a similar respiratory activity in non-photosynthetic plastids has been less studied. Recently, it has been reported that tomato fruit chromoplasts present an oxygen consumption activity linked to ATP synthesis. Etioplasts and amyloplasts contain several electron carriers and some subunits of the ATP synthase, so they could harbor a similar respiratory process. This review provides an update on the study about respiratory processes in chromoplasts, identifying the major gaps that need to be addressed in future research. It also reviews the proteomic data of etioplasts and amyloplasts, which suggest the presence of a respiratory electron transport chain in these plastids. PMID:26236317

Analysis of electron beam induced deposition (EBID) of residual hydrocarbons in electron microscopy

NASA Astrophysics Data System (ADS)

Rykaczewski, Konrad; White, William B.; Fedorov, Andrei G.

2007-03-01

In this work we have developed a comprehensive dynamic model of electron beam induced deposition (EBID) of residual hydrocarbon coupling mass transport, electron transport and scattering, and species decomposition to predict the deposition of carbon nanopillars. The simulations predict the local species and electron density distributions, as well as the three-demensional morphology and the growth rate of the deposit. Since the process occurs in a high vacuum environment, surface diffusion is considered as the primary transport mode of surface-adsorbed hydrocarbon precursor. The governing surface transport equation (STE) of the adsorbed species is derived and solved numerically. The transport, scattering, and absorption of primary electron as well as secondary electron generation are treated using the Monte Carlo method. Low energy secondary electrons are the major contributors to hydrocarbon decomposition due to their energy range matching peak dissociation reaction cross section energies for precursor molecules. The deposit and substrate are treated as a continuous entity allowing the simulation of the growth of a realistically sized deposit rather than a large number of cells representing each individual atom as in previously published simulations [Mitsuishi et al., Ultramicroscopy 103, 17 (2005); Silvis-Cividjian, Ph.D. thesis, University of Delft, 2002]. Such formulation allows for simple coupling of the STE with the dynamic growth of the nanopillar. Three different growth regimes occurring in EBID are identified using scaling analysis, and simulations are used to describe the deposit morphology and precursor surface concentration specific for each growth regime.

Multiple-time-scale motion in molecularly linked nanoparticle arrays.

PubMed

George, Christopher; Szleifer, Igal; Ratner, Mark

2013-01-22

We explore the transport of electrons between electrodes that encase a two-dimensional array of metallic quantum dots linked by molecular bridges (such as α,ω alkaline dithiols). Because the molecules can move at finite temperatures, the entire transport structure comprising the quantum dots and the molecules is in dynamical motion while the charge is being transported. There are then several physical processes (physical excursions of molecules and quantum dots, electronic migration, ordinary vibrations), all of which influence electronic transport. Each can occur on a different time scale. It is therefore not appropriate to use standard approaches to this sort of electron transfer problem. Instead, we present a treatment in which three different theoretical approaches-kinetic Monte Carlo, classical molecular dynamics, and quantum transport-are all employed. In certain limits, some of the dynamical effects are unimportant. But in general, the transport seems to follow a sort of dynamic bond percolation picture, an approach originally introduced as formal models and later applied to polymer electrolytes. Different rate-determining steps occur in different limits. This approach offers a powerful scheme for dealing with multiple time scale transport problems, as will exist in many situations with several pathways through molecular arrays or even individual molecules that are dynamically disordered.

Balance-Equation Approach to Nonuniform Electron Transport in Nonparabolic Semiconductors

NASA Astrophysics Data System (ADS)

Cao, Juncheng; Lei, Xiaolin

1998-10-01

On the basis of the Lei-Ting balance-equation transport theory recently developed for nonparabolic energy band, we propose a hydrodynamic approach to the spatially inhomogeneous electron transport in semiconductor devices. In the present approach, the momentum and energy collision terms are expressed by two nonlinear functions, the frictional acceleration and energy-loss rate, which give a detailed scattering-process-level description of nonstationary and nonlocal charge transport in the system. This approach allows one to calculate selfconsistently the transport parameters within the model itself based on the primary material data (band structure, deformation potential constant, etc.), thus it minimizes the uncertainty associated with the use of some empirical relations for transport coefficients. As a demonstration of the approach, we have carried out a numerical calculation for a submicrometer Si n^+nn^+ diode by assuming an isotropic Kane-type energy band. The results for electron velocity and energy, obtained at much less computing cost than the Monte-Carlo (MC) method, are in good agreement with MC prediction. The influence of heat-flow term on electron transport behaviour, especially on velocity overshoot, is also investigated. The project supported by National Natural Science Foundation of China, National and Shanghai Municipal Commission of Science and Technology, and the Shanghai Foundation for Research and Development of Applied Materials

ESM of ionic and electrochemical phenomena on the nanoscale

DOE PAGES

Kalinin, Sergei V.; Kumar, Amit; Balke, Nina; ...

2011-01-01

Operation of energy storage and conversion devices is ultimately controlled by series of intertwined ionic and electronic transport processes and electrochemical reactions at surfaces and interfaces, strongly mediated by strain and mechanical processes. In a typical fuel cell, these include chemical species transport in porous cathode and anode materials, gas-solid electrochemical reactions at grains and triple-phase boundaries (TPBs), ionic and electronic flows in multicomponent electrodes, and chemical and electronic potential drops at internal interfaces in electrodes and electrolytes. Furthermore, all these phenomena are sensitively affected by the microstructure of materials from device level to the atomic scales. Similar spectrum ofmore » length scales and phenomena underpin operation of other energy systems including primary and secondary batteries, as well as hybrid systems such flow and metal-air/water batteries.« less

Transport coefficients and heat fluxes in non-equilibrium high-temperature flows with electronic excitation

NASA Astrophysics Data System (ADS)

Istomin, V. A.; Kustova, E. V.

2017-02-01

The influence of electronic excitation on transport processes in non-equilibrium high-temperature ionized mixture flows is studied. Two five-component mixtures, N 2 / N2 + / N / N + / e - and O 2 / O2 + / O / O + / e - , are considered taking into account the electronic degrees of freedom for atomic species as well as the rotational-vibrational-electronic degrees of freedom for molecular species, both neutral and ionized. Using the modified Chapman-Enskog method, the transport coefficients (thermal conductivity, shear viscosity and bulk viscosity, diffusion and thermal diffusion) are calculated in the temperature range 500-50 000 K. Thermal conductivity and bulk viscosity coefficients are strongly affected by electronic states, especially for neutral atomic species. Shear viscosity, diffusion, and thermal diffusion coefficients are not sensible to electronic excitation if the size of excited states is assumed to be constant. The limits of applicability for the Stokes relation are discussed; at high temperatures, this relation is violated not only for molecular species but also for electronically excited atomic gases. Two test cases of strongly non-equilibrium flows behind plane shock waves corresponding to the spacecraft re-entry (Hermes and Fire II) are simulated numerically. Fluid-dynamic variables and heat fluxes are evaluated in gases with electronic excitation. In inviscid flows without chemical-radiative coupling, the flow-field is weakly affected by electronic states; however, in viscous flows, their influence can be more important, in particular, on the convective heat flux. The contribution of different dissipative processes to the heat transfer is evaluated as well as the effect of reaction rate coefficients. The competition of diffusion and heat conduction processes reduces the overall effect of electronic excitation on the convective heating, especially for the Fire II test case. It is shown that reliable models of chemical reaction rates are of great importance for accurate predictions of the fluid dynamic variables and heat fluxes.

Electroluminescence Caused by the Transport of Interacting Electrons through Parallel Quantum Dots in a Photon Cavity

NASA Astrophysics Data System (ADS)

Gudmundsson, Vidar; Abdulla, Nzar Rauf; Sitek, Anna; Goan, Hsi-Sheng; Tang, Chi-Shung; Manolescu, Andrei

2018-02-01

We show that a Rabi-splitting of the states of strongly interacting electrons in parallel quantum dots embedded in a short quantum wire placed in a photon cavity can be produced by either the para- or the dia-magnetic electron-photon interactions when the geometry of the system is properly accounted for and the photon field is tuned close to a resonance with the electron system. We use these two resonances to explore the electroluminescence caused by the transport of electrons through the one- and two-electron ground states of the system and their corresponding conventional and vacuum electroluminescense as the central system is opened up by coupling it to external leads acting as electron reservoirs. Our analysis indicates that high-order electron-photon processes are necessary to adequately construct the cavity-photon dressed electron states needed to describe both types of electroluminescence.

The Beauty and Biology of Pollen.

ERIC Educational Resources Information Center

Clay-Poole, Scott T.; Slesnick, Irwin L.

1983-01-01

Describes: basic features of pollen grains (shapes, apertures, layering of wall, exine sculpturing); strategies for pollination (anemophily--wind transported, zoophily--animal transported); and the structures specialized for each process. Gives instructions for using scanning electron microscope photographs and for collecting, identifying, and…

Commercial vehicle operations one-stop electronic purchasing and processing, ITS operational test : final evaluation report

DOT National Transportation Integrated Search

1997-09-01

The United States Department of Transportations (USDOTs) National ITS Program : Plan describes the national strategy for deploying advanced technologies and services into our : transportation system. To emphasize the need-driven (rather than te...

[Role of proton-motive force in the conjugative DNA transport in Staphylococci].

PubMed

Gavriliuk, V G; Vinnikov, A I

1997-01-01

Sensitivity of the conjugative process in staphylococci to the action of uncouplers of oxidative phosphorylation and inhibitors of electron transport systems have been proved, that testifies to the energy-dependent character of conjugative transport of DNA. Proceeding of the conjugation process depends upon the generation of delta microH+ on the membrane of both the donor and recipient cells. contribution of protonmotive forces to providing for the transfer of plasmids during conjugation to staphylococci has been defined.

Solution processed ZnO hybrid nanocomposite with tailored work function for improved electron transport layer in organic photovoltaic devices.

PubMed

Lee, Yun-Ju; Wang, Jian; Cheng, Samuel R; Hsu, Julia W P

2013-09-25

We demonstrate improved organic photovoltaic device performance using solution processed electron transport layers of ZnO nanoparticle (NP) films containing organic additives, poly(vinylpyrrolidone) (PVP), or diethanolamine (DEA), that do not require post processing after film deposition. Inclusion of PVP or DEA decreased the ZnO work function by 0.4 eV through interfacial dipole formation. While PVP did not change the ZnO NP shape or size, DEA modified the ZnO shape from 5 nm × 15 nm nanorods to 5 nm nanoparticles. At an optimized PVP concentration of 0.7 wt %, ZnO NP:PVP electron transport layers (ETLs) improved the efficiency of inverted P3HT:PCBM devices by 37%, primarily through higher fill factor. ZnO NP:PVP and ZnO NP:DEA ETLs increased the open circuit voltage of inverted P3HT:ICBA devices by 0.07 V due to decreasing ETL work function, leading to enhanced built-in field. The relationship between ZnO nanocomposite ETL work function, donor-acceptor energy offset, and device performance is discussed. The effects of the two additives are compared.

Concepts for the material development of phosphorescent organic materials processable from solution and their application in OLEDs

NASA Astrophysics Data System (ADS)

Janietz, S.; Krueger, H.; Thesen, M.; Salert, B.; Wedel, A.

2014-10-01

One example of organic electronics is the application of polymer based light emitting devices (PLEDs). PLEDs are very attractive for large area and fine-pixel displays, lighting and signage. The polymers are more amenable to solution processing by printing techniques which are favourable for low cost production in large areas. With phosphorescent emitters like Ir-complexes higher quantum efficiencies were obtained than with fluorescent systems, especially if multilayer stack systems with separated charge transport and emitting layers were applied in the case of small molecules. Polymers exhibit the ability to integrate all the active components like the hole-, electron-transport and phosphorescent molecules in only one layer. Here, the active components of a phosphorescent system - triplet emitter, hole- and electron transport molecules - can be linked as a side group to a polystyrene main chain. By varying the molecular structures of the side groups as well as the composition of the side chains with respect to the triplet emitter, hole- and electron transport structure, and by blending with suitable glass-forming, so-called small molecules, brightness, efficiency and lifetime of the produced OLEDs can be optimized. By choosing the triplet emitter, such as iridium complexes, different emission colors can be specially set. Different substituted triazine molecules were introduced as side chain into a polystyrene backbone and applied as electron transport material in PLED blend systems. The influence of alkyl chain lengths of the performance will be discussed. For an optimized blend system with a green emitting phosphorescent Ir-complex efficiencies of 60 cd/A and an lifetime improvement of 66.000 h @ 1000 cd/m2 were achieved.

Melting of Wigner Crystal on Helium in Quasi-One-Dimensional Geometry

NASA Astrophysics Data System (ADS)

Ikegami, Hiroki; Akimoto, Hikota; Kono, Kimitoshi

2015-05-01

We discuss melting of a Wigner crystal formed on a free surface of superfluid He, in quasi-one-dimensional (Q1D) channels of width between 5 and 15 m. We reexamine our previous transport data (Ikegami et al. in Phys Rev B 82:201104(R), 2010), in particular, by estimating the number of electrons across the channel in a more accurate way with the aid of numerical calculations of distributions of the electrons in the channels. The results of reexamination indicate more convincingly that the melting of the Wigner crystal in the Q1D geometry is understood by the finite size effect on the Kosterlitz-Thouless-Halperin-Nelson-Young melting process. We also present technical details of the transport measurements of the electrons in a Q1D geometry, including a fabrication method of devices used for the transport measurements, numerical simulations of response of the devices, and a procedure for analyzing transport data.

Electron transport in gated InGaAs and InAsP quantum well wires in selectively grown InP ridge structures

NASA Astrophysics Data System (ADS)

Granger, G.; Kam, A.; Studenikin, S. A.; Sachrajda, A. S.; Aers, G. C.; Williams, R. L.; Poole, P. J.

2010-09-01

The purpose of this work is to fabricate ribbon-like InGaAs and InAsP wires embedded in InP ridge structures and investigate their transport properties. The InP ridge structures that contain the wires are selectively grown by chemical beam epitaxy (CBE) on pre-patterned InP substrates. To optimize the growth and micro-fabrication processes for electronic transport, we explore the Ohmic contact resistance, the electron density, and the mobility as a function of the wire width using standard transport and Shubnikov-de Haas measurements. At low temperatures the ridge structures reveal reproducible mesoscopic conductance fluctuations. We also fabricate ridge structures with submicron gate electrodes that exhibit non-leaky gating and good pinch-off characteristics acceptable for device operation. Using such wrap gate electrodes, we demonstrate that the wires can be split to form quantum dots evidenced by Coulomb blockade oscillations in transport measurements.

Study of transmission function and electronic transport in one dimensional silver nanowire: Ab-initio method using density functional theory (DFT)

NASA Astrophysics Data System (ADS)

Thakur, Anil; Kashyap, Rajinder

2018-05-01

Single nanowire electrode devices have their application in variety of fields which vary from information technology to solar energy. Silver nanowires, made in an aqueous chemical reduction process, can be reacted with gold salt to create bimetallic nanowires. Silver nanowire can be used as electrodes in batteries and have many other applications. In this paper we investigated structural and electronic transport properties of Ag nanowire using density functional theory (DFT) with SIESTA code. Electronic transport properties of Ag nanowire have been studied theoretically. First of all an optimized geometry for Ag nanowire is obtained using DFT calculations, and then the transport relations are obtained using NEGF approach. SIESTA and TranSIESTA simulation codes are used in the calculations respectively. The electrodes are chosen to be the same as the central region where transport is studied, eliminating current quantization effects due to contacts and focusing the electronic transport study to the intrinsic structure of the material. By varying chemical potential in the electrode regions, an I-V curve is traced which is in agreement with the predicted behavior. Bulk properties of Ag are in agreement with experimental values which make the study of electronic and transport properties in silver nanowires interesting because they are promising materials as bridging pieces in nanoelectronics. Transmission coefficient and V-I characteristic of Ag nano wire reveals that silver nanowire can be used as an electrode device.

Hardware-software complex of informing passengers of forecasted route transport arrival at stop

NASA Astrophysics Data System (ADS)

Pogrebnoy, V. Yu; Pushkarev, M. I.; Fadeev, A. S.

2017-02-01

The paper presents the hardware-software complex of informing the passengers of the forecasted route transport arrival. A client-server architecture of the forecasting information system is represented and an electronic information board prototype is described. The scheme of information transfer and processing, starting with receiving navigating telemetric data from a transport vehicle and up to the time of passenger public transport arrival at the stop, as well as representation of the information on the electronic board is illustrated and described. Methods and algorithms of determination of the transport vehicle current location in the city route network are considered in detail. The description of the proposed forecasting model of transport vehicle arrival time at the stop is given. The obtained result is applied in Tomsk for forecasting and displaying the arrival time information at the stops.

Hierarchical quantum master equation approach to electronic-vibrational coupling in nonequilibrium transport through nanosystems

NASA Astrophysics Data System (ADS)

Schinabeck, C.; Erpenbeck, A.; Härtle, R.; Thoss, M.

2016-11-01

Within the hierarchical quantum master equation (HQME) framework, an approach is presented, which allows a numerically exact description of nonequilibrium charge transport in nanosystems with strong electronic-vibrational coupling. The method is applied to a generic model of vibrationally coupled transport considering a broad spectrum of parameters ranging from the nonadiabatic to the adiabatic regime and including both resonant and off-resonant transport. We show that nonequilibrium effects are important in all these regimes. In particular, in the off-resonant transport regime, the inelastic cotunneling signal is analyzed for a vibrational mode in full nonequilibrium, revealing a complex interplay of different transport processes and deviations from the commonly used G0/2 rule of thumb. In addition, the HQME approach is used to benchmark approximate master equation and nonequilibrium Green's function methods.

Electron stripping processes of H⁻ ion beam in the 80 kV high voltage extraction column and low energy beam transport line at LANSCE.

PubMed

Draganic, I N

2016-02-01

Basic vacuum calculations were performed for various operating conditions of the Los Alamos National Neutron Science H(-) Cockcroft-Walton (CW) injector and the Ion Source Test Stand (ISTS). The vacuum pressure was estimated for both the CW and ISTS at five different points: (1) inside the H(-) ion source, (2) in front of the Pierce electrode, (3) at the extraction electrode, (4) at the column electrode, and (5) at the ground electrode. A static vacuum analysis of residual gases and the working hydrogen gas was completed for the normal ion source working regime. Gas density and partial pressure were estimated for the injected hydrogen gas. The attenuation of H(-) beam current and generation of electron current in the high voltage acceleration columns and low energy beam transport lines were calculated. The interaction of H(-) ions on molecular hydrogen (H2) is discussed as a dominant collision process in describing electron stripping rates. These results are used to estimate the observed increase in the ratio of electrons to H(-) ion beam in the ISTS beam transport line.

C70/C70:pentacene/pentacene organic heterojunction as the connecting layer for high performance tandem organic light-emitting diodes: Mechanism investigation of electron injection and transport

NASA Astrophysics Data System (ADS)

Guo, Qingxun; Yang, Dezhi; Chen, Jiangshan; Qiao, Xianfeng; Ahamad, Tansir; Alshehri, Saad M.; Ma, Dongge

2017-03-01

A high performance tandem organic light-emitting diode (OLED) is realized by employing a C70/C70:pentacene/pentacene organic heterojunction as the efficient charge generation layer (CGL). Not only more than two time enhancement of external quantum efficiency but also significant improvement in both power efficiency and lifetime are well achieved. The mechanism investigations find that the electron injection from the CGL to the adjacent electron transport layer (ETL) in tandem devices is injection rate-limited due to the high interface energy barrier between the CGL and the ETL. By the capacitance-frequency (C-F) and low temperature current density-voltage (J-V) characteristic analysis, we confirm that the electron transport is a space-charge-limited current process with exponential trap distribution. These traps are localized states below the lowest unoccupied molecular orbital edge inside the gap and would be filled with the upward shift of the Fermi level during the n-doping process. Furthermore, both the trap density (Ht) and the activation energy (Ea) could be carefully worked out through low temperature J-V measurements, which is very important for developing high performance tandem OLEDs.

Long-distance electron transport occurs globally in marine sediments

NASA Astrophysics Data System (ADS)

Burdorf, Laurine D. W.; Tramper, Anton; Seitaj, Dorina; Meire, Lorenz; Hidalgo-Martinez, Silvia; Zetsche, Eva-Maria; Boschker, Henricus T. S.; Meysman, Filip J. R.

2017-02-01

Recently, long filamentous bacteria have been reported conducting electrons over centimetre distances in marine sediments. These so-called cable bacteria perform an electrogenic form of sulfur oxidation, whereby long-distance electron transport links sulfide oxidation in deeper sediment horizons to oxygen reduction in the upper millimetres of the sediment. Electrogenic sulfur oxidation exerts a strong impact on the local sediment biogeochemistry, but it is currently unknown how prevalent the process is within the seafloor. Here we provide a state-of-the-art assessment of its global distribution by combining new field observations with previous reports from the literature. This synthesis demonstrates that electrogenic sulfur oxidation, and hence microbial long-distance electron transport, is a widespread phenomenon in the present-day seafloor. The process is found in coastal sediments within different climate zones (off the Netherlands, Greenland, the USA, Australia) and thrives on a range of different coastal habitats (estuaries, salt marshes, mangroves, coastal hypoxic basins, intertidal flats). The combination of a widespread occurrence and a strong local geochemical imprint suggests that electrogenic sulfur oxidation could be an important, and hitherto overlooked, component of the marine cycle of carbon, sulfur and other elements.

Inner Radiation Belt Representation of the Energetic Electron Environment: Model and Data Synthesis Using the Salammbo Radiation Belt Transport Code and Los Alamos Geosynchronous and GPS Energetic Particle Data

NASA Technical Reports Server (NTRS)

Friedel, R. H. W.; Bourdarie, S.; Fennell, J.; Kanekal, S.; Cayton, T. E.

2004-01-01

The highly energetic electron environment in the inner magnetosphere (GEO inward) has received a lot of research attention in resent years, as the dynamics of relativistic electron acceleration and transport are not yet fully understood. These electrons can cause deep dielectric charging in any space hardware in the MEO to GEO region. We use a new and novel approach to obtain a global representation of the inner magnetospheric energetic electron environment, which can reproduce the absolute environment (flux) for any spacecraft orbit in that region to within a factor of 2 for the energy range of 100 KeV to 5 MeV electrons, for any levels of magnetospheric activity. We combine the extensive set of inner magnetospheric energetic electron observations available at Los Alamos with the physics based Salammbo transport code, using the data assimilation technique of "nudging". This in effect input in-situ data into the code and allows the diffusion mechanisms in the code to interpolate the data into regions and times of no data availability. We present here details of the methods used, both in the data assimilation process and in the necessary inter-calibration of the input data used. We will present sample runs of the model/data code and compare the results to test spacecraft data not used in the data assimilation process.

Electron swarm properties under the influence of a very strong attachment in SF6 and CF3I obtained by Monte Carlo rescaling procedures

NASA Astrophysics Data System (ADS)

Mirić, J.; Bošnjaković, D.; Simonović, I.; Petrović, Z. Lj; Dujko, S.

2016-12-01

Electron attachment often imposes practical difficulties in Monte Carlo simulations, particularly under conditions of extensive losses of seed electrons. In this paper, we discuss two rescaling procedures for Monte Carlo simulations of electron transport in strongly attaching gases: (1) discrete rescaling, and (2) continuous rescaling. The two procedures are implemented in our Monte Carlo code with an aim of analyzing electron transport processes and attachment induced phenomena in sulfur-hexafluoride (SF6) and trifluoroiodomethane (CF3I). Though calculations have been performed over the entire range of reduced electric fields E/n 0 (where n 0 is the gas number density) where experimental data are available, the emphasis is placed on the analysis below critical (electric gas breakdown) fields and under conditions when transport properties are greatly affected by electron attachment. The present calculations of electron transport data for SF6 and CF3I at low E/n 0 take into account the full extent of the influence of electron attachment and spatially selective electron losses along the profile of electron swarm and attempts to produce data that may be used to model this range of conditions. The results of Monte Carlo simulations are compared to those predicted by the publicly available two term Boltzmann solver BOLSIG+. A multitude of kinetic phenomena in electron transport has been observed and discussed using physical arguments. In particular, we discuss two important phenomena: (1) the reduction of the mean energy with increasing E/n 0 for electrons in \\text{S}{{\\text{F}}6} and (2) the occurrence of negative differential conductivity (NDC) in the bulk drift velocity only for electrons in both \\text{S}{{\\text{F}}6} and CF3I. The electron energy distribution function, spatial variations of the rate coefficient for electron attachment and average energy as well as spatial profile of the swarm are calculated and used to understand these phenomena.

Physical Processes and Applications of the Monte Carlo Radiative Energy Deposition (MRED) Code

NASA Astrophysics Data System (ADS)

Reed, Robert A.; Weller, Robert A.; Mendenhall, Marcus H.; Fleetwood, Daniel M.; Warren, Kevin M.; Sierawski, Brian D.; King, Michael P.; Schrimpf, Ronald D.; Auden, Elizabeth C.

2015-08-01

MRED is a Python-language scriptable computer application that simulates radiation transport. It is the computational engine for the on-line tool CRÈME-MC. MRED is based on c++ code from Geant4 with additional Fortran components to simulate electron transport and nuclear reactions with high precision. We provide a detailed description of the structure of MRED and the implementation of the simulation of physical processes used to simulate radiation effects in electronic devices and circuits. Extensive discussion and references are provided that illustrate the validation of models used to implement specific simulations of relevant physical processes. Several applications of MRED are summarized that demonstrate its ability to predict and describe basic physical phenomena associated with irradiation of electronic circuits and devices. These include effects from single particle radiation (including both direct ionization and indirect ionization effects), dose enhancement effects, and displacement damage effects. MRED simulations have also helped to identify new single event upset mechanisms not previously observed by experiment, but since confirmed, including upsets due to muons and energetic electrons.

Microbial electron transport and energy conservation – the foundation for optimizing bioelectrochemical systems

PubMed Central

Kracke, Frauke; Vassilev, Igor; Krömer, Jens O.

2015-01-01

Microbial electrochemical techniques describe a variety of emerging technologies that use electrode–bacteria interactions for biotechnology applications including the production of electricity, waste and wastewater treatment, bioremediation and the production of valuable products. Central in each application is the ability of the microbial catalyst to interact with external electron acceptors and/or donors and its metabolic properties that enable the combination of electron transport and carbon metabolism. And here also lies the key challenge. A wide range of microbes has been discovered to be able to exchange electrons with solid surfaces or mediators but only a few have been studied in depth. Especially electron transfer mechanisms from cathodes towards the microbial organism are poorly understood but are essential for many applications such as microbial electrosynthesis. We analyze the different electron transport chains that nature offers for organisms such as metal respiring bacteria and acetogens, but also standard biotechnological organisms currently used in bio-production. Special focus lies on the essential connection of redox and energy metabolism, which is often ignored when studying bioelectrochemical systems. The possibility of extracellular electron exchange at different points in each organism is discussed regarding required redox potentials and effect on cellular redox and energy levels. Key compounds such as electron carriers (e.g., cytochromes, ferredoxin, quinones, flavins) are identified and analyzed regarding their possible role in electrode–microbe interactions. This work summarizes our current knowledge on electron transport processes and uses a theoretical approach to predict the impact of different modes of transfer on the energy metabolism. As such it adds an important piece of fundamental understanding of microbial electron transport possibilities to the research community and will help to optimize and advance bioelectrochemical techniques. PMID:26124754

Identifying target processes for microbial electrosynthesis by elementary mode analysis.

PubMed

Kracke, Frauke; Krömer, Jens O

2014-12-30

Microbial electrosynthesis and electro fermentation are techniques that aim to optimize microbial production of chemicals and fuels by regulating the cellular redox balance via interaction with electrodes. While the concept is known for decades major knowledge gaps remain, which make it hard to evaluate its biotechnological potential. Here we present an in silico approach to identify beneficial production processes for electro fermentation by elementary mode analysis. Since the fundamentals of electron transport between electrodes and microbes have not been fully uncovered yet, we propose different options and discuss their impact on biomass and product yields. For the first time 20 different valuable products were screened for their potential to show increased yields during anaerobic electrically enhanced fermentation. Surprisingly we found that an increase in product formation by electrical enhancement is not necessarily dependent on the degree of reduction of the product but rather the metabolic pathway it is derived from. We present a variety of beneficial processes with product yield increases of maximal 36% in reductive and 84% in oxidative fermentations and final theoretical product yields up to 100%. This includes compounds that are already produced at industrial scale such as succinic acid, lysine and diaminopentane as well as potential novel bio-commodities such as isoprene, para-hydroxybenzoic acid and para-aminobenzoic acid. Furthermore, it is shown that the way of electron transport has major impact on achievable biomass and product yields. The coupling of electron transport to energy conservation could be identified as crucial for most processes. This study introduces a powerful tool to determine beneficial substrate and product combinations for electro-fermentation. It also highlights that the maximal yield achievable by bio electrochemical techniques depends strongly on the actual electron transport mechanisms. Therefore it is of great importance to reveal the involved fundamental processes to be able to optimize and advance electro fermentations beyond the level of lab-scale studies.

Model-Based Analysis of the Role of Biological, Hydrological and Geochemical Factors Affecting Uranium Bioremediation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhao, Jiao; Scheibe, Timothy D.; Mahadevan, Radhakrishnan

2011-01-24

Uranium contamination is a serious concern at several sites motivating the development of novel treatment strategies such as the Geobacter-mediated reductive immobilization of uranium. However, this bioremediation strategy has not yet been optimized for the sustained uranium removal. While several reactive-transport models have been developed to represent Geobacter-mediated bioremediation of uranium, these models often lack the detailed quantitative description of the microbial process (e.g., biomass build-up in both groundwater and sediments, electron transport system, etc.) and the interaction between biogeochemical and hydrological process. In this study, a novel multi-scale model was developed by integrating our recent model on electron capacitancemore » of Geobacter (Zhao et al., 2010) with a comprehensive simulator of coupled fluid flow, hydrologic transport, heat transfer, and biogeochemical reactions. This mechanistic reactive-transport model accurately reproduces the experimental data for the bioremediation of uranium with acetate amendment. We subsequently performed global sensitivity analysis with the reactive-transport model in order to identify the main sources of prediction uncertainty caused by synergistic effects of biological, geochemical, and hydrological processes. The proposed approach successfully captured significant contributing factors across time and space, thereby improving the structure and parameterization of the comprehensive reactive-transport model. The global sensitivity analysis also provides a potentially useful tool to evaluate uranium bioremediation strategy. The simulations suggest that under difficult environments (e.g., highly contaminated with U(VI) at a high migration rate of solutes), the efficiency of uranium removal can be improved by adding Geobacter species to the contaminated site (bioaugmentation) in conjunction with the addition of electron donor (biostimulation). The simulations also highlight the interactive effect of initial cell concentration and flow rate on U(VI) reduction.« less

Impact excitation and electron-hole multiplication in graphene and carbon nanotubes.

PubMed

Gabor, Nathaniel M

2013-06-18

In semiconductor photovoltaics, photoconversion efficiency is governed by a simple competition: the incident photon energy is either transferred to the crystal lattice (heat) or transferred to electrons. In conventional materials, energy loss to the lattice is more efficient than energy transferred to electrons, thus limiting the power conversion efficiency. Quantum electronic systems, such as quantum dots, nanowires, and two-dimensional electronic membranes, promise to tip the balance in this competition by simultaneously limiting energy transfer to the lattice and enhancing energy transfer to electrons. By exploring the optical, thermal, and electronic properties of quantum materials, we may perhaps find an ideal optoelectronic material that provides low cost fabrication, facile systems integration, and a means to surpass the standard limit for photoconversion efficiency. Nanoscale carbon materials, such as graphene and carbon nanotubes, provide ideal experimental quantum systems in which to explore optoelectronic behavior for applications in solar energy harvesting. Within essentially the same material, researchers can achieve a broad spectrum of energetic configurations, from a gapless semimetal to a large band-gap semiconducting nanowire. Owing to their nanoscale dimensions, graphene and carbon nanotubes exhibit electronic and optical properties that reflect strong electron-electron interactions. Such strong interactions may lead to exotic low-energy electron transport behavior and high-energy electron scattering processes such as impact excitation and the inverse process of Auger recombination. High-energy processes, which become very important under photoexcitation, may be particularly efficient in nanoscale carbon materials due to the relativistic-like, charged particle band structure and sensitivity to the dielectric environment. In addition, due to the covalently bonded carbon framework that makes up these materials, electron-phonon coupling is very weak. In carbon nanomaterials, strong electron-electron interactions combined with weak electron-phonon interactions results in excellent optical, thermal and electronic properties, the exploration of which promises to reveal fundamentally new physical processes and deliver advanced nanotechnologies. In this Account, we review the results of novel optoelectronic experiments that explore the intrinsic photoresponse of carbon nanomaterials integrated into nanoscale devices. By fabricating gate voltage-controlled photodetectors composed of atomically thin sheets of graphene and individual carbon nanotubes, we are able to fully explore electron transport in these systems under optical illumination. We find that strong electron-electron interactions play a key role in the intrinsic photoresponse of both materials, as evidenced by hot carrier transport in graphene and highly efficient multiple electron-hole pair generation in nanotubes. In both of these quantum systems, photoexcitation leads to high-energy electron-hole pairs that relax energy predominantly into the electronic system, rather than heating the lattice. Due to highly efficient energy transfer from photons into electrons, graphene and carbon nanotubes may be ideal materials for solar energy harvesting devices with efficiencies that could exceed the Shockley-Queisser limit.

Reliable Transport over SpaceWire for James Webb Space Telescope (JWST) Focal Plane Electronics (FPE) Network

NASA Technical Reports Server (NTRS)

Rakow, Glenn; Schnurr, Richard; Dailey, Christopher; Shakoorzadeh, Kamdin

2003-01-01

NASA's James Webb Space Telescope (JWST) faces difficult technical and budgetary challenges to overcome before it is scheduled launch in 2010. The Integrated Science Instrument Module (ISIM), shares these challenges. The major challenge addressed in this paper is the data network used to collect, process, compresses and store Infrared data. A total of 114 Mbps of raw information must be collected from 19 sources and delivered to the two redundant data processing units across a twenty meter deployed thermally restricted interface. Further data must be transferred to the solid-state recorder and the spacecraft. The JWST detectors are kept at cryogenic temperatures to obtain the sensitivity necessary to measure faint energy sources. The Focal Plane Electronics (FPE) that sample the detector, generate packets from the samples, and transmit these packets to the processing electronics must dissipate little power in order to help keep the detectors at these cold temperatures. Separating the low powered front-end electronics from the higher-powered processing electronics, and using a simple high-speed protocol to transmit the detector data minimize the power dissipation near the detectors. Low Voltage Differential Signaling (LVDS) drivers were considered an obvious choice for physical layer because of their high speed and low power. The mechanical restriction on the number cables across the thermal interface force the Image packets to be concentrated upon two high-speed links. These links connect the many image packet sources, Focal Plane Electronics (FPE), located near the cryogenic detectors to the processing electronics on the spacecraft structure. From 12 to 10,000 seconds of raw data are processed to make up an image, various algorithms integrate the pixel data Loss of commands to configure the detectors as well as the loss of science data itself may cause inefficiency in the use of the telescope that are unacceptable given the high cost of the observatory. This combination of requirements necessitates a redundant, fault tolerant, high- speed, low mass, low power network with a low Bit error Rate(1E-9- 1E-12). The ISIM systems team performed many studies of the various network architectures that meeting these requirements. The architecture selected uses the Spacewire protocol, with the addition of a new transport and network layer added to implement end-to-end reliable transport. The network and reliable transport mechanism must be implemented in hardware because of the high average information rate and the restriction on the ability of the detectors to buffer data due to power and size restrictions. This network and transport mechanism was designed to be compatible with existing Spacewire links and routers so that existing equipment and designs may be leveraged upon. The transport layer specification is being coordinated with European Space Agency (ESA), Spacewire Working Group and the Consultative Committee for Space Data System (CCSDS) PlK Standard Onboard Interface (SOIF) panel, with the intent of developing a standard for reliable transport for Spacewire. Changes to the protocol presented are likely since negotiations are ongoing with these groups. A block of RTL VHDL that implements a multi-port Spacewire router with an external user interface will be developed and integrated with an existing Spacewire Link design. The external user interface will be the local interface that sources and sinks packets onto and off of the network (Figure 3). The external user interface implements the network and transport layer and handles acknowledgements and re-tries of packets for reliable transport over the network. Because the design is written in RTL, it may be ported to any technology but will initially be targeted to the new Actel Accelerator series (AX) part. Each link will run at 160 Mbps and the power will be about 0.165 Watt per link worst case in the Actel AX.

A Comparative Study of Spectral Auroral Intensity Predictions From Multiple Electron Transport Models

NASA Astrophysics Data System (ADS)

Grubbs, Guy; Michell, Robert; Samara, Marilia; Hampton, Donald; Hecht, James; Solomon, Stanley; Jahn, Jorg-Micha

2018-01-01

It is important to routinely examine and update models used to predict auroral emissions resulting from precipitating electrons in Earth's magnetotail. These models are commonly used to invert spectral auroral ground-based images to infer characteristics about incident electron populations when in situ measurements are unavailable. In this work, we examine and compare auroral emission intensities predicted by three commonly used electron transport models using varying electron population characteristics. We then compare model predictions to same-volume in situ electron measurements and ground-based imaging to qualitatively examine modeling prediction error. Initial comparisons showed differences in predictions by the GLobal airglOW (GLOW) model and the other transport models examined. Chemical reaction rates and radiative rates in GLOW were updated using recent publications, and predictions showed better agreement with the other models and the same-volume data, stressing that these rates are important to consider when modeling auroral processes. Predictions by each model exhibit similar behavior for varying atmospheric constants, energies, and energy fluxes. Same-volume electron data and images are highly correlated with predictions by each model, showing that these models can be used to accurately derive electron characteristics and ionospheric parameters based solely on multispectral optical imaging data.

Interdye Hole Transport Accelerates Recombination in Dye Sensitized Mesoporous Films.

PubMed

Moia, Davide; Szumska, Anna; Vaissier, Valérie; Planells, Miquel; Robertson, Neil; O'Regan, Brian C; Nelson, Jenny; Barnes, Piers R F

2016-10-12

Charge recombination between oxidized dyes attached to mesoporous TiO 2 and electrons in the TiO 2 was studied in inert electrolytes using transient absorption spectroscopy. Simultaneously, hole transport within the dye monolayers was monitored by transient absorption anisotropy. The rate of recombination decreased when hole transport was inhibited selectively, either by decreasing the dye surface coverage or by changing the electrolyte environment. From Monte Carlo simulations of electron and hole diffusion in a particle, modeled as a cubic structure, we identify the conditions under which hole lifetime depends on the hole diffusion coefficient for the case of normal (disorder free) diffusion. From simulations of transient absorption and transient absorption anisotropy, we find that the rate and the dispersive character of hole transport in the dye monolayer observed spectroscopically can be explained by incomplete coverage and disorder in the monolayer. We show that dispersive transport in the dye monolayer combined with inhomogeneity in the TiO 2 surface reactivity can contribute to the observed stretched electron-hole recombination dynamics and electron density dependence of hole lifetimes. Our experimental and computational analysis of lateral processes at interfaces can be applied to investigate and optimize charge transport and recombination in solar energy conversion devices using electrodes functionalized with molecular light absorbers and catalysts.

Direct Observation of Virtual Electrode Formation Through a Novel Electrolyte-to-Electrode Transition

NASA Astrophysics Data System (ADS)

Siegel, David; El Gabaly, Farid; Bartelt, Norman; McCarty, Kevin

2014-03-01

Novel electrochemical solutions to problems in energy storage and transportation can drive renewable energy to become an economically viable alternative to fossil fuels. In many electrochemical systems, the behavior of a device can be fundamentally limited by the surface area of a triple phase boundary, the boundary region where a gas-phase species, electrode, and electrolyte coincide. When the electrode is an ionic insulator the triple phase boundary is typically a one-dimensional boundary with nanometer-scale thickness: ions cannot transport through the electrode, while electrons cannot be transported through the electrolyte. Here we present direct experimental measurements of a novel electrolyte-to-electrode transition with photoemission electron microscopy, and observe that the surface of an ionically conductive, electronically insulative solid oxide electrolyte undergoes a transition into a mixed electron-ion conductor in the vicinity of a metal electrode. Our direct experimental measurements allow us to characterize this system and address the mechanisms of ionic reactions and transport through comparisons with theoretical modeling to provide us with a physical picture of the processes involved. Our results provide insight into one of the mechanisms of ion transport in an electrochemical cell that may be generalizable to other systems.

MULTI-SPACECRAFT OBSERVATIONS AND TRANSPORT MODELING OF ENERGETIC ELECTRONS FOR A SERIES OF SOLAR PARTICLE EVENTS IN AUGUST 2010

DOE Office of Scientific and Technical Information (OSTI.GOV)

Dröge, W.; Kartavykh, Y. Y.; Dresing, N.

During 2010 August a series of solar particle events was observed by the two STEREO spacecraft as well as near-Earth spacecraft. The events, occurring on August 7, 14, and 18, originated from active regions 11093 and 11099. We combine in situ and remote-sensing observations with predictions from our model of three-dimensional anisotropic particle propagation in order to investigate the physical processes that caused the large angular spreads of energetic electrons during these events. In particular, we address the effects of the lateral transport of the electrons in the solar corona that is due to diffusion perpendicular to the average magneticmore » field in the interplanetary medium. We also study the influence of two coronal mass ejections and associated shock waves on the electron propagation, and a possible time variation of the transport conditions during the above period. For the August 18 event we also utilize electron observations from the MESSENGER spacecraft at a distance of 0.31 au from the Sun for an attempt to separate between radial and longitudinal dependencies in the transport process. Our modelings show that the parallel and perpendicular diffusion mean free paths of electrons can vary significantly not only as a function of the radial distance, but also of the heliospheric longitude. Normalized to a distance of 1 au, we derive values of λ {sub ∥} in the range of 0.15–0.6 au, and values of λ {sub ⊥} in the range of 0.005–0.01 au. We discuss how our results relate to various theoretical models for perpendicular diffusion, and whether there might be a functional relationship between the perpendicular and the parallel mean free path.« less

Multi-spacecraft Observations and Transport Modeling of Energetic Electrons for a Series of Solar Particle Events in August 2010

NASA Astrophysics Data System (ADS)

Dröge, W.; Kartavykh, Y. Y.; Dresing, N.; Klassen, A.

2016-08-01

During 2010 August a series of solar particle events was observed by the two STEREO spacecraft as well as near-Earth spacecraft. The events, occurring on August 7, 14, and 18, originated from active regions 11093 and 11099. We combine in situ and remote-sensing observations with predictions from our model of three-dimensional anisotropic particle propagation in order to investigate the physical processes that caused the large angular spreads of energetic electrons during these events. In particular, we address the effects of the lateral transport of the electrons in the solar corona that is due to diffusion perpendicular to the average magnetic field in the interplanetary medium. We also study the influence of two coronal mass ejections and associated shock waves on the electron propagation, and a possible time variation of the transport conditions during the above period. For the August 18 event we also utilize electron observations from the MESSENGER spacecraft at a distance of 0.31 au from the Sun for an attempt to separate between radial and longitudinal dependencies in the transport process. Our modelings show that the parallel and perpendicular diffusion mean free paths of electrons can vary significantly not only as a function of the radial distance, but also of the heliospheric longitude. Normalized to a distance of 1 au, we derive values of λ ∥ in the range of 0.15-0.6 au, and values of λ ⊥ in the range of 0.005-0.01 au. We discuss how our results relate to various theoretical models for perpendicular diffusion, and whether there might be a functional relationship between the perpendicular and the parallel mean free path.

n-Channel semiconductor materials design for organic complementary circuits.

PubMed

Usta, Hakan; Facchetti, Antonio; Marks, Tobin J

2011-07-19

Organic semiconductors have unique properties compared to traditional inorganic materials such as amorphous or crystalline silicon. Some important advantages include their adaptability to low-temperature processing on flexible substrates, low cost, amenability to high-speed fabrication, and tunable electronic properties. These features are essential for a variety of next-generation electronic products, including low-power flexible displays, inexpensive radio frequency identification (RFID) tags, and printable sensors, among many other applications. Accordingly, the preparation of new materials based on π-conjugated organic molecules or polymers has been a central scientific and technological research focus over the past decade. Currently, p-channel (hole-transporting) materials are the leading class of organic semiconductors. In contrast, high-performance n-channel (electron-transporting) semiconductors are relatively rare, but they are of great significance for the development of plastic electronic devices such as organic field-effect transistors (OFETs). In this Account, we highlight the advances our team has made toward realizing moderately and highly electron-deficient n-channel oligomers and polymers based on oligothiophene, arylenediimide, and (bis)indenofluorene skeletons. We have synthesized and characterized a "library" of structurally related semiconductors, and we have investigated detailed structure-property relationships through optical, electrochemical, thermal, microstructural (both single-crystal and thin-film), and electrical measurements. Our results reveal highly informative correlations between structural parameters at various length scales and charge transport properties. We first discuss oligothiophenes functionalized with perfluoroalkyl and perfluoroarene substituents, which represent the initial examples of high-performance n-channel semiconductors developed in this project. The OFET characteristics of these compounds are presented with an emphasis on structure-property relationships. We then examine the synthesis and properties of carbonyl-functionalized oligomers, which constitute second-generation n-channel oligothiophenes, in both vacuum- and solution-processed FETs. These materials have high carrier mobilities and good air stability. In parallel, exceptionally electron-deficient cyano-functionalized arylenediimide derivatives are discussed as early examples of thermodynamically air-stable, high-performance n-channel semiconductors; they exhibit record electron mobilities of up to 0.64 cm(2)/V·s. Furthermore, we provide an overview of highly soluble ladder-type macromolecular semiconductors as OFET components, which combine ambient stability with solution processibility. A high electron mobility of 0.16 cm(2)/V·s is obtained under ambient conditions for solution-processed films. Finally, examples of polymeric n-channel semiconductors with electron mobilities as high as 0.85 cm(2)/V·s are discussed; these constitute an important advance toward fully printed polymeric electronic circuitry. Density functional theory (DFT) computations reveal important trends in molecular physicochemical and semiconducting properties, which, when combined with experimental data, shed new light on molecular charge transport characteristics. Our data provide the basis for a fundamental understanding of charge transport in high-performance n-channel organic semiconductors. Moreover, our results provide a road map for developing functional, complementary organic circuitry, which requires combining p- and n-channel transistors.

Electronic and Ionic Transport in Processable Conducting Polymers

DTIC Science & Technology

1991-05-28

doping with nitrosonium fluoborate. 6. Polypyrrole containing luminescent ions has been shown to be useful as in-situ probes of ion transport during...blends, ion transport, fibers, theoretical calculations ABSTRACT (Continue on reverse if necessary and identify by block number) A summary of the research...polymer/dopant ion interactions, symmereically and asymmetrically substituted poly(di-2-heterocycle-2,5-disubstitutedphenylenes), poly(5

Multi-field plasma sandpile model in tokamaks and applications

NASA Astrophysics Data System (ADS)

Peng, X. D.; Xu, J. Q.

2016-08-01

A multi-field sandpile model of tokamak plasmas is formulated for the first time to simulate the dynamic process with interaction between avalanche events on the fast/micro time-scale and diffusive transports on the slow/macro time-scale. The main characteristics of the model are that both particle and energy avalanches of sand grains are taken into account simultaneously. New redistribution rules of a sand-relaxing process are defined according to the transport properties of special turbulence which allows the uphill particle transport. Applying the model, we first simulate the steady-state plasma profile self-sustained by drift wave turbulences in the Ohmic discharge of a tokamak. A scaling law as f = a q0 b + c for the relation of both center-density n ( 0 ) and electron (ion) temperatures T e ( 0 ) ( T i ( 0 ) ) with the center-safety-factor q 0 is found. Then interesting work about the nonlocal transport phenomenon observed in tokamak experiments proceeds. It is found that the core electron temperature increases rapidly in response to the edge cold pulse and inversely it decreases in response to the edge heat pulse. The results show that the nonlocal response of core electron temperature depending on the amplitudes of background plasma density and temperature is more remarkable in a range of gas injection rate. Analyses indicate that the avalanche transport caused by plasma drift instabilities with thresholds is a possible physical mechanism for the nonlocal transport in tokamaks. It is believed that the model is capable of being applied to more extensive questions occurring in the transport field.

Energy-Filtered Tunnel Transistor: A New Device Concept Toward Extremely-Low Energy Consumption Electronics

DTIC Science & Technology

2015-12-17

temperature . New device architecture that utilizes cold-electron transport for ultra-low energy consumption electronics has been designed in a configuration...the oxygen has also been found important for the SiC>2 sputter deposition. The sputter was carried out at room temperature . Our optimized process...have been pursued for two electronic devices, 1) room- temperature single-electron transistors, and 2) ultralow energy consumption transistors. For

Chain conformations dictate multiscale charge transport phenomena in disordered semiconducting polymers

PubMed Central

Noriega, Rodrigo; Salleo, Alberto; Spakowitz, Andrew J.

2013-01-01

Existing models for the electronic properties of conjugated polymers do not capture the spatial arrangement of the disordered macromolecular chains over which charge transport occurs. Here, we present an analytical and computational description in which the morphology of individual polymer chains is dictated by well-known statistical models and the electronic coupling between units is determined using Marcus theory. The multiscale transport of charges in these materials (high mobility at short length scales, low mobility at long length scales) is naturally described with our framework. Additionally, the dependence of mobility with electric field and temperature is explained in terms of conformational variability and spatial correlation. Our model offers a predictive approach to connecting processing conditions with transport behavior. PMID:24062459

Chain conformations dictate multiscale charge transport phenomena in disordered semiconducting polymers.

PubMed

Noriega, Rodrigo; Salleo, Alberto; Spakowitz, Andrew J

2013-10-08

Existing models for the electronic properties of conjugated polymers do not capture the spatial arrangement of the disordered macromolecular chains over which charge transport occurs. Here, we present an analytical and computational description in which the morphology of individual polymer chains is dictated by well-known statistical models and the electronic coupling between units is determined using Marcus theory. The multiscale transport of charges in these materials (high mobility at short length scales, low mobility at long length scales) is naturally described with our framework. Additionally, the dependence of mobility with electric field and temperature is explained in terms of conformational variability and spatial correlation. Our model offers a predictive approach to connecting processing conditions with transport behavior.

Effects of water stress on photosynthetic electron transport, photophosphorylation, and metabolite levels of Xanthium strumarium mesophyll cells.

PubMed

Sharkey, T D; Badger, M R

1982-12-01

Several component processes of photosynthesis were measured in osmotically stressed mesophyll cells of Xanthium strumarium L. The ribulose-1,5-bisphosphate regeneration capacity was reduced by water stress. Photophoshorylation was sensitive to water stress but photosynthetic electron transport was unaffected by water potentials down to-40 bar (-4 MPa). The concentrations of several intermediates of the photosynthetic carbon-reduction cycle remained relatively constant and did not indicate that ATP supply was limiting photosynthesis in the water-stressed cells.

Cadmium toxicity to photosynthesis and associated electron transport system of Nostoc linckia

DOE Office of Scientific and Technical Information (OSTI.GOV)

Husaini, Yasmin; Singh, A.K.; Rai, L.C.

1991-01-01

The present work has been undertaken not only to find out the site of action of Cd in cyanobacteria but also to know the mechanism of inhibition of photosynthetic electron transport, a process responsible for the generation of ATP and NADPH, which are essential for carbon fixation. The present study compares the sensitivities of photosystem 1(PS 1), photosystem 2 (PS 2) and redox coupling between the two photosystems of Nostoc linckia exposed to different concentrations of cadmium.

A head-up display format for transport aircraft approach and landing

NASA Technical Reports Server (NTRS)

Bray, R. S.; Scott, B. C.

1981-01-01

An electronic flight-guidance display format was designed for use in evaluations of the collimated head-up display concept applied to transport aircraft landing. In the design process of iterative evaluation and modification, some general principles, or guidelines, applicable to electronic flight displays were suggested. The usefulness of an indication of instantaneous inertial flightpath was clearly demonstrated. Evaluator pilot acceptance of the unfamiliar display concepts was very positive when careful attention was given to indoctrination and training.

Anaerobic humus and Fe(III) reduction and electron transport pathway by a novel humus-reducing bacterium, Thauera humireducens SgZ-1.

PubMed

Ma, Chen; Yu, Zhen; Lu, Qin; Zhuang, Li; Zhou, Shun-Gui

2015-04-01

In this study, an anaerobic batch experiment was conducted to investigate the humus- and Fe(III)-reducing ability of a novel humus-reducing bacterium, Thauera humireducens SgZ-1. Inhibition tests were also performed to explore the electron transport pathways with various electron acceptors. The results indicate that in anaerobic conditions, strain SgZ-1 possesses the ability to reduce a humus analog, humic acids, soluble Fe(III), and Fe(III) oxides. Acetate, propionate, lactate, and pyruvate were suitable electron donors for humus and Fe(III) reduction by strain SgZ-1, while fermentable sugars (glucose and sucrose) were not. UV-visible spectra obtained from intact cells of strain SgZ-1 showed absorption peaks at 420, 522, and 553 nm, characteristic of c-type cytochromes (cyt c). Dithionite-reduced cyt c was reoxidized by Fe-EDTA and HFO (hydrous ferric oxide), which suggests that cyt c within intact cells of strain SgZ-1 has the ability to donate electrons to extracellular Fe(III) species. Inhibition tests revealed that dehydrogenases, quinones, and cytochromes b/c (cyt b/c) were involved in reduction of AQS (9, 10-anthraquinone-2-sulfonic acid, humus analog) and oxygen. In contrast, only NADH dehydrogenase was linked to electron transport to HFO, while dehydrogenases and cyt b/c were found to participate in the reduction of Fe-EDTA. Thus, various different electron transport pathways are employed by strain SgZ-1 for different electron acceptors. The results from this study help in understanding the electron transport processes and environmental responses of the genus Thauera.

Hydrodynamic Electron Flow and Hall Viscosity

NASA Astrophysics Data System (ADS)

Scaffidi, Thomas; Moll, Philip; Kushwaha, Pallavi; Nandi, Nabhanila; Schmidt, Burkhard; MacKenzie, Andrew; Moore, Joel

In metallic samples of small enough size and sufficiently strong electron-electron scattering, the viscosity of the electron gas can become the dominant process governing transport. In this regime, momentum is a long-lived quantity whose evolution is described by an emergent hydrodynamical theory for which bounds on diffusion were conjectured based on an holographic correspondence. Furthermore, breaking time-reversal symmetry can lead to the appearance of an odd component to the viscosity called the Hall viscosity which has attracted a lot of attention recently due to its quantized nature in gapped systems but still eludes experimental confirmation. Based on microscopic calculations, we discuss how to measure the effects of both the even and odd components of the viscosity using hydrodynamic electronic transport in mesoscopic samples under applied magnetic fields. Gordon and Betty Moore Foundation.

The Impacts of Phosphorus Deficiency on the Photosynthetic Electron Transport Chain1[OPEN

PubMed Central

2018-01-01

Phosphorus (P) is an essential macronutrient, and P deficiency limits plant productivity. Recent work showed that P deficiency affects electron transport to photosystem I (PSI), but the underlying mechanisms are unknown. Here, we present a comprehensive biological model describing how P deficiency disrupts the photosynthetic machinery and the electron transport chain through a series of sequential events in barley (Hordeum vulgare). P deficiency reduces the orthophosphate concentration in the chloroplast stroma to levels that inhibit ATP synthase activity. Consequently, protons accumulate in the thylakoids and cause lumen acidification, which inhibits linear electron flow. Limited plastoquinol oxidation retards electron transport to the cytochrome b6f complex, yet the electron transfer rate of PSI is increased under steady-state growth light and is limited under high-light conditions. Under P deficiency, the enhanced electron flow through PSI increases the levels of NADPH, whereas ATP production remains restricted and, hence, reduces CO2 fixation. In parallel, lumen acidification activates the energy-dependent quenching component of the nonphotochemical quenching mechanism and prevents the overexcitation of photosystem II and damage to the leaf tissue. Consequently, plants can be severely affected by P deficiency for weeks without displaying any visual leaf symptoms. All of the processes in the photosynthetic machinery influenced by P deficiency appear to be fully reversible and can be restored in less than 60 min after resupply of orthophosphate to the leaf tissue. PMID:29540590

Sol-gel derived ZnO as an electron transport layer (ETL) for inverted organic solar cells

NASA Astrophysics Data System (ADS)

Tiwari, D. C.; Dwivedi, Shailendra Kumar; Dipak, Phukhrambam; Chandel, Tarun; Sharma, Rishi

2017-05-01

In this work, we present the study of the fabrication process of the sol-gel derived zinc oxide (ZnO) as an electron transport layer (ETL.). The solution processed inverted bulk heterojunction organic solar cells based on a thin film blend of poly (3-hexylthiophene 2, 5-diyl) and [6,6]-phenyl-C61-butyric acid methyl ester is prepared. ZnO thin films are annealed at different temperature to optimize the solar cell performance and their characterization for their structural and optical properties are carried out. We have observed Voc=70mV, Jsc=1.33 µA/cm2 and FF=26% from the inverted heterojunction solar cell.

Parallel processing implementation for the coupled transport of photons and electrons using OpenMP

NASA Astrophysics Data System (ADS)

Doerner, Edgardo

2016-05-01

In this work the use of OpenMP to implement the parallel processing of the Monte Carlo (MC) simulation of the coupled transport for photons and electrons is presented. This implementation was carried out using a modified EGSnrc platform which enables the use of the Microsoft Visual Studio 2013 (VS2013) environment, together with the developing tools available in the Intel Parallel Studio XE 2015 (XE2015). The performance study of this new implementation was carried out in a desktop PC with a multi-core CPU, taking as a reference the performance of the original platform. The results were satisfactory, both in terms of scalability as parallelization efficiency.

Aggregation control in natural brush-printed conjugated polymer films and implications for enhancing charge transport

PubMed Central

Wang, Gang; Huang, Wei; Eastham, Nicholas D.; Fabiano, Simone; Manley, Eric F.; Zeng, Li; Wang, Binghao; Zhang, Xinan; Chen, Zhihua; Li, Ran; Chang, Robert P. H.; Chen, Lin X.; Bedzyk, Michael J.; Melkonyan, Ferdinand S.; Facchetti, Antonio; Marks, Tobin J.

2017-01-01

Shear-printing is a promising processing technique in organic electronics for microstructure/charge transport modification and large-area film fabrication. Nevertheless, the mechanism by which shear-printing can enhance charge transport is not well-understood. In this study, a printing method using natural brushes is adopted as an informative tool to realize direct aggregation control of conjugated polymers and to investigate the interplay between printing parameters, macromolecule backbone alignment and aggregation, and charge transport anisotropy in a conjugated polymer series differing in architecture and electronic structure. This series includes (i) semicrystalline hole-transporting P3HT, (ii) semicrystalline electron-transporting N2200, (iii) low-crystallinity hole-transporting PBDTT-FTTE, and (iv) low-crystallinity conducting PEDOT:PSS. The (semi-)conducting films are characterized by a battery of morphology and microstructure analysis techniques and by charge transport measurements. We report that remarkably enhanced mobilities/conductivities, as high as 5.7×/3.9×, are achieved by controlled growth of nanofibril aggregates and by backbone alignment, with the adjusted R2 (R2adj) correlation between aggregation and charge transport as high as 95%. However, while shear-induced aggregation is important for enhancing charge transport, backbone alignment alone does not guarantee charge transport anisotropy. The correlations between efficient charge transport and aggregation are clearly shown, while mobility and degree of orientation are not always well-correlated. These observations provide insights into macroscopic charge transport mechanisms in conjugated polymers and suggest guidelines for optimization. PMID:29109282

Development and fabrication of a solar cell junction processing system

NASA Technical Reports Server (NTRS)

Bunker, S.

1981-01-01

A solar cell junction processing system was developed and fabricated. A pulsed electron beam for the four inch wafers is being assembled and tested, wafers were successfully pulsed, and solar cells fabricated. Assembly of the transport locks is completed. The transport was operated successfully but not with sufficient reproducibility. An experiment test facility to examine potential scaleup problems associated with the proposed ion implanter design was constructed and operated. Cells were implanted and found to have efficiency identical to the normal Spire implant process.

Efficient planar Sb2S3 solar cells using a low-temperature solution-processed tin oxide electron conductor.

PubMed

Lei, Hongwei; Yang, Guang; Guo, Yaxiong; Xiong, Liangbin; Qin, Pingli; Dai, Xin; Zheng, Xiaolu; Ke, Weijun; Tao, Hong; Chen, Zhao; Li, Borui; Fang, Guojia

2016-06-28

Efficient planar antimony sulfide (Sb2S3) heterojunction solar cells have been made using chemical bath deposited (CBD) Sb2S3 as the absorber, low-temperature solution-processed tin oxide (SnO2) as the electron conductor and poly (3-hexylthiophene) (P3HT) as the hole conductor. A solar conversion efficiency of 2.8% was obtained at 1 sun illumination using a planar device consisting of F-doped SnO2 substrate/SnO2/CBD-Sb2S3/P3HT/Au, whereas the solar cells based on a titanium dioxide (TiO2) electron conductor exhibited a power conversion efficiency of 1.9%. Compared with conventional Sb2S3 sensitized solar cells, the high-temperature processed mesoscopic TiO2 scaffold is no longer needed. More importantly, a low-temperature solution-processed SnO2 layer was introduced for electron transportation to substitute the high-temperature sintered dense blocking TiO2 layer. Our planar solar cells not only have simple geometry with fewer steps to fabricate but also show enhanced performance. The higher efficiency of planar Sb2S3 solar cell devices based on a SnO2 electron conductor is attributed to their high transparency, uniform surface, efficient electron transport properties of SnO2, suitable energy band alignment, and reduced recombination at the interface of SnO2/Sb2S3.

Core-shell nanophosphor architecture: toward efficient energy transport in inorganic/organic hybrid solar cells.

PubMed

Li, Qinghua; Yuan, Yongbiao; Chen, Zihan; Jin, Xiao; Wei, Tai-huei; Li, Yue; Qin, Yuancheng; Sun, Weifu

2014-08-13

In this work, a core-shell nanostructure of samarium phosphates encapsulated into a Eu(3+)-doped silica shell has been successfully fabricated, which has been confirmed by X-ray diffraction, transmission electron microscopy (TEM), and high-resolution TEM. Moreover, we report the energy transfer process from the Sm(3+) to emitters Eu(3+) that widens the light absorption range of the hybrid solar cells (HSCs) and the strong enhancement of the electron-transport of TiO2/poly(3-hexylthiophene) (P3HT) bulk heterojunction (BHJ) HSCs by introducing the unique core-shell nanoarchitecture. Furthermore, by applying femtosecond transient absorption spectroscopy, we successfully obtain the electron transport lifetimes of BHJ systems with or without incorporating the core-shell nanophosphors (NPs). Concrete evidence has been provided that the doping of core-shell NPs improves the efficiency of electron transfers from donor to acceptor, but the hole transport almost remains unchanged. In particular, the hot electron transfer lifetime was shortened from 30.2 to 16.7 ps, i.e., more than 44% faster than pure TiO2 acceptor. Consequently, a notable power conversion efficiency of 3.30% for SmPO4@Eu(3+):SiO2 blended TiO2/P3HT HSCs is achieved at 5 wt % as compared to 1.98% of pure TiO2/P3HT HSCs. This work indicates that the core-shell NPs can efficiently broaden the absorption region, facilitate electron-transport of BHJ, and enhance photovoltaic performance of inorganic/organic HSCs.

Electrochemical impedance spectroscopy for study of electronic structure in disordered organic semiconductors—Possibilities and limitations

NASA Astrophysics Data System (ADS)

Schauer, F.; Nádaždy, V.; Gmucová, K.

2018-04-01

There is potential in applying conjugated polymers in novel organic optoelectronic devices, where a comprehensive understanding of the fundamental processes and energetics involved during transport and recombination is still lacking, limiting further device optimization. The electronic transport modeling and its optimization need the energy distribution of transport and defect states, expressed by the energy distribution of the Density of States (DOS) function, as input/comparative parameters. We present the Energy Resolved-Electrochemical Impedance Spectroscopy (ER-EIS) method for the study of transport and defect electronic states in organic materials. The method allows mapping over unprecedentedly wide energy and DOS ranges. The ER-EIS spectroscopic method is based on the small signal interaction between the surface of the organic film and the liquid electrolyte containing reduction-oxidation (redox) species, which is similar to the extraction of an electron by an acceptor and capture of an electron by a donor at a semiconductor surface. The desired DOS of electronic transport and defect states can be derived directly from the measured redox response signal to the small voltage perturbation at the instantaneous position of the Fermi energy, given by the externally applied voltage. The theory of the ER-EIS method and conditions for its validity for solid polymers are presented in detail. We choose four case studies on poly(3-hexylthiophene-2,5-diyl) and poly[methyl(phenyl)silane] to show the possibilities of the method to investigate the electronic structure expressed by DOS of polymers with a high resolution of about 6 orders of magnitude and in a wide energy range of 6 eV.

The Role of Diffusion in the Transport of Energetic Electrons during Solar Flares

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bian, Nicolas H.; Kontar, Eduard P.; Emslie, A. Gordon, E-mail: nicolas.bian@glasgow.gla.ac.uk, E-mail: emslieg@wku.edu

2017-02-01

The transport of the energy contained in suprathermal electrons in solar flares plays a key role in our understanding of many aspects of flare physics, from the spatial distributions of hard X-ray emission and energy deposition in the ambient atmosphere to global energetics. Historically the transport of these particles has been largely treated through a deterministic approach, in which first-order secular energy loss to electrons in the ambient target is treated as the dominant effect, with second-order diffusive terms (in both energy and angle) generally being either treated as a small correction or even neglected. Here, we critically analyze thismore » approach, and we show that spatial diffusion through pitch-angle scattering necessarily plays a very significant role in the transport of electrons. We further show that a satisfactory treatment of the diffusion process requires consideration of non-local effects, so that the electron flux depends not just on the local gradient of the electron distribution function but on the value of this gradient within an extended region encompassing a significant fraction of a mean free path. Our analysis applies generally to pitch-angle scattering by a variety of mechanisms, from Coulomb collisions to turbulent scattering. We further show that the spatial transport of electrons along the magnetic field of a flaring loop can be modeled rather effectively as a Continuous Time Random Walk with velocity-dependent probability distribution functions of jump sizes and occurrences, both of which can be expressed in terms of the scattering mean free path.« less

Hydrogen is a preferred intermediate in the energy-conserving electron transport chain of Methanosarcina barkeri.

PubMed

Kulkarni, Gargi; Kridelbaugh, Donna M; Guss, Adam M; Metcalf, William W

2009-09-15

Methanogens use an unusual energy-conserving electron transport chain that involves reduction of a limited number of electron acceptors to methane gas. Previous biochemical studies suggested that the proton-pumping F(420)H(2) dehydrogenase (Fpo) plays a crucial role in this process during growth on methanol. However, Methanosarcina barkeri Delta fpo mutants constructed in this study display no measurable phenotype on this substrate, indicating that Fpo plays a minor role, if any. In contrast, Delta frh mutants lacking the cytoplasmic F(420)-reducing hydrogenase (Frh) are severely affected in their ability to grow and make methane from methanol, and double Delta fpo/Delta frh mutants are completely unable to use this substrate. These data suggest that the preferred electron transport chain involves production of hydrogen gas in the cytoplasm, which then diffuses out of the cell, where it is reoxidized with transfer of electrons into the energy-conserving electron transport chain. This hydrogen-cycling metabolism leads directly to production of a proton motive force that can be used by the cell for ATP synthesis. Nevertheless, M. barkeri does have the flexibility to use the Fpo-dependent electron transport chain when needed, as shown by the poor growth of the Delta frh mutant. Our data suggest that the rapid enzymatic turnover of hydrogenases may allow a competitive advantage via faster growth rates in this freshwater organism. The mutant analysis also confirms the proposed role of Frh in growth on hydrogen/carbon dioxide and suggests that either Frh or Fpo is needed for aceticlastic growth of M. barkeri.

Transition Metal-Oxide Free Perovskite Solar Cells Enabled by a New Organic Charge Transport Layer.

PubMed

Chang, Sehoon; Han, Ggoch Ddeul; Weis, Jonathan G; Park, Hyoungwon; Hentz, Olivia; Zhao, Zhibo; Swager, Timothy M; Gradečak, Silvija

2016-04-06

Various electron and hole transport layers have been used to develop high-efficiency perovskite solar cells. To achieve low-temperature solution processing of perovskite solar cells, organic n-type materials are employed to replace the metal oxide electron transport layer (ETL). Although PCBM (phenyl-C61-butyric acid methyl ester) has been widely used for this application, its morphological instability in films (i.e., aggregation) is detrimental. Herein, we demonstrate the synthesis of a new fullerene derivative (isobenzofulvene-C60-epoxide, IBF-Ep) that serves as an electron transporting material for methylammonium mixed lead halide-based perovskite (CH3NH3PbI(3-x)Cl(x)) solar cells, both in the normal and inverted device configurations. We demonstrate that IBF-Ep has superior morphological stability compared to the conventional acceptor, PCBM. IBF-Ep provides higher photovoltaic device performance as compared to PCBM (6.9% vs 2.5% in the normal and 9.0% vs 5.3% in the inverted device configuration). Moreover, IBF-Ep devices show superior tolerance to high humidity (90%) in air. By reaching power conversion efficiencies up to 9.0% for the inverted devices with IBF-Ep as the ETL, we demonstrate the potential of this new material as an alternative to metal oxides for perovskite solar cells processed in air.

Requirements analysis report for transport estimation, preconstruction, construction, decision support and electronic bidding systems

DOT National Transportation Integrated Search

2009-01-01

Info Tech conducted an on-site visit at the Connecticut Department of Transportation in Newington : from October 27-31, 2008. The purpose of the visit was to conduct an analysis of ConnDOTs : processes and to review the operations and business sys...

Proteomics Analysis Reveals Abnormal Electron Transport and Excessive Oxidative Stress Cause Mitochondrial Dysfunction in Placental Tissues of Early-Onset Preeclampsia.

PubMed

Xu, Zhongwei; Jin, Xiaohan; Cai, Wei; Zhou, Maobin; Shao, Ping; Yang, Zhen; Fu, Rong; Cao, Jin; Liu, Yan; Yu, Fang; Fan, Rong; Zhang, Yan; Zou, Shuang; Zhou, Xin; Yang, Ning; Chen, Xu; Li, Yuming

2018-04-20

Early-onset preeclampsia (EOS-PE) refers to preeclampsia that occurred before 34 gestation weeks. This study is conducted to explore the relationship between mitochondrial dysfunction and the pathogenesis of EOS-PE using proteomic strategy. To identify altering expressed mitochondrial proteins between severe EOS-PE and healthy pregnancies, enrichment of mitochondria coupled with iTRAQ-based quantitative proteomic method is performed. Immunohistochemistry (IHC) and western blot are performed to detect the alteration of changing expression proteins, and confirmed the accuracy of proteomic results. A total of 1372 proteins were quantified and 132 altering expressed proteins were screened, including 86 downregulated expression proteins and 46 upregulated expression proteins (p < 0.05). Bioinformatics analysis showed that differentially expressed proteins participated in numerous biological processes, including oxidation-reduction process, respiratory electron transport chain, and oxidative phosphorylation. Especially, mitochondria-related molecules, PRDX2, PARK7, BNIP3, BCL2, PDHA1, SUCLG1, ACADM, and NDUFV1, are involved in energy-production process in the matrix and membrane of mitochondria. Results of the experiment show that abnormal electron transport, excessive oxidative stress, and mitochondrion disassembly might be the main cause of mitochondrial dysfunction, and is related to the pathogenesis of EOS-PE. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Improvement of the photovoltaic parameters of perovskite solar cells using a reduced-graphene-oxide-modified titania layer and soluble copper phthalocyanine as a hole transporter.

PubMed

Nouri, Esmaiel; Mohammadi, Mohammad Reza; Xu, Zong-Xiang; Dracopoulos, Vassilios; Lianos, Panagiotis

2018-01-24

Functional perovskite solar cells can be made by using a simple, inexpensive and stable soluble tetra-n-butyl-substituted copper phthalocyanine (CuBuPc) as a hole transporter. In the present study, TiO 2 /reduced graphene oxide (T/RGO) hybrids were synthesized via an in situ solvothermal process and used as electron acceptor/transport mediators in mesoscopic perovskite solar cells based on soluble CuBuPc as a hole transporter and on graphene oxide (GO) as a buffer layer. The impact of the RGO content on the optoelectronic properties of T/RGO hybrids and on the solar cell performance was studied, suggesting improved electron transport characteristics and photovoltaic parameters. An enhanced electron lifetime and recombination resistance led to an increase in the short circuit current density, open circuit voltage and fill factor. The device based on a T/RGO mesoporous layer with an optimal RGO content of 0.2 wt% showed 22% higher photoconversion efficiency and higher stability compared with pristine TiO 2 -based devices.

Electron stripping processes of H{sup −} ion beam in the 80 kV high voltage extraction column and low energy beam transport line at LANSCE

DOE Office of Scientific and Technical Information (OSTI.GOV)

Draganic, I. N., E-mail: draganic@lanl.gov

Basic vacuum calculations were performed for various operating conditions of the Los Alamos National Neutron Science H{sup −} Cockcroft-Walton (CW) injector and the Ion Source Test Stand (ISTS). The vacuum pressure was estimated for both the CW and ISTS at five different points: (1) inside the H{sup −} ion source, (2) in front of the Pierce electrode, (3) at the extraction electrode, (4) at the column electrode, and (5) at the ground electrode. A static vacuum analysis of residual gases and the working hydrogen gas was completed for the normal ion source working regime. Gas density and partial pressure weremore » estimated for the injected hydrogen gas. The attenuation of H{sup −} beam current and generation of electron current in the high voltage acceleration columns and low energy beam transport lines were calculated. The interaction of H{sup −} ions on molecular hydrogen (H{sub 2}) is discussed as a dominant collision process in describing electron stripping rates. These results are used to estimate the observed increase in the ratio of electrons to H{sup −} ion beam in the ISTS beam transport line.« less

DOE Office of Scientific and Technical Information (OSTI.GOV)

Meusel, O., E-mail: o.meusel@iap.uni-frankfurt.de; Droba, M.; Noll, D.

The transport of intense ion beams is affected by the collective behavior of this kind of multi-particle and multi-species system. The space charge expressed by the generalized perveance dominates the dynamical process of thermalisation, which leads to emittance growth. To prevent changes of intrinsic beam properties and to reduce the intensity dependent focusing forces, space charge compensation seems to be an adequate solution. In the case of positively charged ion beams, electrons produced by residual gas ionization and secondary electrons provide the space charge compensation. The influence of the compensation particles on the beam transport and the local degree ofmore » space charge compensation is given by different beam properties as well as the ion beam optics. Especially for highly charged ion beams, space charge compensation in combination with poor vacuum conditions leads to recombination processes and therefore increased beam losses. Strategies for providing a compensation-electron reservoir at very low residual gas pressures will be discussed.« less

Reflection high energy electron diffraction observation of surface mass transport at the two- to three-dimensional growth transition of InAs on GaAs(001)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Patella, F.; Arciprete, F.; Fanfoni, M.

2005-12-19

We have followed by reflection high-energy electron diffraction the nucleation of InAs quantum dots on GaAs(001), grown by molecular-beam epitaxy with growth interruptions. Surface mass transport gives rise, at the critical InAs thickness, to a huge nucleation of three-dimensional islands within 0.2 monolayers (ML). Such surface mass diffusion has been evidenced by observing the transition of the reflection high-energy electron diffraction pattern from two- to three-dimensional during the growth interruption after the deposition of 1.59 ML of InAs. It is suggested that the process is driven by the As{sub 2} adsorption-desorption process and by the lowering of the In bindingmore » energy due to compressive strain. The last condition is met first in the region surrounding dots at step edges where nucleation predominantly occurs.« less

GSFC specification electronic data processing magnetic recording tape

NASA Technical Reports Server (NTRS)

Tinari, D. F.; Perry, J. L.

1980-01-01

The design requirements are given for magnetic oxide coated, electronic data processing tape, wound on reels. Magnetic recording tape types covered by this specification are intended for use on digital tape transports using the Non-Return-to-Zero-change-on-ones (NRZI) recording method for recording densities up to and including 800 characters per inch (cpi) and the Phase-Encoding (PE) recording method for a recording density of 1600 cpi.

Anisotropic Electron Tail Generation during Tearing Mode Magnetic Reconnection

NASA Astrophysics Data System (ADS)

Dubois, Ami

2017-10-01

Magnetic reconnection (MR) plays an important role in particle transport, energization, and acceleration in space, astrophysical, and laboratory plasmas. In the MST RFP, discrete MR events release large amounts of energy from the equilibrium magnetic field, a large fraction of which is transferred to the ions in a non-collisional process. Key features are anisotropic heating, mass and charge dependence, and energetic ion tail formation. Unlike the ions, the thermal electron temperature decreases at MR events, which is consistent with enhanced electron heat transport due to increased magnetic stochasticity. However, new high-speed x-ray spectrum measurements reveal transient formation of a non-Maxwellian energetic electron tail during MR. The energetic tail is characterized by a power-law, E-γ, with the spectral index (γ) decreasing from 4.2 to 2.2 at MR, and then increasing rapidly to 6.8 due to increased stochastic transport. The x-ray emission peaks in a radial view and is symmetric in the toroidal direction, indicating an anisotropic electron tail is generated. The toroidal symmetry of the electron tail implies runaway acceleration is not a dominant process, consistent with the net emf, ηJll, being smaller than the Dreicer field. Modeling of bremsstrahlung emission shows that a power-law electron tail distribution that is localized near the magnetic axis will yield strong perpendicular anisotropy, consistent with x-ray measurements in the radial and toroidal views. A strong correlation between high energy x-ray flux and tearing mode dynamics suggests a turbulent mechanism is active. This implies that the electron tail formation most likely results from a turbulent wave-particle interaction. This work is supported by the US DOE and NSF.

Electron beam transport in heterogeneous slab media from MeV down to eV.

PubMed

Yousfi, M; Leger, J; Loiseau, J F; Held, B; Eichwald, O; Defoort, B; Dupillier, J M

2006-01-01

An optimized Monte Carlo method based on the null collision technique and on the treatment of individual interactions is used for the simulation of the electron transport in multilayer materials from high energies (MeV or several hundred of keV) down to low cutoff energies (between 1 and 10 eV). In order to better understand the electron transport and the energy deposition at the interface in the composite application framework, two layer materials are considered (carbon and polystyrene with densities of 1.7 g cm(-3) and 1.06 g cm(-3), respectively) under two slab or three slab configurations as, e.g. a thin layer of carbon sandwiched between two polystyrene layers. The electron-matter cross-sections (electron-carbon and electron-polystyrene) used in the case of pure material (carbon and polystyrene) as well as our Monte-Carlo code have been first validated. The boundary interface layer is considered without any mean free path truncation and with a rigorous treatment of the backscattered and also the forward scattered electrons from one layer to another. The large effect of the choice of a low cutoff energy and the dissociation process consideration are also clearly shown in the heterogeneous multi-layer media more particularly on the secondary electron emission, inelastic collision number and energy spectra.

Spatial interferences in the electron transport of heavy-fermion materials

NASA Astrophysics Data System (ADS)

Zhang, Shu-feng; Liu, Yu; Song, Hai-Feng; Yang, Yi-feng

2016-08-01

The scanning tunneling microscopy/spectroscopy and the point contact spectroscopy represent major progress in recent heavy-fermion research. Both have revealed important information on the composite nature of the emergent heavy-electron quasiparticles. However, a detailed and thorough microscopic understanding of the similarities and differences in the underlying physical processes of these techniques is still lacking. Here we study the electron transport in the normal state of the periodic Anderson lattice by using the Keldysh nonequilibrium Green's function technique. In addition to the well-known Fano interference between the conduction and f -electron channels, our results further reveal the effect of spatial interference between different spatial paths at the interface on the differential conductance and their interesting interplay with the band features such as the hybridization gap and the Van Hove singularity. We find that the spatial interference leads to a weighted average in the momentum space for the electron transport and could cause suppression of the electronic band features under certain circumstances. In particular, it reduces the capability of probing the f -electron spectral weight near the edges of the hybridization gap for large interface depending on the Fermi surface of the lead. Our results indicate an intrinsic inefficiency of the point contact spectroscopy in probing the f electrons.

Resonant tunneling across a ferroelectric domain wall

NASA Astrophysics Data System (ADS)

Li, M.; Tao, L. L.; Velev, J. P.; Tsymbal, E. Y.

2018-04-01

Motivated by recent experimental observations, we explore electron transport properties of a ferroelectric tunnel junction (FTJ) with an embedded head-to-head ferroelectric domain wall, using first-principles density-functional theory calculations. We consider a FTJ with L a0.5S r0.5Mn O3 electrodes separated by a BaTi O3 barrier layer and show that an in-plane charged domain wall in the ferroelectric BaTi O3 can be induced by polar interfaces. The resulting V -shaped electrostatic potential profile across the BaTi O3 layer creates a quantum well and leads to the formation of a two-dimensional electron gas, which stabilizes the domain wall. The confined electronic states in the barrier are responsible for resonant tunneling as is evident from our quantum-transport calculations. We find that the resonant tunneling is an orbital selective process, which leads to sharp spikes in the momentum- and energy-resolved transmission spectra. Our results indicate that domain walls embedded in FTJs can be used to control the electron transport.

Electron transport characteristics of silicon nanowires by metal-assisted chemical etching

NASA Astrophysics Data System (ADS)

Qi, Yangyang; Wang, Zhen; Zhang, Mingliang; Wang, Xiaodong; Ji, An; Yang, Fuhua

2014-03-01

The electron transport characteristics of silicon nanowires (SiNWs) fabricated by metal-assisted chemical etching with different doping concentrations were studied. By increasing the doping concentration of the starting Si wafer, the resulting SiNWs were prone to have a rough surface, which had important effects on the contact and the electron transport. A metal-semiconductor-metal model and a thermionic field emission theory were used to analyse the current-voltage (I-V) characteristics. Asymmetric, rectifying and symmetric I-V curves were obtained. The diversity of the I-V curves originated from the different barrier heights at the two sides of the SiNWs. For heavily doped SiNWs, the critical voltage was one order of magnitude larger than that of the lightly doped, and the resistance obtained by differentiating the I-V curves at large bias was also higher. These were attributed to the lower electron tunnelling possibility and higher contact barrier, due to the rough surface and the reduced doping concentration during the etching process.

Energy gap states and tunneling currents in semiconducting graphene

NASA Astrophysics Data System (ADS)

Szczesniak, Dominik; Hoehn, Ross; Kais, Sabre

It has been predicted that when graphene is supported on a substrate or doped with foreign atom species, the inherent linear electronic dispersion of its pristine form can be strongly altered. Worthy of special attention is the situation when the interactions between graphene and the substrate or dopants lead to an opening of the finite electronic gap in the fermionic spectrum of this nano-material, and strongly influence its transport and optical properties. Herein, the fundamental electronic transport properties of such perturbed graphene are discussed in the framework of the complex band structure analysis, which not only accounts for the propagating but also the evanescent electronic states. Various scenarios responsible for the band gap opening and manipulation of its characteristics are considered, these considerations may entirely account for the aforementioned perturbations to the pristine graphene. It is shown, that the these perturbations are responsible for inducing gap states which allow electrons to directly tunnel between the conduction and valence bands in perturbed graphene. The resulting tunneling states are analyzed in a comprehensive manner, suggesting their great importance for the transport processes across graphene-based semiconducting nanostructures.

High Efficiency Inverted Planar Perovskite Solar Cells with Solution-Processed NiOx Hole Contact.

PubMed

Yin, Xuewen; Yao, Zhibo; Luo, Qiang; Dai, Xuezeng; Zhou, Yu; Zhang, Ye; Zhou, Yangying; Luo, Songping; Li, Jianbao; Wang, Ning; Lin, Hong

2017-01-25

NiO x is a promising hole-transporting material for perovskite solar cells due to its high hole mobility, good stability, and easy processability. In this work, we employed a simple solution-processed NiO x film as the hole-transporting layer in perovskite solar cells. When the thickness of the perovskite layer increased from 270 to 380 nm, the light absorption and photogenerated carrier density were enhanced and the transporting distance of electron and hole would also increase at the same time, resulting in a large charge transfer resistance and a long hole-extracted process in the device, characterized by the UV-vis, photoluminescence, and electrochemical impedance spectroscopy spectra. Combining both of these factors, an optimal thickness of 334.2 nm was prepared with the perovskite precursor concentration of 1.35 M. Moreover, the optimal device fabrication conditions were further achieved by optimizing the thickness of NiO x hole-transporting layer and PCBM electron selective layer. As a result, the best power conversion efficiency of 15.71% was obtained with a J sc of 20.51 mA·cm -2 , a V oc of 988 mV, and a FF of 77.51% with almost no hysteresis. A stable efficiency of 15.10% was caught at the maximum power point. This work provides a promising route to achieve higher efficiency perovskite solar cells based on NiO or other inorganic hole-transporting materials.

Vertical electron transport in van der Waals heterostructures with graphene layers

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ryzhii, V., E-mail: v-ryzhii@riec.tohoku.ac.jp; Center for Photonics and Infrared Engineering, Bauman Moscow State Technical University and Institute of Ultra High Frequency Semiconductor Electronics of RAS, Moscow 111005; Otsuji, T.

We propose and analyze an analytical model for the self-consistent description of the vertical electron transport in van der Waals graphene-layer (GL) heterostructures with the GLs separated by the barriers layers. The top and bottom GLs serve as the structure emitter and collector. The vertical electron transport in such structures is associated with the propagation of the electrons thermionically emitted from GLs above the inter-GL barriers. The model under consideration describes the processes of the electron thermionic emission from and the electron capture to GLs. It accounts for the nonuniformity of the self-consistent electric field governed by the Poisson equationmore » which accounts for the variation of the electron population in GLs. The model takes also under consideration the cooling of electrons in the emitter layer due to the Peltier effect. We find the spatial distributions of the electric field and potential with the high-electric-field domain near the emitter GL in the GL heterostructures with different numbers of GLs. Using the obtained spatial distributions of the electric field, we calculate the current-voltage characteristics. We demonstrate that the Peltier cooling of the two-dimensional electron gas in the emitter GL can strongly affect the current-voltage characteristics resulting in their saturation. The obtained results can be important for the optimization of the hot-electron bolometric terahertz detectors and different devices based on GL heterostructures.« less

Probing plasmodesmata function with biochemical inhibitors.

PubMed

White, Rosemary G

2015-01-01

To investigate plasmodesmata (PD) function, a useful technique is to monitor the effect on cell-to-cell transport of applying an inhibitor of a physiological process, protein, or other cell component of interest. Changes in PD transport can then be monitored in one of several ways, most commonly by measuring the cell-to-cell movement of fluorescent tracer dyes or of free fluorescent proteins. Effects on PD structure can be detected in thin sections of embedded tissue observed using an electron microscope, most commonly a Transmission Electron Microscope (TEM). This chapter outlines commonly used inhibitors, methods for treating different tissues, how to detect altered cell-to-cell transport and PD structure, and important caveats.

Highly efficient single-layer dendrimer light-emitting diodes with balanced charge transport

NASA Astrophysics Data System (ADS)

Anthopoulos, Thomas D.; Markham, Jonathan P. J.; Namdas, Ebinazar B.; Samuel, Ifor D. W.; Lo, Shih-Chun; Burn, Paul L.

2003-06-01

High-efficiency single-layer-solution-processed green light-emitting diodes based on a phosphorescent dendrimer are demonstrated. A peak external quantum efficiency of 10.4% (35 cd/A) was measured for a first generation fac-tris(2-phenylpyridine) iridium cored dendrimer when blended with 4,4'-bis(N-carbazolyl)biphenyl and electron transporting 1,3,5-tris(2-N-phenylbenzimidazolyl)benzene at 8.1 V. A maximum power efficiency of 12.8 lm/W was measured also at 8.1 V and 550 cd/m2. These results indicate that, by simple blending of bipolar and electron-transporting molecules, highly efficient light-emitting diodes can be made employing a very simple device structure.

Hydrogen transport behavior of beryllium

NASA Astrophysics Data System (ADS)

Anderl, R. A.; Hankins, M. R.; Longhurst, G. R.; Pawelko, R. J.; Macaulay-Newcombe, R. G.

1992-12-01

Beryllium is being evaluated for use as a plasma-facing material in the International Thermonuclear Experimental Reactor (ITER). One concern in the evaluation is the retention and permeation of tritium implanted into the plasma-facing surface. We performed laboratory-scale studies to investigate mechanisms that influence hydrogen transport and retention in beryllium foil specimens of rolled powder metallurgy product and rolled ingot cast beryllium. Specimen characterization was accomplished using scanning electron microscopy, Auger electron spectroscopy, and Rutherford backscattering spectrometry (RBS) techniques. Hydrogen transport was investigated using ion-beam permeation experiments and nuclear reaction analysis (NRA). Results indicate that trapping plays a significant role in permeation, re-emission, and retention, and that surface processes at both upstream and downstream surfaces are also important.

Band-like transport in highly crystalline graphene films from defective graphene oxides.

PubMed

Negishi, R; Akabori, M; Ito, T; Watanabe, Y; Kobayashi, Y

2016-07-01

The electrical transport property of the reduced graphene oxide (rGO) thin-films synthesized from defective GO through thermal treatment in a reactive ethanol environment at high temperature above 1000 °C shows a band-like transport with small thermal activation energy (Ea~10 meV) that occurs during high carrier mobility (~210 cm(2)/Vs). Electrical and structural analysis using X-ray absorption fine structure, the valence band photo-electron, Raman spectra and transmission electron microscopy indicate that a high temperature process above 1000 °C in the ethanol environment leads to an extraordinary expansion of the conjugated π-electron system in rGO due to the efficient restoration of the graphitic structure. We reveal that Ea decreases with the increasing density of states near the Fermi level due to the expansion of the conjugated π-electron system in the rGO. This means that Ea corresponds to the energy gap between the top of the valence band and the bottom of the conduction band. The origin of the band-like transport can be explained by the carriers, which are more easily excited into the conduction band due to the decreasing energy gap with the expansion of the conjugated π-electron system in the rGO.

Band-like transport in highly crystalline graphene films from defective graphene oxides

NASA Astrophysics Data System (ADS)

Negishi, R.; Akabori, M.; Ito, T.; Watanabe, Y.; Kobayashi, Y.

2016-07-01

The electrical transport property of the reduced graphene oxide (rGO) thin-films synthesized from defective GO through thermal treatment in a reactive ethanol environment at high temperature above 1000 °C shows a band-like transport with small thermal activation energy (Ea~10 meV) that occurs during high carrier mobility (~210 cm2/Vs). Electrical and structural analysis using X-ray absorption fine structure, the valence band photo-electron, Raman spectra and transmission electron microscopy indicate that a high temperature process above 1000 °C in the ethanol environment leads to an extraordinary expansion of the conjugated π-electron system in rGO due to the efficient restoration of the graphitic structure. We reveal that Ea decreases with the increasing density of states near the Fermi level due to the expansion of the conjugated π-electron system in the rGO. This means that Ea corresponds to the energy gap between the top of the valence band and the bottom of the conduction band. The origin of the band-like transport can be explained by the carriers, which are more easily excited into the conduction band due to the decreasing energy gap with the expansion of the conjugated π-electron system in the rGO.

Inverted organic photovoltaic device with a new electron transport layer

NASA Astrophysics Data System (ADS)

Kim, Hyeong Pil; Yusoff, Abd Rashid bin Mohd; Kim, Hyo Min; Lee, Hee Jae; Seo, Gi Jun; Jang, Jin

2014-03-01

We demonstrate that there is a new solution-processed electron transport layer, lithium-doped zinc oxide (LZO), with high-performance inverted organic photovoltaic device. The device exhibits a fill factor of 68.58%, an open circuit voltage of 0.86 V, a short-circuit current density of -9.35 cm/mA2 along with 5.49% power conversion efficiency. In addition, we studied the performance of blend ratio dependence on inverted organic photovoltaics. Our device also demonstrates a long stability shelf life over 4 weeks in air.

Design rules for charge-transport efficient host materials for phosphorescent organic light-emitting diodes.

PubMed

May, Falk; Al-Helwi, Mustapha; Baumeier, Björn; Kowalsky, Wolfgang; Fuchs, Evelyn; Lennartz, Christian; Andrienko, Denis

2012-08-22

The use of blue phosphorescent emitters in organic light-emitting diodes (OLEDs) imposes demanding requirements on a host material. Among these are large triplet energies, the alignment of levels with respect to the emitter, the ability to form and sustain amorphous order, material processability, and an adequate charge carrier mobility. A possible design strategy is to choose a π-conjugated core with a high triplet level and to fulfill the other requirements by using suitable substituents. Bulky substituents, however, induce large spatial separations between conjugated cores, can substantially reduce intermolecular electronic couplings, and decrease the charge mobility of the host. In this work we analyze charge transport in amorphous 2,8-bis(triphenylsilyl)dibenzofuran, an electron-transporting material synthesized to serve as a host in deep-blue OLEDs. We show that mesomeric effects delocalize the frontier orbitals over the substituents recovering strong electronic couplings and lowering reorganization energies, especially for electrons, while keeping energetic disorder small. Admittance spectroscopy measurements reveal that the material has indeed a high electron mobility and a small Poole-Frenkel slope, supporting our conclusions. By linking electronic structure, molecular packing, and mobility, we provide a pathway to the rational design of hosts with high charge mobilities.

Discrimination between spin-dependent charge transport and spin-dependent recombination in π-conjugated polymers by correlated current and electroluminescence-detected magnetic resonance

NASA Astrophysics Data System (ADS)

Kavand, Marzieh; Baird, Douglas; van Schooten, Kipp; Malissa, Hans; Lupton, John M.; Boehme, Christoph

2016-08-01

Spin-dependent processes play a crucial role in organic electronic devices. Spin coherence can give rise to spin mixing due to a number of processes such as hyperfine coupling, and leads to a range of magnetic field effects. However, it is not straightforward to differentiate between pure single-carrier spin-dependent transport processes which control the current and therefore the electroluminescence, and spin-dependent electron-hole recombination which determines the electroluminescence yield and in turn modulates the current. We therefore investigate the correlation between the dynamics of spin-dependent electric current and spin-dependent electroluminescence in two derivatives of the conjugated polymer poly(phenylene-vinylene) using simultaneously measured pulsed electrically detected (pEDMR) and optically detected (pODMR) magnetic resonance spectroscopy. This experimental approach requires careful analysis of the transient response functions under optical and electrical detection. At room temperature and under bipolar charge-carrier injection conditions, a correlation of the pEDMR and the pODMR signals is observed, consistent with the hypothesis that the recombination currents involve spin-dependent electronic transitions. This observation is inconsistent with the hypothesis that these signals are caused by spin-dependent charge-carrier transport. These results therefore provide no evidence that supports earlier claims that spin-dependent transport plays a role for room-temperature magnetoresistance effects. At low temperatures, however, the correlation between pEDMR and pODMR is weakened, demonstrating that more than one spin-dependent process influences the optoelectronic materials' properties. This conclusion is consistent with prior studies of half-field resonances that were attributed to spin-dependent triplet exciton recombination, which becomes significant at low temperatures when the triplet lifetime increases.

Room-Temperature Processing of TiOx Electron Transporting Layer for Perovskite Solar Cells.

PubMed

Deng, Xiaoyu; Wilkes, George C; Chen, Alexander Z; Prasad, Narasimha S; Gupta, Mool C; Choi, Joshua J

2017-07-20

In order to realize high-throughput roll-to-roll manufacturing of flexible perovskite solar cells, low-temperature processing of all device components must be realized. However, the most commonly used electron transporting layer in high-performance perovskite solar cells is based on TiO 2 thin films processed at high temperature (>450 °C). Here, we demonstrate room temperature solution processing of the TiO x layer that performs as well as the high temperature TiO 2 layer in perovskite solar cells, as evidenced by a champion solar cell efficiency of 16.3%. Using optical spectroscopy, electrical measurements, and X-ray diffraction, we show that the room-temperature processed TiO x is amorphous with organic residues, and yet its optical and electrical properties are on par with the high-temperature TiO 2 . Flexible perovskite solar cells that employ a room-temperature TiO x layer with a power conversion efficiency of 14.3% are demonstrated.

Non-Local Diffusion of Energetic Electrons during Solar Flares

NASA Astrophysics Data System (ADS)

Bian, N. H.; Emslie, G.; Kontar, E.

2017-12-01

The transport of the energy contained in suprathermal electrons in solar flares plays a key role in our understanding of many aspects of flare physics, from the spatial distributions of hard X-ray emission and energy deposition in the ambient atmosphere to global energetics. Historically the transport of these particles has been largely treated through a deterministic approach, in which first-order secular energy loss to electrons in the ambient target is treated as the dominant effect, with second-order diffusive terms (in both energy and angle) generally being either treated as a small correction or even neglected. Here, we critically analyze this approach, and we show that spatial diffusion through pitch-angle scattering necessarily plays a very significant role in the transport of electrons. We further show that a satisfactory treatment of the diffusion process requires consideration of non-local effects, so that the electron flux depends not just on the local gradient of the electron distribution function but on the value of this gradient within an extended region encompassing a significant fraction of a mean free path. Our analysis applies generally to pitch-angle scattering by a variety of mechanisms, from Coulomb collisions to turbulent scattering. We further show that the spatial transport of electrons along the magnetic field of a flaring loop can be modeled as a Continuous Time Random Walk with velocity-dependent probability distribution functions of jump sizes and occurrences, both of which can be expressed in terms of the scattering mean free path.

The Impacts of Phosphorus Deficiency on the Photosynthetic Electron Transport Chain.

PubMed

Carstensen, Andreas; Herdean, Andrei; Schmidt, Sidsel Birkelund; Sharma, Anurag; Spetea, Cornelia; Pribil, Mathias; Husted, Søren

2018-05-01

Phosphorus (P) is an essential macronutrient, and P deficiency limits plant productivity. Recent work showed that P deficiency affects electron transport to photosystem I (PSI), but the underlying mechanisms are unknown. Here, we present a comprehensive biological model describing how P deficiency disrupts the photosynthetic machinery and the electron transport chain through a series of sequential events in barley ( Hordeum vulgare ). P deficiency reduces the orthophosphate concentration in the chloroplast stroma to levels that inhibit ATP synthase activity. Consequently, protons accumulate in the thylakoids and cause lumen acidification, which inhibits linear electron flow. Limited plastoquinol oxidation retards electron transport to the cytochrome b 6 f complex, yet the electron transfer rate of PSI is increased under steady-state growth light and is limited under high-light conditions. Under P deficiency, the enhanced electron flow through PSI increases the levels of NADPH, whereas ATP production remains restricted and, hence, reduces CO 2 fixation. In parallel, lumen acidification activates the energy-dependent quenching component of the nonphotochemical quenching mechanism and prevents the overexcitation of photosystem II and damage to the leaf tissue. Consequently, plants can be severely affected by P deficiency for weeks without displaying any visual leaf symptoms. All of the processes in the photosynthetic machinery influenced by P deficiency appear to be fully reversible and can be restored in less than 60 min after resupply of orthophosphate to the leaf tissue. © 2018 American Society of Plant Biologists. All Rights Reserved.

Unearthing the secrets of mitochondrial ROS and glutathione in bioenergetics.

PubMed

Mailloux, Ryan J; McBride, Skye L; Harper, Mary-Ellen

2013-12-01

During the cellular oxidation of fuels, electrons are used to power the proton pumps of the mitochondrial electron transport chain (ETC) and ultimately drive ATP synthesis and the reduction of molecular oxygen to water. During these oxidative processes, some electrons can 'spin off' during fuel oxidation and electron transport to univalently reduce O2, forming reactive oxygen species (ROS). In excess, ROS can be detrimental; however, at low concentrations oxyradicals are essential signaling molecules. Mitochondria thus use a battery of systems to finely control types and levels of ROS, including antioxidants. Several antioxidant systems depend on glutathione. Here, we review mitochondrial ROS homeostatic systems, including emerging knowledge about roles of glutathione in redox balance and the control of protein function by post-translational modification. Copyright © 2013 Elsevier Ltd. All rights reserved.

Direct detection of a transport-blocking trap in a nanoscaled silicon single-electron transistor by radio-frequency reflectometry

DOE Office of Scientific and Technical Information (OSTI.GOV)

Villis, B. J.; Sanquer, M.; Jehl, X.

2014-06-09

The continuous downscaling of transistors results in nanoscale devices which require fewer and fewer charged carriers for their operation. The ultimate charge controlled device, the single-electron transistor (SET), controls the transfer of individual electrons. It is also the most sensitive electrometer, and as a result the electron transport through it can be dramatically affected by nearby charges. Standard direct-current characterization techniques, however, are often unable to unambiguously detect and resolve the origin of the observed changes in SET behavior arising from changes in the charge state of a capacitively coupled trap. Using a radio-frequency (RF) reflectometry technique, we are ablemore » to unequivocally detect this process, in very close agreement with modeling of the trap's occupation probability.« less

Hydrodynamic Electron Flow and Hall Viscosity

NASA Astrophysics Data System (ADS)

Scaffidi, Thomas; Nandi, Nabhanila; Schmidt, Burkhard; Mackenzie, Andrew P.; Moore, Joel E.

2017-06-01

In metallic samples of small enough size and sufficiently strong momentum-conserving scattering, the viscosity of the electron gas can become the dominant process governing transport. In this regime, momentum is a long-lived quantity whose evolution is described by an emergent hydrodynamical theory. Furthermore, breaking time-reversal symmetry leads to the appearance of an odd component to the viscosity called the Hall viscosity, which has attracted considerable attention recently due to its quantized nature in gapped systems but still eludes experimental confirmation. Based on microscopic calculations, we discuss how to measure the effects of both the even and odd components of the viscosity using hydrodynamic electronic transport in mesoscopic samples under applied magnetic fields.

Hydrodynamic Electron Flow and Hall Viscosity.

PubMed

Scaffidi, Thomas; Nandi, Nabhanila; Schmidt, Burkhard; Mackenzie, Andrew P; Moore, Joel E

2017-06-02

In metallic samples of small enough size and sufficiently strong momentum-conserving scattering, the viscosity of the electron gas can become the dominant process governing transport. In this regime, momentum is a long-lived quantity whose evolution is described by an emergent hydrodynamical theory. Furthermore, breaking time-reversal symmetry leads to the appearance of an odd component to the viscosity called the Hall viscosity, which has attracted considerable attention recently due to its quantized nature in gapped systems but still eludes experimental confirmation. Based on microscopic calculations, we discuss how to measure the effects of both the even and odd components of the viscosity using hydrodynamic electronic transport in mesoscopic samples under applied magnetic fields.

Acceptor Percolation Determines How Electron-Accepting Additives Modify Transport of Ambipolar Polymer Organic Field-Effect Transistors.

PubMed

Ford, Michael J; Wang, Ming; Bustillo, Karen C; Yuan, Jianyu; Nguyen, Thuc-Quyen; Bazan, Guillermo C

2018-06-18

Organic field-effect transistors (OFETs) that utilize ambipolar polymer semiconductors can benefit from the ability of both electron and hole conduction, which is necessary for complementary circuits. However, simultaneous hole and electron transport in organic field-effect transistors result in poor ON/OFF ratios, limiting potential applications. Solution processing methods have been developed to control charge transport properties and transform ambipolar conduction to hole-only conduction. The electron-acceptor phenyl-C61-butyric acid methyl ester (PC 61 BM), when mixed in solution with an ambipolar semiconducting polymer, can reduce electron conduction. Unipolar p-type OFETs with high, well-defined ON/OFF ratios and without detrimental effects on hole conduction are achieved for a wide range of blend compositions, from 95:5 to 5:95 wt % semiconductor polymer:PC 61 BM. When introducing the alternative acceptor N, N'-bis(1-ethylpropyl)-3,4:9,10-perylenediimide (PDI), high ON/OFF ratios are achieved for 95:5 wt % semiconductor polymer:PDI; however, electron conduction increases for 50:50 and 5:95 wt % semiconductor polymer:PDI. As described within, we show that electron conduction is practically eliminated when additive domains do not percolate across the OFET channel, that is, electrons are "morphologically trapped". Morphologies were characterized by optical, electron, and atomic force microscopy as well as X-ray scattering techniques. PC 61 BM was substituted with an endohedral Lu 3 N fullerene, which enhanced contrast in electron microscopy and allowed for more detailed insight into the blend morphologies. Blends with alternative, nonfullerene acceptors further emphasize the importance of morphology and acceptor percolation, providing insights for such blends that control ambipolar transport and ON/OFF ratios.

Non-Markovian full counting statistics in quantum dot molecules

PubMed Central

Xue, Hai-Bin; Jiao, Hu-Jun; Liang, Jiu-Qing; Liu, Wu-Ming

2015-01-01

Full counting statistics of electron transport is a powerful diagnostic tool for probing the nature of quantum transport beyond what is obtainable from the average current or conductance measurement alone. In particular, the non-Markovian dynamics of quantum dot molecule plays an important role in the nonequilibrium electron tunneling processes. It is thus necessary to understand the non-Markovian full counting statistics in a quantum dot molecule. Here we study the non-Markovian full counting statistics in two typical quantum dot molecules, namely, serially coupled and side-coupled double quantum dots with high quantum coherence in a certain parameter regime. We demonstrate that the non-Markovian effect manifests itself through the quantum coherence of the quantum dot molecule system, and has a significant impact on the full counting statistics in the high quantum-coherent quantum dot molecule system, which depends on the coupling of the quantum dot molecule system with the source and drain electrodes. The results indicated that the influence of the non-Markovian effect on the full counting statistics of electron transport, which should be considered in a high quantum-coherent quantum dot molecule system, can provide a better understanding of electron transport through quantum dot molecules. PMID:25752245

Ultrafast Electron Dynamics in Solar Energy Conversion.

PubMed

Ponseca, Carlito S; Chábera, Pavel; Uhlig, Jens; Persson, Petter; Sundström, Villy

2017-08-23

Electrons are the workhorses of solar energy conversion. Conversion of the energy of light to electricity in photovoltaics, or to energy-rich molecules (solar fuel) through photocatalytic processes, invariably starts with photoinduced generation of energy-rich electrons. The harvesting of these electrons in practical devices rests on a series of electron transfer processes whose dynamics and efficiencies determine the function of materials and devices. To capture the energy of a photogenerated electron-hole pair in a solar cell material, charges of opposite sign have to be separated against electrostatic attractions, prevented from recombining and being transported through the active material to electrodes where they can be extracted. In photocatalytic solar fuel production, these electron processes are coupled to chemical reactions leading to storage of the energy of light in chemical bonds. With the focus on the ultrafast time scale, we here discuss the light-induced electron processes underlying the function of several molecular and hybrid materials currently under development for solar energy applications in dye or quantum dot-sensitized solar cells, polymer-fullerene polymer solar cells, organometal halide perovskite solar cells, and finally some photocatalytic systems.

Charge Transport Processes in Molecular Junctions

NASA Astrophysics Data System (ADS)

Smith, Christopher Eugene

Molecular electronics (ME) has evolved into a rich area of exploration that combines the fields of chemistry, materials, electronic engineering and computational modeling to explore the physics behind electronic conduction at the molecular level. Through studying charge transport properties of single molecules and nanoscale molecular materials the field has gained the potential to bring about new avenues for the miniaturization of electrical components where quantum phenomena are utilized to achieve solid state molecular device functionality. Molecular junctions are platforms that enable these studies and consist of a single molecule or a small group of molecules directly connected to electrodes. The work presented in this thesis has built upon the current understanding of the mechanisms of charge transport in ordered junctions using self-assembled monolayer (SAM) molecular thin films. Donor and acceptor compounds were synthesized and incorporated into SAMs grown on metal substrates then the transport properties were measured with conducting probe atomic force microscopy (CP-AFM). In addition to experimentally measured current-voltage (I-V) curves, the transport properties were addressed computationally and modeled theoretically. The key objectives of this project were to 1) investigate the impact of molecular structure on hole and electron charge transport, 2) understand the nature of the charge carriers and their structure-transport properties through long (<4 nm) conjugated molecular wires, and 3) quantitatively extract interfacial properties characteristic to macroscopic junctions, such as energy level alignment and molecule-contact electronic coupling from experimental I-V curves. Here, we lay ground work for creating a more complete picture of charge transport in macroscopically ordered molecular junctions of controlled architecture, length and charge carrier. The polaronic nature of hopping transport has been predicted in long, conjugated molecular wires. Using quantum-based calculations, we modeled 'p-type' polaron transport through oligophenylenethiophene (OPTI) wires and assigned transport activation energies to specific modes of nuclear motion. We also show control over 'n-type', LUMO-mediated transport in short ( 2 nm) redox-active perylenediimide (PDI) SAMs bound to contacts through isocyano linkers. By changing the contact work function (φ) and temperature, we were able to verify thermally-assisted LUMO transport. Transition voltage spectroscopy and the single level model was employed to fit the experimental I-V curves and extract the electronic coupling (epsilon) and the EF-LUMO offset (epsilonl). It was found that epsilonl does not change with φ (LUMO pinning), while Gamma changes with both φ and temperature. Further, the PDI SAMs could be reversibly chemically gated to modulate the transport. These results help advance our understanding of transport behavior in semiconducting molecular thin films, and open opportunities to engineer improved electronic functionality into molecular devices.

Fused electron deficient semiconducting polymers for air stable electron transport.

PubMed

Onwubiko, Ada; Yue, Wan; Jellett, Cameron; Xiao, Mingfei; Chen, Hung-Yang; Ravva, Mahesh Kumar; Hanifi, David A; Knall, Astrid-Caroline; Purushothaman, Balaji; Nikolka, Mark; Flores, Jean-Charles; Salleo, Alberto; Bredas, Jean-Luc; Sirringhaus, Henning; Hayoz, Pascal; McCulloch, Iain

2018-01-29

Conventional semiconducting polymer synthesis typically involves transition metal-mediated coupling reactions that link aromatic units with single bonds along the backbone. Rotation around these bonds contributes to conformational and energetic disorder and therefore potentially limits charge delocalisation, whereas the use of transition metals presents difficulties for sustainability and application in biological environments. Here we show that a simple aldol condensation reaction can prepare polymers where double bonds lock-in a rigid backbone conformation, thus eliminating free rotation along the conjugated backbone. This polymerisation route requires neither organometallic monomers nor transition metal catalysts and offers a reliable design strategy to facilitate delocalisation of frontier molecular orbitals, elimination of energetic disorder arising from rotational torsion and allowing closer interchain electronic coupling. These characteristics are desirable for high charge carrier mobilities. Our polymers with a high electron affinity display long wavelength NIR absorption with air stable electron transport in solution processed organic thin film transistors.

Different methods to fabricate efficient planar perovskite solar cells based on solution-processing Nb2O5 as electron transporting layer

NASA Astrophysics Data System (ADS)

Guo, Heng; Yang, Jian; Pu, Bingxue; Zhang, Haiyan; Niu, Xiaobin

2018-01-01

Organo-lead perovskites as light harvesters have represented a hot field of research on high-efficiency perovskite solar cells. Previous approaches to increasing the solar cell efficiency have focused on optimization of the morphology of perovskite film. In fact, the electron transporting layer (ETL) also has a significant impact on solar cell performance. Herein, we introduce a facile and low temperature solution-processing method to deposit Nb2O5 film as ETL for PSCs. Based on Nb2O5 ETL, we investigate the effect of the annealing time for the perovskite films via different solution processing, relating it to the perovskite film morphology and its influence on the device working mechanisms. These results shed light on the origin of photovoltaic performance voltage in perovskite solar cells, and provide a path to further increase their efficiency.

Electromagnetic Basis of Metabolism and Heredity

NASA Technical Reports Server (NTRS)

Freund, Friedemann; Stolc, Viktor

2016-01-01

Living organisms control their cellular biological clocks to maintain functional oscillation of the redox cycle, also called the "metabolic cycle" or "respiratory cycle". Organization of cellular processes requires parallel processing on a synchronized time-base. These clocks coordinate the timing of all biochemical processes in the cell, including energy production, DNA replication, and RNA transcription. When this universal time keeping function is perturbed by exogenous induction of reactive oxygen species (ROS), the rate of metabolism changes. This causes oxidative stress, aging and mutations. Therefore, good temporal coordination of the redox cycle not only actively prevents chemical conflict between the reductive and oxidative partial reactions; it also maintains genome integrity and lifespan. Moreover, this universal biochemical rhythm can be disrupted by ROS induction in vivo. This in turn can be achieved by blocking the electron transport chain either endogenously or exogenously by various metabolites, e.g. hydrogen sulfide (H2S), highly diffusible drugs, and carbon monoxide (CO). Alternatively, the electron transport in vivo can be attenuated via a coherent or interfering transfer of energy from exogenous ultralow frequency (ULF) and extremely low frequency (ELF) electromagnetic (EM) fields, suggesting that-on Earth-such ambient fields are an omnipresent (and probably crucially important) factor for the time-setting basis of universal biochemical reactions in living cells. Our work demonstrated previously un-described evidence for quantum effects in biology by electromagnetic coupling below thermal noise at the universal electron transport chain (ETC) in vivo.

Electron-phonon interaction model and prediction of thermal energy transport in SOI transistor.

PubMed

Jin, Jae Sik; Lee, Joon Sik

2007-11-01

An electron-phonon interaction model is proposed and applied to thermal transport in semiconductors at micro/nanoscales. The high electron energy induced by the electric field in a transistor is transferred to the phonon system through electron-phonon interaction in the high field region of the transistor. Due to this fact, a hot spot occurs, which is much smaller than the phonon mean free path in the Si-layer. The full phonon dispersion model based on the Boltzmann transport equation (BTE) with the relaxation time approximation is applied for the interactions among different phonon branches and different phonon frequencies. The Joule heating by the electron-phonon scattering is modeled through the intervalley and intravalley processes for silicon by introducing average electron energy. The simulation results are compared with those obtained by the full phonon dispersion model which treats the electron-phonon scattering as a volumetric heat source. The comparison shows that the peak temperature in the hot spot region is considerably higher and more localized than the previous results. The thermal characteristics of each phonon mode are useful to explain the above phenomena. The optical mode phonons of negligible group velocity obtain the highest energy density from electrons, and resides in the hot spot region without any contribution to heat transport, which results in a higher temperature in that region. Since the acoustic phonons with low group velocity show the higher energy density after electron-phonon scattering, they induce more localized heating near the hot spot region. The ballistic features are strongly observed when phonon-phonon scattering rates are lower than 4 x 10(10) S(-1).

Exciton generation/dissociation/charge-transfer enhancement in inorganic/organic hybrid solar cells by robust single nanocrystalline LnPxOy (Ln = Eu, Y) doping.

PubMed

Jin, Xiao; Sun, Weifu; Chen, Zihan; Wei, Taihuei; Chen, Chuyang; He, Xingdao; Yuan, Yongbiao; Li, Yue; Li, Qinghua

2014-06-11

Low-temperature solution-processed photovoltaics suffer from low efficiencies because of poor exciton or electron-hole transfer. Inorganic/organic hybrid solar cell, although still in its infancy, has attracted great interest thus far. One of the promising ways to enhance exciton dissociation or electron-hole transport is the doping of lanthanide phosphate ions. However, the underlying photophysical mechanism remains poorly understood. Herein, by applying femtosecond transient absorption spectroscopy, we successfully distinguished hot electron, less energetic electron, hole transport from electron-hole recombination. Concrete evidence has been provided that lanthanide phosphate doping improves the efficiency of both hot electron and "less energetic" electron transfers from donor to acceptor, but the hole transport almost remains unchanged. In particular, the hot electron transfer lifetime was shortened from 30.2 to 12.7 ps, that is, more than 60% faster than pure TiO2 acceptor. Such improvement was ascribed to the facts that the conduction band (CB) edge energy level of TiO2 has been elevated by 0.2 eV, while the valence band level almost remains unchanged, thus not only narrowing the energy offset between CB levels of TiO2 and P3HT, but also meanwhile enlarging the band gap of TiO2 itself that permits one to inhibit electron-hole recombination within TiO2. Consequently, lanthanide phosphate doped TiO2/P3HT bulk-heterojunction solar cell has been demonstrated to be a promising hybrid solar cell, and a notable power conversion efficiency of 2.91% is therefore attained. This work indicates that lanthanide compound ions can efficiently facilitate exciton generation, dissociation, and charge transport, thus enhancing photovoltaic performance.

Electron-Impact-Ionization and Electron-Attachment Cross Sections of Radicals Important in Transient Gaseous Discharges.

DTIC Science & Technology

1988-02-05

for understanding the microscopic processes of electrical discharges and for designing gaseous discharge switches. High power gaseous discharge switches...half-maximum) energy resolution. The electron gun and ion extraction were of the same design of Srivastava at the Jet Propulsion Laboratory. Ions...photons. - The observed current switching can be applied to the design of discharge switches. Elec- tron transport parameters are needed for the

Electronic processes in TTF-derived complexes studied by IR spectroscopy

NASA Astrophysics Data System (ADS)

Graja, Andrzej

2001-09-01

We focus our attention on the plasma-edge-like dispersion of the reflectance spectra of the selected bis(ethylenodithio)tetrathiafulvalene (BEDT-TTF)-derived organic conductors. The standard procedure to determine the electron transport parameters in low-dimensional organic conductors consists of fitting the appropriate theoretical models with the experimental reflectance data. This procedure provides us with basic information like plasma frequency, the optical effective mass of charge carriers, their number, mean free path and damping constant. Therefore, it is concluded that the spectroscopy is a powerful tool to study the electronic processes in conducting organic solids.

The intrinsic disorder related alloy scattering in ZrNiSn half-Heusler thermoelectric materials

PubMed Central

Xie, Hanhui; Wang, Heng; Fu, Chenguang; Liu, Yintu; Snyder, G. Jeffrey; Zhao, Xinbing; Zhu, Tiejun

2014-01-01

The intrinsic structural disorder dramatically affects the thermal and electronic transport in semiconductors. Although normally considered an ordered compound, the half-Heusler ZrNiSn displays many transport characteristics of a disordered alloy. Similar to the (Zr,Hf)NiSn based solid solutions, the unsubstituted ZrNiSn compound also exhibits charge transport dominated by alloy scattering, as demonstrated in this work. The unexpected charge transport, even in ZrNiSn which is normally considered fully ordered, can be explained by the Ni partially filling interstitial sites in this half-Heusler system. The influence of the disordering and defects in crystal structure on the electron transport process has also been quantitatively analyzed in ZrNiSn1-xSbx with carrier concentration nH ranging from 5.0×1019 to 2.3×1021 cm−3 by changing Sb dopant content. The optimized carrier concentration nH ≈ 3–4×1020 cm−2 results in ZT ≈ 0.8 at 875K. This work suggests that MNiSn (M = Hf, Zr, Ti) and perhaps most other half-Heusler thermoelectric materials should be considered highly disordered especially when trying to understand the electronic and phonon structure and transport features. PMID:25363573

Transport and magnetic properties of disordered Li xV yO 2 ( x=0.8 and y=0.8)

NASA Astrophysics Data System (ADS)

Du, Fei; Li, Ang; Liu, Daliang; Zhan, Shiying; Hu, Fang; Wang, Chunzhong; Chen, Yan; Feng, Shouhua; Chen, Gang

2009-07-01

The magnetic and electron transport properties of rhombohedral Li xV yO 2 ( x=0.8 and y=0.8) are studied. The dc susceptibility of Li xV yO 2 can be well fitted to the modified Curie-Weiss law, which verified the paramagnetic ground state. The magnetic hysteresis and ac susceptibility also confirm this paramagnetism. The Li xV yO 2 exhibits semiconducting behavior, which is explained by thermal activated process at high temperature and variable-range hopping mechanism at low temperature. Anderson localization plays an important role in both the electron transport behavior and the magnetic behavior due to the site disorder between the Li + ion and V 4+ ion.

Empirical models of the electron temperature and density in the nightside venus ionosphere.

PubMed

Brace, L H; Theis, R F; Niemann, H B; Mayr, H G; Hoegy, W R; Nagy, A F

1979-07-06

Empirical models of the electron temperature and electron density of the late afternoon and nightside Venus ionosphere have been derived from Pioneer Venus measurements acquired between 10 December 1978 and 23 March 1979. The models describe the average ionosphere conditions near 18 degrees N latitude between 150 and 700 kilometers altitude for solar zenith angles of 80 degrees to 180 degrees . The average index of solar flux was 200. A major feature of the density model is the factor of 10 decrease beyond 90 degrees followed by a very gradual decrease between 120 degrees and 180 degrees . The density at 150 degrees is about five times greater than observed by Venera 9 and 10 at solar minimum (solar flux approximately 80), a difference that is probably related to the effects of increased solar activity on the processes that maintain the nightside ionosphere. The nightside electron density profile from the model (above 150 kilometers) can be reproduced theoretically either by transport of 0(+) ions from the dayside or by precipitation of low-energy electrons. The ion transport process would require a horizontal flow velocity of about 300 meters per second, a value that is consistent with other Pioneer Venus observations. Although currently available energetic electron data do not yet permit the role of precipitation to be evaluated quantitatively, this process is clearly involved to some extent in the formation of the nightside ionosphere. Perhaps the most surprising feature of the temperature model is that the electron temperature remains high throughout the nightside ionosphere. These high nocturnal temperatures and the existence of a well-defined nightside ionopause suggest that energetic processes occur across the top of the entire nightside ionosphere, maintaining elevated temperatures. A heat flux of 2 x 10(10) electron volts per square centimeter per second, introduced at the ionopause, is consistent with the average electron temperature profile on the nightside at a solar zenith angle of 140 degrees .

Light-induced electronic non-equilibrium in plasmonic particles.

PubMed

Kornbluth, Mordechai; Nitzan, Abraham; Seideman, Tamar

2013-05-07

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

41 CFR 102-118.35 - What definitions apply to this part?

Code of Federal Regulations, 2010 CFR

2010-07-01

... published formats and codes as authorized by the applicable Federal Information Processing Standards... techniques for carrying out transportation transactions using electronic transmissions of the information...

Spin relaxation 1/f noise in graphene

NASA Astrophysics Data System (ADS)

Omar, S.; Guimarães, M. H. D.; Kaverzin, A.; van Wees, B. J.; Vera-Marun, I. J.

2017-02-01

We report the first measurement of 1/f type noise associated with electronic spin transport, using single layer graphene as a prototypical material with a large and tunable Hooge parameter. We identify the presence of two contributions to the measured spin-dependent noise: contact polarization noise from the ferromagnetic electrodes, which can be filtered out using the cross-correlation method, and the noise originated from the spin relaxation processes. The noise magnitude for spin and charge transport differs by three orders of magnitude, implying different scattering mechanisms for the 1/f fluctuations in the charge and spin transport processes. A modulation of the spin-dependent noise magnitude by changing the spin relaxation length and time indicates that the spin-flip processes dominate the spin-dependent noise.

QmeQ 1.0: An open-source Python package for calculations of transport through quantum dot devices

NASA Astrophysics Data System (ADS)

Kiršanskas, Gediminas; Pedersen, Jonas Nyvold; Karlström, Olov; Leijnse, Martin; Wacker, Andreas

2017-12-01

QmeQ is an open-source Python package for numerical modeling of transport through quantum dot devices with strong electron-electron interactions using various approximate master equation approaches. The package provides a framework for calculating stationary particle or energy currents driven by differences in chemical potentials or temperatures between the leads which are tunnel coupled to the quantum dots. The electronic structures of the quantum dots are described by their single-particle states and the Coulomb matrix elements between the states. When transport is treated perturbatively to lowest order in the tunneling couplings, the possible approaches are Pauli (classical), first-order Redfield, and first-order von Neumann master equations, and a particular form of the Lindblad equation. When all processes involving two-particle excitations in the leads are of interest, the second-order von Neumann approach can be applied. All these approaches are implemented in QmeQ. We here give an overview of the basic structure of the package, give examples of transport calculations, and outline the range of applicability of the different approximate approaches.

Electron and hole transport in ambipolar, thin film pentacene transistors

NASA Astrophysics Data System (ADS)

Saudari, Sangameshwar R.; Kagan, Cherie R.

2015-01-01

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

Designing Two-Dimensional Dirac Heterointerfaces of Few-Layer Graphene and Tetradymite-Type Sb2Te3 for Thermoelectric Applications.

PubMed

Jang, Woosun; Lee, Jiwoo; In, Chihun; Choi, Hyunyong; Soon, Aloysius

2017-12-06

Despite the ubiquitous nature of the Peltier effect in low-dimensional thermoelectric devices, the influence of finite temperature on the electronic structure and transport in the Dirac heterointerfaces of the few-layer graphene and layered tetradymite, Sb 2 Te 3 (which coincidently have excellent thermoelectric properties) are not well understood. In this work, using the first-principles density-functional theory calculations, we investigate the detailed atomic and electronic structure of these Dirac heterointerfaces of graphene and Sb 2 Te 3 and further re-examine the effect of finite temperature on the electronic band structures using a phenomenological temperature-broadening model based on Fermi-Dirac statistics. We then proceed to understand the underlying charge redistribution process in this Dirac heterointerfaces and through solving the Boltzmann transport equation, we present the theoretical evidence of electron-hole asymmetry in its electrical conductivity as a consequence of this charge redistribution mechanism. We finally propose that the hexagonal-stacked Dirac heterointerfaces are useful as efficient p-n junction building blocks in the next-generation thermoelectric devices where the electron-hole asymmetry promotes the thermoelectric transport by "hot" excited charge carriers.

Tuning electronic transport via hepta-alanine peptides junction by tryptophan doping.

PubMed

Guo, Cunlan; Yu, Xi; Refaely-Abramson, Sivan; Sepunaru, Lior; Bendikov, Tatyana; Pecht, Israel; Kronik, Leeor; Vilan, Ayelet; Sheves, Mordechai; Cahen, David

2016-09-27

Charge migration for electron transfer via the polypeptide matrix of proteins is a key process in biological energy conversion and signaling systems. It is sensitive to the sequence of amino acids composing the protein and, therefore, offers a tool for chemical control of charge transport across biomaterial-based devices. We designed a series of linear oligoalanine peptides with a single tryptophan substitution that acts as a "dopant," introducing an energy level closer to the electrodes' Fermi level than that of the alanine homopeptide. We investigated the solid-state electron transport (ETp) across a self-assembled monolayer of these peptides between gold contacts. The single tryptophan "doping" markedly increased the conductance of the peptide chain, especially when its location in the sequence is close to the electrodes. Combining inelastic tunneling spectroscopy, UV photoelectron spectroscopy, electronic structure calculations by advanced density-functional theory, and dc current-voltage analysis, the role of tryptophan in ETp is rationalized by charge tunneling across a heterogeneous energy barrier, via electronic states of alanine and tryptophan, and by relatively efficient direct coupling of tryptophan to a Au electrode. These results reveal a controlled way of modulating the electrical properties of molecular junctions by tailor-made "building block" peptides.

Spin-orbit coupling, electron transport and pairing instabilities in two-dimensional square structures

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kocharian, Armen N.; Fernando, Gayanath W.; Fang, Kun

Rashba spin-orbit effects and electron correlations in the two-dimensional cylindrical lattices of square geometries are assessed using mesoscopic two-, three- and four-leg ladder structures. Here the electron transport properties are systematically calculated by including the spin-orbit coupling in tight binding and Hubbard models threaded by a magnetic flux. These results highlight important aspects of possible symmetry breaking mechanisms in square ladder geometries driven by the combined effect of a magnetic gauge field spin-orbit interaction and temperature. The observed persistent current, spin and charge polarizations in the presence of spin-orbit coupling are driven by separation of electron and hole charges andmore » opposite spins in real-space. The modeled spin-flip processes on the pairing mechanism induced by the spin-orbit coupling in assembled nanostructures (as arrays of clusters) engineered in various two-dimensional multi-leg structures provide an ideal playground for understanding spatial charge and spin density inhomogeneities leading to electron pairing and spontaneous phase separation instabilities in unconventional superconductors. Such studies also fall under the scope of current challenging problems in superconductivity and magnetism, topological insulators and spin dependent transport associated with numerous interfaces and heterostructures.« less

Model-based confirmation of alternative substrates of mitochondrial electron transport chain.

PubMed

Kleessen, Sabrina; Araújo, Wagner L; Fernie, Alisdair R; Nikoloski, Zoran

2012-03-30

Discrimination of metabolic models based on high throughput metabolomics data, reflecting various internal and external perturbations, is essential for identifying the components that contribute to the emerging behavior of metabolic processes. Here, we investigate 12 different models of the mitochondrial electron transport chain (ETC) in Arabidopsis thaliana during dark-induced senescence in order to elucidate the alternative substrates to this metabolic pathway. Our findings demonstrate that the coupling of the proposed computational approach, based on dynamic flux balance analysis, with time-resolved metabolomics data results in model-based confirmations of the hypotheses that, during dark-induced senescence in Arabidopsis, (i) under conditions where the main substrate for the ETC are not fully available, isovaleryl-CoA dehydrogenase and 2-hydroxyglutarate dehydrogenase are able to donate electrons to the ETC, (ii) phytanoyl-CoA does not act even as an indirect substrate of the electron transfer flavoprotein/electron-transfer flavoprotein:ubiquinone oxidoreductase complex, and (iii) the mitochondrial γ-aminobutyric acid transporter has functional significance in maintaining mitochondrial metabolism. Our study provides a basic framework for future in silico studies of alternative pathways in mitochondrial metabolism under extended darkness whereby the role of its components can be computationally discriminated based on available molecular profile data.

Electronic Transport and Quantum Hall Effect in Bipolar Graphene p-n-p Junctions

NASA Astrophysics Data System (ADS)

Özyilmaz, Barbaros; Jarillo-Herrero, Pablo; Efetov, Dmitri; Abanin, Dmitry A.; Levitov, Leonid S.; Kim, Philip

2007-10-01

We have developed a device fabrication process to pattern graphene into nanostructures of arbitrary shape and control their electronic properties using local electrostatic gates. Electronic transport measurements have been used to characterize locally gated bipolar graphene p-n-p junctions. We observe a series of fractional quantum Hall conductance plateaus at high magnetic fields as the local charge density is varied in the p and n regions. These fractional plateaus, originating from chiral edge states equilibration at the p-n interfaces, exhibit sensitivity to interedge backscattering which is found to be strong for some of the plateaus and much weaker for other plateaus. We use this effect to explore the role of backscattering and estimate disorder strength in our graphene devices.

Correlation-driven insulator-metal transition in near-ideal vanadium dioxide films

DOE PAGES

Gray, A. X.; Jeong, J.; Aetukuri, N. P.; ...

2016-03-18

We use polarization- and temperature-dependent x-ray absorption spectroscopy, in combination with photoelectron microscopy, x-ray diffraction, and electronic transport measurements, to study the driving force behind the insulator-metal transition in VO 2. We show that both the collapse of the insulating gap and the concomitant change in crystal symmetry in homogeneously strained single-crystalline VO 2 films are preceded by the purely electronic softening of Coulomb correlations within V-V singlet dimers. Furthermore, this process starts 7 K (±0.3 K) below the transition temperature, as conventionally defined by electronic transport and x-ray diffraction measurements, and sets the energy scale for driving the near-room-temperaturemore » insulator-metal transition in this technologically promising material.« less

26-Day Variations of 7 MeV Electrons at high Latitudes and their Implications on the Heliospheric Magnetic Field

NASA Astrophysics Data System (ADS)

Sternal, Oliver; Engelbrecht, Eugene; Burger, Renier; Dunzlaff, Phillip; Ferreira, Stefan; Fichtner, Horst; Heber, Bernd; Kopp, Andreas; Potgieter, Marius; Scherer, Klaus

The transport of energetic particles in the heliosphere is usually described by the Parker trans-port equation including the physical processes of diffusion, drift, convection and adiabatic energy changes. The Ulysses spacecraft provides unique insight into the flux of MeV electrons at high latitudes. In this contribution, we compare our model results for the Parker HMF model and the Fisk-type Schwadron-Parker HMF model to Ulysses measurements. The elec-tron flux at high latitudes has been used as a remote sensing method to investigate the imprint of a Fisk-type HMF. We show here for the first time that such an imprint exists and deduce a limitation on the Fisk HMF angle β.

Enhanced Electron Affinity and Exciton Confinement in Exciplex-Type Host: Power Efficient Solution-Processed Blue Phosphorescent OLEDs with Low Turn-on Voltage.

PubMed

Ban, Xinxin; Sun, Kaiyong; Sun, Yueming; Huang, Bin; Jiang, Wei

2016-01-27

A benzimidazole/phosphine oxide hybrid 1,3,5-tris(1-(4-(diphenylphosphoryl)phenyl)-1H-benzo[d]imidazol-2-yl)benzene (TPOB) was newly designed and synthesized as the electron-transporting component to form an exciplex-type host with the conventional hole-transporting material tris(4-carbazoyl-9-ylphenyl)amine (TCTA). Because of the enhanced triplet energy and electron affinity of TPOB, the energy leakage from exciplex-state to the constituting molecule was eliminated. Using energy transfer from exciplex-state, solution-processed blue phosphorescent organic light-emitting diodes (PHOLEDs) achieved an extremely low turn-on voltage of 2.8 V and impressively high power efficiency of 22 lm W(-1). In addition, the efficiency roll-off was very small even at luminance up to 10 000 cd m(-2), which suggested the balanced charge transfer in the emission layer. This study demonstrated that molecular modulation was an effective way to develop efficient exciplex-type host for high performanced PHOLEDs.

Copper silicide/silicon nanowire heterostructures: in situ TEM observation of growth behaviors and electron transport properties.

PubMed

Chiu, Chung-Hua; Huang, Chun-Wei; Chen, Jui-Yuan; Huang, Yu-Ting; Hu, Jung-Chih; Chen, Lien-Tai; Hsin, Cheng-Lun; Wu, Wen-Wei

2013-06-07

Copper silicide has been studied in the applications of electronic devices and catalysts. In this study, Cu3Si/Si nanowire heterostructures were fabricated through solid state reaction in an in situ transmission electron microscope (TEM). The dynamic diffusion of the copper atoms in the growth process and the formation mechanism are characterized. We found that two dimensional stacking faults (SF) may retard the growth of Cu3Si. Due to the evidence of the block of edge-nucleation (heterogeneous) by the surface oxide, center-nucleation (homogeneous) is suggested to dominate the silicidation. Furthermore, the electrical transport properties of various silicon channel length with Cu3Si/Si heterostructure interfaces and metallic Cu3Si NWs have been investigated. The observations not only provided an alternative pathway to explore the formation mechanisms and interface properties of Cu3Si/Si, but also suggested the potential application of Cu3Si at nanoscale for future processing in nanotechnology.

Non-thermal equilibrium plasma-liquid interactions with femtolitre droplets

NASA Astrophysics Data System (ADS)

Maguire, Paul; Mahony, Charles; Bingham, Andrew; Patel, Jenish; Rutherford, David; McDowell, David; Mariotti, Davide; Bennet, Euan; Potts, Hugh; Diver, Declan

2014-10-01

Plasma-induced non-equilibrium liquid chemistry is little understood. It depends on a complex interplay of interface and near surface processes, many involving energy-dependent electron-induced reactions and the transport of transient species such as hydrated electrons. Femtolitre liquid droplets, with an ultra-high ratio of surface area to volume, were transported through a low-temperature atmospheric pressure RF microplasma with transit times of 1--10 ms. Under a range of plasma operating conditions, we observe a number of non-equilibrium chemical processes that are dominated by energetic electron bombardment. Gas temperature and plasma parameters (ne ~ 1013 cm-3, Te < 4 eV) were determined while size and droplet velocity profiles were obtained using a microscope coupled to a fast ICCD camera under low light conditions. Laminar mixed-phase droplet flow is achieved and the plasma is seen to significantly deplete only the slower, smaller droplet component due possibly to the interplay between evaporation, Rayleigh instabilities and charge emission. Funding from EPSRC acknowledged (Grants EP/K006088/1 and EP/K006142/1).

A Computational and Theoretical Study of Conductance in Hydrogen-bonded Molecular Junctions

NASA Astrophysics Data System (ADS)

Wimmer, Michael

This thesis is devoted to the theoretical and computational study of electron transport in molecular junctions where one or more hydrogen bonds are involved in the process. While electron transport through covalent bonds has been extensively studied, in recent work the focus has been shifted towards hydrogen-bonded systems due to their ubiquitous presence in biological systems and their potential in forming nano-junctions between molecular electronic devices and biological systems. This analysis allows us to significantly expand our comprehension of the experimentally observed result that the inclusion of hydrogen bonding in a molecular junction significantly impacts its transport properties, a fact that has important implications for our understanding of transport through DNA, and nano-biological interfaces in general. In part of this work I have explored the implications of quasiresonant transport in short chains of weakly-bonded molecular junctions involving hydrogen bonds. I used theoretical and computational analysis to interpret recent experiments and explain the role of Fano resonances in the transmission properties of the junction. In a different direction, I have undertaken the study of the transversal conduction through nucleotide chains that involve a variable number of different hydrogen bonds, e.g. NH˙˙˙O, OH˙˙˙O, and NH˙˙˙N, which are the three most prevalent hydrogen bonds in biological systems and organic electronics. My effort here has focused on the analysis of electronic descriptors that allow a simplified conceptual and computational understanding of transport properties. Specifically, I have expanded our previous work where the molecular polarizability was used as a conductance descriptor to include the possibility of atomic and bond partitions of the molecular polarizability. This is important because it affords an alternative molecular description of conductance that is not based on the conventional view of molecular orbitals as transport channels. My findings suggest that the hydrogen-bond networks are crucial in understanding the conductance of these junctions. A broader impact of this work pertains the fact that characterizing transport through hydrogen bonding networks may help in developing faster and cost-effective approaches to personalized medicine, to advance DNA sequencing and implantable electronics, and to progress in the design and application of new drugs.

Multispectral Visible/Infrared Sensors Based on Polymer-Metal Nanocomposites

DTIC Science & Technology

2010-01-06

transport in the dielectric zone is governed by an activated tunneling process, while the electron transport in the metallic zone can be described by...electrical pathway has formed at this stage, and thermally activated tunneling dominates the charge transport. At very high metal concentration, metallic...25 -20 -15 -10 -5 0 5 10 Cu rre nt , m A Bias Voltage, V Dark Bright Bright >850 nm Figure 12a. Optical absorption spectrum of Blackberry dye

Electronic Data Interchange in Defense Transportation

DTIC Science & Technology

1987-10-01

entry into a nearly paperless transportation environment. • Prescribe DoD’s use of the EDI standards developed by the transportation industry and lead...information into a format for internal use so that it can be processed. * Key Entry Costs. Data will no longer need to be entered manually into a terminal or...that commercial standards cannot meet, DoD must create standards. A vehicle for creating those DoD-unique standards now exists. That vehicle , the

Charge transport in organic multi-layer devices under electric and optical fields

NASA Astrophysics Data System (ADS)

Park, June Hyoung

2007-12-01

Charge transport in small organic molecules and conjugated conducting polymers under electric or optical fields is studied by using field effect transistors and photo-voltaic cells with multiple thin layers. With these devices, current under electric field, photo-current under optical field, and luminescence of optical materials are measured to characterize organic and polymeric materials. For electric transport studies, poly(3,4-ethylenedioxythiophene) doped by polystyrenesulfonic acid is used, which is conductive with conductivity of approximately 25 S/cm. Despite their high conductance, field effect transistors based on the films are successfully built and characterized by monitoring modulations of drain current by gate voltage and IV characteristic curves. Due to very thin insulating layers of poly(vinylphenol), the transistors are relative fast under small gate voltage variation although heavy ions are involved in charge transport. In IV characteristic curves, saturation effects can be observed. Analysis using conventional field effect transistor model indicates high mobility of charge carriers, 10 cm2/V·sec, which is not consistent with the mobility of the conducting polymer. It is proposed that the effect of a small density of ions injected via polymer dielectric upon application of gate voltage and the ion compensation of key hopping sites accounts for the operation of the field effect transistors. For the studies of transport under optical field, photovoltaic cells with 3 different dendrons, which are efficient to harvest photo-excited electrons, are used. These dendrons consist of two electron-donors (tetraphenylporphyrin) and one electron-accepter (naphthalenediimide). Steady-state fluorescence measurements show that inter-molecular interaction is dominant in solid dendron film, although intra-molecular interaction is still present. Intra-molecular interaction is suggested by different fluorescence lifetimes between solutions of donor and dendrons. This intra-molecular interaction has two processes, transport via pi-stackings and transport via linking functional groups in the dendrons. IV characteristic spectra of the photovoltaic cells suggest that the transport route of photo-excited charges depends on wavelength of incident light on the cells. For excitation by the Soret band and the lowest Q band, a photo-excited electron can transport directly to a neighbor dendron. For excitation by high-energy Q bands, a photo-excited electron transports via the electron-accepters.

On the physics of dispersive electron transport characteristics in SnO2 nanoparticle-based dye sensitized solar cells.

PubMed

Ashok, Aditya; Vijayaraghavan, S N; Unni, Gautam E; Nair, Shantikumar V; Shanmugam, Mariyappan

2018-04-27

The present study elucidates dispersive electron transport mediated by surface states in tin oxide (SnO 2 ) nanoparticle-based dye sensitized solar cells (DSSCs). Transmission electron microscopic studies on SnO 2 show a distribution of ∼10 nm particles exhibiting (111) crystal planes with inter-planar spacing of 0.28 nm. The dispersive transport, experienced by photo-generated charge carriers in the bulk of SnO 2 , is observed to be imposed by trapping and de-trapping processes via SnO 2 surface states present close to the band edge. The DSSC exhibits 50% difference in performance observed between the forward (4%) and reverse (6%) scans due to the dispersive transport characteristics of the charge carriers in the bulk of the SnO 2 . The photo-generated charge carriers are captured and released by the SnO 2 surface states that are close to the conduction band-edge resulting in a very significant variation; this is confirmed by the hysteresis observed in the forward and reverse scan current-voltage measurements under AM1.5 illumination. The hysteresis behavior assures that the charge carriers are accumulated in the bulk of electron acceptor due to the trapping, and released by de-trapping mediated by surface states observed during the forward and reverse scan measurements.

On the physics of dispersive electron transport characteristics in SnO2 nanoparticle-based dye sensitized solar cells

NASA Astrophysics Data System (ADS)

Ashok, Aditya; Vijayaraghavan, S. N.; Unni, Gautam E.; Nair, Shantikumar V.; Shanmugam, Mariyappan

2018-04-01

The present study elucidates dispersive electron transport mediated by surface states in tin oxide (SnO2) nanoparticle-based dye sensitized solar cells (DSSCs). Transmission electron microscopic studies on SnO2 show a distribution of ˜10 nm particles exhibiting (111) crystal planes with inter-planar spacing of 0.28 nm. The dispersive transport, experienced by photo-generated charge carriers in the bulk of SnO2, is observed to be imposed by trapping and de-trapping processes via SnO2 surface states present close to the band edge. The DSSC exhibits 50% difference in performance observed between the forward (4%) and reverse (6%) scans due to the dispersive transport characteristics of the charge carriers in the bulk of the SnO2. The photo-generated charge carriers are captured and released by the SnO2 surface states that are close to the conduction band-edge resulting in a very significant variation; this is confirmed by the hysteresis observed in the forward and reverse scan current-voltage measurements under AM1.5 illumination. The hysteresis behavior assures that the charge carriers are accumulated in the bulk of electron acceptor due to the trapping, and released by de-trapping mediated by surface states observed during the forward and reverse scan measurements.

Switching Hole and Electron Transports of Molecules on Metal Oxides by Energy Level Alignment Tuning.

PubMed

Bao, Zhong-Min; Xu, Rui-Peng; Li, Chi; Xie, Zhong-Zhi; Zhao, Xin-Dong; Zhang, Yi-Bo; Li, Yan-Qing; Tang, Jian-Xin

2016-08-31

Charge transport at organic/inorganic hybrid contacts significantly affects the performance of organic optoelectronic devices because the unfavorable energy level offsets at these interfaces can hinder charge injection or extraction due to large barrier heights. Herein, we report a technologically relevant method to functionalize a traditional hole-transport layer of solution-processed nickel oxide (NiOx) with various interlayers. The photoemission spectroscopy measurements reveal the continuous tuning of the NiOx substrate work function ranging from 2.5 to 6.6 eV, enabling the alignment transition of energy levels between the Schottky-Mott limit and Fermi level pinning at the organic/composite NiOx interface. As a result, switching hole and electron transport for the active organic material on the composite NiOx layer is achieved due to the controlled carrier injection/extraction barriers. The experimental findings indicate that tuning the work function of metal oxides with optimum energy level offsets can facilitate the charge transport at organic/electrode contacts.

Flexible ITO-free organic solar cells applying aqueous solution-processed V2O5 hole transport layer: An outdoor stability study

NASA Astrophysics Data System (ADS)

Lima, F. Anderson S.; Beliatis, Michail J.; Roth, Bérenger; Andersen, Thomas R.; Bortoti, Andressa; Reyna, Yegraf; Castro, Eryza; Vasconcelos, Igor F.; Gevorgyan, Suren A.; Krebs, Frederik C.; Lira-Cantu, Mónica

2016-02-01

Solution processable semiconductor oxides have opened a new paradigm for the enhancement of the lifetime of thin film solar cells. Their fabrication by low-cost and environmentally friendly solution-processable methods makes them ideal barrier (hole and electron) transport layers. In this work, we fabricate flexible ITO-free organic solar cells (OPV) by printing methods applying an aqueous solution-processed V2O5 as the hole transport layer (HTL) and compared them to devices applying PEDOT:PSS. The transparent conducting electrode was PET/Ag/PEDOT/ZnO, and the OPV configuration was PET/Ag/PEDOT/ZnO/P3HT:PC60BM/HTL/Ag. Outdoor stability analyses carried out for more than 900 h revealed higher stability for devices fabricated with the aqueous solution-processed V2O5.

Reverse electron transport effects on NADH formation and metmyoglobin reduction.

PubMed

Belskie, K M; Van Buiten, C B; Ramanathan, R; Mancini, R A

2015-07-01

The objective was to determine if NADH generated via reverse electron flow in beef mitochondria can be used for electron transport-mediated reduction and metmyoglobin reductase pathways. Beef mitochondria were isolated from bovine hearts (n=5) and reacted with combinations of succinate, NAD, and mitochondrial inhibitors to measure oxygen consumption and NADH formation. Mitochondria and metmyoglobin were reacted with succinate, NAD, and mitochondrial inhibitors to measure electron transport-mediated metmyoglobin reduction and metmyoglobin reductase activity. Addition of succinate and NAD increased oxygen consumption, NADH formation, electron transport-mediated metmyoglobin reduction, and reductase activity (p<0.05). Addition of antimycin A prevented electron flow beyond complex III, therefore, decreasing oxygen consumption and electron transport-mediated metmyoglobin reduction. Addition of rotenone prevented reverse electron flow, increased oxygen consumption, increased electron transport-mediated metmyoglobin reduction, and decreased NADH formation. Succinate and NAD can generate NADH in bovine tissue postmortem via reverse electron flow and this NADH can be used by both electron transport-mediated and metmyoglobin reductase pathways. Copyright © 2015 Elsevier Ltd. All rights reserved.

Thermal transport across metal silicide-silicon interfaces: First-principles calculations and Green's function transport simulations

NASA Astrophysics Data System (ADS)

Sadasivam, Sridhar; Ye, Ning; Feser, Joseph P.; Charles, James; Miao, Kai; Kubis, Tillmann; Fisher, Timothy S.

2017-02-01

Heat transfer across metal-semiconductor interfaces involves multiple fundamental transport mechanisms such as elastic and inelastic phonon scattering, and electron-phonon coupling within the metal and across the interface. The relative contributions of these different transport mechanisms to the interface conductance remains unclear in the current literature. In this work, we use a combination of first-principles calculations under the density functional theory framework and heat transport simulations using the atomistic Green's function (AGF) method to quantitatively predict the contribution of the different scattering mechanisms to the thermal interface conductance of epitaxial CoSi2-Si interfaces. An important development in the present work is the direct computation of interfacial bonding from density functional perturbation theory (DFPT) and hence the avoidance of commonly used "mixing rules" to obtain the cross-interface force constants from bulk material force constants. Another important algorithmic development is the integration of the recursive Green's function (RGF) method with Büttiker probe scattering that enables computationally efficient simulations of inelastic phonon scattering and its contribution to the thermal interface conductance. First-principles calculations of electron-phonon coupling reveal that cross-interface energy transfer between metal electrons and atomic vibrations in the semiconductor is mediated by delocalized acoustic phonon modes that extend on both sides of the interface, and phonon modes that are localized inside the semiconductor region of the interface exhibit negligible coupling with electrons in the metal. We also provide a direct comparison between simulation predictions and experimental measurements of thermal interface conductance of epitaxial CoSi2-Si interfaces using the time-domain thermoreflectance technique. Importantly, the experimental results, performed across a wide temperature range, only agree well with predictions that include all transport processes: elastic and inelastic phonon scattering, electron-phonon coupling in the metal, and electron-phonon coupling across the interface.

Improved electron injection in all-solution-processed n-type organic field-effect transistors with an inkjet-printed ZnO electron injection layer

NASA Astrophysics Data System (ADS)

Roh, Jeongkyun; Kim, Hyeok; Park, Myeongjin; Kwak, Jeonghun; Lee, Changhee

2017-10-01

Interface engineering for the improved injection properties of all-solution-processed n-type organic field-effect transistors (OFETs) arising from the use of an inkjet-printed ZnO electron injection layer were demonstrated. The characteristics of ZnO in terms of electron injection and transport were investigated, and then we employed ZnO as the electron injection layer via inkjet-printing during the fabrication of all-solution-processed, n-type OFETs. With the inkjet-printed ZnO electron injection layer, the devices exhibited approximately five-fold increased mobility (0.0058 cm2/V s to 0.030 cm2/V s), more than two-fold increased charge concentration (2.76 × 1011 cm-2 to 6.86 × 1011 cm-2), and two orders of magnitude reduced device resistance (120 MΩ cm to 3 MΩ cm). Moreover, n-type polymer form smoother film with ZnO implying denser packing of polymer, which results in higher mobility.

Mechanisms of transport and electron transfer at conductive polymer/liquid interfaces

NASA Astrophysics Data System (ADS)

Ratcliff, Erin

Organic semiconductors (OSCs) have incredible prospects for next-generation, flexible electronic devices including bioelectronics, thermoelectrics, opto-electronics, and energy storage and conversion devices. Yet many fundamental challenges still exist. First, solution processing prohibits definitive control over microstructure, which is fundamental for controlling electrical, ionic, and thermal transport properties. Second, OSCs generally suffer from poor electrical conductivities due to a combination of low carriers and low mobility. Third, polymeric semiconductors have potential-dependent, dynamically evolving electronic and chemical states, leading to complex interfacial charge transfer properties in contact with liquids. This talk will focus on the use of alternative synthetic strategies of oxidative chemical vapor deposition and electrochemical deposition to control physical, electronic, and chemical structure. We couple our synthetic efforts with energy-, time-, and spatially resolved spectroelectrochemical and microscopy techniques to understand the critical interfacial chemistry-microstructure-property relationships: first at the macroscale, and then moving towards the nanoscale. In particular, approaches to better understand electron transfer events at polymer/liquid interfaces as a function of: 1.) chemical composition; 2.) electronic density of states (DOS); and 3.) crystallinity and microstructure will be discussed.

Monte Carlo Simulation of THz Radiation Detection in GaN MOSFET n+nn+ Channel with Uncentered Gate in n-region

NASA Astrophysics Data System (ADS)

Palermo, C.; Torres, J.; Varani, L.; Gružinskis, V.; Starikov, E.; Shiktorov, P.; Ašmontas, S.; Sužiedelis, A.

2017-10-01

Electron transport and drain current noise in the wurtzite GaN MOSFET have been studied by Monte Carlo particle simulation which simultaneously solves the Boltzmann transport and pseudo-2D Poisson equations. A proper design of GaN MOSFET n+nn+ channel with uncentered gate in n-region to reach the maximum detection sensitivity is proposed. It is shown that the main role in formation of longitudinal transport asymmetry and THz radiation detection is played by optical phonon emission process. It is found that the detection current at 300 K is maximal in frequency range from 0.5 to 7 THz. At higher frequenciea the detection current rapidly decreases due to the inertia of electron motion.

Scanning tunneling spectroscopy of molecular thin films and semiconductor nanostructures

NASA Astrophysics Data System (ADS)

Gaan, Sandeep

Work presented in this thesis mostly deals with nano-scale study of electronic properties of organic semiconducting molecules using pentacene (Pn) as a model system and compared with various SiC surfaces to gain more insight into physical processes at nano-scale. In addition, InAs quantum dots (QDs) in a GaAs matrix are studied to probe electronic states of individual QDs. Scanning tunneling microscopy (STM) and spectroscopy (STS) are the primary experimental techniques used to probe local electronic properties on the nano-scale. Vacuum sublimated Pn thin films were deposited onto SiC substrates for STM/STS experiments. STM studies show high quality ordered Pn films. Atomic force microscopy (AFM) images reveal dendritic growth pattern of these films. Local density of states (LDOS) measurements using STS reveals a HOMO-LUMO bandgap. In order to study charge transport properties of Pn films, different amount of charge were injected into the sample by systematically changing the tip-sample separation. Saturation of the tunnel current was observed at positive sample voltages (LUMO states). This effect was attributed to a transport/space charge limitation in tunnel current by treating it as a situation analogous to charge injection into insulators which gives rise to space charge limited current (also previously observed in the case of organic semiconductors). Using a simple model we were able to derive a hopping rate that characterizes nano-scale transport in Pn films at least in the vicinity of the STM probe-tip. We have studied effect of transport limitation in the tunnel current for various semiconductor surfaces. In order to probe surfaces of varying conductivities, we have used Si-rich SiC surfaces such as 3x3 and 3x3 -R30° (both Mott-Hubbard insulators) as well as a highly conducting C-rich graphene surface, and compared those results with the data obtained from Pn. We observe variation of the decay constant kappa (which characterizes the tunneling process) on these surfaces of varying conductivities. The graphene surface shows no transport limitation in the tunnel current, as evidenced by only small changes in kappa as a function of tunnel current for these surfaces. This result is in sharp contrast to the case of Pn where kappa rapidly decays to zero with increasing tunnel current due to transport/space charge limited effects in the semiconductor. Thus, the change is kappa value in STM experiments is reflective of non-ideal behavior of the tunneling. As a specific case of transport limitation on the nano-scale we have also studied InAs QDs grown in a GaAs matrix. We observe that the occupation of discrete quantized states in the dots with electrons has a significant effect on tunneling spectra. When the QD state is occupied by an electron the potential in the dot is modified such that this state does not contribute to the tunnel current. The state then remains "invisible" in the tunneling spectra. Only in presence of transport channels in the vicinity of the dots can the electron localized in the QD state leak out to the substrate, and only then does the state appears in the spectrum. In our experiments these transport channels arise from steps which form as a result of in situ cleaving process for cross-sectional STM (XSTM) measurements.

Effect of magnetic fluctuations on the confinement and dynamics of runaway electrons in the HT-7 tokamak

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhou, R. J.; Hu, L. Q.; Li, E. Z.

2013-03-15

The nature of runaway electrons is such that the confinement and dynamics of the electrons can be strongly affected by magnetic fluctuations in plasma. Experimental results in the HT-7 tokamak indicated significant losses of runaway electrons due to magnetic fluctuations, but the loss processes did not only rely on the fluctuation amplitude. Efficient radial runaway transport required that there were no more than small regions of the plasma volume in which there was very low transport of runaways. A radial runaway diffusion coefficient of D{sub r} Almost-Equal-To 10 m{sup 2}s{sup -1} was derived for the loss processes, and diffusion coefficientmore » near the resonant magnetic surfaces and shielding factor #Greek Upsilon With Hook Symbol#=0.8 were deduced. Test particle equations were used to analyze the effect of magnetic fluctuations on runaway dynamics. It was found that the maximum energy that runaways can gain is very sensitive to the value of {alpha}{sub s} (i.e., the fraction of plasma volume with reduced transport). {alpha}{sub s}=(0.28-0.33) was found for the loss processes in the experiment, and maximum runaway energy could be controlled in the range of E=(4 MeV-6 MeV) in this case. Additionally, to control the maximum runaway energy below 5 MeV, the normalized electric field needed to be under a critical value D{sub {alpha}}=6.8, and the amplitude normalized magnetic fluctuations b(tilde sign) needed to be at least of the order of b(tilde sign) Almost-Equal-To 3 Multiplication-Sign 10{sup -5}.« less

ecode - Electron Transport Algorithm Testing v. 1.0

DOE Office of Scientific and Technical Information (OSTI.GOV)

Franke, Brian C.; Olson, Aaron J.; Bruss, Donald Eugene

2016-10-05

ecode is a Monte Carlo code used for testing algorithms related to electron transport. The code can read basic physics parameters, such as energy-dependent stopping powers and screening parameters. The code permits simple planar geometries of slabs or cubes. Parallelization consists of domain replication, with work distributed at the start of the calculation and statistical results gathered at the end of the calculation. Some basic routines (such as input parsing, random number generation, and statistics processing) are shared with the Integrated Tiger Series codes. A variety of algorithms for uncertainty propagation are incorporated based on the stochastic collocation and stochasticmore » Galerkin methods. These permit uncertainty only in the total and angular scattering cross sections. The code contains algorithms for simulating stochastic mixtures of two materials. The physics is approximate, ranging from mono-energetic and isotropic scattering to screened Rutherford angular scattering and Rutherford energy-loss scattering (simple electron transport models). No production of secondary particles is implemented, and no photon physics is implemented.« less

An essential role of the mitochondrial electron transport chain in cell proliferation is to enable aspartate synthesis

PubMed Central

Birsoy, Kıvanç; Wang, Tim; Chen, Walter; Freinkman, Elizaveta; Abu-Remaileh, Monther; Sabatini, David M.

2015-01-01

Summary The mitochondrial electron transport chain (ETC) enables many metabolic processes, but why its inhibition suppresses cell proliferation is unclear. It is also not well understood why pyruvate supplementation allows cells lacking ETC function to proliferate. We used a CRISPR-based genetic screen to identify genes whose loss sensitizes human cells to phenformin, a complex I inhibitor. The screen yielded GOT1, the cytosolic aspartate aminotransferase, loss of which kills cells upon ETC inhibition. GOT1 normally consumes aspartate to transfer electrons into mitochondria, but, upon ETC inhibition, it reverses to generate aspartate in the cytosol, which partially compensates for the loss of mitochondrial aspartate synthesis. Pyruvate stimulates aspartate synthesis in a GOT1-dependent fashion, which is required for pyruvate to rescue proliferation of cells with ETC dysfunction. Aspartate supplementation or overexpression of an aspartate transporter allows cells without ETC activity to proliferate. Thus, enabling aspartate synthesis is an essential role of the ETC in cell proliferation. PMID:26232224

Plasmonic hot electron transport drives nano-localized chemistry

PubMed Central

Cortés, Emiliano; Xie, Wei; Cambiasso, Javier; Jermyn, Adam S.; Sundararaman, Ravishankar; Narang, Prineha; Schlücker, Sebastian; Maier, Stefan A.

2017-01-01

Nanoscale localization of electromagnetic fields near metallic nanostructures underpins the fundamentals and applications of plasmonics. The unavoidable energy loss from plasmon decay, initially seen as a detriment, has now expanded the scope of plasmonic applications to exploit the generated hot carriers. However, quantitative understanding of the spatial localization of these hot carriers, akin to electromagnetic near-field maps, has been elusive. Here we spatially map hot-electron-driven reduction chemistry with 15 nm resolution as a function of time and electromagnetic field polarization for different plasmonic nanostructures. We combine experiments employing a six-electron photo-recycling process that modify the terminal group of a self-assembled monolayer on plasmonic silver nanoantennas, with theoretical predictions from first-principles calculations of non-equilibrium hot-carrier transport in these systems. The resulting localization of reactive regions, determined by hot-carrier transport from high-field regions, paves the way for improving efficiency in hot-carrier extraction science and nanoscale regio-selective surface chemistry. PMID:28348402

An Essential Role of the Mitochondrial Electron Transport Chain in Cell Proliferation Is to Enable Aspartate Synthesis.

PubMed

Birsoy, Kıvanç; Wang, Tim; Chen, Walter W; Freinkman, Elizaveta; Abu-Remaileh, Monther; Sabatini, David M

2015-07-30

The mitochondrial electron transport chain (ETC) enables many metabolic processes, but why its inhibition suppresses cell proliferation is unclear. It is also not well understood why pyruvate supplementation allows cells lacking ETC function to proliferate. We used a CRISPR-based genetic screen to identify genes whose loss sensitizes human cells to phenformin, a complex I inhibitor. The screen yielded GOT1, the cytosolic aspartate aminotransferase, loss of which kills cells upon ETC inhibition. GOT1 normally consumes aspartate to transfer electrons into mitochondria, but, upon ETC inhibition, it reverses to generate aspartate in the cytosol, which partially compensates for the loss of mitochondrial aspartate synthesis. Pyruvate stimulates aspartate synthesis in a GOT1-dependent fashion, which is required for pyruvate to rescue proliferation of cells with ETC dysfunction. Aspartate supplementation or overexpression of an aspartate transporter allows cells without ETC activity to proliferate. Thus, enabling aspartate synthesis is an essential role of the ETC in cell proliferation. Copyright © 2015 Elsevier Inc. All rights reserved.

Organic solar cells: understanding the role of Förster resonance energy transfer.

PubMed

Feron, Krishna; Belcher, Warwick J; Fell, Christopher J; Dastoor, Paul C

2012-12-12

Organic solar cells have the potential to become a low-cost sustainable energy source. Understanding the photoconversion mechanism is key to the design of efficient organic solar cells. In this review, we discuss the processes involved in the photo-electron conversion mechanism, which may be subdivided into exciton harvesting, exciton transport, exciton dissociation, charge transport and extraction stages. In particular, we focus on the role of energy transfer as described by F¨orster resonance energy transfer (FRET) theory in the photoconversion mechanism. FRET plays a major role in exciton transport, harvesting and dissociation. The spectral absorption range of organic solar cells may be extended using sensitizers that efficiently transfer absorbed energy to the photoactive materials. The limitations of F¨orster theory to accurately calculate energy transfer rates are discussed. Energy transfer is the first step of an efficient two-step exciton dissociation process and may also be used to preferentially transport excitons to the heterointerface, where efficient exciton dissociation may occur. However, FRET also competes with charge transfer at the heterointerface turning it in a potential loss mechanism. An energy cascade comprising both energy transfer and charge transfer may aid in separating charges and is briefly discussed. Considering the extent to which the photo-electron conversion efficiency is governed by energy transfer, optimisation of this process offers the prospect of improved organic photovoltaic performance and thus aids in realising the potential of organic solar cells.

Shock wave as a probe of flux-dimited thermal transport in laser-heated solids

NASA Astrophysics Data System (ADS)

Smith, K.; Forsman, A.; Chiu, G.

1996-11-01

Laser-generated shock waves in solids result from the ablation of the target material. Where radiation transport is negligible, the ablation process is dominated by electron thermal conduction. This offers an opportunity to probe the degree of transport inhibition (compared with classical heat flow) for steep temperature gradients in a dense plasma. Using a 1-dimensional hydrodynamic code, we have examined the effect of flux-limited thermal conduction on the amplitude of the resulting shock wave.

Nicholas Metropolis Award for Outstanding Doctoral Thesis Work in Computational Physics Talk: Understanding Nano-scale Electronic Systems via Large-scale Computation

NASA Astrophysics Data System (ADS)

Cao, Chao

2009-03-01

Nano-scale physical phenomena and processes, especially those in electronics, have drawn great attention in the past decade. Experiments have shown that electronic and transport properties of functionalized carbon nanotubes are sensitive to adsorption of gas molecules such as H2, NO2, and NH3. Similar measurements have also been performed to study adsorption of proteins on other semiconductor nano-wires. These experiments suggest that nano-scale systems can be useful for making future chemical and biological sensors. Aiming to understand the physical mechanisms underlying and governing property changes at nano-scale, we start off by investigating, via first-principles method, the electronic structure of Pd-CNT before and after hydrogen adsorption, and continue with coherent electronic transport using non-equilibrium Green’s function techniques combined with density functional theory. Once our results are fully analyzed they can be used to interpret and understand experimental data, with a few difficult issues to be addressed. Finally, we discuss a newly developed multi-scale computing architecture, OPAL, that coordinates simultaneous execution of multiple codes. Inspired by the capabilities of this computing framework, we present a scenario of future modeling and simulation of multi-scale, multi-physical processes.

Donor-acceptor cocrystal based on hexakis(alkoxy)triphenylene and perylenediimide derivatives with an ambipolar transporting property

NASA Astrophysics Data System (ADS)

Su, Yajun; Li, Yan; Liu, Jiangang; Xing, Rubo; Han, Yanchun

2015-01-01

An organic donor-acceptor cocrystal with an ambipolar transporting property was constructed based on N,N'-bis(1-ethylpropyl)-perylene-3,4,9,10-tetracarboxylic diimide (EP-PDI) and 2,3,6,7,10,11-hexakis-(hexyloxy)-triphenylene (H6TP). The cocrystal with an alternating stacking of H6TP and EP-PDI molecules was formed through both drop-casting and spin-coating processes, especially at the optimized ratios of H6TP/EP-PDI (2/1, 1/1). The formation of the cocrystal was driven by the strong π-π interaction and the weaker steric hindrance, resulting from the smaller side groups, between the donor and acceptor molecules. Field effect transistors (FETs) based on the H6TP/EP-PDI cocrystal exhibited relatively balanced hole/electron transport, with a hole mobility of 1.14 × 10-3 cm2 V-1 s-1 and an electron mobility of 1.40 × 10-3 cm2 V-1 s-1.An organic donor-acceptor cocrystal with an ambipolar transporting property was constructed based on N,N'-bis(1-ethylpropyl)-perylene-3,4,9,10-tetracarboxylic diimide (EP-PDI) and 2,3,6,7,10,11-hexakis-(hexyloxy)-triphenylene (H6TP). The cocrystal with an alternating stacking of H6TP and EP-PDI molecules was formed through both drop-casting and spin-coating processes, especially at the optimized ratios of H6TP/EP-PDI (2/1, 1/1). The formation of the cocrystal was driven by the strong π-π interaction and the weaker steric hindrance, resulting from the smaller side groups, between the donor and acceptor molecules. Field effect transistors (FETs) based on the H6TP/EP-PDI cocrystal exhibited relatively balanced hole/electron transport, with a hole mobility of 1.14 × 10-3 cm2 V-1 s-1 and an electron mobility of 1.40 × 10-3 cm2 V-1 s-1. Electronic supplementary information (ESI) available. See DOI: 10.1039/c4nr05915h

Electronic properties of conductive pili of the metal-reducing bacterium Geobacter sulfurreducens probed by scanning tunneling microscopy.

PubMed

Veazey, Joshua P; Reguera, Gemma; Tessmer, Stuart H

2011-12-01

The metal-reducing bacterium Geobacter sulfurreducens produces conductive protein appendages known as "pilus nanowires" to transfer electrons to metal oxides and to other cells. These processes can be harnessed for the bioremediation of toxic metals and the generation of electricity in bioelectrochemical cells. Key to these applications is a detailed understanding of how these nanostructures conduct electrons. However, to the best of our knowledge, their mechanism of electron transport is not known. We used the capability of scanning tunneling microscopy (STM) to probe conductive materials with higher spatial resolution than other scanning probe methods to gain insights into the transversal electronic behavior of native, cell-anchored pili. Despite the presence of insulating cellular components, the STM topography resolved electronic molecular substructures with periodicities similar to those reported for the pilus shaft. STM spectroscopy revealed electronic states near the Fermi level, consistent with a conducting material, but did not reveal electronic states expected for cytochromes. Furthermore, the transversal conductance was asymmetric, as previously reported for assemblies of helical peptides. Our results thus indicate that the Geobacter pilus shaft has an intrinsic electronic structure that could play a role in charge transport.

Electrolyte-gated transistors based on phenyl-C61-butyric acid methyl ester (PCBM) films: bridging redox properties, charge carrier transport and device performance.

PubMed

Lan, Tian; Soavi, Francesca; Marcaccio, Massimo; Brunner, Pierre-Louis; Sayago, Jonathan; Santato, Clara

2018-05-24

The n-type organic semiconductor phenyl-C61-butyric acid methyl ester (PCBM), a soluble fullerene derivative well investigated for organic solar cells and transistors, can undergo several successive reversible, diffusion-controlled, one-electron reduction processes. We exploited such processes to shed light on the correlation between electron transfer properties, ionic and electronic transport as well as device performance in ionic liquid (IL)-gated transistors. Two ILs were considered, based on bis(trifluoromethylsulfonyl)imide [TFSI] as the anion and 1-ethyl-3-methylimidazolium [EMIM] or 1-butyl-1-methylpyrrolidinium [PYR14] as the cation. The aromatic structure of [EMIM] and its lower steric hindrance with respect to [PYR14] favor a 3D (bulk) electrochemical doping. As opposed to this, for [PYR14] the doping seems to be 2D (surface-confined). If the n-doping of the PCBM is pursued beyond the first electrochemical process, the transistor current vs. gate-source voltage plots in [PYR14][TFSI] feature a maximum that points to the presence of finite windows of high conductivity in IL-gated PCBM transistors.

Low temperature synthesis of hierarchical TiO 2 nanostructures for high performance perovskite solar cells by pulsed laser deposition

DOE PAGES

Yang, Bin; Mahjouri-Samani, Masoud; Rouleau, Christopher M.; ...

2016-06-10

A promising way to advance perovskite solar cells is to improve the quality of the electron transport material e.g., titanium dioxide (TiO 2) in a direction that increases electron transport and extraction. Although dense TiO 2 films are easily grown in solution, efficient electron extraction suffers due to a lack of interfacial contact area with the perovskite. Conversely, mesoporous films do offer high surface-area-to-volume ratios, thereby promoting efficient electron extraction, but their morphology is relatively difficult to control via conventional solution synthesis methods. Here, a pulsed laser deposition method was used to assemble TiO 2 nanoparticles into TiO 2 hierarchicalmore » nanoarchitectures having the anatase crystal structure, and prototype solar cells employing these structures yielded power conversion efficiencies of ~ 14%. Our approach demonstrates a way to grow high aspect-ratio TiO 2 nanostructures for improved interfacial contact between TiO 2 and perovskite materials, leading to high electron-hole pair separation and electron extraction efficiencies for superior photovoltaic performance. In addition, compared to conventional solution-processed TiO 2 films that require 500 °C to obtain a good crystallinity, our relatively low temperature (300 °C) TiO 2 processing method may promote reduced energy-consumption during device fabrication as well as enable compatibility with various flexible polymer substrates.« less

The microorganisms used for working in microbial fuel cells

NASA Astrophysics Data System (ADS)

Konovalova, E. Yu.; Stom, D. I.; Zhdanova, G. O.; Yuriev, D. A.; Li, Youming; Barbora, Lepakshi; Goswami, Pranab

2018-04-01

Investigated the use as biological object in microbial fuel cells (MFC) of various microorganisms performing the transport of electrons in the processing of various substrates. Most MFC, uses complex substrates. Such MFC filled with associations of microorganisms. The article deals with certain types of microorganisms for use in the MFC, shows the characteristics of molecular electron transfer mechanisms microorganisms into the environment.

Center for Electrocatalysis, Transport Phenomena, and Materials (CETM) for Innovative Energy Storage - Final Report

DOE Office of Scientific and Technical Information (OSTI.GOV)

Soloveichik, Grigorii

2015-11-30

EFRC vision. The direct use of organic hydrides in fuel cells as virtual hydrogen carriers that generate stable organic molecules, protons, and electrons upon electro-oxidation and can be electrochemically charged by re-hydrogenating the oxidized carrier was the major focus of the Center for Electrocatalysis, Transport Phenomena and Materials for Innovative Energy Storage (EFRC-ETM). Compared to a hydrogen-on-demand design that includes thermal decomposition of organic hydrides in a catalytic reactor, the proposed approach is much simpler and does not require additional dehydrogenation catalysts or heat exchangers. Further, this approach utilizes the advantages of a flow battery (i.e., separation of power andmore » energy, ease of transport and storage of liquid fuels) with fuels that have system energy densities similar to current hydrogen PEM fuel cells. EFRC challenges. Two major EFRC challenges were electrocatalysis and transport phenomena. The electrocatalysis challenge addresses fundamental processes which occur at a single molecular catalyst (microscopic level) and involve electron and proton transfer between the hydrogen rich and hydrogen depleted forms of organic liquid fuel and the catalyst. To form stable, non-radical dehydrogenation products from the organic liquid fuel, it is necessary to ensure fast transport of at least two electrons and two protons (per double bond formation). The same is true for the reverse hydrogenation reaction. The transport phenomena challenge addresses transport of electrons to/from the electrocatalyst and the current collector as well as protons across the polymer membrane. Additionally it addresses prevention of organic liquid fuel, water and oxygen transport through the PEM. In this challenge, the transport of protons or molecules involves multiple sites or a continuum (macroscopic level) and water serves as a proton conducting medium for the majority of known sulfonic acid based PEMs. Proton transfer in the presence of prospective organic liquid fuels was studied. During EFRC program various types of electrocatalysts, classes of fuels, and membranes have been investigated.« less

Multiscale three-dimensional simulations of charge gain and transport in diamond

NASA Astrophysics Data System (ADS)

Dimitrov, D. A.; Busby, R.; Cary, J. R.; Ben-Zvi, I.; Rao, T.; Smedley, J.; Chang, X.; Keister, J. W.; Wu, Q.; Muller, E.

2010-10-01

A promising new concept of a diamond-amplified photocathode for generation of high-current, high-brightness, and low thermal emittance electron beams was recently proposed and is currently under active development. Detailed understanding of physical processes with multiple energy and time scales is required to design reliable and efficient diamond-amplifier cathodes. We have implemented models, within the VORPAL computational framework, to simulate secondary electron generation and charge transport in diamond in order to facilitate the investigation of the relevant effects involved. The models include inelastic scattering of electrons and holes for generation of electron-hole pairs, elastic, phonon, and charge impurity scattering. We describe the integrated modeling capabilities we developed and present results on charge gain and collection efficiency as a function of primary electron energy and applied electric field. We compare simulation results with available experimental data. The simulations show an overall qualitative agreement with the observed charge gain from transmission mode experiments and have enabled better understanding of the collection efficiency measurements.

Ultrafast terahertz snapshots of excitonic Rydberg states and electronic coherence in an organometal halide perovskite

DOE PAGES

Luo, Liang; Men, Long; Liu, Zhaoyu; ...

2017-06-01

How photoexcitations evolve into Coulomb-bound electron and hole pairs, called excitons, and unbound charge carriers is a key cross-cutting issue in photovoltaics and optoelectronics. Until now, the initial quantum dynamics following photoexcitation remains elusive in the hybrid perovskite system. Furthermore we reveal excitonic Rydberg states with distinct formation pathways by observing the multiple resonant, internal quantum transitions using ultrafast terahertz quasi-particle transport. Nonequilibrium emergent states evolve with a complex co-existence of excitons, carriers and phonons, where a delayed buildup of excitons under on- and off-resonant pumping conditions allows us to distinguish between the loss of electronic coherence and hot statemore » cooling processes. The nearly ~1 ps dephasing time, efficient electron scattering with discrete terahertz phonons and intermediate binding energy of ~13.5 meV in perovskites are distinct from conventional photovoltaic semiconductors. In addition to providing implications for coherent energy conversion, these are potentially relevant to the development of light-harvesting and electron-transport devices.« less

Ultrafast terahertz snapshots of excitonic Rydberg states and electronic coherence in an organometal halide perovskite

DOE Office of Scientific and Technical Information (OSTI.GOV)

Luo, Liang; Men, Long; Liu, Zhaoyu

How photoexcitations evolve into Coulomb-bound electron and hole pairs, called excitons, and unbound charge carriers is a key cross-cutting issue in photovoltaics and optoelectronics. Until now, the initial quantum dynamics following photoexcitation remains elusive in the hybrid perovskite system. Furthermore we reveal excitonic Rydberg states with distinct formation pathways by observing the multiple resonant, internal quantum transitions using ultrafast terahertz quasi-particle transport. Nonequilibrium emergent states evolve with a complex co-existence of excitons, carriers and phonons, where a delayed buildup of excitons under on- and off-resonant pumping conditions allows us to distinguish between the loss of electronic coherence and hot statemore » cooling processes. The nearly ~1 ps dephasing time, efficient electron scattering with discrete terahertz phonons and intermediate binding energy of ~13.5 meV in perovskites are distinct from conventional photovoltaic semiconductors. In addition to providing implications for coherent energy conversion, these are potentially relevant to the development of light-harvesting and electron-transport devices.« less

Magnetic field manipulation of spin current in a single-molecule magnet tunnel junction with two-electron Coulomb interaction

NASA Astrophysics Data System (ADS)

Zhang, Chao; Yao, Hui; Nie, Yi-Hang; Liang, Jiu-Qing; Niu, Peng-Bin

2018-04-01

In this work, we study the generation of spin-current in a single-molecule magnet (SMM) tunnel junction with Coulomb interaction of transport electrons and external magnetic field. In the absence of field the spin-up and -down currents are symmetric with respect to the initial polarizations of molecule. The existence of magnetic field breaks the time-reversal symmetry, which leads to unsymmetrical spin currents of parallel and antiparallel polarizations. Both the amplitude and polarization direction of spin current can be controlled by the applied magnetic field. Particularly when the magnetic field increases to a certain value the spin-current with antiparallel polarization is reversed along with the magnetization reversal of the SMM. The two-electron occupation indeed enhances the transport current compared with the single-electron process. However the increase of Coulomb interaction results in the suppression of spin-current amplitude at the electron-hole symmetry point. We propose a scheme to compensate the suppression with the magnetic field.

Reactive Oxygen Species Production by Forward and Reverse Electron Fluxes in the Mitochondrial Respiratory Chain

PubMed Central

Selivanov, Vitaly A.; Votyakova, Tatyana V.; Pivtoraiko, Violetta N.; Zeak, Jennifer; Sukhomlin, Tatiana; Trucco, Massimo; Roca, Josep; Cascante, Marta

2011-01-01

Reactive oxygen species (ROS) produced in the mitochondrial respiratory chain (RC) are primary signals that modulate cellular adaptation to environment, and are also destructive factors that damage cells under the conditions of hypoxia/reoxygenation relevant for various systemic diseases or transplantation. The important role of ROS in cell survival requires detailed investigation of mechanism and determinants of ROS production. To perform such an investigation we extended our rule-based model of complex III in order to account for electron transport in the whole RC coupled to proton translocation, transmembrane electrochemical potential generation, TCA cycle reactions, and substrate transport to mitochondria. It fits respiratory electron fluxes measured in rat brain mitochondria fueled by succinate or pyruvate and malate, and the dynamics of NAD+ reduction by reverse electron transport from succinate through complex I. The fitting of measured characteristics gave an insight into the mechanism of underlying processes governing the formation of free radicals that can transfer an unpaired electron to oxygen-producing superoxide and thus can initiate the generation of ROS. Our analysis revealed an association of ROS production with levels of specific radicals of individual electron transporters and their combinations in species of complexes I and III. It was found that the phenomenon of bistability, revealed previously as a property of complex III, remains valid for the whole RC. The conditions for switching to a state with a high content of free radicals in complex III were predicted based on theoretical analysis and were confirmed experimentally. These findings provide a new insight into the mechanisms of ROS production in RC. PMID:21483483

Combined Modeling of Acceleration, Transport, and Hydrodynamic Response in Solar Flares. 1; The Numerical Model

NASA Technical Reports Server (NTRS)

Liu, Wei; Petrosian, Vahe; Mariska, John T.

2009-01-01

Acceleration and transport of high-energy particles and fluid dynamics of atmospheric plasma are interrelated aspects of solar flares, but for convenience and simplicity they were artificially separated in the past. We present here self consistently combined Fokker-Planck modeling of particles and hydrodynamic simulation of flare plasma. Energetic electrons are modeled with the Stanford unified code of acceleration, transport, and radiation, while plasma is modeled with the Naval Research Laboratory flux tube code. We calculated the collisional heating rate directly from the particle transport code, which is more accurate than those in previous studies based on approximate analytical solutions. We repeated the simulation of Mariska et al. with an injection of power law, downward-beamed electrons using the new heating rate. For this case, a -10% difference was found from their old result. We also used a more realistic spectrum of injected electrons provided by the stochastic acceleration model, which has a smooth transition from a quasi-thermal background at low energies to a non thermal tail at high energies. The inclusion of low-energy electrons results in relatively more heating in the corona (versus chromosphere) and thus a larger downward heat conduction flux. The interplay of electron heating, conduction, and radiative loss leads to stronger chromospheric evaporation than obtained in previous studies, which had a deficit in low-energy electrons due to an arbitrarily assumed low-energy cutoff. The energy and spatial distributions of energetic electrons and bremsstrahlung photons bear signatures of the changing density distribution caused by chromospheric evaporation. In particular, the density jump at the evaporation front gives rise to enhanced emission, which, in principle, can be imaged by X-ray telescopes. This model can be applied to investigate a variety of high-energy processes in solar, space, and astrophysical plasmas.

Energy dependence of relativistic electron variations in the outer radiation belt during the recovery phase of magnetic storms: Arase/XEP observations

NASA Astrophysics Data System (ADS)

Higashio, N.; Takashima, T.; Seki, K.; Yoshizumi, M.; Teramoto, M.; Hori, T.; Kurita, S.; Matsuoka, A.

2017-12-01

The Arase satellite was launched in December 2016. The extremely high-energy electron experiments(XEP) onboard Arase measures electrons in the energy range of 400 keV - 20 MeV. After the launch, the XEP has observed variations of the relativistic electrons successfully in the inner magnetosphere. There are roughly two candidate processes of electron acceleration. The first one is the adiabatic acceleration due to the radial transport of electrons from the plasma sheet to the inner magnetosphere. Interaction with ultra-low frequency (ULF) waves are a plausible candidate to drive the radial transport. Another acceleration process is the non-adiabatic acceleration of sub-relativistic electrons to the relativistic energies in the heart of the radiation belt. The interaction with very-low frequency (VLF) waves is considered to play an important role in the internal acceleration. One of the science goals of the XEP instrument is to understand the acceleration mechanisms of the relativistic electrons. In order to investigate the electron acceleration processes, we here focus on three geomagnetic storms occurred on March 27, April 4, and May 28, 2017, respectively. In these events, relativistic electrons in the outer belt showed a typical time variation, i.e., decrease in the main phase and then increase in the recovery phase. On one hand, the increase rates of the electrons are different between the storms. The March 27 storm, which is caused by the arrival of the high-speed coronal hole stream, accompanies a large increase of the relativistic electrons. The April 4 storm, which has a rapid Dst development and recovery, shows less acceleration and does not recover to the pre-storm level. The May 28 storm is caused by a CME and with moderate increase of the relativistic electrons especially in the small L region (L=[3,4]) . We will report on energy dependence of the increase rate and location of the relativistic electrons during the recovery phase, and their comparison between the three geomagnetic storms.

Nonequilibrium Transport and the Bernoulli Effect of Electrons in a Two-Dimensional Electron Gas

NASA Astrophysics Data System (ADS)

Kaya, Ismet I.

2013-02-01

Nonequilibrium transport of charged carriers in a two-dimensional electron gas is summarized from an experimental point of view. The transport regime in which the electron-electron interactions are enhanced at high bias leads to a range of striking effects in a two-dimensional electron gas. This regime of transport is quite different than the ballistic transport in which particles propagate coherently with no intercarrier energy transfer and the diffusive transport in which the momentum of the electron system is lost with the involvement of the phonons. Quite a few hydrodynamic phenomena observed in classical gasses have the electrical analogs in the current flow. When intercarrier scattering events dominate the transport, the momentum sharing via narrow angle scattering among the hot and cold electrons lead to negative resistance and electron pumping which can be viewed as the analog of the Bernoulli-Venturi effect observed classical gasses. The recent experimental findings and the background work in the field are reviewed.

Temperature Dependence of Brillouin Light Scattering Spectra of Acoustic Phonons in Silicon

NASA Astrophysics Data System (ADS)

Somerville, Kevin; Klimovich, Nikita; An, Kyongmo; Sullivan, Sean; Weathers, Annie; Shi, Li; Li, Xiaoqin

2015-03-01

Thermal management represents an outstanding challenge in many areas of technology. Electrons, optical phonons, and acoustic phonons are often driven out of local equilibrium in electronic devices or during laser-material interaction processes. Interest in non-equilibrium transport processes has motivated the development of Raman spectroscopy as a local temperature sensor of optical phonons and intermediate frequency acoustic phonons, whereas Brillouin light scattering (BLS) has recently been explored as a temperature sensor of low-frequency acoustic phonons. Here, we report temperature dependent BLS spectra of silicon, with Raman spectra taken simultaneously for comparison. The origins of the observed temperature dependence of the BLS peak position, linewidth, and intensity are examined in order to evaluate their potential use as temperature sensors for acoustic phonons. We determine that the integrated BLS intensity can be used measure the temperature of specific acoustic phonon modes. This work is supported by National Science Foundation (NSF) Thermal Transport Processes Program under Grant CBET-1336968.

Marangoni Convection during Free Electron Laser Nitriding of Titanium

NASA Astrophysics Data System (ADS)

Höche, Daniel; Müller, Sven; Rapin, Gerd; Shinn, Michelle; Remdt, Elvira; Gubisch, Maik; Schaaf, Peter

2009-08-01

Pure titanium was treated by free electron laser (FEL) radiation in a nitrogen atmosphere. As a result, nitrogen diffusion occurs and a TiN coating was synthesized. Local gradients of interfacial tension due to the local heating lead to a Marangoni convection, which determines the track properties. Because of the experimental inaccessibility of time-dependent occurrences, finite element calculations were performed, to determine the physical processes such as heat transfer, melt flow, and mass transport. In order to calculate the surface deformation of the gas-liquid interface, the level set approach was used. The equations were modified and coupled with heat-transfer and diffusion equations. The process was characterized by dimensionless numbers such as the Reynolds, Peclet, and capillary numbers, to obtain more information about the acting forces and the coating development. Moreover, the nitrogen distribution was calculated using the corresponding transport equation. The simulations were compared with cross-sectional micrographs of the treated titanium sheets and checked for their validity. Finally, the process presented is discussed and compared with similar laser treatments.

Room-Temperature and Aqueous Solution-Processed Two-Dimensional TiS2 as an Electron Transport Layer for Highly Efficient and Stable Planar n-i-p Perovskite Solar Cells.

PubMed

Huang, Peng; Yuan, Ligang; Zhang, Kaicheng; Chen, Qiaoyun; Zhou, Yi; Song, Bo; Li, Yongfang

2018-05-02

In this study, a room-temperature and aqueous solution-processed two-dimensional (2D) transition-metal dichalcogenide TiS 2 was applied as an electron transport layer (ETL) in planar n-i-p perovskite solar cells (Pero-SCs). Upon insertion of the 2D TiS 2 ETL with UV-ozone (UVO) treatment, the power conversion efficiency (PCE) of the planar Pero-SCs was optimized to 18.79%. To the best of our knowledge, this value should be the highest efficiency to date among those PCEs of the n-i-p Pero-SCs with room-temperature-processed metal compound ETLs. More importantly, the n-i-p Pero-SCs with the UVO-treated 2D TiS 2 as an ETL also show extremely high stability, where the average PCE remained over 95% of its initial value after 816 h storage without encapsulation.

Mode of Action Studies on Nitrodiphenyl Ether Herbicides

PubMed Central

Bowyer, John R.; Smith, Beverly J.; Camilleri, Patrick; Lee, Susan A.

1987-01-01

5-[2-Chloro-4-(trifluoromethyl)phenoxy]-2-nitroacetophenone oxime-o-(acetic acid, methyl ester) (DPEI), is a potent nitrodiphenyl ether herbicide which causes rapid leaf wilting, membrane lipid peroxidation, and chlorophyll destruction in a process which is both light- and O2-dependent. These effects resemble those of other nitrodiphenyl ether herbicides. Unlike paraquat, the herbicidal effects of DPEI are only slightly reduced by pretreatment with the photosynthetic electron transport inhibitor 3-(3,4-dichlorophenyl)-1,1-dimethylurea. DPEI is a weak inhibitor of photosynthetic electron transport (I50 15 micromolar for water to paraquat) in vitro, with at least one site of action at the cytochrome b6f complex. Ultrastructural studies and measurements of ethane formation resulting from lipid peroxidation indicate that mutants of barley lacking photosystem I (PSI) (viridis-zb63) or photosystem II (viridis-zd69) are resistant to paraquat but susceptible to DPEI. The results indicate that electron transfer through both photosystems is not essential for the toxic effects of nitrodiphenyl ether herbicides. Furthermore, the results show that neither cyclic electron transport around PSI, nor the diversion of electrons from PSI to O2 when NADPH consumption is blocked are essential for the phytotoxicity of nitrodiphenyl ether herbicides. Images Fig. 2 Fig. 3 Fig. 4 PMID:16665297

Challenge for more precise e- and ion-transport in gases and liquids

NASA Astrophysics Data System (ADS)

White, Ron

2016-09-01

The full potential of technologies driven by non-equilibrium electron and ion processes in gases, liquids and soft-matter can only be realised once the basic physics has been mastered. The central component in this pursuit is an ever increasing need for the precise determination of electron and ion transport in such media. Over the last few decades, the group at James Cook University and collaborators have developed a suite of multi-term Boltzmann equation solutions to treat temporal and spatial non-locality for electrons and ions in electric and magnetic fields in gaseous systems. In this presentation, we will highlight recent developments including (i) a space-time multi-term solution of Boltzmann's equation; (ii) a unified treatment of electron and ion solutions of Boltzmann's equation which avoids mass ratio expansions; (iii) the treatment dense gases and liquids, including coherent scattering, screened potentials and (self) trapped bubble state effects, the latter of which can give rise to fractional transport behaviour, and (iv) the application to consider the self-consistency of cross-sections for electrons in biomolecules. Contributors: G. Boyle, P. Stokes, M. Casey, N. Garland, D. Cocks, D. Konovalov, S. Dujko, R. E. Robson, K. F. Ness, M. Brunger, S. Buckman, J. de Urquijo and Z. Lj. Petrovic. Support: Australian Research Council.

Model-based Confirmation of Alternative Substrates of Mitochondrial Electron Transport Chain

PubMed Central

Kleessen, Sabrina; Araújo, Wagner L.; Fernie, Alisdair R.; Nikoloski, Zoran

2012-01-01

Discrimination of metabolic models based on high throughput metabolomics data, reflecting various internal and external perturbations, is essential for identifying the components that contribute to the emerging behavior of metabolic processes. Here, we investigate 12 different models of the mitochondrial electron transport chain (ETC) in Arabidopsis thaliana during dark-induced senescence in order to elucidate the alternative substrates to this metabolic pathway. Our findings demonstrate that the coupling of the proposed computational approach, based on dynamic flux balance analysis, with time-resolved metabolomics data results in model-based confirmations of the hypotheses that, during dark-induced senescence in Arabidopsis, (i) under conditions where the main substrate for the ETC are not fully available, isovaleryl-CoA dehydrogenase and 2-hydroxyglutarate dehydrogenase are able to donate electrons to the ETC, (ii) phytanoyl-CoA does not act even as an indirect substrate of the electron transfer flavoprotein/electron-transfer flavoprotein:ubiquinone oxidoreductase complex, and (iii) the mitochondrial γ-aminobutyric acid transporter has functional significance in maintaining mitochondrial metabolism. Our study provides a basic framework for future in silico studies of alternative pathways in mitochondrial metabolism under extended darkness whereby the role of its components can be computationally discriminated based on available molecular profile data. PMID:22334689

Optical characteristics and parameters of gas-discharge plasma in a mixture of mercury dibromide vapor with neon

NASA Astrophysics Data System (ADS)

Malinina, A. A.; Malinin, A. N.

2013-12-01

Results are presented from studies of the optical characteristics and parameters of plasma of a dielectric barrier discharge in a mixture of mercury dibromide vapor with neon—the working medium of a non-coaxial exciplex gas-discharge emitter. The electron energy distribution function, the transport characteristics, the specific power losses for electron processes, the electron density and temperature, and the rate constants for the processes of elastic and inelastic electron scattering by the working mixture components are determined as functions of the reduced electric field. The rate constant of the process leading to the formation of exciplex mercury monobromide molecules is found to be 1.6 × 10-14 m3/s for a reduced electric field of E/ N = 15 Td, at which the maximum emission intensity in the blue-green spectral region (λmax = 502 nm) was observed in this experiment.

Contribution of Cyclic and Pseudo-cyclic Electron Transport to the Formation of Proton Motive Force in Chloroplasts.

PubMed

Shikanai, Toshiharu; Yamamoto, Hiroshi

2017-01-09

Photosynthetic electron transport is coupled to proton translocation across the thylakoid membrane, resulting in the formation of a trans-thylakoid proton gradient (ΔpH) and membrane potential (Δψ). Ion transporters and channels localized to the thylakoid membrane regulate the contribution of each component to the proton motive force (pmf). Although both ΔpH and Δψ contribute to ATP synthesis as pmf, only ΔpH downregulates photosynthetic electron transport via the acidification of the thylakoid lumen by inducing thermal dissipation of excessive absorbed light energy from photosystem II antennae and slowing down of the electron transport through the cytochrome b 6 f complex. To optimize the tradeoff between efficient light energy utilization and protection of both photosystems against photodamage, plants have to regulate the pmf amplitude and its components, ΔpH and Δψ. Cyclic electron transport around photosystem I (PSI) is a major regulator of the pmf amplitude by generating pmf independently of the net production of NADPH by linear electron transport. Chloroplast ATP synthase relaxes pmf for ATP synthesis, and its activity should be finely tuned for maintaining the size of the pmf during steady-state photosynthesis. Pseudo-cyclic electron transport mediated by flavodiiron protein (Flv) forms a large electron sink, which is essential for PSI photoprotection in fluctuating light in cyanobacteria. Flv is conserved from cyanobacteria to gymnosperms but not in angiosperms. The Arabidopsis proton gradient regulation 5 (pgr5) mutant is defective in the main pathway of PSI cyclic electron transport. By introducing Physcomitrella patens genes encoding Flvs, the function of PSI cyclic electron transport was substituted by that of Flv-dependent pseudo-cyclic electron transport. In transgenic plants, the size of the pmf was complemented to the wild-type level but the contribution of ΔpH to the total pmf was lower than that in the wild type. In the pgr5 mutant, the size of the pmf was drastically lowered by the absence of PSI cyclic electron transport. In the mutant, ΔpH occupied the majority of pmf, suggesting the presence of a mechanism for the homeostasis of luminal pH in the light. To avoid damage to photosynthetic electron transport by periods of excess solar energy, plants employ an intricate regulatory network involving alternative electron transport pathways, ion transporters/channels, and pH-dependent mechanisms for downregulating photosynthetic electron transport. Copyright © 2017 The Author. Published by Elsevier Inc. All rights reserved.

The sporulation of the green alga Ulva prolifera is controlled by changes in photosynthetic electron transport chain.

PubMed

Wang, Hui; Lin, Apeng; Gu, Wenhui; Huan, Li; Gao, Shan; Wang, Guangce

2016-04-22

Sporulation and spore release are essential phases of the life cycle in algae and land plants. Ulva prolifera, which is an ideal organism for studying sporulation and spore release, was used as the experimental material in the present study. The determination of photosynthetic parameters, combined with microscopic observation, treatment with photosynthetic inhibitors, limitation of carbon acquisition, and protein mass spectrometry, was employed in this experiment. Cycle electron transport (CEF) was found enhanced at the onset of sporangia formation. The inhibition effect of dibromothymoquinone (DBMIB) towards sporulation was always strong during the sporulation process whereas the inhibition effect of 3-(3',4'-dichlorophenyl)-1,1-dimethylurea (DCMU) was continuously declined accompanied with the progress of sporulation. The changes of photosynthesis resulted from the limitation of CO2 acquisition could stimulate sporulation onset. Quantitative protein analysis showed that enzymes involved in carbon fixation, including RUBISCO and pyruvate orthophosphate dikinase, declined during sporogenesis, while proteins involved in sporulation, including tubulin and centrin, increased. These results suggest that enhanced cyclic electron flow (CEF) and oxidation of the plastoquinone pool are essential for sporangia formation onset, and changes in photosynthetic electron transport chain have significant impacts on sporulation of the green algae.

Nanoscale Electron Transport Measurements of Immobilized Cytochrome P450 Proteins

PubMed Central

Bostick, Christopher D.; Flora, Darcy R.; Gannett, Peter M.; Tracy, Timothy S.; Lederman, David

2015-01-01

Gold nanopillars, functionalized with an organic self-assembled monolayer, can be used to measure the electrical conductance properties of immobilized proteins without aggregation. Measurements of the conductance of nanopillars with cytochrome P450 2C9 (CYP2C9) proteins using conducting probe atomic force microscopy demonstrate that a correlation exists between the energy barrier height between hopping sites and CYP2C9 metabolic activity. Measurements performed as a function of tip force indicate that, when subjected to a large force, the protein is more stable in the presence of a substrate. This agrees with the hypothesis that substrate entry into the active site helps to stabilize the enzyme. The relative distance between hopping sites also increases with increasing force, possibly because protein functional groups responsible for electron transport depend on the structure of the protein. The inhibitor sulfaphenazole, in addition to the previously studied aniline, increased the barrier height for electron transfer and thereby makes CYP2C9 reduction more difficult and inhibits metabolism. This suggests that P450 Type II binders may decrease the ease of electron transport processes in the enzyme, in addition to occupying the active site. PMID:25804257

Electronic Two-Transition-Induced Enhancement of Emission Efficiency in Polymer Light-Emitting Diodes

PubMed Central

Chen, Ren-Ai; Wang, Cong; Li, Sheng; George, Thomas F.

2013-01-01

With the development of experimental techniques, effective injection and transportation of electrons is proven as a way to obtain polymer light-emitting diodes (PLEDs) with high quantum efficiency. This paper reveals a valid mechanism for the enhancement of quantum efficiency in PLEDs. When an external electric field is applied, the interaction between a negative polaron and triplet exciton leads to an electronic two-transition process, which induces the exciton to emit light and thus improve the emission efficiency of PLEDs. PMID:28809346

Tunable mega-ampere electron current propagation in solids by dynamic control of lattice melt

DOE PAGES

MacLellan, D.  A.; Carroll, D.  C.; Gray, R.  J.; ...

2014-10-31

The influence of lattice-melt-induced resistivity gradients on the transport of mega-ampere currents of fast electrons in solids is investigated numerically and experimentally using laser-accelerated protons to induce isochoric heating. Tailoring the heating profile enables the resistive magnetic fields which strongly influence the current propagation to be manipulated. This tunable laser-driven process enables important fast electron beam properties, including the beam divergence, profile, and symmetry to be actively tailored, and without recourse to complex target manufacture.

Mechanically controllable break junctions for molecular electronics.

PubMed

Xiang, Dong; Jeong, Hyunhak; Lee, Takhee; Mayer, Dirk

2013-09-20

A mechanically controllable break junction (MCBJ) represents a fundamental technique for the investigation of molecular electronic junctions, especially for the study of the electronic properties of single molecules. With unique advantages, the MCBJ technique has provided substantial insight into charge transport processes in molecules. In this review, the techniques for sample fabrication, operation and the various applications of MCBJs are introduced and the history, challenges and future of MCBJs are discussed. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Quantum teleportation and entanglement swapping of electron spins in superconducting hybrid structures

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bubanja, Vladimir, E-mail: vladimir.bubanja@callaghaninnovation.govt.nz

2015-06-15

We present schemes for quantum teleportation and entanglement swapping of electronic spin states in hybrid superconductor–normal-metal systems. The proposed schemes employ subgap transport whereby the lowest order processes involve Cooper pair-electron and double Cooper-pair cotunneling in quantum teleportation and entanglement swapping protocols, respectively. The competition between elastic cotunneling and Cooper-pair splitting results in the success probability of 25% in both cases. Described implementations of these protocols are within reach of present-day experimental techniques.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Stolterfoht, Martin; Armin, Ardalan; Pandey, Ajay K.

Photovoltaic performance in relation to charge transport is studied in efficient (7.6%) organic solar cells (PTB7:PC{sub 71}BM). Both electron and hole mobilities are experimentally measured in efficient solar cells using the resistance dependent photovoltage technique, while the inapplicability of classical techniques, such as space charge limited current and photogenerated charge extraction by linearly increasing voltage is discussed. Limits in the short-circuit current originate from optical losses, while charge transport is shown not to be a limiting process. Efficient charge extraction without recombination can be achieved with a mobility of charge carriers much lower than previously expected. The presence of dispersivemore » transport with strongly distributed mobilities in high efficiency solar cells is demonstrated. Reduced non-Langevin recombination is shown to be beneficial for solar cells with imbalanced, low, and dispersive electron and hole mobilities.« less

Momentum transport and nonlocality in heat-flux-driven magnetic reconnection in high-energy-density plasmas.

PubMed

Liu, Chang; Fox, William; Bhattacharjee, Amitava; Thomas, Alexander G R; Joglekar, Archis S

2017-10-01

Recent theory has demonstrated a novel physics regime for magnetic reconnection in high-energy-density plasmas where the magnetic field is advected by heat flux via the Nernst effect. Here we elucidate the physics of the electron dissipation layer in this regime. Through fully kinetic simulation and a generalized Ohm's law derived from first principles, we show that momentum transport due to a nonlocal effect, the heat-flux-viscosity, provides the dissipation mechanism for magnetic reconnection. Scaling analysis, and simulations show that the reconnection process comprises a magnetic field compression stage and quasisteady reconnection stage, and the characteristic width of the current sheet in this regime is several electron mean-free paths. These results show the important interplay between nonlocal transport effects and generation of anisotropic components to the distribution function.

Three-dimensional architecture hybrid perovskite solar cells using CdS nanorod arrays as an electron transport layer

NASA Astrophysics Data System (ADS)

Song, Zihang; Tong, Guoqing; Li, Huan; Li, Guopeng; Ma, Shuai; Yu, Shimeng; Liu, Qian; Jiang, Yang

2018-01-01

Three-dimensional (3D) architecture perovskite solar cells (PSCs) using CdS nanorod (NR) arrays as an electron transport layer were designed and prepared layer-by-layer via a physical-chemical vapor deposition (P-CVD) process. The CdS NRs not only provided a scaffold to the perovskite film, but also increased the interfacial contact between the perovskite film and electron transport layer. As an optimized result, a high power conversion efficiency of 12.46% with a short-circuit current density of 19.88 mA cm-2, an open-circuit voltage of 1.01 V and a fill factor of 62.06% was obtained after 12 h growth of CdS NRs. It was four times the efficiency of contrast planar structure with a similar thickness. The P-CVD method assisted in achieving flat and voidless CH3NH3PbI3-x Cl x perovskite film and binding the CdS NRs and perovskite film together. The different density of CdS NRs had obvious effects on light transmittance of 350-550 nm, the interfacial area and the difficulty of combining layers. Moreover, the efficient 1D transport paths for electrons and multiple absorption of light, which are generated in 3D architecture, were beneficial to realize a decent power conversion efficiency.

Spray-combustion synthesis: Efficient solution route to high-performance oxide transistors

PubMed Central

Yu, Xinge; Smith, Jeremy; Zhou, Nanjia; Zeng, Li; Guo, Peijun; Xia, Yu; Alvarez, Ana; Aghion, Stefano; Lin, Hui; Yu, Junsheng; Chang, Robert P. H.; Bedzyk, Michael J.; Ferragut, Rafael; Marks, Tobin J.; Facchetti, Antonio

2015-01-01

Metal-oxide (MO) semiconductors have emerged as enabling materials for next generation thin-film electronics owing to their high carrier mobilities, even in the amorphous state, large-area uniformity, low cost, and optical transparency, which are applicable to flat-panel displays, flexible circuitry, and photovoltaic cells. Impressive progress in solution-processed MO electronics has been achieved using methodologies such as sol gel, deep-UV irradiation, preformed nanostructures, and combustion synthesis. Nevertheless, because of incomplete lattice condensation and film densification, high-quality solution-processed MO films having technologically relevant thicknesses achievable in a single step have yet to be shown. Here, we report a low-temperature, thickness-controlled coating process to create high-performance, solution-processed MO electronics: spray-combustion synthesis (SCS). We also report for the first time, to our knowledge, indium-gallium-zinc-oxide (IGZO) transistors having densification, nanoporosity, electron mobility, trap densities, bias stability, and film transport approaching those of sputtered films and compatible with conventional fabrication (FAB) operations. PMID:25733848

Spray-combustion synthesis: efficient solution route to high-performance oxide transistors.

PubMed

Yu, Xinge; Smith, Jeremy; Zhou, Nanjia; Zeng, Li; Guo, Peijun; Xia, Yu; Alvarez, Ana; Aghion, Stefano; Lin, Hui; Yu, Junsheng; Chang, Robert P H; Bedzyk, Michael J; Ferragut, Rafael; Marks, Tobin J; Facchetti, Antonio

2015-03-17

Metal-oxide (MO) semiconductors have emerged as enabling materials for next generation thin-film electronics owing to their high carrier mobilities, even in the amorphous state, large-area uniformity, low cost, and optical transparency, which are applicable to flat-panel displays, flexible circuitry, and photovoltaic cells. Impressive progress in solution-processed MO electronics has been achieved using methodologies such as sol gel, deep-UV irradiation, preformed nanostructures, and combustion synthesis. Nevertheless, because of incomplete lattice condensation and film densification, high-quality solution-processed MO films having technologically relevant thicknesses achievable in a single step have yet to be shown. Here, we report a low-temperature, thickness-controlled coating process to create high-performance, solution-processed MO electronics: spray-combustion synthesis (SCS). We also report for the first time, to our knowledge, indium-gallium-zinc-oxide (IGZO) transistors having densification, nanoporosity, electron mobility, trap densities, bias stability, and film transport approaching those of sputtered films and compatible with conventional fabrication (FAB) operations.

New secondary batteries utilizing electronically conductive polymer cathodes

NASA Technical Reports Server (NTRS)

Martin, Charles R.; White, Ralph E.

1987-01-01

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

Cell death in a harmful algal bloom causing species Alexandrium tamarense upon an algicidal bacterium induction.

PubMed

Zhang, Huajun; Lv, Jinglin; Peng, Yun; Zhang, Su; An, Xinli; Xu, Hong; Zhang, Jun; Tian, Yun; Zheng, Wei; Zheng, Tianling

2014-09-01

Harmful algal blooms occur throughout the world, destroying aquatic ecosystems and threatening human health. The culture supernatant of the marine algicidal bacteria DHQ25 was able to lysis dinoflagellate Alexandrium tamarense. Loss of photosynthetic pigments, accompanied by a decline in Photosystem II (PSII) photochemical efficiency (Fv/Fm), in A. tamarense was detected under bacterial supernatant stress. Transmission electron microscope analysis showed obvious morphological modifications of chloroplast dismantling as a part of the algicidal process. The PSII electron transport chain was seriously blocked, with its reaction center damaged. This damage was detected in a relative transcriptional level of psbA and psbD genes, which encode the D1 and D2 proteins in the PSII reaction center. And the block in the electron transport chain of PSII might generate excessive reactive oxygen species (ROS) which could destroy the membrane system and pigment synthesis and activated enzymic antioxidant systems including superoxide dismutase (SOD) and catalase (CAT). This study indicated that marine bacteria with indirect algicidal activity played an important role in the changes of photosynthetic process in a harmful algal bloom species.

Intrinsic and extrinsic electrical and thermal transport of bulk black phosphorus

NASA Astrophysics Data System (ADS)

Hu, Sile; Xiang, Junsen; Lv, Meng; Zhang, Jiahao; Zhao, Hengcan; Li, Chunhong; Chen, Genfu; Wang, Wenhong; Sun, Peijie

2018-01-01

We report a comprehensive investigation of the electrical, thermal, and thermoelectric transport properties of bulk single-crystalline black phosphorus in wide temperature (2-300 K) and field (0-9 T) ranges. Electrical transport below T ≈ 250 K is found to be dominated by extrinsic hole-type charge carriers with large mobility exceeding 104 cm2/V s at low temperatures. While thermal transport measurements reveal an enhanced in-plane thermal conductivity maximum κ = 180 W/m K at T ≈ 25 K, it appears still to be largely constrained by extrinsic phonon scattering processes, e.g., the electron-phonon process, in addition to intrinsic umklapp scattering. The thermoelectric power and Nernst effect seem to be strongly influenced by ambipolar transport of charge carriers with opposite signs in at least the high-temperature region above 200 K, which diminishes the thermoelectric power factor of this material. Our results provide a timely update to the transport properties of bulk black phosphorus for future fundamental and applied research.

Magnetic and electrical transport properties of the pyrochlore iridate Bi2-xCoxIr2O7

NASA Astrophysics Data System (ADS)

Feng, Yuan; Zhu, Shoujin; Bian, Jian; Chen, Feng; Chen, Shiyun; Ma, Cuiling; Liu, Hui; Fang, Baolong

2018-04-01

In the present paper, we have studied the magnetic order and electrical transport properties of frustrated magnet Bi2-xCoxIr2O7 (x = 0, 0.2, 0.4, 0.6) polycrystalline. The behavior of the electrical resistivity above 50 K in the composites emanate from the electron-electron scattering processes. Grain boundary effects play a dominant role in the conduction process. It is also found from M-T data that the antiferromagnetic interaction and frustration enhances with increasing content of Co. Effective magnetic moments show a possibility of mixed valence state of Co (Co3+ and Co4+). The M-H data of doped samples taken at 2 K show hysteresis loops, which suggests the existence of ferromagnetic interaction originated from canted antiferromagnetic state. The magnetic behavior results from the competition between ferromagnetic and antiferromagnetic interaction at each magnetic site.

Impact of the electron-transport layer on the performance of solution-processed small-molecule organic solar cells.

PubMed

Long, Guankui; Wan, Xiangjian; Kan, Bin; Hu, Zhicheng; Yang, Xuan; Zhang, Yi; Zhang, Mingtao; Wu, Hongbing; Huang, Fei; Su, Shijian; Cao, Yong; Chen, Yongsheng

2014-08-01

Although the performance of polymer solar cells has been improved significantly recently through careful optimization with different interlayers for the same materials, more improvement is needed in this respect for small-molecule-based solar cells, particularly for the electron-transport layers (ETLs). In this work, three different solution-processed ETLs, PFN, ZnO nanoparticles, and LiF, were investigated and compared in the performance of small-molecule-based devices, and power conversion efficiencies (PCEs) of 8.32, 7.30, and 7.38% were achieved, respectively. The mechanism for the ETL-induced enhancement has been studied, and different ETLs have a significantly different impact on the device performance. The clearly improved performance of PFN is attributed to the combination of reduced bimolecular recombination and increased effective photon absorption in the active layer. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Engineering charge transport by heterostructuring solution-processed semiconductors

NASA Astrophysics Data System (ADS)

Voznyy, Oleksandr; Sutherland, Brandon R.; Ip, Alexander H.; Zhitomirsky, David; Sargent, Edward H.

2017-06-01

Solution-processed semiconductor devices are increasingly exploiting heterostructuring — an approach in which two or more materials with different energy landscapes are integrated into a composite system. Heterostructured materials offer an additional degree of freedom to control charge transport and recombination for more efficient optoelectronic devices. By exploiting energetic asymmetry, rationally engineered heterostructured materials can overcome weaknesses, augment strengths and introduce emergent physical phenomena that are otherwise inaccessible to single-material systems. These systems see benefit and application in two distinct branches of charge-carrier manipulation. First, they influence the balance between excitons and free charges to enhance electron extraction in solar cells and photodetectors. Second, they promote radiative recombination by spatially confining electrons and holes, which increases the quantum efficiency of light-emitting diodes. In this Review, we discuss advances in the design and composition of heterostructured materials, consider their implementation in semiconductor devices and examine unexplored paths for future advancement in the field.

Achieving High Current Density of Perovskite Solar Cells by Modulating the Dominated Facets of Room-Temperature DC Magnetron Sputtered TiO2 Electron Extraction Layer.

PubMed

Huang, Aibin; Lei, Lei; Zhu, Jingting; Yu, Yu; Liu, Yan; Yang, Songwang; Bao, Shanhu; Cao, Xun; Jin, Ping

2017-01-25

The short circuit current density of perovskite solar cell (PSC) was boosted by modulating the dominated plane facets of TiO 2 electron transport layer (ETL). Under optimized condition, TiO 2 with dominant {001} facets showed (i) low incident light loss, (ii) highly smooth surface and excellent wettability for precursor solution, (iii) efficient electron extraction, and (iv) high conductivity in perovskite photovoltaic application. A current density of 24.19 mA cm -2 was achieved as a value near the maximum limit. The power conversion efficiency was improved to 17.25%, which was the record value of PSCs with DC magnetron sputtered carrier transport layer. What is more, the room-temperature process had a great significance for the cost reduction and flexible application of PSCs.

A nonlocal electron conduction model for multidimensional radiation hydrodynamics codes

NASA Astrophysics Data System (ADS)

Schurtz, G. P.; Nicolaï, Ph. D.; Busquet, M.

2000-10-01

Numerical simulation of laser driven Inertial Confinement Fusion (ICF) related experiments require the use of large multidimensional hydro codes. Though these codes include detailed physics for numerous phenomena, they deal poorly with electron conduction, which is the leading energy transport mechanism of these systems. Electron heat flow is known, since the work of Luciani, Mora, and Virmont (LMV) [Phys. Rev. Lett. 51, 1664 (1983)], to be a nonlocal process, which the local Spitzer-Harm theory, even flux limited, is unable to account for. The present work aims at extending the original formula of LMV to two or three dimensions of space. This multidimensional extension leads to an equivalent transport equation suitable for easy implementation in a two-dimensional radiation-hydrodynamic code. Simulations are presented and compared to Fokker-Planck simulations in one and two dimensions of space.

Low energy electron beam processing of YBCO thin films

NASA Astrophysics Data System (ADS)

Chromik, Š.; Camerlingo, C.; Sojková, M.; Štrbík, V.; Talacko, M.; Malka, I.; Bar, I.; Bareli, G.; Jung, G.

2017-02-01

Effects of low energy 30 keV electron irradiation of superconducting YBa2Cu3O7-δ thin films have been investigated by means of transport and micro-Raman spectroscopy measurements. The critical temperature and the critical current of 200 nm thick films initially increase with increasing fluency of the electron irradiation, reach the maximum at fluency 3 - 4 × 1020 electrons/cm2, and then decrease with further fluency increase. In much thinner films (75 nm), the critical temperature increases while the critical current decreases after low energy electron irradiation with fluencies below 1020 electrons/cm2. The Raman investigations suggest that critical temperature increase in irradiated films is due to healing of broken Cusbnd O chains that results in increased carrier's concentration in superconducting CuO2 planes. Changes in the critical current are controlled by changes in the density of oxygen vacancies acting as effective pinning centers for flux vortices. The effects of low energy electron irradiation of YBCO turned out to result from a subtle balance of many processes involving oxygen removal, both by thermal activation and kick-off processes, and ordering of chains environment by incident electrons.

Momentum transport and non-local transport in heat-flux-driven magnetic reconnection in HEDP

NASA Astrophysics Data System (ADS)

Liu, Chang; Fox, Will; Bhattacharjee, Amitava

2016-10-01

Strong magnetic fields are readily generated in high-energy-density plasmas and can affect the heat confinement properties of the plasma. Magnetic reconnection can in turn be important as an inverse process, which destroys or reconfigures the magnetic field. Recent theory has demonstrated a novel physics regime for reconnection in high-energy-density plasmas where the magnetic field is advected into the reconnection layer by plasma heat flux via the Nernst effect. In this work we elucidate the physics of the electron dissipation layer in this heat-flux-driven regime. Through fully kinetic simulation and a new generalized Ohm's law, we show that momentum transport due to the heat-flux-viscosity effect provides the dissipation mechanism to allow magnetic field line reconnection. Scaling analysis and simulations show that the characteristic width of the current sheet in this regime is several electron mean-free-paths. These results additionally show a coupling between non-local transport and momentum transport, which in turn affects the dynamics of the magnetic field. This work was supported by the U.S. Department of Energy under Contract No. DE-SC0008655.

Structure of the transporter associated with antigen processing trapped by herpes simplex virus

PubMed Central

Oldham, Michael L; Grigorieff, Nikolaus; Chen, Jue

2016-01-01

The transporter associated with antigen processing (TAP) is an ATP-binding cassette (ABC) transporter essential to cellular immunity against viral infection. Some persistent viruses have evolved strategies to inhibit TAP so that they may go undetected by the immune system. The herpes simplex virus for example evades immune surveillance by blocking peptide transport with a small viral protein ICP47. In this study, we determined the structure of human TAP bound to ICP47 by electron cryo-microscopy (cryo-EM) to 4.0 Å. The structure shows that ICP47 traps TAP in an inactive conformation distinct from the normal transport cycle. The specificity and potency of ICP47 inhibition result from contacts between the tip of the helical hairpin and the apex of the transmembrane cavity. This work provides a clear molecular description of immune evasion by a persistent virus. It also establishes the molecular structure of TAP to facilitate mechanistic studies of the antigen presentation process. DOI: http://dx.doi.org/10.7554/eLife.21829.001 PMID:27935481

Lithography process for patterning HgI2 photonic devices

DOEpatents

Mescher, Mark J.; James, Ralph B.; Hermon, Haim

2004-11-23

A photolithographic process forms patterns on HgI.sub.2 surfaces and defines metal sublimation masks and electrodes to substantially improve device performance by increasing the realizable design space. Techniques for smoothing HgI.sub.2 surfaces and for producing trenches in HgI.sub.2 are provided. A sublimation process is described which produces etched-trench devices with enhanced electron-transport-only behavior.

The cytochrome b6f complex at the crossroad of photosynthetic electron transport pathways.

PubMed

Tikhonov, Alexander N

2014-08-01

Regulation of photosynthetic electron transport at the level of the cytochrome b6f complex provides efficient performance of the chloroplast electron transport chain (ETC). In this review, after brief overview of the structural organization of the chloroplast ETC, the consideration of the problem of electron transport control is focused on the plastoquinone (PQ) turnover and its interaction with the b6f complex. The data available show that the rates of plastoquinol (PQH2) formation in PSII and its diffusion to the b6f complex do not limit the overall rate of electron transfer between photosystem II (PSII) and photosystem I (PSI). Analysis of experimental and theoretical data demonstrates that the rate-limiting step in the intersystem chain of electron transport is determined by PQH2 oxidation at the Qo-site of the b6f complex, which is accompanied by the proton release into the thylakoid lumen. The acidification of the lumen causes deceleration of PQH2 oxidation, thus impeding the intersystem electron transport. Two other mechanisms of regulation of the intersystem electron transport have been considered: (i) "state transitions" associated with the light-induced redistribution of solar energy between PSI and PSII, and (ii) redistribution of electron fluxes between alternative pathways (noncyclic electron transport and cyclic electron flow around PSI). Copyright © 2013 Elsevier Masson SAS. All rights reserved.

Organic Donor-Acceptor Complexes as Novel Organic Semiconductors.

PubMed

Zhang, Jing; Xu, Wei; Sheng, Peng; Zhao, Guangyao; Zhu, Daoben

2017-07-18

Organic donor-acceptor (DA) complexes have attracted wide attention in recent decades, resulting in the rapid development of organic binary system electronics. The design and synthesis of organic DA complexes with a variety of component structures have mainly focused on metallicity (or even superconductivity), emission, or ferroelectricity studies. Further efforts have been made in high-performance electronic investigations. The chemical versatility of organic semiconductors provides DA complexes with a great number of possibilities for semiconducting applications. Organic DA complexes extend the semiconductor family and promote charge separation and transport in organic field-effect transistors (OFETs) and organic photovoltaics (OPVs). In OFETs, the organic complex serves as an active layer across extraordinary charge pathways, ensuring the efficient transport of induced charges. Although an increasing number of organic semiconductors have been reported to exhibit good p- or n-type properties (mobilities higher than 1 or even 10 cm 2 V -1 s -1 ), critical scientific challenges remain in utilizing the advantages of existing semiconductor materials for more and wider applications while maintaining less complicated synthetic or device fabrication processes. DA complex materials have revealed new insight: their unique molecular packing and structure-property relationships. The combination of donors and acceptors could offer practical advantages compared with their unimolecular materials. First, growing crystals of DA complexes with densely packed structures will reduce impurities and traps from the self-assembly process. Second, complexes based on the original structural components could form superior mixture stacking, which can facilitate charge transport depending on the driving force in the coassembly process. Third, the effective use of organic semiconductors can lead to tunable band structures, allowing the operation mode (p- or n-type) of the transistor to be systematically controlled by changing the components. Finally, theoretical calculations based on cocrystals with unique stacking could widen our understanding of structure-property relationships and in turn help us design high-performance semiconductors based on DA complexes. In this Account, we focus on discussing organic DA complexes as a new class of semiconducting materials, including their design, growth methods, packing modes, charge-transport properties, and structure-property relationships. We have also fabricated and investigated devices based on these binary crystals. This interdisciplinary work combines techniques from the fields of self-assembly, crystallography, condensed-matter physics, and theoretical chemistry. Researchers have designed new complex systems, including donor and acceptor compounds that self-assemble in feasible ways into highly ordered cocrystals. We demonstrate that using this crystallization method can easily realize ambipolar or unipolar transport. To further improve device performance, we propose several design strategies, such as using new kinds of donors and acceptors, modulating the energy alignment of the donor (ionization potential, IP) and acceptor (electron affinity, EA) components, and extending the π-conjugated backbones. In addition, we have found that when we use molecular "doping" (2:1 cocrystallization), the charge-transport nature of organic semiconductors can be switched from hole-transport-dominated to electron-transport-dominated. We expect that the formation of cocrystals through the complexation of organic donor and acceptor species will serve as a new strategy to develop semiconductors for organic electronics with superior performances over their corresponding individual components.

Transient electroluminescence on pristine and degraded phosphorescent blue OLEDs

NASA Astrophysics Data System (ADS)

Niu, Quan; Blom, Paul W. M.; May, Falk; Heimel, Paul; Zhang, Minlu; Eickhoff, Christian; Heinemeyer, Ute; Lennartz, Christian; Crǎciun, N. Irina

2017-11-01

In state-of-the-art blue phosphorescent organic light-emitting diode (PHOLED) device architectures, electrons and holes are injected into the emissive layer, where they are carried by the emitting and hole transporting units, respectively. Using transient electroluminescence measurements, we disentangle the contribution of the electrons and holes on the transport and efficiency of both pristine and degraded PHOLEDs. By varying the concentration of hole transporting units, we show that for pristine PHOLEDs, the transport is electron dominated. Furthermore, degradation of the PHOLEDs upon electrical aging is not related to the hole transport but is governed by a decrease in the electron transport due to the formation of electron traps.

Efficient organic solar cells using copper(I) iodide (CuI) hole transport layers

DOE Office of Scientific and Technical Information (OSTI.GOV)

Peng, Ying; Department of Physics and Centre for Plastic Electronics, Blackett Laboratory, Imperial College London, London SW7 2AZ; Yaacobi-Gross, Nir

We report the fabrication of high power conversion efficiency (PCE) polymer/fullerene bulk heterojunction (BHJ) photovoltaic cells using solution-processed Copper (I) Iodide (CuI) as hole transport layer (HTL). Our devices exhibit a PCE value of ∼5.5% which is equivalent to that obtained for control devices based on the commonly used conductive polymer poly(3,4-ethylenedioxythiophene): polystyrenesulfonate as HTL. Inverted cells with PCE >3% were also demonstrated using solution-processed metal oxide electron transport layers, with a CuI HTL evaporated on top of the BHJ. The high optical transparency and suitable energetics of CuI make it attractive for application in a range of inexpensive large-area optoelectronicmore » devices.« less

Organic Solar Cells: Understanding the Role of Förster Resonance Energy Transfer

PubMed Central

Feron, Krishna; Belcher, Warwick J.; Fell, Christopher J.; Dastoor, Paul C.

2012-01-01

Organic solar cells have the potential to become a low-cost sustainable energy source. Understanding the photoconversion mechanism is key to the design of efficient organic solar cells. In this review, we discuss the processes involved in the photo-electron conversion mechanism, which may be subdivided into exciton harvesting, exciton transport, exciton dissociation, charge transport and extraction stages. In particular, we focus on the role of energy transfer as described by Förster resonance energy transfer (FRET) theory in the photoconversion mechanism. FRET plays a major role in exciton transport, harvesting and dissociation. The spectral absorption range of organic solar cells may be extended using sensitizers that efficiently transfer absorbed energy to the photoactive materials. The limitations of Förster theory to accurately calculate energy transfer rates are discussed. Energy transfer is the first step of an efficient two-step exciton dissociation process and may also be used to preferentially transport excitons to the heterointerface, where efficient exciton dissociation may occur. However, FRET also competes with charge transfer at the heterointerface turning it in a potential loss mechanism. An energy cascade comprising both energy transfer and charge transfer may aid in separating charges and is briefly discussed. Considering the extent to which the photo-electron conversion efficiency is governed by energy transfer, optimisation of this process offers the prospect of improved organic photovoltaic performance and thus aids in realising the potential of organic solar cells. PMID:23235328

Different Functions of Phylogenetically Distinct Bacterial Complex I Isozymes

DOE Office of Scientific and Technical Information (OSTI.GOV)

Spero, Melanie A.; Brickner, Joshua R.; Mollet, Jordan T.

NADH:quinone oxidoreductase (complex I) is a bioenergetic enzyme that transfers electrons from NADH to quinone, conserving the energy of this reaction by contributing to the proton motive force. While the importance of NADH oxidation to mitochondrial aerobic respiration is well documented, the contribution of complex I to bacterial electron transport chains has been tested in only a few species. Here, we analyze the function of two phylogenetically distinct complex I isozymes in Rhodobacter sphaeroides, an alphaproteobacterium that contains well-characterized electron transport chains. We found that R. sphaeroides complex I activity is important for aerobic respiration and required for anaerobic dimethylmore » sulfoxide (DMSO) respiration (in the absence of light), photoautotrophic growth, and photoheterotrophic growth (in the absence of an external electron acceptor). Our data also provide insight into the functions of the phylogenetically distinct R. sphaeroides complex I enzymes (complex I A and complex I E) in maintaining a cellular redox state during photoheterotrophic growth. We propose that the function of each isozyme during photoheterotrophic growth is either NADH synthesis (complex I A) or NADH oxidation (complex I E). The canonical alphaproteobacterial complex I isozyme (complex I A) was also shown to be important for routing electrons to nitrogenase-mediated H 2 production, while the horizontally acquired enzyme (complex I E) was dispensable in this process. Unlike the singular role of complex I in mitochondria, we predict that the phylogenetically distinct complex I enzymes found across bacterial species have evolved to enhance the functions of their respective electron transport chains. Cells use a proton motive force (PMF), NADH, and ATP to support numerous processes. In mitochondria, complex I uses NADH oxidation to generate a PMF, which can drive ATP synthesis. This study analyzed the function of complex I in bacteria, which contain more-diverse and more-flexible electron transport chains than mitochondria. We tested complex I function in Rhodobacter sphaeroides, a bacterium predicted to encode two phylogenetically distinct complex I isozymes. R. sphaeroides cells lacking both isozymes had growth defects during all tested modes of growth, illustrating the important function of this enzyme under diverse conditions. We conclude that the two isozymes are not functionally redundant and predict that phylogenetically distinct complex I enzymes have evolved to support the diverse lifestyles of bacteria.« less

Different Functions of Phylogenetically Distinct Bacterial Complex I Isozymes

DOE PAGES

Spero, Melanie A.; Brickner, Joshua R.; Mollet, Jordan T.; ...

2016-02-01

NADH:quinone oxidoreductase (complex I) is a bioenergetic enzyme that transfers electrons from NADH to quinone, conserving the energy of this reaction by contributing to the proton motive force. While the importance of NADH oxidation to mitochondrial aerobic respiration is well documented, the contribution of complex I to bacterial electron transport chains has been tested in only a few species. Here, we analyze the function of two phylogenetically distinct complex I isozymes in Rhodobacter sphaeroides, an alphaproteobacterium that contains well-characterized electron transport chains. We found that R. sphaeroides complex I activity is important for aerobic respiration and required for anaerobic dimethylmore » sulfoxide (DMSO) respiration (in the absence of light), photoautotrophic growth, and photoheterotrophic growth (in the absence of an external electron acceptor). Our data also provide insight into the functions of the phylogenetically distinct R. sphaeroides complex I enzymes (complex I A and complex I E) in maintaining a cellular redox state during photoheterotrophic growth. We propose that the function of each isozyme during photoheterotrophic growth is either NADH synthesis (complex I A) or NADH oxidation (complex I E). The canonical alphaproteobacterial complex I isozyme (complex I A) was also shown to be important for routing electrons to nitrogenase-mediated H 2 production, while the horizontally acquired enzyme (complex I E) was dispensable in this process. Unlike the singular role of complex I in mitochondria, we predict that the phylogenetically distinct complex I enzymes found across bacterial species have evolved to enhance the functions of their respective electron transport chains. Cells use a proton motive force (PMF), NADH, and ATP to support numerous processes. In mitochondria, complex I uses NADH oxidation to generate a PMF, which can drive ATP synthesis. This study analyzed the function of complex I in bacteria, which contain more-diverse and more-flexible electron transport chains than mitochondria. We tested complex I function in Rhodobacter sphaeroides, a bacterium predicted to encode two phylogenetically distinct complex I isozymes. R. sphaeroides cells lacking both isozymes had growth defects during all tested modes of growth, illustrating the important function of this enzyme under diverse conditions. We conclude that the two isozymes are not functionally redundant and predict that phylogenetically distinct complex I enzymes have evolved to support the diverse lifestyles of bacteria.« less

Carrier multiplication and charge transport in artificial quantum-dot solids probed by ultrafast photocurrent spectroscopy (Conference Presentation)

NASA Astrophysics Data System (ADS)

Klimov, Victor I.

2017-05-01

Understanding and controlling carrier transport and recombination dynamics in colloidal quantum dot films is key to their application in electronic and optoelectronic devices. Towards this end, we have conducted transient photocurrent measurements to monitor transport through quantum confined band edge states in lead selenide quantum dots films as a function of pump fluence, temperature, electrical bias, and surface treatment. Room temperature dynamics reveal two distinct timescales of intra-dot geminate processes followed by non-geminate inter-dot processes. The non-geminate kinetics is well described by the recombination of holes with photoinjected and pre-existing electrons residing in mid-gap states. We find the mobility of the quantum-confined states shows no temperature dependence down to 6 K, indicating a tunneling mechanism of early time photoconductance. We present evidence of the importance of the exciton fine structure in controlling the low temperature photoconductance, whereby the nanoscale enhanced exchange interaction between electrons and holes in quantum dots introduces a barrier to charge separation. Finally, side-by-side comparison of photocurrent transients using excitation with low- and high-photon energies (1.5 vs. 3.0 eV) reveals clear signatures of carrier multiplication (CM), that is, generation of multiple excitons by single photons. Based on photocurrent measurements of quantum dot solids and optical measurements of solution based samples, we conclude that the CM efficiency is unaffected by strong inter-dot coupling. Therefore, the results of previous numerous spectroscopic CM studies conducted on dilute quantum dot suspensions should, in principle, be reproducible in electronically coupled QD films used in devices.

Modifying the Interface Edge to Control the Electrical Transport Properties of Nanocontacts to Nanowires.

PubMed

Lord, Alex M; Ramasse, Quentin M; Kepaptsoglou, Despoina M; Evans, Jonathan E; Davies, Philip R; Ward, Michael B; Wilks, Steve P

2017-02-08

Selecting the electrical properties of nanomaterials is essential if their potential as manufacturable devices is to be reached. Here, we show that the addition or removal of native semiconductor material at the edge of a nanocontact can be used to determine the electrical transport properties of metal-nanowire interfaces. While the transport properties of as-grown Au nanocatalyst contacts to semiconductor nanowires are well-studied, there are few techniques that have been explored to modify the electrical behavior. In this work, we use an iterative analytical process that directly correlates multiprobe transport measurements with subsequent aberration-corrected scanning transmission electron microscopy to study the effects of chemical processes that create structural changes at the contact interface edge. A strong metal-support interaction that encapsulates the Au nanocontacts over time, adding ZnO material to the edge region, gives rise to ohmic transport behavior due to the enhanced quantum-mechanical tunneling path. Removal of the extraneous material at the Au-nanowire interface eliminates the edge-tunneling path, producing a range of transport behavior that is dependent on the final interface quality. These results demonstrate chemically driven processes that can be factored into nanowire-device design to select the final properties.

Fractional conductance oscillations in quantum rings: wave packet picture of transport in a few-electron system.

PubMed

Chwiej, T; Szafran, B

2013-04-17

We study electron transfer across a two-terminal quantum ring using a time-dependent description of the scattering process. For the considered scattering event the quantum ring is initially charged with one or two electrons, with another electron incident to the ring from the input channel. We study the electron transfer probability (T) as a function of the external magnetic field. We determine the periodicity of T for a varied number of electrons confined within the ring. For that purpose we develop a method to describe the wave packet dynamics for a few electrons participating in the scattering process, taking into full account the electron-electron correlations. We find that electron transfer across the quantum ring initially charged by a single electron acquires a distinct periodicity of half of the magnetic flux quantum (Φ0/2), corresponding to the formation of a transient two-electron state inside the ring. In the case of a three-electron scattering problem with two electrons initially occupying the ring, a period of Φ0/3 for T is formed in the limit of thin channels. The effect of disorder present in the confinement potential of the ring is also discussed.

Concept of Quantum Geometry in Optoelectronic Processes in Solids: Application to Solar Cells.

PubMed

Nagaosa, Naoto; Morimoto, Takahiro

2017-07-01

The concept of topology is becoming more and more relevant to the properties and functions of electronic materials including various transport phenomena and optical responses. A pedagogical introduction is given here to the basic ideas and their applications to optoelectronic processes in solids. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Pulsed Laser-Assisted Focused Electron-Beam-Induced Etching of Titanium with XeF 2 : Enhanced Reaction Rate and Precursor Transport

DOE PAGES

Noh, J. H.; Fowlkes, J. D.; Timilsina, R.; ...

2015-01-28

We introduce a laser-assisted focused electron-beam-induced etching (LA-FEBIE) process which is a versatile, direct write nanofabrication method that allows nanoscale patterning and editing; we do this in order to enhance the etch rate of electron-beam-induced etching. The results demonstrate that the titanium electron stimulated etch rate via the XeF2 precursor can be enhanced up to a factor of 6 times with an intermittent pulsed laser assist. Moreover, the evolution of the etching process is correlated to in situ stage current measurements and scanning electron micrographs as a function of time. Finally, the increased etch rate is attributed to photothermally enhancedmore » Ti–F reaction and TiF4 desorption and in some regimes enhanced XeF2 surface diffusion to the reaction zone.« less

Electron transport chains in organohalide-respiring bacteria and bioremediation implications.

PubMed

Wang, Shanquan; Qiu, Lan; Liu, Xiaowei; Xu, Guofang; Siegert, Michael; Lu, Qihong; Juneau, Philippe; Yu, Ling; Liang, Dawei; He, Zhili; Qiu, Rongliang

In situ remediation employing organohalide-respiring bacteria represents a promising solution for cleanup of persistent organohalide pollutants. The organohalide-respiring bacteria conserve energy by utilizing H 2 or organic compounds as electron donors and organohalides as electron acceptors. Reductive dehalogenase (RDase), a terminal reductase of the electron transport chain in organohalide-respiring bacteria, is the key enzyme that catalyzes halogen removal. Accumulating experimental evidence thus far suggests that there are distinct models for respiratory electron transfer in organohalide-respirers of different lineages, e.g., Dehalococcoides, Dehalobacter, Desulfitobacterium and Sulfurospirillum. In this review, to connect the knowledge in organohalide-respiratory electron transport chains to bioremediation applications, we first comprehensively review molecular components and their organization, together with energetics of the organohalide-respiratory electron transport chains, as well as recent elucidation of intramolecular electron shuttling and halogen elimination mechanisms of RDases. We then highlight the implications of organohalide-respiratory electron transport chains in stimulated bioremediation. In addition, major challenges and further developments toward understanding the organohalide-respiratory electron transport chains and their bioremediation applications are identified and discussed. Copyright © 2018 Elsevier Inc. All rights reserved.

Homoepitaxial graphene tunnel barriers for spin transport

NASA Astrophysics Data System (ADS)

Friedman, Adam L.; van't Erve, Olaf M. J.; Robinson, Jeremy T.; Whitener, Keith E.; Jonker, Berend T.

2016-05-01

Tunnel barriers are key elements for both charge-and spin-based electronics, offering devices with reduced power consumption and new paradigms for information processing. Such devices require mating dissimilar materials, raising issues of heteroepitaxy, interface stability, and electronic states that severely complicate fabrication and compromise performance. Graphene is the perfect tunnel barrier. It is an insulator out-of-plane, possesses a defect-free, linear habit, and is impervious to interdiffusion. Nonetheless, true tunneling between two stacked graphene layers is not possible in environmental conditions usable for electronics applications. However, two stacked graphene layers can be decoupled using chemical functionalization. Here, we demonstrate that hydrogenation or fluorination of graphene can be used to create a tunnel barrier. We demonstrate successful tunneling by measuring non-linear IV curves and a weakly temperature dependent zero-bias resistance. We demonstrate lateral transport of spin currents in non-local spin-valve structures, and determine spin lifetimes with the non-local Hanle effect. We compare the results for hydrogenated and fluorinated tunnel and we discuss the possibility that ferromagnetic moments in the hydrogenated graphene tunnel barrier affect the spin transport of our devices.

A dynamic model of the radiation-belt electron phase-space density based on POLAR/HIST measurements

NASA Astrophysics Data System (ADS)

Vassiliadis, D.; Green, J. C.

2007-12-01

The response of the energetic-electron phase-space density (PSD) in the radiation belts is subject to a delicate combination of acceleration and loss processes which are strongly determined by the magnetospheric configuration and field disturbance level. We quantify the response of the density to stormtime fields as observed by the HIST detector on board POLAR. Several distinct modes are identified, characterized by peak second- and third- adiabatic invariants and peak delay time. The modes represent quasiadiabatic transport due to ring current activity; high L* (~6), day-long acceleration linked to ULF wave-particle interaction; and low-L* (~3), minute- to hour-long acceleration interpreted to be due to transient inductive fields or VLF wave-particle interaction. The net transport due to these responses is not always or everywhere diffusive, therefore we quantify the degree of departure from diffusive transport for specific storm intervals and radial ranges. Taken together the response modes comprise a dynamic, nonlinear model which allows us to better understand the historic variability of the high-energy tail of the electron distribution in the inner magnetosphere.

Focused electron beam induced deposition: A perspective

PubMed Central

Porrati, Fabrizio; Schwalb, Christian; Winhold, Marcel; Sachser, Roland; Dukic, Maja; Adams, Jonathan; Fantner, Georg

2012-01-01

Summary Background: Focused electron beam induced deposition (FEBID) is a direct-writing technique with nanometer resolution, which has received strongly increasing attention within the last decade. In FEBID a precursor previously adsorbed on a substrate surface is dissociated in the focus of an electron beam. After 20 years of continuous development FEBID has reached a stage at which this technique is now particularly attractive for several areas in both, basic and applied research. The present topical review addresses selected examples that highlight this development in the areas of charge-transport regimes in nanogranular metals close to an insulator-to-metal transition, the use of these materials for strain- and magnetic-field sensing, and the prospect of extending FEBID to multicomponent systems, such as binary alloys and intermetallic compounds with cooperative ground states. Results: After a brief introduction to the technique, recent work concerning FEBID of Pt–Si alloys and (hard-magnetic) Co–Pt intermetallic compounds on the nanometer scale is reviewed. The growth process in the presence of two precursors, whose flux is independently controlled, is analyzed within a continuum model of FEBID that employs rate equations. Predictions are made for the tunability of the composition of the Co–Pt system by simply changing the dwell time of the electron beam during the writing process. The charge-transport regimes of nanogranular metals are reviewed next with a focus on recent theoretical advancements in the field. As a case study the transport properties of Pt–C nanogranular FEBID structures are discussed. It is shown that by means of a post-growth electron-irradiation treatment the electronic intergrain-coupling strength can be continuously tuned over a wide range. This provides unique access to the transport properties of this material close to the insulator-to-metal transition. In the last part of the review, recent developments in mechanical strain-sensing and the detection of small, inhomogeneous magnetic fields by employing nanogranular FEBID structures are highlighted. Conclusion: FEBID has now reached a state of maturity that allows a shift of the focus towards the development of new application fields, be it in basic research or applied. This is shown for selected examples in the present review. At the same time, when seen from a broader perspective, FEBID still has to live up to the original idea of providing a tool for electron-controlled chemistry on the nanometer scale. This has to be understood in the sense that, by providing a suitable environment during the FEBID process, the outcome of the electron-induced reactions can be steered in a controlled way towards yielding the desired composition of the products. The development of a FEBID-specialized surface chemistry is mostly still in its infancy. Next to application development, it is this aspect that will likely be a guiding light for the future development of the field of focused electron beam induced deposition. PMID:23019557

Tunneling explains efficient electron transport via protein junctions.

PubMed

Fereiro, Jerry A; Yu, Xi; Pecht, Israel; Sheves, Mordechai; Cuevas, Juan Carlos; Cahen, David

2018-05-15

Metalloproteins, proteins containing a transition metal ion cofactor, are electron transfer agents that perform key functions in cells. Inspired by this fact, electron transport across these proteins has been widely studied in solid-state settings, triggering the interest in examining potential use of proteins as building blocks in bioelectronic devices. Here, we report results of low-temperature (10 K) electron transport measurements via monolayer junctions based on the blue copper protein azurin (Az), which strongly suggest quantum tunneling of electrons as the dominant charge transport mechanism. Specifically, we show that, weakening the protein-electrode coupling by introducing a spacer, one can switch the electron transport from off-resonant to resonant tunneling. This is a consequence of reducing the electrode's perturbation of the Cu(II)-localized electronic state, a pattern that has not been observed before in protein-based junctions. Moreover, we identify vibronic features of the Cu(II) coordination sphere in transport characteristics that show directly the active role of the metal ion in resonance tunneling. Our results illustrate how quantum mechanical effects may dominate electron transport via protein-based junctions.

49 CFR 228.205 - Access to electronic records.

Code of Federal Regulations, 2013 CFR

2013-10-01

... 49 Transportation 4 2013-10-01 2013-10-01 false Access to electronic records. 228.205 Section 228.205 Transportation Other Regulations Relating to Transportation (Continued) FEDERAL RAILROAD...; SLEEPING QUARTERS Electronic Recordkeeping § 228.205 Access to electronic records. (a) FRA inspectors and...

49 CFR 228.205 - Access to electronic records.

Code of Federal Regulations, 2012 CFR

2012-10-01

... 49 Transportation 4 2012-10-01 2012-10-01 false Access to electronic records. 228.205 Section 228.205 Transportation Other Regulations Relating to Transportation (Continued) FEDERAL RAILROAD...; SLEEPING QUARTERS Electronic Recordkeeping § 228.205 Access to electronic records. (a) FRA inspectors and...

49 CFR 228.205 - Access to electronic records.

Code of Federal Regulations, 2014 CFR

2014-10-01

... 49 Transportation 4 2014-10-01 2014-10-01 false Access to electronic records. 228.205 Section 228.205 Transportation Other Regulations Relating to Transportation (Continued) FEDERAL RAILROAD...; SLEEPING QUARTERS Electronic Recordkeeping § 228.205 Access to electronic records. (a) FRA inspectors and...

Beam transport and monitoring for laser plasma accelerators

NASA Astrophysics Data System (ADS)

Nakamura, K.; Sokollik, T.; van Tilborg, J.; Gonsalves, A. J.; Shaw, B.; Shiraishi, S.; Mittal, R.; De Santis, S.; Byrd, J. M.; Leemans, W.

2012-12-01

The controlled transport and imaging of relativistic electron beams from laser plasma accelerators (LPAs) are critical for their diagnostics and applications. Here we present the design and progress in the implementation of the transport and monitoring system for an undulator based electron beam diagnostic. Miniature permanent-magnet quadrupoles (PMQs) are employed to realize controlled transport of the LPA electron beams, and cavity based electron beam position monitors for non-invasive beam position detection. Also presented is PMQ calibration by using LPA electron beams with broadband energy spectrum. The results show promising performance for both transporting and monitoring. With the proper transport system, XUV-photon spectra from THUNDER will provide the momentum distribution of the electron beam with the resolution above what can be achieved by the magnetic spectrometer currently used in the LOASIS facility.

Skin Bioengineering: Noninvasive Transdermal Monitoring

DTIC Science & Technology

2005-01-01

involves the application of a small and defined electrical current to the skin. This process causes increased molecular transport through the skin and has...flow of electrons is translated into an ion flux across the skin. A power supply establishes the electric field that causes electrons to migrate in...a model designed to mimic the developing cutaneous barrier in a premature neonate (Sekkat et al 2002). While the idea appears feasible for full-term

TiO2 reinforced PMMA-TiO2 nanocomposite for its application in organic light emitting diode (OLED) as electron transport layer material

NASA Astrophysics Data System (ADS)

Kandulna, R.; Choudhary, R. B.; Singh, R.

2018-04-01

PMMA, TiO2 and PMMA-TiO2 nanocomposite were successfully synthesized in the laboratory via free radical polymerization process. The formation of PMMA corresponding change in the nanostructure with the embodiment of TiO2 nanofillers was confirmed by X-ray diffraction technique (XRD) analysis. Irregular tetragonal bipyramidal arrangement of TiO2 was formed within the spherical type structure of PMMA polymeric matrix, as examined by the surface morphological image. Relatively higher electron-hole non-radiative recombination of PMMA-TiO2 nanocomposite corresponded to blue-violet band, blue band, and green band was examined from PL spectra. An enhanced current density ˜ 165 % was observed with significantly improved p-type conductivity for PMMA-TiO2 nanocomposite. The improved specific capacitance with high dielectric constant and high electron-hole recombination rate confirmed that it can possibly use as electron transport layer material in the OLED devices fabrication.

Monte Carlo simulation study of positron generation in ultra-intense laser-solid interactions

NASA Astrophysics Data System (ADS)

Yan, Yonghong; Wu, Yuchi; Zhao, Zongqing; Teng, Jian; Yu, Jinqing; Liu, Dongxiao; Dong, Kegong; Wei, Lai; Fan, Wei; Cao, Leifeng; Yao, Zeen; Gu, Yuqiu

2012-02-01

The Monte Carlo transport code Geant4 has been used to study positron production in the transport of laser-produced hot electrons in solid targets. The dependence of the positron yield on target parameters and the hot-electron temperature has been investigated in thick targets (mm-scale), where only the Bethe-Heitler process is considered. The results show that Au is the best target material, and an optimal target thickness exists for generating abundant positrons at a given hot-electron temperature. The positron angular distributions and energy spectra for different hot electron temperatures were studied without considering the sheath field on the back of the target. The effect of the target rear sheath field for positron acceleration was studied by numerical simulation while including an electrostatic field in the Monte Carlo model. It shows that the positron energy can be enhanced and quasi-monoenergetic positrons are observed owing to the effect of the sheath field.

Cation-limited kinetic model for microbial extracellular electron transport via an outer membrane cytochrome C complex

PubMed Central

Okamoto, Akihiro; Tokunou, Yoshihide; Saito, Junki

2016-01-01

Outer-membrane c-type cytochrome (OM c-Cyt) complexes in several genera of iron-reducing bacteria, such as Shewanella and Geobacter, are capable of transporting electrons from the cell interior to extracellular solids as a terminal step of anaerobic respiration. The kinetics of this electron transport has implications for controlling the rate of microbial electron transport during bioenergy or biochemical production, iron corrosion, and natural mineral cycling. Herein, we review the findings from in-vivo and in-vitro studies examining electron transport kinetics through single OM c-Cyt complexes in Shewanella oneidensis MR-1. In-vitro electron flux via a purified OM c-Cyt complex, comprised of MtrA, B, and C proteins from S. oneidensis MR-1, embedded in a proteoliposome system is reported to be 10- to 100-fold faster compared with in-vivo estimates based on measurements of electron flux per cell and OM c-Cyts density. As the proteoliposome system is estimated to have 10-fold higher cation flux via potassium channels than electrons, we speculate that the slower rate of electron-coupled cation transport across the OM is responsible for the significantly lower electron transport rate that is observed in-vivo. As most studies to date have primarily focused on the energetics or kinetics of interheme electron hopping in OM c-Cyts in this microbial electron transport mechanism, the proposed model involving cation transport provides new insight into the rate detemining step of EET, as well as the role of self-secreted flavin molecules bound to OM c-Cyt and proton management for energy conservation and production in S. oneidensis MR-1. PMID:27924259

Recent Advances in the Inverted Planar Structure of Perovskite Solar Cells.

PubMed

Meng, Lei; You, Jingbi; Guo, Tzung-Fang; Yang, Yang

2016-01-19

Inorganic-organic hybrid perovskite solar cells research could be traced back to 2009, and initially showed 3.8% efficiency. After 6 years of efforts, the efficiency has been pushed to 20.1%. The pace of development was much faster than that of any type of solar cell technology. In addition to high efficiency, the device fabrication is a low-cost solution process. Due to these advantages, a large number of scientists have been immersed into this promising area. In the past 6 years, much of the research on perovskite solar cells has been focused on planar and mesoporous device structures employing an n-type TiO2 layer as the bottom electron transport layer. These architectures have achieved champion device efficiencies. However, they still possess unwanted features. Mesoporous structures require a high temperature (>450 °C) sintering process for the TiO2 scaffold, which will increase the cost and also not be compatible with flexible substrates. While the planar structures based on TiO2 (regular structure) usually suffer from a large degree of J-V hysteresis. Recently, another emerging structure, referred to as an "inverted" planar device structure (i.e., p-i-n), uses p-type and n-type materials as bottom and top charge transport layers, respectively. This structure derived from organic solar cells, and the charge transport layers used in organic photovoltaics were successfully transferred into perovskite solar cells. The p-i-n structure of perovskite solar cells has shown efficiencies as high as 18%, lower temperature processing, flexibility, and, furthermore, negligible J-V hysteresis effects. In this Account, we will provide a comprehensive comparison of the mesoporous and planar structures, and also the regular and inverted of planar structures. Later, we will focus the discussion on the development of the inverted planar structure of perovskite solar cells, including film growth, band alignment, stability, and hysteresis. In the film growth part, several methods for obtaining high quality perovskite films are reviewed. In the interface engineering parts, the effect of hole transport layer on subsequent perovskite film growth and their interface band alignment, and also the effect of electron transport layers on charge transport and interface contact will be discussed. As concerns stability, the role of charge transport layers especially the top electron transport layer in the devices stability will be concluded. In the hysteresis part, possible reasons for hysteresis free in inverted planar structure are provided. At the end of this Account, future development and possible solutions to the remaining challenges facing the commercialization of perovskite solar cells are discussed.

Electron Injections: A Study of Electron Acceleration by Multiple Dipolarizing Flux Bundles Using an Analytical Model

NASA Astrophysics Data System (ADS)

Gabrielse, C.; Angelopoulos, V.; Artemyev, A.; Runov, A.; Harris, C.

2016-12-01

We study energetic electron injections using an analytical model that self-consistently describes electric and magnetic field perturbations of transient, localized dipolarizing flux bundles (DFBs). Previous studies using THEMIS, Van Allen Probes, and the Magnetospheric Multiscale Mission have shown that injections can occur on short (minutes) or long (10s of minutes) timescales. These studies suggest that the short timescale injections correspond to a single DFB, whereas long timescale injections are likely caused by an aggregate of multiple DFBs, each incrementally heating the particle population. We therefore model the effects of multiple DFBs on the electron population using multi-spacecraft observations of the fields and particle fluxes to constrain the model parameters. The analytical model is the first of its kind to model multiple dipolarization fronts in order to better understand the transport and acceleration process throughout the plasma sheet. It can reproduce most injection signatures at multiple locations simultaneously, reaffirming earlier findings that multiple earthward-traveling DFBs can both transport and accelerate electrons to suprathermal energies, and can thus be considered the injections' primary driver.

Monte Carlo random walk simulation of electron transport in confined porous TiO{sub 2} as a promising candidate for photo-electrode of nano-crystalline solar cells

DOE Office of Scientific and Technical Information (OSTI.GOV)

Javadi, M.; Abdi, Y., E-mail: y.abdi@ut.ac.ir

2015-08-14

Monte Carlo continuous time random walk simulation is used to study the effects of confinement on electron transport, in porous TiO{sub 2}. In this work, we have introduced a columnar structure instead of the thick layer of porous TiO{sub 2} used as anode in conventional dye solar cells. Our simulation results show that electron diffusion coefficient in the proposed columnar structure is significantly higher than the diffusion coefficient in the conventional structure. It is shown that electron diffusion in the columnar structure depends both on the cross section area of the columns and the porosity of the structure. Also, wemore » demonstrate that such enhanced electron diffusion can be realized in the columnar photo-electrodes with a cross sectional area of ∼1 μm{sup 2} and porosity of 55%, by a simple and low cost fabrication process. Our results open up a promising approach to achieve solar cells with higher efficiencies by engineering the photo-electrode structure.« less

Monte Carlo random walk simulation of electron transport in confined porous TiO2 as a promising candidate for photo-electrode of nano-crystalline solar cells

NASA Astrophysics Data System (ADS)

Javadi, M.; Abdi, Y.

2015-08-01

Monte Carlo continuous time random walk simulation is used to study the effects of confinement on electron transport, in porous TiO2. In this work, we have introduced a columnar structure instead of the thick layer of porous TiO2 used as anode in conventional dye solar cells. Our simulation results show that electron diffusion coefficient in the proposed columnar structure is significantly higher than the diffusion coefficient in the conventional structure. It is shown that electron diffusion in the columnar structure depends both on the cross section area of the columns and the porosity of the structure. Also, we demonstrate that such enhanced electron diffusion can be realized in the columnar photo-electrodes with a cross sectional area of ˜1 μm2 and porosity of 55%, by a simple and low cost fabrication process. Our results open up a promising approach to achieve solar cells with higher efficiencies by engineering the photo-electrode structure.

Heterojunction oxide thin-film transistors with unprecedented electron mobility grown from solution.

PubMed

Faber, Hendrik; Das, Satyajit; Lin, Yen-Hung; Pliatsikas, Nikos; Zhao, Kui; Kehagias, Thomas; Dimitrakopulos, George; Amassian, Aram; Patsalas, Panos A; Anthopoulos, Thomas D

2017-03-01

Thin-film transistors made of solution-processed metal oxide semiconductors hold great promise for application in the emerging sector of large-area electronics. However, further advancement of the technology is hindered by limitations associated with the extrinsic electron transport properties of the often defect-prone oxides. We overcome this limitation by replacing the single-layer semiconductor channel with a low-dimensional, solution-grown In 2 O 3 /ZnO heterojunction. We find that In 2 O 3 /ZnO transistors exhibit band-like electron transport, with mobility values significantly higher than single-layer In 2 O 3 and ZnO devices by a factor of 2 to 100. This marked improvement is shown to originate from the presence of free electrons confined on the plane of the atomically sharp heterointerface induced by the large conduction band offset between In 2 O 3 and ZnO. Our finding underscores engineering of solution-grown metal oxide heterointerfaces as an alternative strategy to thin-film transistor development and has the potential for widespread technological applications.

Heterojunction oxide thin-film transistors with unprecedented electron mobility grown from solution

PubMed Central

Faber, Hendrik; Das, Satyajit; Lin, Yen-Hung; Pliatsikas, Nikos; Zhao, Kui; Kehagias, Thomas; Dimitrakopulos, George; Amassian, Aram; Patsalas, Panos A.; Anthopoulos, Thomas D.

2017-01-01

Thin-film transistors made of solution-processed metal oxide semiconductors hold great promise for application in the emerging sector of large-area electronics. However, further advancement of the technology is hindered by limitations associated with the extrinsic electron transport properties of the often defect-prone oxides. We overcome this limitation by replacing the single-layer semiconductor channel with a low-dimensional, solution-grown In2O3/ZnO heterojunction. We find that In2O3/ZnO transistors exhibit band-like electron transport, with mobility values significantly higher than single-layer In2O3 and ZnO devices by a factor of 2 to 100. This marked improvement is shown to originate from the presence of free electrons confined on the plane of the atomically sharp heterointerface induced by the large conduction band offset between In2O3 and ZnO. Our finding underscores engineering of solution-grown metal oxide heterointerfaces as an alternative strategy to thin-film transistor development and has the potential for widespread technological applications. PMID:28435867

Programmable hyperspectral image mapper with on-array processing

NASA Technical Reports Server (NTRS)

Cutts, James A. (Inventor)

1995-01-01

A hyperspectral imager includes a focal plane having an array of spaced image recording pixels receiving light from a scene moving relative to the focal plane in a longitudinal direction, the recording pixels being transportable at a controllable rate in the focal plane in the longitudinal direction, an electronic shutter for adjusting an exposure time of the focal plane, whereby recording pixels in an active area of the focal plane are removed therefrom and stored upon expiration of the exposure time, an electronic spectral filter for selecting a spectral band of light received by the focal plane from the scene during each exposure time and an electronic controller connected to the focal plane, to the electronic shutter and to the electronic spectral filter for controlling (1) the controllable rate at which the recording is transported in the longitudinal direction, (2) the exposure time, and (3) the spectral band so as to record a selected portion of the scene through M spectral bands with a respective exposure time t(sub q) for each respective spectral band q.

Influence of phonon-assisted tunneling on the linear thermoelectric transport through molecular quantum dots

NASA Astrophysics Data System (ADS)

Khedri, A.; Meden, V.; Costi, T. A.

2017-11-01

We investigate the effect of vibrational degrees of freedom on the linear thermoelectric transport through a single-level quantum dot described by the spinless Anderson-Holstein impurity model. To study the effects of strong electron-phonon coupling, we use the nonperturbative numerical renormalization group approach. We also compare our results, at weak to intermediate coupling, with those obtained by employing the functional renormalization group method, finding good agreement in this parameter regime. When applying a gate voltage at finite temperatures, the inelastic scattering processes, induced by phonon-assisted tunneling, result in an interesting interplay between electrical and thermal transport. We explore different parameter regimes and identify situations for which the thermoelectric power as well as the dimensionless figure of merit are significantly enhanced via a Mahan-Sofo type of mechanism. We show, in particular, that this occurs at strong electron-phonon coupling and in the antiadiabatic regime.

On the nature of high field charge transport in reinforced silicone dielectrics: Experiment and simulation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Huang, Yanhui, E-mail: huangy12@rpi.edu; Schadler, Linda S.

The high field charge injection and transport properties in reinforced silicone dielectrics were investigated by measuring the time-dependent space charge distribution and the current under dc conditions up to the breakdown field and were compared with the properties of other dielectric polymers. It is argued that the energy and spatial distribution of localized electronic states are crucial in determining these properties for polymer dielectrics. Tunneling to localized states likely dominates the charge injection process. A transient transport regime arises due to the relaxation of charge carriers into deep traps at the energy band tails and is successfully verified by amore » Monte Carlo simulation using the multiple-hopping model. The charge carrier mobility is found to be highly heterogeneous due to the non-uniform trapping. The slow moving electron packet exhibits a negative field dependent drift velocity possibly due to the spatial disorder of traps.« less

Improvements on non-equilibrium and transport Green function techniques: The next-generation TRANSIESTA

NASA Astrophysics Data System (ADS)

Papior, Nick; Lorente, Nicolás; Frederiksen, Thomas; García, Alberto; Brandbyge, Mads

2017-03-01

We present novel methods implemented within the non-equilibrium Green function code (NEGF) TRANSIESTA based on density functional theory (DFT). Our flexible, next-generation DFT-NEGF code handles devices with one or multiple electrodes (Ne ≥ 1) with individual chemical potentials and electronic temperatures. We describe its novel methods for electrostatic gating, contour optimizations, and assertion of charge conservation, as well as the newly implemented algorithms for optimized and scalable matrix inversion, performance-critical pivoting, and hybrid parallelization. Additionally, a generic NEGF "post-processing" code (TBTRANS/PHTRANS) for electron and phonon transport is presented with several novelties such as Hamiltonian interpolations, Ne ≥ 1 electrode capability, bond-currents, generalized interface for user-defined tight-binding transport, transmission projection using eigenstates of a projected Hamiltonian, and fast inversion algorithms for large-scale simulations easily exceeding 106 atoms on workstation computers. The new features of both codes are demonstrated and bench-marked for relevant test systems.

Effects of applied dc radial electric fields on particle transport in a bumpy torus plasma

NASA Technical Reports Server (NTRS)

Roth, J. R.

1978-01-01

The influence of applied dc radial electric fields on particle transport in a bumpy torus plasma is studied. The plasma, magnetic field, and ion heating mechanism are operated in steady state. Ion kinetic temperature is more than a factor of ten higher than electron temperature. The electric fields raise the ions to energies on the order of kilovolts and then point radially inward or outward. Plasma number density profiles are flat or triangular across the plasma diameter. It is suggested that the radial transport processes are nondiffusional and dominated by strong radial electric fields. These characteristics are caused by the absence of a second derivative in the density profile and the flat electron temperature profiles. If the electric field acting on the minor radius of the toroidal plasma points inward, plasma number density and confinement time are increased.

High-fidelity plasma codes for burn physics

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cooley, James; Graziani, Frank; Marinak, Marty

Accurate predictions of equation of state (EOS), ionic and electronic transport properties are of critical importance for high-energy-density plasma science. Transport coefficients inform radiation-hydrodynamic codes and impact diagnostic interpretation, which in turn impacts our understanding of the development of instabilities, the overall energy balance of burning plasmas, and the efficacy of self-heating from charged-particle stopping. Important processes include thermal and electrical conduction, electron-ion coupling, inter-diffusion, ion viscosity, and charged particle stopping. However, uncertainties in these coefficients are not well established. Fundamental plasma science codes, also called high-fidelity plasma codes, are a relatively recent computational tool that augments both experimental datamore » and theoretical foundations of transport coefficients. This paper addresses the current status of HFPC codes and their future development, and the potential impact they play in improving the predictive capability of the multi-physics hydrodynamic codes used in HED design.« less

Momentum transport and nonlocality in heat-flux-driven magnetic reconnection in high-energy-density plasmas

DOE PAGES

Liu, Chang; Fox, William; Bhattacharjee, Amitava; ...

2017-10-06

Recent theory has demonstrated a novel physics regime for magnetic reconnection in high-energy-density plasmas where the magnetic field is advected by heat flux via the Nernst effect. In this paper, we elucidate the physics of the electron dissipation layer in this regime. Through fully kinetic simulation and a generalized Ohm's law derived from first principles, we show that momentum transport due to a nonlocal effect, the heat-flux-viscosity, provides the dissipation mechanism for magnetic reconnection. Scaling analysis, and simulations show that the reconnection process comprises a magnetic field compression stage and quasisteady reconnection stage, and the characteristic width of the currentmore » sheet in this regime is several electron mean-free paths. Finally, these results show the important interplay between nonlocal transport effects and generation of anisotropic components to the distribution function.« less

Blue emitting 1,8-naphthalimides with electron transport properties for organic light emitting diode applications

NASA Astrophysics Data System (ADS)

Ulla, Hidayath; Kiran, M. Raveendra; Garudachari, B.; Ahipa, T. N.; Tarafder, Kartick; Adhikari, Airody Vasudeva; Umesh, G.; Satyanarayan, M. N.

2017-09-01

In this article, the synthesis, characterization and use of two novel naphthalimides as electron-transporting emitter materials for organic light emitting diode (OLED) applications are reported. The molecules were obtained by substituting electron donating chloro-phenoxy group at the C-4 position. A detailed optical, thermal, electrochemical and related properties were systematically studied. Furthermore, theoretical calculations (DFT) were performed to get a better understanding of the electronic structures. The synthesized molecules were used as electron transporters and emitters in OLEDs with three different device configurations. The devices with the molecules showed blue emission with efficiencies of 1.89 cdA-1, 0.98 lmW-1, 0.71% at 100 cdm-2. The phosphorescent devices with naphthalimides as electron transport materials displayed better performance in comparison to the device without any electron transporting material and were analogous with the device using standard electron transporting material, Alq3. The results demonstrate that the naphthalimides could play a significant part in the progress of OLEDs.

Transport mirages in single-molecule devices

NASA Astrophysics Data System (ADS)

Gaudenzi, R.; Misiorny, M.; Burzurí, E.; Wegewijs, M. R.; van der Zant, H. S. J.

2017-03-01

Molecular systems can exhibit a complex, chemically tailorable inner structure which allows for targeting of specific mechanical, electronic, and optical properties. At the single-molecule level, two major complementary ways to explore these properties are molecular quantum-dot structures and scanning probes. This article outlines comprehensive principles of electron-transport spectroscopy relevant to both these approaches and presents a new, high-resolution experiment on a high-spin single-molecule junction exemplifying these principles. Such spectroscopy plays a key role in further advancing our understanding of molecular and atomic systems, in particular, the relaxation of their spin. In this joint experimental and theoretical analysis, particular focus is put on the crossover between the resonant regime [single-electron tunneling] and the off-resonant regime [inelastic electron (co)tunneling spectroscopy (IETS)]. We show that the interplay of these two processes leads to unexpected mirages of resonances not captured by either of the two pictures alone. Although this turns out to be important in a large fraction of the possible regimes of level positions and bias voltages, it has been given little attention in molecular transport studies. Combined with nonequilibrium IETS—four-electron pump-probe excitations—these mirages provide crucial information on the relaxation of spin excitations. Our encompassing physical picture is supported by a master-equation approach that goes beyond weak coupling. The present work encourages the development of a broader connection between the fields of molecular quantum-dot and scanning probe spectroscopy.

The Cytochrome b 6 f Complex: Biophysical Aspects of Its Functioning in Chloroplasts.

PubMed

Tikhonov, Alexander N

2018-01-01

This chapter presents an overview of structural properties of the cytochrome (Cyt) b 6 f complex and its functioning in chloroplasts. The Cyt b 6 f complex stands at the crossroad of photosynthetic electron transport pathways, providing connectivity between Photosystem (PSI) and Photosysten II (PSII) and pumping protons across the membrane into the thylakoid lumen. After a brief review of the chloroplast electron transport chain, the consideration is focused on the structural organization of the Cyt b 6 f complex and its interaction with plastoquinol (PQH 2 , reduced form of plastoquinone), a mediator of electron transfer from PSII to the Cyt b 6 f complex. The processes of PQH 2 oxidation by the Cyt b 6 f complex have been considered within the framework of the Mitchell's Q-cycle. The overall rate of the intersystem electron transport is determined by PQH 2 turnover at the quinone-binding site Q o of the Cyt b 6 f complex. The rate of PQH 2 oxidation is controlled by the intrathylakoid pH in , which value determines the protonation/deprotonation events in the Q o -center. Two other regulatory mechanisms associated with the Cyt b 6 f complex are briefly overviewed: (i) redistribution of electron fluxes between alternative (linear and cyclic) pathways, and (ii) "state transitions" related to redistribution of solar energy between PSI and PSII.

Characterization of pi-Conjugated Polymers for Transistor and Photovoltaic Applications

NASA Astrophysics Data System (ADS)

Paulsen, Bryan D.

pi-Conjugated polymers represent a unique class of optoelectronic materials. Being polymers, they are solution processable and inherently "soft" materials. This makes them attractive candidates for the production of roll-to-roll printed electronic devices on flexible substrates. The optical and electronic properties of pi-conjugated polymers are synthetically tunable allowing material sets to be tailored to specific applications. Two of the most heavily researched applications are the thin film transistor, the building block of electronic circuits, and the bulk heterojunction solar cell, which holds great potential as a renewable energy source. Key to developing commercially feasible pi-conjugated polymer devices is a thorough understanding of the electronic structure and charge transport behavior of these materials in relationship with polymer structure. Here this structure property relationship has been investigated through electrical and electrochemical means in concert with a variety of other characterization techniques and device test beds. The tunability of polymer optical band gap and frontier molecular orbital energy level was investigated in systems of vinyl incorporating statistical copolymers. Energy levels and band gaps are crucial parameters in developing efficient photovoltaic devices, with control of these parameters being highly desirable. Additionally, charge transport and density of electronic states were investigated in pi-conjugated polymers at extremely high electrochemically induced charge density. Finally, the effects of molecular weight on pi-conjugated polymer optical properties, energy levels, charge transport, morphology, and photovoltaic device performance was examined.

The inter-relationship of ascorbate transport, metabolism and mitochondrial, plastidic respiration.

PubMed

Szarka, András; Bánhegyi, Gábor; Asard, Han

2013-09-20

Ascorbate, this multifaceted small molecular weight carbohydrate derivative, plays important roles in a range of cellular processes in plant cells, from the regulation of cell cycle, through cell expansion and senescence. Beyond these physiological functions, ascorbate has a critical role in responses to abiotic stresses, such as high light, high salinity, or drought. The biosynthesis, recycling, and intracellular transport are important elements of the balancing of ascorbate level to the always-changing conditions and demands. A bidirectional tight relationship was described between ascorbate biosynthesis and the mitochondrial electron transfer chain (mETC), since L-galactono-1,4-lactone dehydrogenase (GLDH), the enzyme catalyzing the ultimate step of ascorbate biosynthesis, uses oxidized cytochrome c as the only electron acceptor and has a role in the assembly of Complex I. A similar bidirectional relationship was revealed between the photosynthetic apparatus and ascorbate biosynthesis since the electron flux through the photosynthetic ETC affects the biosynthesis of ascorbate and the level of ascorbate could affect photosynthesis. The details of this regulatory network of photosynthetic electron transfer, respiratory electron transfer, and ascorbate biosynthesis are still not clear, as are the potential regulatory role and the regulation of intracellular ascorbate transport and fluxes. The elucidation of the role of ascorbate as an important element of the network of photosynthetic, respiratory ETC and tricarboxylic acid cycle will contribute to understanding plant cell responses to different stress conditions.

Impact of weak water deficit on growth, photosynthetic primary processes and storage processes in pine and spruce seedlings.

PubMed

Zlobin, Ilya E; Ivanov, Yury V; Kartashov, Alexander V; Sarvin, Boris A; Stavrianidi, Andrey N; Kreslavski, Vladimir D; Kuznetsov, Vladimir V

2018-05-19

We investigated the influence of 40 days of drought on growth, storage processes and primary photosynthetic processes in 3-month-old Scots pine and Norway spruce seedlings growing in perlite culture. Water stress significantly affected seedling water status, whereas absolute dry biomass growth was not substantially influenced. Water stress induced an increase in non-structural carbohydrate content (sugars, sugar alcohols, starch) in the aboveground part of pine seedlings in contrast to spruce seedlings. Due to the relatively low content of sugars and sugar alcohols in seedling organs, their expected contribution to osmotic potential changes was quite low. In contrast to biomass accumulation and storage, photosynthetic primary processes were substantially influenced by water shortage. In spruce seedlings, PSII was more sensitive to water stress than PSI. In particular, electron transport in PSI was stable under water stress despite the substantial decrease of electron transport in PSII. The increase in thermal energy dissipation due to enhancement of non-photochemical quenching (NPQ) was evident in both species under water stress. Simultaneously, the yields of non-regulated energy dissipation in PSII were decreased in pine seedlings under drought. A relationship between growth, photosynthetic activities and storage processes is analysed under weak water deficit.

Spin Dependent Transport Properties of Metallic and Semiconducting Nanostructures

NASA Astrophysics Data System (ADS)

Sapkota, Keshab R.

Present computing and communication devices rely on two different classes of technologies; information processing devices are based on electrical charge transport in semiconducting materials while information storage devices are based on orientation of electron spins in magnetic materials. A realization of a hybrid-type device that is based on charge as well as spin properties of electrons would perform both of these actions thereby enhancing computation power to many folds and reducing power consumptions. This dissertation focuses on the fabrication of such spin-devices based on metallic and semiconducting nanostructures which can utilize spin as well as charge properties of electrons. A simplified design of the spin-device consists of a spin injector, a semiconducting or metallic channel, and a spin detector. The channel is the carrier of the spin signal from the injector to the detector and therefore plays a crucial role in the manipulation of spin properties in the device. In this work, nanostructures like nanowires and nanostripes are used to function the channel in the spin-device. Methods like electrospinning, hydrothermal, and wet chemical were used to synthesize nanowires while physical vapor deposition followed by heat treatment in controlled environment was used to synthesis nanostripes. Spin-devices fabrication of the synthesized nanostructures were carried out by electron beam lithography process. The details of synthesis of nanostructures, device fabrication procedures and measurement techniques will be discussed in the thesis. We have successfully fabricated the spin-devices of tellurium nanowire, indium nanostripe, and indium oxide nanostripe and studied their spin transport properties for the first time. These spin-devices show large spin relaxation length compared to normal metals like copper and offer potentials for the future technologies. Further, Heusler alloys nanowires like nanowires of Co 2FeAl were synthesized and studied for electrical transport properties since such systems are halfmetallic in nature and promise the possibilities of spin injection and detection. The study was extended to dilute magnetic semiconducting nanowire system of Cd1-xMnxTe which possess both magnetic and semiconducting properties. In summary, the studies made in this thesis will offer a new understanding of spin transport behavior for future technology.

Constraining Data Mining with Physical Models: Voltage- and Oxygen Pressure-Dependent Transport in Multiferroic Nanostructures

DOE Office of Scientific and Technical Information (OSTI.GOV)

Strelcov, Evgheni; Belianinov, Alexei; Hsieh, Ying-Hui

Development of new generation electronic devices requires understanding and controlling the electronic transport in ferroic, magnetic, and optical materials, which is hampered by two factors. First, the complications of working at the nanoscale, where interfaces, grain boundaries, defects, and so forth, dictate the macroscopic characteristics. Second, the convolution of the response signals stemming from the fact that several physical processes may be activated simultaneously. Here, we present a method of solving these challenges via a combination of atomic force microscopy and data mining analysis techniques. Rational selection of the latter allows application of physical constraints and enables direct interpretation ofmore » the statistically significant behaviors in the framework of the chosen physical model, thus distilling physical meaning out of raw data. We demonstrate our approach with an example of deconvolution of complex transport behavior in a bismuth ferrite–cobalt ferrite nanocomposite in ambient and ultrahigh vacuum environments. Measured signal is apportioned into four electronic transport patterns, showing different dependence on partial oxygen and water vapor pressure. These patterns are described in terms of Ohmic conductance and Schottky emission models in the light of surface electrochemistry. Finally and furthermore, deep data analysis allows extraction of local dopant concentrations and barrier heights empowering our understanding of the underlying dynamic mechanisms of resistive switching.« less

Electron beam transport analysis of W-band sheet beam klystron

NASA Astrophysics Data System (ADS)

Wang, Jian-Xun; Barnett, Larry R.; Luhmann, Neville C.; Shin, Young-Min; Humphries, Stanley

2010-04-01

The formation and transport of high-current density electron beams are of critical importance for the success of a number of millimeter wave and terahertz vacuum devices. To elucidate design issues and constraints, the electron gun and periodically cusped magnet stack of the original Stanford Linear Accelerator Center designed W-band sheet beam klystron circuit, which exhibited poor beam transmission (≤55%), have been carefully investigated through theoretical and numerical analyses taking advantage of three-dimensional particle tracking solvers. The re-designed transport system is predicted to exhibit 99.76% (cold) and 97.38% (thermal) beam transmission, respectively, under space-charge-limited emission simulations. The optimized design produces the required high aspect ratio (10:1) sheet beam with 3.2 A emission current with highly stable propagation. In the completely redesigned model containing all the circuit elements, more than 99% beam transmission is experimentally observed at the collector located about 160 mm distant from the cathode surface. Results are in agreement of the predictions of two ray-tracing simulators, CST PARTICLE STUDIO and OMNITRAK which also predict the observed poor transmission in the original design. The quantitative analysis presents practical factors in the modeling process to design a magnetic lens structure to stably transport the elliptical beam along the long drift tube.

Constraining Data Mining with Physical Models: Voltage- and Oxygen Pressure-Dependent Transport in Multiferroic Nanostructures

DOE PAGES

Strelcov, Evgheni; Belianinov, Alexei; Hsieh, Ying-Hui; ...

2015-08-27

Development of new generation electronic devices requires understanding and controlling the electronic transport in ferroic, magnetic, and optical materials, which is hampered by two factors. First, the complications of working at the nanoscale, where interfaces, grain boundaries, defects, and so forth, dictate the macroscopic characteristics. Second, the convolution of the response signals stemming from the fact that several physical processes may be activated simultaneously. Here, we present a method of solving these challenges via a combination of atomic force microscopy and data mining analysis techniques. Rational selection of the latter allows application of physical constraints and enables direct interpretation ofmore » the statistically significant behaviors in the framework of the chosen physical model, thus distilling physical meaning out of raw data. We demonstrate our approach with an example of deconvolution of complex transport behavior in a bismuth ferrite–cobalt ferrite nanocomposite in ambient and ultrahigh vacuum environments. Measured signal is apportioned into four electronic transport patterns, showing different dependence on partial oxygen and water vapor pressure. These patterns are described in terms of Ohmic conductance and Schottky emission models in the light of surface electrochemistry. Finally and furthermore, deep data analysis allows extraction of local dopant concentrations and barrier heights empowering our understanding of the underlying dynamic mechanisms of resistive switching.« less

Isomer and Fluorination Effects among Fluorine Substituted Hydrocarbon C3/C4 Molecules in Electron Impact Ionization

NASA Astrophysics Data System (ADS)

Patel, U. R.; Joshipura, K. N.

2015-05-01

Electron collision processes are very important in both man-made and natural plasmas, for determining the energy balances and transport properties of electrons. Electron -molecule scattering leading to ionization represents one of the most fundamental processes in collision physics. In the gas phase, the total efficiency of the process is described by the absolute total electron impact ionization cross section. Carbon based materials are some of the widely used materials for a divertor plate and magnetically confined fusion devices. In the ``ITER,'' it is very important for steady state operation to have an estimate of the lifetime of carbon plasma facing components. Apart from fusion plasma relevance, the present theoretical study is very important in modeling and controlling other electron assisted processes in many areas. Hydrocarbons play an important role for plasma diagnostics as impurities in the Tokamak fusion divertor, as seed gases for the production of radicals and ions in low temperature plasma processing. Fluorine substituted hydrocarbons (perfluorocarbons) are important as reactants in plasma assisted fabrication processes. In the present work, we have calculated total ionization cross sections Qion for C3/C4 Hydrocarbon isomers by electron impact, and comparisons are made mutually to observe isomer effect. Comparisons are also made by substituting H atom by F atom and revealing fluorination effect. The present calculations are quite significant owing to the lack of experimental data, with just an isolated previous theoretical work in some cases.

Electron transport in solid targets and in the active mixture of a CO2 laser amplifier

NASA Astrophysics Data System (ADS)

Galkowski, A.

The paper examines the use of the NIKE code for the Monte Carlo computation of the deposited energy profile and other characteristics of the absorption process of an electron beam in a solid target and the spatial distribution of primary ionization in the active mixture of a CO2 laser amplifier. The problem is considered in connection with the generation of intense electron beams and the acceleration of thin metal foils, as well as in connection with the electric discharge pumping of a CO2 laser amplifier.

Liquid Argon TPC Signal Formation, Signal Processing and Hit Reconstruction

DOE Office of Scientific and Technical Information (OSTI.GOV)

Baller, Bruce

2017-03-11

This document describes the early stage of the reconstruction chain that was developed for the ArgoNeuT and MicroBooNE experiments at Fermilab. These experiments study accelerator neutrino interactions that occur in a Liquid Argon Time Projection Chamber. Reconstructing the properties of particles produced in these interactions requires knowledge of the micro-physics processes that affect the creation and transport of ionization electrons to the readout system. A wire signal deconvolution technique was developed to convert wire signals to a standard form for hit reconstruction, to remove artifacts in the electronics chain and to remove coherent noise.

Beam transport and monitoring for laser plasma accelerators

DOE Office of Scientific and Technical Information (OSTI.GOV)

Nakamura, K.; Sokollik, T.; Tilborg, J. van

The controlled transport and imaging of relativistic electron beams from laser plasma accelerators (LPAs) are critical for their diagnostics and applications. Here we present the design and progress in the implementation of the transport and monitoring system for an undulator based electron beam diagnostic. Miniature permanent-magnet quadrupoles (PMQs) are employed to realize controlled transport of the LPA electron beams, and cavity based electron beam position monitors for non-invasive beam position detection. Also presented is PMQ calibration by using LPA electron beams with broadband energy spectrum. The results show promising performance for both transporting and monitoring. With the proper transport system,more » XUV-photon spectra from THUNDER will provide the momentum distribution of the electron beam with the resolution above what can be achieved by the magnetic spectrometer currently used in the LOASIS facility.« less

Electrically induced spontaneous emission in open electronic system

NASA Astrophysics Data System (ADS)

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

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

Investigation of charge injection and transport behavior in multilayer structure consisted of ferromagnetic metal and organic polymer under external fields

NASA Astrophysics Data System (ADS)

Zhao, Hua; Meng, Wei-Feng

2017-10-01

In this paper a five layer organic electronic device with alternately placed ferromagnetic metals and organic polymers: ferromagnetic metal/organic layer/ferromagnetic metal/organic layer/ferromagnetic metal, which is injected a spin-polarized electron from outsides, is studied theoretically using one-dimensional tight binding model Hamiltonian. We calculated equilibrium state behavior after an electron with spin is injected into the organic layer of this structure, charge density distribution and spin polarization density distribution of this injected spin-polarized electron, and mainly studied possible transport behavior of the injected spin polarized electron in this multilayer structure under different external electric fields. We analyze the physical process of the injected electron in this multilayer system. It is found by our calculation that the injected spin polarized electron exists as an electron-polaron state with spin polarization in the organic layer and it can pass through the middle ferromagnetic layer from the right-hand organic layer to the left-hand organic layer by the action of increasing external electric fields, which indicates that this structure may be used as a possible spin-polarized charge electronic device and also may provide a theoretical base for the organic electronic devices and it is also found that in the boundaries between the ferromagnetic layer and the organic layer there exist induced interface local dipoles due to the external electric fields.

Modeling of Diamond Field-Emitter-Arrays for high brightness photocathode applications

NASA Astrophysics Data System (ADS)

Kwan, Thomas; Huang, Chengkun; Piryatinski, Andrei; Lewellen, John; Nichols, Kimberly; Choi, Bo; Pavlenko, Vitaly; Shchegolkov, Dmitry; Nguyen, Dinh; Andrews, Heather; Simakov, Evgenya

2017-10-01

We propose to employ Diamond Field-Emitter-Arrays (DFEAs) as high-current-density ultra-low-emittance photocathodes for compact laser-driven dielectric accelerators capable of generating ultra-high brightness electron beams for advanced applications. We develop a semi-classical Monte-Carlo photoemission model for DFEAs that includes carriers' transport to the emitter surface and tunneling through the surface under external fields. The model accounts for the electronic structure size quantization affecting the transport and tunneling process within the sharp diamond tips. We compare this first principle model with other field emission models, such as the Child-Langmuir and Murphy-Good models. By further including effects of carrier photoexcitation, we perform simulations of the DFEAs' photoemission quantum yield and the emitted electron beam. Details of the theoretical model and validation against preliminary experimental data will be presented. Work ssupported by LDRD program at LANL.

Highly Efficient Inverted Perovskite Solar Cells with CdSe QDs/LiF Electron Transporting Layer

NASA Astrophysics Data System (ADS)

Tan, Furui; Xu, Weizhe; Hu, Xiaodong; Yu, Ping; Zhang, Weifeng

2017-12-01

Organic/inorganic hybrid perovskite solar cell has emerged as a very promising candidate for the next generation of near-commercial photovoltaic devices. Here in this work, we focus on the inverted perovskite solar cells and have found that remarkable photovoltaic performance could be obtained when using cadmium selenide (CdSe) quantum dots (QDs) as electron transporting layer (ETL) and lithium fluoride (LiF) as the buffer, with respect to the traditionally applied and high-cost [6,6]-phenyl-C61-butyric acid methyl ester (PCBM). The easily processed and low-cost CdSe QDs/LiF double layer could facilitate convenient electron-transfer and collection at the perovskite/cathode interface, promoting an optoelectric conversion efficiency of as high as 15.1%, very close to that with the traditional PCBM ETL. Our work provides another promising choice on the ETL materials for the highly efficient and low-cost perovskite solar cells.

Calcium binding and transport by coenzyme Q.

PubMed

Bogeski, Ivan; Gulaboski, Rubin; Kappl, Reinhard; Mirceski, Valentin; Stefova, Marina; Petreska, Jasmina; Hoth, Markus

2011-06-22

Coenzyme Q10 (CoQ10) is one of the essential components of the mitochondrial electron-transport chain (ETC) with the primary function to transfer electrons along and protons across the inner mitochondrial membrane (IMM). The concomitant proton gradient across the IMM is essential for the process of oxidative phosphorylation and consequently ATP production. Cytochrome P450 (CYP450) monoxygenase enzymes are known to induce structural changes in a variety of compounds and are expressed in the IMM. However, it is unknown if CYP450 interacts with CoQ10 and how such an interaction would affect mitochondrial function. Using voltammetry, UV-vis spectrometry, electron paramagnetic resonance (EPR), nuclear magnetic resonance (NMR), fluorescence microscopy and high performance liquid chromatography-mass spectrometry (HPLC-MS), we show that both CoQ10 and its analogue CoQ1, when exposed to CYP450 or alkaline media, undergo structural changes through a complex reaction pathway and form quinone structures with distinct properties. Hereby, one or both methoxy groups at positions 2 and 3 on the quinone ring are replaced by hydroxyl groups in a time-dependent manner. In comparison with the native forms, the electrochemically reduced forms of the new hydroxylated CoQs have higher antioxidative potential and are also now able to bind and transport Ca(2+) across artificial biomimetic membranes. Our results open new perspectives on the physiological importance of CoQ10 and its analogues, not only as electron and proton transporters, but also as potential regulators of mitochondrial Ca(2+) and redox homeostasis.

49 CFR 220.315 - Operational tests and inspections; further restrictions on use of electronic devices.

Code of Federal Regulations, 2010 CFR

2010-10-01

... restrictions on use of electronic devices. 220.315 Section 220.315 Transportation Other Regulations Relating to Transportation (Continued) FEDERAL RAILROAD ADMINISTRATION, DEPARTMENT OF TRANSPORTATION RAILROAD COMMUNICATIONS Electronic Devices § 220.315 Operational tests and inspections; further restrictions on use of electronic...

Control of Electron Flow Direction in Photoexcited Cycloplatinated Complex Containing Conjugated Polymer-Single Walled Carbon Nanotube Hybrids.

PubMed

Xiong, Wenjuan; Du, Lili; Lo, Kin Cheung; Shi, Haiting; Takaya, Tomohisa; Iwata, Koichi; Chan, Wai Kin; Phillips, David Lee

2018-06-25

Conjugated polymers incorporated with cycloplatinated complexes (P1-Pt and P2-Pt) were used as dispersants for single walled carbon nanotubes (SWCNTs). Significant changes in the UV-vis absorption spectra were observed after the formation of the polymer/SWCNT hybrids. Molecular dynamics (MD) simulations revealed the presence of a strong interaction between the cycloplatinated complex moieties and the SWCNT surface. The photoinduced electron transfer processes in these hybrids were strongly dependent on the type of the comonomer unit. Upon photoexcitation, the excited P1-Pt donates electrons to the SWCNT, while P2-Pt accepts electrons from the photoexcited SWCNT. These observations were supported by results from Raman and femtosecond time-resolved transient absorption spectroscopy experiments. The strong electronic interaction between the Pt complexes and the SWCNT gives rise to a new hybrid system that has a controllable photo-induced electron transfer flow, which are important in regulating the charge transport processes SWCNT-based optoelectronic devices.

Single-Nanoparticle Photoelectrochemistry at a Nanoparticulate TiO2 -Filmed Ultramicroelectrode.

PubMed

Peng, Yue-Yi; Ma, Hui; Ma, Wei; Long, Yi-Tao; Tian, He

2018-03-26

An ultrasensitive photoelectrochemical method for achieving real-time detection of single nanoparticle collision events is presented. Using a micrometer-thick nanoparticulate TiO 2 -filmed Au ultra-microelectrode (TiO 2 @Au UME), a sub-millisecond photocurrent transient was observed for an individual N719-tagged TiO 2 (N719@TiO 2 ) nanoparticle and is due to the instantaneous collision process. Owing to a trap-limited electron diffusion process as the rate-limiting step, a random three-dimensional diffusion model was developed to simulate electron transport dynamics in TiO 2 film. The combination of theoretical simulation and high-resolution photocurrent measurement allow electron-transfer information of a single N719@TiO 2 nanoparticle to be quantified at single-molecule accuracy and the electron diffusivity and the electron-collection efficiency of TiO 2 @Au UME to be estimated. This method provides a test for studies of photoinduced electron transfer at the single-nanoparticle level. © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Electron transport in biomolecular gaseous and liquid systems: theory, experiment and self-consistent cross-sections

NASA Astrophysics Data System (ADS)

White, R. D.; Cocks, D.; Boyle, G.; Casey, M.; Garland, N.; Konovalov, D.; Philippa, B.; Stokes, P.; de Urquijo, J.; González-Magaña, O.; McEachran, R. P.; Buckman, S. J.; Brunger, M. J.; Garcia, G.; Dujko, S.; Petrovic, Z. Lj

2018-05-01

Accurate modelling of electron transport in plasmas, plasma-liquid and plasma-tissue interactions requires (i) the existence of accurate and complete sets of cross-sections, and (ii) an accurate treatment of electron transport in these gaseous and soft-condensed phases. In this study we present progress towards the provision of self-consistent electron-biomolecule cross-section sets representative of tissue, including water and THF, by comparison of calculated transport coefficients with those measured using a pulsed-Townsend swarm experiment. Water–argon mixtures are used to assess the self-consistency of the electron-water vapour cross-section set proposed in de Urquijo et al (2014 J. Chem. Phys. 141 014308). Modelling of electron transport in liquids and soft-condensed matter is considered through appropriate generalisations of Boltzmann’s equation to account for spatial-temporal correlations and screening of the electron potential. The ab initio formalism is applied to electron transport in atomic liquids and compared with available experimental swarm data for these noble liquids. Issues on the applicability of the ab initio formalism for krypton are discussed and addressed through consideration of the background energy of the electron in liquid krypton. The presence of self-trapping (into bubble/cluster states/solvation) in some liquids requires a reformulation of the governing Boltzmann equation to account for the combined localised–delocalised nature of the resulting electron transport. A generalised Boltzmann equation is presented which is highlighted to produce dispersive transport observed in some liquid systems.

F"orster-type mechanism of the redox-driven proton pump

NASA Astrophysics Data System (ADS)

Mourokh, Lev; Smirnov, Anatoly; Nori, Franco

2007-03-01

We propose a model to describe an electronically-driven proton pump in the cytochrome c oxidase (CcO). We examine the situation when the electron transport between the two sites embedded into the inner membrane of the mitochondrion occurs in parallel with the proton transfer from the protonable site that is close to the negative (inner) side of the membrane to the other protonable site located nearby the positive (outer) surface of the membrane. In addition to the conventional electron and proton tunnelings between the sites, the Coulomb interaction between electrons and protons localized on the corresponding sites leads to so-called F"orster transfer, i.e. to the process when the simultaneous electron and proton tunnelings are accompanied by the resonant energy transfer between the electrons and protons. Our calculations based on reasonable parameters have demonstrated that the F"orster process facilitates the proton pump at physiological temperatures. We have examined the effects of an electron voltage build-up, external temperature, and molecular electrostatics driving the electron and proton energies to the resonant conditions, and have shown that these parameters can control the proton pump operation.

COMBINED MODELING OF ACCELERATION, TRANSPORT, AND HYDRODYNAMIC RESPONSE IN SOLAR FLARES. I. THE NUMERICAL MODEL

DOE Office of Scientific and Technical Information (OSTI.GOV)

Liu Wei; Petrosian, Vahe; Mariska, John T.

2009-09-10

Acceleration and transport of high-energy particles and fluid dynamics of atmospheric plasma are interrelated aspects of solar flares, but for convenience and simplicity they were artificially separated in the past. We present here self-consistently combined Fokker-Planck modeling of particles and hydrodynamic simulation of flare plasma. Energetic electrons are modeled with the Stanford unified code of acceleration, transport, and radiation, while plasma is modeled with the Naval Research Laboratory flux tube code. We calculated the collisional heating rate directly from the particle transport code, which is more accurate than those in previous studies based on approximate analytical solutions. We repeated themore » simulation of Mariska et al. with an injection of power law, downward-beamed electrons using the new heating rate. For this case, a {approx}10% difference was found from their old result. We also used a more realistic spectrum of injected electrons provided by the stochastic acceleration model, which has a smooth transition from a quasi-thermal background at low energies to a nonthermal tail at high energies. The inclusion of low-energy electrons results in relatively more heating in the corona (versus chromosphere) and thus a larger downward heat conduction flux. The interplay of electron heating, conduction, and radiative loss leads to stronger chromospheric evaporation than obtained in previous studies, which had a deficit in low-energy electrons due to an arbitrarily assumed low-energy cutoff. The energy and spatial distributions of energetic electrons and bremsstrahlung photons bear signatures of the changing density distribution caused by chromospheric evaporation. In particular, the density jump at the evaporation front gives rise to enhanced emission, which, in principle, can be imaged by X-ray telescopes. This model can be applied to investigate a variety of high-energy processes in solar, space, and astrophysical plasmas.« less

Attosecond Electron Processes in Materials: Excitons, Plasmons, and Charge Dynamics

DTIC Science & Technology

2015-05-19

focused using a f=1.5 m lens into a 250 micron hollow core fiber (HCF) filled with neon gas at atmospheric pressure to stretch the pulse spectrum from... insulator to metal transition. Introduction: The goal of this work was to understand the generation, transport, and manipulation of electronic charge...chemically sensitive probe pulse utilizing specific core level transitions in atoms that are part of a material under study. The measurements follow

An investigation of anaerobic methane oxidation by consortia of methanotrophic archaea and bacterial partners using nanoSIMS and process-based modeling

NASA Astrophysics Data System (ADS)

Shi, Y.; Kempes, C.; Chadwick, G.; McGlynn, S.; He, X.; Orphan, V. J.; Meile, C. D.

2016-02-01

The anaerobic oxidation of methane in marine sediments plays an important role in the global methane cycle. Mediated by a microbial consortium consisting of archaea and bacteria, it is estimated that almost 80% of all the methane that arises from marine sediments is oxidized anaerobically by this process (Reeburgh 2007, Chemical Reviews 107, 486-513). We used reactive transport modeling to compare and contrast potential mechanisms of methane oxidation. This included acetate, hydrogen, formate, and disulfide acting as intermediates that are exchanged between archaea and bacteria. Moreover, we investigated electron transport through nanowires, facilitating the electron exchange between the microbial partners. It was shown that reaction kinetics, transport intensities, and energetic considerations all could decisively impact the overall rate of methane consumption. Informed by observed microbial cell distribution, we applied the model to a range of spatial distribution patterns of archaea and bacteria. We found that a consortium with evenly distributed archaeal and bacterial cells has the potential to more efficiently oxidize methane, because the vicinity of bacteria and archaea counteracts the build up of products and therefore prevents the thermodynamic shutdown of microbial metabolism. Single cell stable isotope enrichment in archaeal-bacterial consortia observed by nanoSIMS revealed rather uniform levels of anabolic activity within consortia with different spatial distribution patterns. Comparison to model simulation illustrates that efficient exchange is necessary to reproduce such observations and prevent conditions that are energetically unfavorable for methane oxidation to take place. Model simulations indicate that a recently described mechanism of direct interspecies electron transport between the methanotrophic archaea and its bacterial partner through a conductive matrix (McGlynn et al. 2015, Nature, 10.1038/nature15512) is consistent with observations.

41 CFR 102-118.80 - Who is responsible for keeping my agency's electronic commerce transportation billing records?

Code of Federal Regulations, 2014 CFR

2014-01-01

... electronic transportation billing documents to: General Services Administration Transportation Audit Division... 41 Public Contracts and Property Management 3 2014-01-01 2014-01-01 false Who is responsible for keeping my agency's electronic commerce transportation billing records? 102-118.80 Section 102-118.80...

41 CFR 102-118.80 - Who is responsible for keeping my agency's electronic commerce transportation billing records?

Code of Federal Regulations, 2012 CFR

2012-01-01

... electronic transportation billing documents to: General Services Administration Transportation Audit Division... 41 Public Contracts and Property Management 3 2012-01-01 2012-01-01 false Who is responsible for keeping my agency's electronic commerce transportation billing records? 102-118.80 Section 102-118.80...

41 CFR 102-118.80 - Who is responsible for keeping my agency's electronic commerce transportation billing records?

Code of Federal Regulations, 2010 CFR

2010-07-01

... electronic transportation billing documents to: General Services Administration Transportation Audit Division... 41 Public Contracts and Property Management 3 2010-07-01 2010-07-01 false Who is responsible for keeping my agency's electronic commerce transportation billing records? 102-118.80 Section 102-118.80...

41 CFR 102-118.80 - Who is responsible for keeping my agency's electronic commerce transportation billing records?

Code of Federal Regulations, 2013 CFR

2013-07-01

... electronic transportation billing documents to: General Services Administration Transportation Audit Division... 41 Public Contracts and Property Management 3 2013-07-01 2013-07-01 false Who is responsible for keeping my agency's electronic commerce transportation billing records? 102-118.80 Section 102-118.80...

41 CFR 102-118.80 - Who is responsible for keeping my agency's electronic commerce transportation billing records?

Code of Federal Regulations, 2011 CFR

2011-01-01

... electronic transportation billing documents to: General Services Administration Transportation Audit Division... 41 Public Contracts and Property Management 3 2011-01-01 2011-01-01 false Who is responsible for keeping my agency's electronic commerce transportation billing records? 102-118.80 Section 102-118.80...

Structural Ordering of Semiconducting Polymers and Small-Molecules for Organic Electronics

NASA Astrophysics Data System (ADS)

O'Hara, Kathryn Allison

Semiconducting polymers and small-molecules can be readily incorporated into electronic devices such as organic photovoltaics (OPVs), thermoelectrics (OTEs), organic light emitting diodes (OLEDs), and organic thin film transistors (OTFTs). Organic materials offer the advantage of being processable from solution to form flexible and lightweight thin films. The molecular design, processing, and resulting thin film morphology of semiconducting polymers drastically affect the optical and electronic properties. Charge transport within films of semiconducting polymers relies on the nanoscale organization to ensure electronic coupling through overlap of molecular orbitals and to provide continuous transport pathways. While the angstrom-scale packing details can be studied using X-ray scattering methods, an understanding of the mesoscale, or the length scale over which smaller ordered regions connect, is much harder to achieve. Grain boundaries play an important role in semiconducting polymer thin films where the average grain size is much smaller than the total distance which charges must traverse in order to reach the electrodes in a device. The majority of semiconducting polymers adopt a lamellar packing structure in which the conjugated backbones align in parallel pi-stacks separated by the alkyl side-chains. Only two directions of transport are possible--along the conjugated backbone and in the pi-stacking direction. Currently, the discussion of transport between crystallites is centered around the idea of tie-chains, or "bridging" polymer chains connecting two ordered regions. However, as molecular structures become increasingly complex with the development of new donor-acceptor copolymers, additional forms of connectivity between ordered domains should be considered. High resolution transmission electron microscopy (HRTEM) is a powerful tool for directly imaging the crystalline grain boundaries in polymer and small-molecule thin films. Recently, structures comparable to quadrites were discovered in the semiconducting polymer, PSBTBT, where the angle of chain overlap could be predicted by the geometry of the backbone and alkyl side-chains. Such structures are hypothesized to improve the electronic connectivity and enable 3D transport. Now, it has been determined that another semiconducting polymer, PBDTTPD, forms cross-chain structures in thin films. PBDTTPD is a low band-gap donor-acceptor copolymer used in high efficiency OPVs. The effect of the alkyl side-chains on intercrystallite order is determined by examining three different derivatives of the PBDTTPD polymer with HRTEM. Additionally, the expansion and contraction of films during thermal annealing and slow cooling is monitored through in-situ grazing incidence wide-angle X-ray scattering (GIWAXS) measurements. Results show that minor variations in side-chain structure drive both crystallite orientation and the formation of crossed structures. Overall, these studies suggest design principles to continue to advance the field of organic electronics.

Absence of ballistic charge transport in the half-filled 1D Hubbard model

NASA Astrophysics Data System (ADS)

Carmelo, J. M. P.; Nemati, S.; Prosen, T.

2018-05-01

Whether in the thermodynamic limit of lattice length L → ∞, hole concentration mηz = - 2 Sηz/L = 1 -ne → 0, nonzero temperature T > 0, and U / t > 0 the charge stiffness of the 1D Hubbard model with first neighbor transfer integral t and on-site repulsion U is finite or vanishes and thus whether there is or there is no ballistic charge transport, respectively, remains an unsolved and controversial issue, as different approaches yield contradictory results. (Here Sηz = - (L -Ne) / 2 is the η-spin projection and ne =Ne / L the electronic density.) In this paper we provide an upper bound on the charge stiffness and show that (similarly as at zero temperature), for T > 0 and U / t > 0 it vanishes for mηz → 0 within the canonical ensemble in the thermodynamic limit L → ∞. Moreover, we show that at high temperature T → ∞ the charge stiffness vanishes as well within the grand-canonical ensemble for L → ∞ and chemical potential μ →μu where (μ -μu) ≥ 0 and 2μu is the Mott-Hubbard gap. The lack of charge ballistic transport indicates that charge transport at finite temperatures is dominated by a diffusive contribution. Our scheme uses a suitable exact representation of the electrons in terms of rotated electrons for which the numbers of singly occupied and doubly occupied lattice sites are good quantum numbers for U / t > 0. In contrast to often less controllable numerical studies, the use of such a representation reveals the carriers that couple to the charge probes and provides useful physical information on the microscopic processes behind the exotic charge transport properties of the 1D electronic correlated system under study.

Photoacoustic monitoring of water transport process in calcareous stone coated with biopolymers

NASA Astrophysics Data System (ADS)

May-Crespo, J.; Ortega-Morales, B. O.; Camacho-Chab, J. C.; Quintana, P.; Alvarado-Gil, J. J.; Gonzalez-García, G.; Reyes-Estebanez, M.; Chan-Bacab, M. J.

2016-12-01

Moisture is a critical control of chemical and physical processes leading to stone deterioration. These processes can be enhanced by microbial biofilms and associated exopolymers (EPS). There is limited current understanding of the water transport process across rocks covered by EPS. In the present work, we employed the photoacoustic technique to study the influence of three biopolymers (xanthan, microbactan and arabic gum) in the water transport process of two types of limestone rock of similar mineralogy but contrasting porosity. Both controls of RL (low porosity) and RP (high porosity) presented the higher values of water diffusion coefficient ( D) than biopolymer-coated samples, indicating that biopolymer layers slowed down the transport of water. This trend was steeper for RP samples as water was transported seven times faster than in the more porous rock. Important differences of D values were observed among samples coated by different biopolymers. Scanning electron microscopy and optical microscopy showed that surface topography was different between both types of rocks; adherence of coatings was seen predominantly in the less porous rocks samples. FTIR and NMR analysis showed the presence of pyruvate and acetate in microbactan and xanthan gum, suggesting their participation on adherence to the calcareous surfaces, sealing surface pores. These results indicate that water transport at rock interfaces is dependent on the chemistry of biopolymer and surface porosity. The implications for reduced water transport in stone conservation under the influence of biopolymers include both enhanced and lower deterioration rates along with altered efficiency of biocide treatment of epilithic biofilms.

Frequency quenching of microwave-induced resistance oscillations in a high-mobility two-dimensional electron gas

NASA Astrophysics Data System (ADS)

Studenikin, S. A.; Sachrajda, A. S.; Gupta, J. A.; Wasilewski, Z. R.; Fedorych, O. M.; Byszewski, M.; Maude, D. K.; Potemski, M.; Hilke, M.; West, K. W.; Pfeiffer, L. N.

2007-10-01

The frequency dependence of microwave-induced resistance oscillations (MIROs) has been studied experimentally in high-mobility electron GaAs/AlGaAs structures to explore the limits at which these oscillations can be observed. It is found that in dc transport experiments at frequencies above 120GHz , MIROs start to quench, while above 230GHz , they completely disappear. The results will need to be understood theoretically but are qualitatively discussed within a model in which forced electronic charge oscillations (plasmons) play an intermediate role in the interaction process between the radiation and the single-particle electron excitations between Landau levels.

Computation of electron transport and relaxation properties in gases based on improved multi-term approximation of Boltzmann equation

NASA Astrophysics Data System (ADS)

Cai, X. J.; Wang, X. X.; Zou, X. B.; Lu, Z. W.

2018-01-01

An understanding of electron kinetics is of importance in various applications of low temperature plasmas. We employ a series of model and real gases to investigate electron transport and relaxation properties based on improved multi-term approximation of the Boltzmann equation. First, a comparison of different methods to calculate the interaction integrals has been carried out; the effects of free parameters, such as vmax, lmax, and the arbitrary temperature Tb, on the convergence of electron transport coefficients are analyzed. Then, the modified attachment model of Ness et al. and SF6 are considered to investigate the effect of attachment on the electron transport properties. The deficiency of the pulsed Townsend technique to measure the electron transport and reaction coefficients in electronegative gases is highlighted when the reduced electric field is small. In order to investigate the effect of external magnetic field on the electron transport properties, Ar plasmas in high power impulse sputtering devices are considered. In the end, the electron relaxation properties of the Reid model under the influence of electric and magnetic fields are demonstrated.

Towards lightweight and flexible high performance nanocrystalline silicon solar cells through light trapping and transport layers

NASA Astrophysics Data System (ADS)

Gray, Zachary R.

This thesis investigates ways to enhance the efficiency of thin film solar cells through the application of both novel nano-element array light trapping architectures and nickel oxide hole transport/electron blocking layers. Experimental results independently demonstrate a 22% enhancement in short circuit current density (JSC) resulting from a nano-element array light trapping architecture and a ˜23% enhancement in fill factor (FF) and ˜16% enhancement in open circuit voltage (VOC) resulting from a nickel oxide transport layer. In each case, the overall efficiency of the device employing the light trapping or transport layer was superior to that of the corresponding control device. Since the efficiency of a solar cell scales with the product of JSC, FF, and VOC, it follows that the results of this thesis suggest high performance thin film solar cells can be realized in the event light trapping architectures and transport layers can be simultaneously optimized. The realizations of these performance enhancements stem from extensive process optimization for numerous light trapping and transport layer fabrication approaches. These approaches were guided by numerical modeling techniques which will also be discussed. Key developments in this thesis include (1) the fabrication of nano-element topographies conducive to light trapping using various fabrication approaches, (2) the deposition of defect free nc-Si:H onto structured topographies by switching from SiH4 to SiF 4 PECVD gas chemistry, and (3) the development of the atomic layer deposition (ALD) growth conditions for NiO. Keywords: light trapping, nano-element array, hole transport layer, electron blocking layer, nickel oxide, nanocrystalline silicon, aluminum doped zinc oxide, atomic layer deposition, plasma enhanced chemical vapor deposition, electron beam lithography, ANSYS HFSS.

Homoepitaxial graphene tunnel barriers for spin transport

NASA Astrophysics Data System (ADS)

Friedman, Adam

Tunnel barriers are key elements for both charge-and spin-based electronics, offering devices with reduced power consumption and new paradigms for information processing. Such devices require mating dissimilar materials, raising issues of heteroepitaxy, interface stability, and electronic states that severely complicate fabrication and compromise performance. Graphene is the perfect tunnel barrier. It is an insulator out-of-plane, possesses a defect-free, linear habit, and is impervious to interdiffusion. Nonetheless, true tunneling between two stacked graphene layers is not possible in environmental conditions (magnetic field, temperature, etc.) usable for electronics applications. However, two stacked graphene layers can be decoupled using chemical functionalization. We demonstrate successful tunneling, charge, and spin transport with a fluorinated graphene tunnel barrier on a graphene channel. We show that while spin transport stops short of room temperature, spin polarization efficiency values are the highest of any graphene spin devices. We also demonstrate that hydrogenation of graphene can also be used to create a tunnel barrier. We begin with a four-layer stack of graphene and hydrogenate the top few layers to decouple them from the graphene transport channel beneath. We demonstrate successful tunneling by measuring non-linear IV curves and a weakly temperature dependent zero-bias resistance. We demonstrate lateral transport of spin currents in non-local spin-valve structures and determine spin lifetimes with the non-local Hanle effect to be commensurate with previous studies. The measured spin polarization efficiencies for hydrogenated graphene are higher than most oxide tunnel barriers on graphene, but not as high as with fluorinated graphene tunnel barriers. However, here we show that spin transport persists up to room temperature. Our results for the hydrogenated graphene tunnel barriers are compared with fluorinated tunnel barriers and we discuss the possibility that magnetic moments in the graphene tunnel barriers affect the spin transport of our devices.

Towards predictive many-body calculations of phonon-limited carrier mobilities in semiconductors

NASA Astrophysics Data System (ADS)

Poncé, Samuel; Margine, Elena R.; Giustino, Feliciano

2018-03-01

We probe the accuracy limit of ab initio calculations of carrier mobilities in semiconductors, within the framework of the Boltzmann transport equation. By focusing on the paradigmatic case of silicon, we show that fully predictive calculations of electron and hole mobilities require many-body quasiparticle corrections to band structures and electron-phonon matrix elements, the inclusion of spin-orbit coupling, and an extremely fine sampling of inelastic scattering processes in momentum space. By considering all these factors we obtain excellent agreement with experiment, and we identify the band effective masses as the most critical parameters to achieve predictive accuracy. Our findings set a blueprint for future calculations of carrier mobilities, and pave the way to engineering transport properties in semiconductors by design.

Diffraction effects and inelastic electron transport in angle-resolved microscopic imaging applications.

PubMed

Winkelmann, A; Nolze, G; Vespucci, S; Naresh-Kumar, G; Trager-Cowan, C; Vilalta-Clemente, A; Wilkinson, A J; Vos, M

2017-09-01

We analyse the signal formation process for scanning electron microscopic imaging applications on crystalline specimens. In accordance with previous investigations, we find nontrivial effects of incident beam diffraction on the backscattered electron distribution in energy and momentum. Specifically, incident beam diffraction causes angular changes of the backscattered electron distribution which we identify as the dominant mechanism underlying pseudocolour orientation imaging using multiple, angle-resolving detectors. Consequently, diffraction effects of the incident beam and their impact on the subsequent coherent and incoherent electron transport need to be taken into account for an in-depth theoretical modelling of the energy- and momentum distribution of electrons backscattered from crystalline sample regions. Our findings have implications for the level of theoretical detail that can be necessary for the interpretation of complex imaging modalities such as electron channelling contrast imaging (ECCI) of defects in crystals. If the solid angle of detection is limited to specific regions of the backscattered electron momentum distribution, the image contrast that is observed in ECCI and similar applications can be strongly affected by incident beam diffraction and topographic effects from the sample surface. As an application, we demonstrate characteristic changes in the resulting images if different properties of the backscattered electron distribution are used for the analysis of a GaN thin film sample containing dislocations. © 2017 The Authors. Journal of Microscopy published by JohnWiley & Sons Ltd on behalf of Royal Microscopical Society.

Electron and proton transfer in chloroplasts in silico. 2: The effect of diffusion limitations on the process of photosynthesis in spatially inhomogeneous thylakoids

NASA Astrophysics Data System (ADS)

Vershubskii, A. V.; Tikhonov, A. N.

2017-07-01

The lateral mobility of protons and mobile electron carriers (plastoquinone and plastocyanin) is subjected to diffusion limitations; the effect of these limitations on the kinetics of photoinduced pH i changes has been investigated in the present work for metabolic states 3 (conditions of intensive ATP synthesis) and 4 (the state of photosynthetic control). Computer simulations were based on a mathematical model of electron and proton transport in chloroplasts developed earlier by the authors. Non-uniform distribution of electron carriers and ATP synthase complexes in the membranes of grana and intergranal thylakoids was taken into account in the model. The kinetics of intrathylakoid pH i changes and the lateral profiles of distribution of the mobile electron transporters in granal and intergranal thylakoids were studied. The formation of non-uniform pH i profiles (with lumen acidification in the central parts of the grana being substantially slower than in the stromal thylakoids) was shown to occur under the conditions of ATP synthesis. Variation of the diffusion coefficients of intrathylakoid hydrogen ions and mobile electron carriers (plastoquinone and plastocyanin) can have substantial effects on the lateral pH i profiles and the redox state of the mobile electron carriers.

Exploding Pusher Targets for Electron-Ion Coupling Measurements

NASA Astrophysics Data System (ADS)

Whitley, Heather D.; Pino, Jesse; Schneider, Marilyn; Shepherd, Ronnie; Benedict, Lorin; Bauer, Joseph; Graziani, Frank; Garbett, Warren

2015-11-01

Over the past several years, we have conducted theoretical investigations of electron-ion coupling and electronic transport in plasmas. In the regime of weakly coupled plasmas, we have identified models that we believe describe the physics well, but experimental data is still needed to validate the models. We are currently designing spectroscopic experiments to study electron-ion equilibration and/or electron heat transport using exploding pusher (XP) targets for experiments at the National Ignition Facility. Two platforms are being investigated: an indirect drive XP (IDXP) with a plastic ablator and a polar-direct drive XP (PDXP) with a glass ablator. The fill gas for both designs is D2. We propose to use a higher-Z dopant, such as Ar, as a spectroscopic tracer for time-resolved electron and ion temperature measurements. We perform 1D simulations using the ARES hydrodynamic code, in order to produce the time-resolved plasma conditions, which are then post-processed with CRETIN to assess the feasibility of a spectroscopic measurement. We examine target performance with respect to variations in gas fill pressure, ablator thickness, atom fraction of the Ar dopant, and drive energy, and assess the sensitivity of the predicted spectra to variations in the models for electron-ion equilibration and thermal conductivity. Prepared by LLNL under Contract DE-AC52-07NA27344. LLNL-ABS-675219.

Design and initial testing of a piezoelectric sensor to quantify aeolian sand transport

NASA Astrophysics Data System (ADS)

Raygosa-Barahona, Ruben; Ruiz-Martinez, Gabriel; Mariño-Tapia, Ismael; Heyser-Ojeda, Emilio

2016-09-01

This paper describes a sensor for measuring the mass flux of aeolian sand transport based on a low-cost piezo-electric transducer. The device is able to measure time series of aeolian sand transport. Maximum fluxes of 27 mg per second can be achieved. The design includes a sand trap, an electronic amplifier circuit and an embedded system for data collection. A field test was performed, where the basis for signal interpretation and the corresponding measurements of aeolian sand transport are presented. The sensor successfully measures fluxes driven by sea breezes of 10 ms-1, showing the importance of this process for dune-building in the region.

Tuning the conductivity along atomic chains by selective chemisorption

NASA Astrophysics Data System (ADS)

Edler, F.; Miccoli, I.; Stöckmann, J. P.; Pfnür, H.; Braun, C.; Neufeld, S.; Sanna, S.; Schmidt, W. G.; Tegenkamp, C.

2017-03-01

Adsorption of Au on vicinal Si(111) surfaces results in growth of long-range ordered metallic quantum wires. In this paper, we utilized site-specific and selective adsorption of oxygen to modify chemically the transport via different channels in the systems Si(553)-Au and Si(557)-Au. They were analyzed by electron diffraction and four-tip STM-based transport experiments. Modeling of the adsorption process by density functional theory shows that the adatoms and rest atoms on Si(557)-Au provide energetically favored adsorption sites, which predominantly alter the transport along the wire direction. Since this structural motif is missing on Si(553)-Au, the transport channels remain almost unaffected by oxidation.

Microscopical and functional aspects of calcium-transport and deposition in terrestrial isopods.

PubMed

Ziegler, Andreas; Fabritius, Helge; Hagedorn, Monica

2005-01-01

Terrestrial isopods (Crustacea) are excellent model organisms to study epithelial calcium-transport and the regulation of biomineralization processes. They molt frequently and resorb cuticular CaCO(3) before the molt to prevent excessive loss of Ca(2+) ions when the old cuticle is shed. The resorbed mineral is stored in CaCO(3) deposits within the ecdysial gap of the first four anterior sternites. After the molt, the deposits are quickly resorbed to mineralise the posterior part of the new cuticle. The deposits contain numerous small spherules composed of an organic matrix and amorphous CaCO(3), which has a high solubility and, therefore, facilitates quick mobilization of Ca(2+) and HCO(3)(-) ions. During the formation and resorption of the deposits large amounts of Ca(2+), HCO(3)(-) and H(+) are transported across the anterior sternal epithelial cells. Within the last years, various light and electron microscopical techniques have been used to characterize the CaCO(3) deposits and the cellular mechanisms involved in biomineralization. The work on the CaCO(3) deposits includes studies on the ultrastructure of the deposits, the sequence of events during deposit formation and dissolution, and the mineral composition of the sternal deposits. The differentiation of the anterior sternal epithelial cells and the mechanisms of epithelial ion transport required for the mineralization and demineralisation of the deposits was studied using various analytical light and electron microscopical techniques including polarized light microscopy, immunocytochemistry, electron microprobe analysis, electron energy loss spectroscopy and electron spectroscopic imaging. Comparative analysis of deposit morphology and the differentiation of the sternal epithelia provide information on the evolution of CaCO(3) deposit formation in relation to the degree of adaptation to terrestrial environments.

Identification of Early Nuclear Target Genes of Plastidial Redox Signals that Trigger the Long-Term Response of Arabidopsis to Light Quality Shifts.

PubMed

Dietzel, Lars; Gläßer, Christine; Liebers, Monique; Hiekel, Stefan; Courtois, Florence; Czarnecki, Olaf; Schlicke, Hagen; Zubo, Yan; Börner, Thomas; Mayer, Klaus; Grimm, Bernhard; Pfannschmidt, Thomas

2015-08-01

Natural illumination conditions are highly variable and because of their sessile life style, plants are forced to acclimate to them at the cellular and molecular level. Changes in light intensity or quality induce changes in the reduction/oxidation (redox) state of the photosynthetic electron chain that acts as a trigger for compensatory acclimation responses comprising functional and structural adjustments of photosynthesis and metabolism. Such responses include redox-controlled changes in plant gene expression in the nucleus and organelles. Here we describe a strategy for the identification of early redox-regulated genes (ERGs) in the nucleus of the model organism Arabidopsis thaliana that respond significantly 30 or 60 min after the generation of a reduction signal in the photosynthetic electron transport chain. By comparing the response of wild-type plants with that of the acclimation mutant stn7, we could specifically identify ERGs. The results reveal a significant impact of chloroplast redox signals on distinct nuclear gene groups including genes for the mitochondrial electron transport chain, tetrapyrrole biosynthesis, carbohydrate metabolism, and signaling lipid synthesis. These expression profiles are clearly different from those observed in response to the reduction of photosynthetic electron transport by high light treatments. Thus, the ERGs identified are unique to redox imbalances in photosynthetic electron transport and were then used for analyzing potential redox-responsive cis-elements, trans-factors, and chromosomal regulatory hot spots. The data identify a novel redox-responsive element and indicate extensive redox control at transcriptional and chromosomal levels that point to an unprecedented impact of redox signals on epigenetic processes. Copyright © 2015 The Author. Published by Elsevier Inc. All rights reserved.

Unified computational model of transport in metal-insulating oxide-metal systems

NASA Astrophysics Data System (ADS)

Tierney, B. D.; Hjalmarson, H. P.; Jacobs-Gedrim, R. B.; Agarwal, Sapan; James, C. D.; Marinella, M. J.

2018-04-01

A unified physics-based model of electron transport in metal-insulator-metal (MIM) systems is presented. In this model, transport through metal-oxide interfaces occurs by electron tunneling between the metal electrodes and oxide defect states. Transport in the oxide bulk is dominated by hopping, modeled as a series of tunneling events that alter the electron occupancy of defect states. Electron transport in the oxide conduction band is treated by the drift-diffusion formalism and defect chemistry reactions link all the various transport mechanisms. It is shown that the current-limiting effect of the interface band offsets is a function of the defect vacancy concentration. These results provide insight into the underlying physical mechanisms of leakage currents in oxide-based capacitors and steady-state electron transport in resistive random access memory (ReRAM) MIM devices. Finally, an explanation of ReRAM bipolar switching behavior based on these results is proposed.

49 CFR 234.315 - Electronic recordkeeping.

Code of Federal Regulations, 2012 CFR

2012-10-01

... 49 Transportation 4 2012-10-01 2012-10-01 false Electronic recordkeeping. 234.315 Section 234.315 Transportation Other Regulations Relating to Transportation (Continued) FEDERAL RAILROAD ADMINISTRATION... railroad adequately limits and controls accessibility to the records retained in its electronic database...

49 CFR 234.315 - Electronic recordkeeping.

Code of Federal Regulations, 2014 CFR

2014-10-01

... 49 Transportation 4 2014-10-01 2014-10-01 false Electronic recordkeeping. 234.315 Section 234.315 Transportation Other Regulations Relating to Transportation (Continued) FEDERAL RAILROAD ADMINISTRATION... railroad adequately limits and controls accessibility to the records retained in its electronic database...

49 CFR 234.315 - Electronic recordkeeping.

Code of Federal Regulations, 2013 CFR

2013-10-01

... 49 Transportation 4 2013-10-01 2013-10-01 false Electronic recordkeeping. 234.315 Section 234.315 Transportation Other Regulations Relating to Transportation (Continued) FEDERAL RAILROAD ADMINISTRATION... railroad adequately limits and controls accessibility to the records retained in its electronic database...

Quaternary Cu2ZnSnS4 quantum dot-sensitized solar cells: Synthesis, passivation and ligand exchange

NASA Astrophysics Data System (ADS)

Bai, Bing; Kou, Dongxing; Zhou, Wenhui; Zhou, Zhengji; Tian, Qingwen; Meng, Yuena; Wu, Sixin

2016-06-01

The quaternary Cu2ZnSnS4 (CZTS) QDs had been successfully introduced into quantum dot-sensitized solar cells (QDSC) via hydrolysis approach in our previous work [Green Chem. 2015, vol. 17, p. 4377], but the obtained cell efficiency was still limited by low open-circuit voltage and fill factor. Herein, we use 1-dodecanethiol (DDT) as capping ligand for fairly small-sized CZTS QDs synthesis to improve their intrinsic properties. Since this strong bonded capping ligand can not be replaced by 3-mercaptopropionic acid (MPA) directly, the nature cation (Cu, Zn or Sn)-DDT units of QDs are first exchanged by the preconjugated Cd-oleate via successive ionic layer adsorption and reaction (SILAR) procedure accompanied with the formation of a core/shell structure. The weak bonded oleic acid (OA) can be finally replaced by MPA and the constructed water soluble CZTS/CdSe QDSC achieves an impressive conversion efficiency of 4.70%. The electron transport and recombination dynamic processes are confirmed by intensity-modulated photocurrent spectroscopy (IMPS)/intensity-modulated photovoltage spectroscopy (IMVS) measurements. It is found that the removal of long alkyl chain is conducive to improve the electron transport process and the type-II core/shell structure is beneficial to accelerate electron transport and retard charge recombination. This effective ligand removal strategy is proved to be more convenient for the applying of quaternary QDs in QDSC and would boost a more powerful efficiency in the future work.

Insights into ionic transport and structural changes in magnetite during multiple-electron transfer reactions

DOE PAGES

Zhang, Wei; Bock, David C.; Pelliccione, Christopher J.; ...

2016-03-08

Metal oxides, such as Fe 3O 4, hold promise for future battery applications due to their abundance, low cost, and opportunity for high lithium storage capacity. In order to better understand the mechanisms of multiple-electron transfer reactions leading to high capacity in Fe 3O 4, a comprehensive investigation on local ionic transport and ordering is made by probing site occupancies of anions (O 2–) and cations (Li +, Fe 3+/Fe 2+) using multiple synchrotron X-ray and electron-beam techniques, in combination with ab-initio calculations. Results from this study provide the first experimental evidence that the cubic-close-packed (ccp) O-anion array in Femore » 3O 4 is sustained throughout the lithiation and delithiation processes, thereby enabling multiple lithium intercalation and conversion reactions. Cation displacement/reordering occurs within the ccp O-anion framework, which leads to a series of phase transformations, starting from the inverse spinel phase and turning into intermediate rock-salt-like phases (Li xFe 3O 4; 0 < x < 2), then into a cation-segregated phase (Li 2O•FeO), and finally converting into metallic Fe and Li 2O. Subsequent delithiation and lithiation processes involve interconversion between metallic Fe and FeO-like phases. Lastly, these results may offer new insights into the structure-determined ionic transport and electrochemical reactions in metal oxides, and those of other compounds sharing a ccp anion framework, reminiscent of magnetite.« less

Numerical study of plasma generation process and internal antenna heat loadings in J-PARC RF negative ion source

DOE Office of Scientific and Technical Information (OSTI.GOV)

Shibata, T., E-mail: shibat@post.j-parc.jp; Ueno, A.; Oguri, H.

A numerical model of plasma transport and electromagnetic field in the J-PARC (Japan Proton Accelerator Research Complex) radio frequency ion source has been developed to understand the relation between antenna coil heat loadings and plasma production/transport processes. From the calculation, the local plasma density increase is observed in the region close to the antenna coil. Electrons are magnetized by the magnetic field line with absolute magnetic flux density 30–120 Gauss which leads to high local ionization rate. The results suggest that modification of magnetic configuration can be made to reduce plasma heat flux onto the antenna.

Intrachain versus interchain electron transport in poly(fluorene-alt-benzothiadiazole): a quantum-chemical insight.

PubMed

Van Vooren, Antoine; Kim, Ji-Seon; Cornil, Jérôme

2008-05-16

Poly(9,9-di-n-octylfluorene-alt-benzothiadiazole) [F8BT], displays very different charge-transport properties for holes versus electrons when comparing annealed and pristine thin films and transport parallel (intrachain) and perpendicular (interchain) to the polymer axes. The present theoretical contribution focuses on the electron-transport properties of F8BT chains and compares the efficiency of intrachain versus interchain transport in the hopping regime. The theoretical results rationalize significantly lowered electron mobility in annealed F8BT thin films and the smaller mobility anisotropy (mu( parallel)/mu( perpendicular)) measured for electrons in aligned films (i.e. 5-7 compared to 10-15 for holes).

A long way to the electrode: how do Geobacter cells transport their electrons?

PubMed

Bonanni, Pablo Sebastián; Schrott, Germán David; Busalmen, Juan Pablo

2012-12-01

The mechanism of electron transport in Geobacter sulfurreducens biofilms is a topic under intense study and debate. Although some proteins were found to be essential for current production, the specific role that each one plays in electron transport to the electrode remains to be elucidated and a consensus on the mechanism of electron transport has not been reached. In the present paper, to understand the state of the art in the topic, electron transport from inside of the cell to the electrode in Geobacter sulfurreducens biofilms is analysed, reviewing genetic studies, biofilm conductivity assays and electrochemical and spectro-electrochemical experiments. Furthermore, crucial data still required to achieve a deeper understanding are highlighted.

Radiation belt electron acceleration during the 17 March 2015 geomagnetic storm: Observations and simulations

DOE PAGES

Li, W.; Ma, Q.; Thorne, R. M.; ...

2016-06-10

Various physical processes are known to cause acceleration, loss, and transport of energetic electrons in the Earth's radiation belts, but their quantitative roles in different time and space need further investigation. During the largest storm over the past decade (17 March 2015), relativistic electrons experienced fairly rapid acceleration up to ~7 MeV within 2 days after an initial substantial dropout, as observed by Van Allen Probes. In the present paper, we evaluate the relative roles of various physical processes during the recovery phase of this large storm using a 3-D diffusion simulation. By quantitatively comparing the observed and simulated electronmore » evolution, we found that chorus plays a critical role in accelerating electrons up to several MeV near the developing peak location and produces characteristic flat-top pitch angle distributions. By only including radial diffusion, the simulation underestimates the observed electron acceleration, while radial diffusion plays an important role in redistributing electrons and potentially accelerates them to even higher energies. Moreover, plasmaspheric hiss is found to provide efficient pitch angle scattering losses for hundreds of keV electrons, while its scattering effect on > 1 MeV electrons is relatively slow. Although an additional loss process is required to fully explain the overestimated electron fluxes at multi-MeV, the combined physical processes of radial diffusion and pitch angle and energy diffusion by chorus and hiss reproduce the observed electron dynamics remarkably well, suggesting that quasi-linear diffusion theory is reasonable to evaluate radiation belt electron dynamics during this big storm.« less

Radiation belt electron acceleration during the 17 March 2015 geomagnetic storm: Observations and simulations

DOE Office of Scientific and Technical Information (OSTI.GOV)

Li, W.; Ma, Q.; Thorne, R. M.

Various physical processes are known to cause acceleration, loss, and transport of energetic electrons in the Earth's radiation belts, but their quantitative roles in different time and space need further investigation. During the largest storm over the past decade (17 March 2015), relativistic electrons experienced fairly rapid acceleration up to ~7 MeV within 2 days after an initial substantial dropout, as observed by Van Allen Probes. In the present paper, we evaluate the relative roles of various physical processes during the recovery phase of this large storm using a 3-D diffusion simulation. By quantitatively comparing the observed and simulated electronmore » evolution, we found that chorus plays a critical role in accelerating electrons up to several MeV near the developing peak location and produces characteristic flat-top pitch angle distributions. By only including radial diffusion, the simulation underestimates the observed electron acceleration, while radial diffusion plays an important role in redistributing electrons and potentially accelerates them to even higher energies. Moreover, plasmaspheric hiss is found to provide efficient pitch angle scattering losses for hundreds of keV electrons, while its scattering effect on > 1 MeV electrons is relatively slow. Although an additional loss process is required to fully explain the overestimated electron fluxes at multi-MeV, the combined physical processes of radial diffusion and pitch angle and energy diffusion by chorus and hiss reproduce the observed electron dynamics remarkably well, suggesting that quasi-linear diffusion theory is reasonable to evaluate radiation belt electron dynamics during this big storm.« less

Conditions for diffusion-limited and reaction-limited recombination in nanostructured solar cells

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ansari-Rad, Mehdi, E-mail: ansari.rad@ut.ac.ir; Department of Physics, University of Shahrood, Shahrood; Anta, Juan A., E-mail: anta@upo.es

2014-04-07

The performance of Dye-sensitized solar cells (DSC) and related devices made of nanostructured semiconductors relies on a good charge separation, which in turn is achieved by favoring charge transport against recombination. Although both processes occur at very different time scales, hence ensuring good charge separation, in certain cases the kinetics of transport and recombination can be connected, either in a direct or an indirect way. In this work, the connection between electron transport and recombination in nanostructured solar cells is studied both theoretically and by Monte Carlo simulation. Calculations using the Multiple-Trapping model and a realistic trap distribution for nanostructuredmore » TiO{sub 2} show that for attempt-to-jump frequencies higher than 10{sup 11}–10{sup 13} Hz, the system adopts a reaction limited (RL) regime, with a lifetime which is effectively independent from the speed of the electrons in the transport level. For frequencies lower than those, and depending on the concentration of recombination centers in the material, the system enters a diffusion-limited regime (DL), where the lifetime increases if the speed of free electrons decreases. In general, the conditions for RL or DL recombination depend critically on the time scale difference between recombination kinetics and free-electron transport. Hence, if the former is too rapid with respect to the latter, the system is in the DL regime and total thermalization of carriers is not possible. In the opposite situation, a RL regime arises. Numerical data available in the literature, and the behavior of the lifetime with respect to (1) density of recombination centers and (2) probability of recombination at a given center, suggest that a typical DSC in operation stays in the RL regime with complete thermalization, although a transition to the DL regime may occur for electrolytes or hole conductors where recombination is especially rapid or where there is a larger dispersion of energies of electron acceptors.« less

Research and development of low cost processes for integrated solar arrays. Final report, April 15, 1974--January 14, 1976

DOE Office of Scientific and Technical Information (OSTI.GOV)

Graham, C.D.; Kulkarni, S.; Louis, E.

1976-05-01

Results of a program to study process routes leading to a low cost large area integrated silicon solar array manufacture for terrestrial applications are reported. Potential processes for the production of solar-grade silicon are evaluated from thermodynamic, economic, and technical feasibility points of view. Upgrading of the present arc-furnace process is found most favorable. Experimental studies of the Si/SiF/sub 4/ transport and purification process show considerable impurity removal and reasonable transport rates. Silicon deformation experiments indicate production of silicon sheet by rolling at 1350/sup 0/C is feasible. Significant recrystallization by strain-anneal technique has been observed. Experimental recrystallization studies using anmore » electron beam line source are discussed. A maximum recrystallization velocity of approximately 9 m/hr is calculated for silicon sheet. A comparative process rating technique based on detailed cost analysis is presented.« less

Electrical property of macroscopic graphene composite fibers prepared by chemical vapor deposition

NASA Astrophysics Data System (ADS)

Sun, Haibin; Fu, Can; Gao, Yanli; Guo, Pengfei; Wang, Chunlei; Yang, Wenchao; Wang, Qishang; Zhang, Chongwu; Wang, Junya; Xu, Junqi

2018-07-01

Graphene fibers are promising candidates in portable and wearable electronics due to their tiny volume, flexibility and wearability. Here, we successfully synthesized macroscopic graphene composite fibers via a two-step process, i.e. first electrospinning and then chemical vapor deposition (CVD). Briefly, the well-dispersed PAN nanofibers were sprayed onto the copper surface in an electrified thin liquid jet by electrospinning. Subsequently, CVD growth process induced the formation of graphene films using a PAN-solid source of carbon and a copper catalyst. Finally, crumpled and macroscopic graphene composite fibers were obtained from carbon nanofiber/graphene composite webs by self-assembly process in the deionized water. Temperature-dependent conduct behavior reveals that electron transport of the graphene composite fibers belongs to hopping mechanism and the typical electrical conductivity reaches 4.59 × 103 S m‑1. These results demonstrated that the graphene composite fibers are promising for the next-generation flexible and wearable electronics.

Thin films as a platform for understanding the conversion mechanism of FeF2 cathodes in lithium-ion microbatteries

NASA Astrophysics Data System (ADS)

Santos-Ortiz, Reinaldo

Conversion material electrodes such as FeF2 possess the potential to deliver transformative improvements in lithium ion battery performance because they permit a reversible change of more than one Li-ion per 3d metal cation. They outperform current state of the art intercalation cathodes such as LiCoO2, which have volumetric and gravimetric energy densities that are intrinsically limited by single electron transfer. Current studies focus on composite electrodes that are formed by mixing with carbon (FeF 2-C), wherein the carbon is expected to act as a binder to support the matrix and facilitate electronic conduction. These binders complicate the understanding of the electrode-electrolyte interface (SEI) passivation layer growth, of Li agglomeration, of ion and electron transport, and of the basic phase transformation processes under electrochemical cycling. This research uses thin-films as a model platform for obtaining basic understanding to the structural and chemical foundations of the phase conversion processes. Thin film cathodes are free of the binders used in nanocomposite structures and may potentially provide direct basic insight to the evolution of the SEI passivation layer, electron and ion transport, and the electrochemical behavior of true complex phases. The present work consisted of three main tasks (1) Development of optimized processes to deposit FeF2 and LiPON thin-films with the required phase purity and microstructure; (2) Understanding their electron and ion transport properties and; (3) Obtaining insight to the correlation between structure and capacity in thin-film microbatteries with FeF2 thin-film cathode and LiPON thin-film solid electrolyte. Optimized pulsed laser deposition (PLD) growth produced polycrystalline FeF2 films with excellent phase purity and P42/mnm crystallographic symmetry. A schematic band diagram was deduced using a combination of UPS, XPS and UV-Vis spectroscopies. Room temperature Hall measurements reveal that as-deposited FeF2 is n-type with an electron mobility of 0.33 cm 2/V.s and a resistivity was 0.255 O.cm. The LiPON films were deposited by reactive sputtering in nitrogen, and the results indicate that the ionic conductivity is dependent on the amount of nitrogen incorporated into the film during processing. The highest ionic conductivity obtained was 1.431.9E-6 Scm-1 and corresponded to a chemical composition of Li1.9PO3.3N.21.

Inner Magnetospheric Superthermal Electron Transport: Photoelectron and Plasma Sheet Electron Sources

NASA Technical Reports Server (NTRS)

Khazanov, G. V.; Liemohn, M. W.; Kozyra, J. U.; Moore, T. E.

1998-01-01

Two time-dependent kinetic models of superthermal electron transport are combined to conduct global calculations of the nonthermal electron distribution function throughout the inner magnetosphere. It is shown that the energy range of validity for this combined model extends down to the superthermal-thermal intersection at a few eV, allowing for the calculation of the en- tire distribution function and thus an accurate heating rate to the thermal plasma. Because of the linearity of the formulas, the source terms are separated to calculate the distributions from the various populations, namely photoelectrons (PEs) and plasma sheet electrons (PSEs). These distributions are discussed in detail, examining the processes responsible for their formation in the various regions of the inner magnetosphere. It is shown that convection, corotation, and Coulomb collisions are the dominant processes in the formation of the PE distribution function and that PSEs are dominated by the interplay between the drift terms. Of note is that the PEs propagate around the nightside in a narrow channel at the edge of the plasmasphere as Coulomb collisions reduce the fluxes inside of this and convection compresses the flux tubes inward. These distributions are then recombined to show the development of the total superthermal electron distribution function in the inner magnetosphere and their influence on the thermal plasma. PEs usually dominate the dayside heating, with integral energy fluxes to the ionosphere reaching 10(exp 10) eV/sq cm/s in the plasmasphere, while heating from the PSEs typically does not exceed 10(exp 8) eV/sq cm/s. On the nightside, the inner plasmasphere is usually unheated by superthermal electrons. A feature of these combined spectra is that the distribution often has upward slopes with energy, particularly at the crossover from PE to PSE dominance, indicating that instabilities are possible.

Transport processes in magnetically confined plasmas in the nonlinear regime.

PubMed

Sonnino, Giorgio

2006-06-01

A field theory approach to transport phenomena in magnetically confined plasmas is presented. The thermodynamic field theory (TFT), previously developed for treating the generic thermodynamic system out of equilibrium, is applied to plasmas physics. Transport phenomena are treated here as the effect of the field linking the thermodynamic forces with their conjugate flows combined with statistical mechanics. In particular, the Classical and the Pfirsch-Schluter regimes are analyzed by solving the thermodynamic field equations of the TFT in the weak-field approximation. We found that, the TFT does not correct the expressions of the ionic heat fluxes evaluated by the neoclassical theory in these two regimes. On the other hand, the fluxes of matter and electronic energy (heat flow) is further enhanced in the nonlinear Classical and Pfirsch-Schluter regimes. These results seem to be in line with the experimental observations. The complete set of the electronic and ionic transport equations in the nonlinear Banana regime, is also reported. A paper showing the comparison between our theoretic results and the experimental observations in the JET machine is currently in preparation.

Investigation of nitrogen transport in active screen plasma nitriding processes - Uphill diffusion effect

NASA Astrophysics Data System (ADS)

Jasinski, J. J.; Fraczek, T.; Kurpaska, L.; Lubas, M.; Sitarz, M.

2018-07-01

The paper presents a structure of a nitrided layer formed with active screen plasma nitriding (ASPN) technique, which is a modification of plasma nitriding. The model investigated material was Fe Armco. The nitriding processes were carried out at 773 K for 6 h and 150 Pa. The main objective of this study was to confirm nitrogen migration effect and its influence on the nitride layer formation in different area of the layer interfaces (ε/ε+γ‧/γ‧). The results of the tests were evaluated using scanning electron microscopy (SEM, SEM/EBSD), transmission electron microscopy - electron energy loss spectroscopy (TEM-EFTEM), secondary ion mass spectroscopy (SIMS) and Wavelength Dispersive X-Ray Spectrometry (WDS). The analysis of the results suggests that the structures of the nitrided layers and nitrides morphology differ for various parameters and are dependent on the surface layer saturation mechanism for each of the temperatures and process parameters. New approaches in diffusion of nitrogen and carbon atoms and optimizing process were also analyzed. Nitrogen and also carbon transport in the sublayer was observed by several effects i.e. uphill diffusion effect which confirmed migration of the atoms in diffusive layer towards top surface (ε/ε+γ‧ interface) and stress change effect in the nitrogen saturation area of the (Fe(C,N)+γ‧) layer. Results showed in the paper might be used both for optimization of ASPN processes, modeling of nitrided layers formation mechanism and for controlling the nitrided layers morphology when nitriding different Fe based materials.

Unconventional transport in ultraclean graphene constriction devices

NASA Astrophysics Data System (ADS)

Pita Vidal, Marta; Ma, Qiong; Watanabe, Kenji; Taniguchi, Takashi; Jarillo-Herrero, Pablo

Under mesoscopic conditions, strong electron-electron interactions and weak electron-phonon coupling in graphene lead to hydrodynamic behavior of electrons, resulting in unusual and unexpected transport phenomena. Specifically, this hydrodynamical collective cooperation of electrons is predicted to enhance the flow of electrical current, leading to a striking higher-than-ballistic conductance through a narrow geometrical constriction. To access the hydrodynamic regime, we fabricated high-quality, low-disorder graphene nano-constriction devices encapsulated by hexagonal boron nitride, where electron-electron scattering dominates impurity scattering. We will report on our systematic four-probe conductance measurements on devices with different constriction widths as a function of number density and temperature. The observation of quantum transport phenomena that are inconsistent with the non-interacting ballistic free-fermion model would suggest a macroscopic transport signature of electron viscosity.

Steering the Properties of MoOx Hole Transporting Layers in OPVs and OLEDs: Interface Morphology vs. Electronic Structure

PubMed Central

Marchal, Wouter; Verboven, Inge; Kesters, Jurgen; Moeremans, Boaz; De Dobbelaere, Christopher; Bonneux, Gilles; Elen, Ken; Conings, Bert; Maes, Wouter; Boyen, Hans Gerd; Deferme, Wim; Van Bael, Marlies; Hardy, An

2017-01-01

The identification, fine-tuning, and process optimization of appropriate hole transporting layers (HTLs) for organic solar cells is indispensable for the production of efficient and sustainable functional devices. In this study, the optimization of a solution-processed molybdenum oxide (MoOx) layer fabricated from a combustion precursor is carried out via the introduction of zirconium and tin additives. The evaluation of the output characteristics of both organic photovoltaic (OPV) and organic light emitting diode (OLED) devices demonstrates the beneficial influence upon the addition of the Zr and Sn ions compared to the generic MoOx precursor. A dopant effect in which the heteroatoms and the molybdenum oxide form a chemical identity with fundamentally different structural properties could not be observed, as the additives do not affect the molybdenum oxide composition or electronic band structure. An improved surface roughness due to a reduced crystallinity was found to be a key parameter leading to the superior performance of the devices employing modified HTLs. PMID:28772483

Steering the Properties of MoOx Hole Transporting Layers in OPVs and OLEDs: Interface Morphology vs. Electronic Structure.

PubMed

Marchal, Wouter; Verboven, Inge; Kesters, Jurgen; Moeremans, Boaz; De Dobbelaere, Christopher; Bonneux, Gilles; Elen, Ken; Conings, Bert; Maes, Wouter; Boyen, Hans Gerd; Deferme, Wim; Van Bael, Marlies; Hardy, An

2017-01-30

The identification, fine-tuning, and process optimization of appropriate hole transporting layers (HTLs) for organic solar cells is indispensable for the production of efficient and sustainable functional devices. In this study, the optimization of a solution-processed molybdenum oxide (MoOx) layer fabricated from a combustion precursor is carried out via the introduction of zirconium and tin additives. The evaluation of the output characteristics of both organic photovoltaic (OPV) and organic light emitting diode (OLED) devices demonstrates the beneficial influence upon the addition of the Zr and Sn ions compared to the generic MoOx precursor. A dopant effect in which the heteroatoms and the molybdenum oxide form a chemical identity with fundamentally different structural properties could not be observed, as the additives do not affect the molybdenum oxide composition or electronic band structure. An improved surface roughness due to a reduced crystallinity was found to be a key parameter leading to the superior performance of the devices employing modified HTLs.

Recent progress in understanding electron thermal transport in NSTX

DOE PAGES

Ren, Y.; Belova, E.; Gorelenkov, N.; ...

2017-03-10

The anomalous level of electron thermal transport inferred in magnetically confined configurations is one of the most challenging problems for the ultimate realization of fusion power using toroidal devices: tokamaks, spherical tori and stellarators. It is generally believed that plasma instabilities driven by the abundant free energy in fusion plasmas are responsible for the electron thermal transport. The National Spherical Torus eXperiment (NSTX) (Ono et al 2000 Nucl. Fusion 40 557) provides a unique laboratory for studying plasma instabilities and their relation to electron thermal transport due to its low toroidal field, high plasma beta, low aspect ratio and largemore » ExB flow shear. Recent findings on NSTX have shown that multiple instabilities are required to explain observed electron thermal transport, given the wide range of equilibrium parameters due to different operational scenarios and radial regions in fusion plasmas. Here we review the recent progresses in understanding anomalous electron thermal transport in NSTX and focus on mechanisms that could drive electron thermal transport in the core region. The synergy between experiment and theoretical/ numerical modeling is essential to achieving these progresses. The plans for newly commissioned NSTX-Upgrade will also be discussed.« less

Diffusive transport of energetic electrons in the solar corona: X-ray and radio diagnostics

NASA Astrophysics Data System (ADS)

Musset, S.; Kontar, E. P.; Vilmer, N.

2018-02-01

Context. Imaging spectroscopy in X-rays with RHESSI provides the possibility to investigate the spatial evolution of X-ray emitting electron distribution and therefore, to study transport effects on energetic electrons during solar flares. Aims: We study the energy dependence of the scattering mean free path of energetic electrons in the solar corona. Methods: We used imaging spectroscopy with RHESSI to study the evolution of energetic electrons distribution in various parts of the magnetic loop during the 2004 May 21 flare. We compared these observations with the radio observations of the gyrosynchrotron radiation of the same flare and with the predictions of a diffusive transport model. Results: X-ray analysis shows a trapping of energetic electrons in the corona and a spectral hardening of the energetic electron distribution between the top of the loop and the footpoints. Coronal trapping of electrons is stronger for radio-emitting electrons than for X-ray-emitting electrons. These observations can be explained by a diffusive transport model. Conclusions: We show that the combination of X-ray and radio diagnostics is a powerful tool to study electron transport in the solar corona in different energy domains. We show that the diffusive transport model can explain our observations, and in the range 25-500 keV, the scattering mean free path of electrons decreases with electron energy. We can estimate for the first time the scattering mean free path dependence on energy in the corona.

Full-Scale Model of Subionospheric VLF Signal Propagation Based on First-Principles Charged Particle Transport Calculations

NASA Astrophysics Data System (ADS)

Kouznetsov, A.; Cully, C. M.; Knudsen, D. J.

2016-12-01

Changes in D-Region ionization caused by energetic particle precipitation are monitored by the Array for Broadband Observations of VLF/ELF Emissions (ABOVE) - a network of receivers deployed across Western Canada. The observed amplitudes and phases of subionospheric-propagating VLF signals from distant artificial transmitters depend sensitively on the free electron population created by precipitation of energetic charged particles. Those include both primary (electrons, protons and heavier ions) and secondary (cascades of ionized particles and electromagnetic radiation) components. We have designed and implemented a full-scale model to predict the received VLF signals based on first-principle charged particle transport calculations coupled to the Long Wavelength Propagation Capability (LWPC) software. Calculations of ionization rates and free electron densities are based on MCNP-6 (a general-purpose Monte Carlo N- Particle) software taking advantage of its capability of coupled neutron/photon/electron transport and novel library of cross-sections for low-energetic electron and photon interactions with matter. Cosmic ray calculations of background ionization are based on source spectra obtained both from PAMELA direct Cosmic Rays spectra measurements and based on the recently-implemented MCNP 6 galactic cosmic-ray source, scaled using our (Calgary) neutron monitor measurement results. Conversion from calculated fluxes (MCNP F4 tallies) to ionization rates for low-energy electrons are based on the total ionization cross-sections for oxygen and nitrogen molecules from the National Institute of Standard and Technology. We use our model to explore the complexity of the physical processes affecting VLF propagation.

Solution-processed zinc oxide/polyethylenimine nanocomposites as tunable electron transport layers for highly efficient bulk heterojunction polymer solar cells.

PubMed

Chen, Hsiu-Cheng; Lin, Shu-Wei; Jiang, Jian-Ming; Su, Yu-Wei; Wei, Kung-Hwa

2015-03-25

In this study, we employed polyethylenimine-doped sol-gel-processed zinc oxide composites (ZnO:PEI) as efficient electron transport layers (ETL) for facilitating electron extraction in inverted polymer solar cells. Using ultraviolet photoelectron spectroscopy, synchrotron grazing-incidence small-angle X-ray scattering and transmission electron microscopy, we observed that ZnO:PEI composite films' energy bands could be tuned considerably by varying the content of PEI up to 7 wt %-the conduction band ranged from 4.32 to 4.0 eV-and the structural order of ZnO in the ZnO:PEI thin films would be enhanced to align perpendicular to the ITO electrode, particularly at 7 wt % PEI, facilitating electron transport vertically. We then prepared two types of bulk heterojunction systems-based on poly(3-hexylthiophene) (P3HT):phenyl-C61-butryric acid methyl ester (PC61BM) and benzo[1,2-b:4,5-b́]dithiophene-thiophene-2,1,3-benzooxadiazole (PBDTTBO):phenyl-C71-butryric acid methyl ester (PC71BM)-that incorporated the ZnO:PEI composite layers. When using a composite of ZnO:PEI (93:7, w/w) as the ETL, the power conversion efficiency (PCE) of the P3HT:PC61BM (1:1, w/w) device improved to 4.6% from a value of 3.7% for the corresponding device that incorporated pristine ZnO as the ETL-a relative increase of 24%. For the PBDTTBO:PC71BM (1:2, w/w) device featuring the same amount of PEI blended in the ETL, the PCE improved to 8.7% from a value of 7.3% for the corresponding device that featured pure ZnO as its ETL-a relative increase of 20%. Accordingly, ZnO:PEI composites can be effective ETLs within organic photovoltaics.

Energy-filtered cold electron transport at room temperature.

PubMed

Bhadrachalam, Pradeep; Subramanian, Ramkumar; Ray, Vishva; Ma, Liang-Chieh; Wang, Weichao; Kim, Jiyoung; Cho, Kyeongjae; Koh, Seong Jin

2014-09-10

Fermi-Dirac electron thermal excitation is an intrinsic phenomenon that limits functionality of various electron systems. Efforts to manipulate electron thermal excitation have been successful when the entire system is cooled to cryogenic temperatures, typically <1 K. Here we show that electron thermal excitation can be effectively suppressed at room temperature, and energy-suppressed electrons, whose energy distribution corresponds to an effective electron temperature of ~45 K, can be transported throughout device components without external cooling. This is accomplished using a discrete level of a quantum well, which filters out thermally excited electrons and permits only energy-suppressed electrons to participate in electron transport. The quantum well (~2 nm of Cr2O3) is formed between source (Cr) and tunnelling barrier (SiO2) in a double-barrier-tunnelling-junction structure having a quantum dot as the central island. Cold electron transport is detected from extremely narrow differential conductance peaks in electron tunnelling through CdSe quantum dots, with full widths at half maximum of only ~15 mV at room temperature.

Atomically thin p-n junctions with van der Waals heterointerfaces.

PubMed

Lee, Chul-Ho; Lee, Gwan-Hyoung; van der Zande, Arend M; Chen, Wenchao; Li, Yilei; Han, Minyong; Cui, Xu; Arefe, Ghidewon; Nuckolls, Colin; Heinz, Tony F; Guo, Jing; Hone, James; Kim, Philip

2014-09-01

Semiconductor p-n junctions are essential building blocks for electronic and optoelectronic devices. In conventional p-n junctions, regions depleted of free charge carriers form on either side of the junction, generating built-in potentials associated with uncompensated dopant atoms. Carrier transport across the junction occurs by diffusion and drift processes influenced by the spatial extent of this depletion region. With the advent of atomically thin van der Waals materials and their heterostructures, it is now possible to realize a p-n junction at the ultimate thickness limit. Van der Waals junctions composed of p- and n-type semiconductors--each just one unit cell thick--are predicted to exhibit completely different charge transport characteristics than bulk heterojunctions. Here, we report the characterization of the electronic and optoelectronic properties of atomically thin p-n heterojunctions fabricated using van der Waals assembly of transition-metal dichalcogenides. We observe gate-tunable diode-like current rectification and a photovoltaic response across the p-n interface. We find that the tunnelling-assisted interlayer recombination of the majority carriers is responsible for the tunability of the electronic and optoelectronic processes. Sandwiching an atomic p-n junction between graphene layers enhances the collection of the photoexcited carriers. The atomically scaled van der Waals p-n heterostructures presented here constitute the ultimate functional unit for nanoscale electronic and optoelectronic devices.

Long-range energy transport in single supramolecular nanofibres at room temperature

NASA Astrophysics Data System (ADS)

Haedler, Andreas T.; Kreger, Klaus; Issac, Abey; Wittmann, Bernd; Kivala, Milan; Hammer, Natalie; Köhler, Jürgen; Schmidt, Hans-Werner; Hildner, Richard

2015-07-01

Efficient transport of excitation energy over long distances is a key process in light-harvesting systems, as well as in molecular electronics. However, in synthetic disordered organic materials, the exciton diffusion length is typically only around 10 nanometres (refs 4, 5), or about 50 nanometres in exceptional cases, a distance that is largely determined by the probability laws of incoherent exciton hopping. Only for highly ordered organic systems has the transport of excitation energy over macroscopic distances been reported--for example, for triplet excitons in anthracene single crystals at room temperature, as well as along single polydiacetylene chains embedded in their monomer crystalline matrix at cryogenic temperatures (at 10 kelvin, or -263 degrees Celsius). For supramolecular nanostructures, uniaxial long-range transport has not been demonstrated at room temperature. Here we show that individual self-assembled nanofibres with molecular-scale diameter efficiently transport singlet excitons at ambient conditions over more than four micrometres, a distance that is limited only by the fibre length. Our data suggest that this remarkable long-range transport is predominantly coherent. Such coherent long-range transport is achieved by one-dimensional self-assembly of supramolecular building blocks, based on carbonyl-bridged triarylamines, into well defined H-type aggregates (in which individual monomers are aligned cofacially) with substantial electronic interactions. These findings may facilitate the development of organic nanophotonic devices and quantum information technology.

Methodology trends on gamma and electron radiation damage simulation studies in solids under high fluency irradiation environments

NASA Astrophysics Data System (ADS)

Cruz Inclán, Carlos M.; González Lazo, Eduardo; Rodríguez Rodríguez, Arturo; Guzmán Martínez, Fernando; Abreu Alfonso, Yamiel; Piñera Hernández, Ibrahin; Leyva Fabelo, Antonio

2017-09-01

The present work deals with the numerical simulation of gamma and electron radiation damage processes under high brightness and radiation particle fluency on regard to two new radiation induced atom displacement processes, which concern with both, the Monte Carlo Method based numerical simulation of the occurrence of atom displacement process as a result of gamma and electron interactions and transport in a solid matrix and the atom displacement threshold energies calculated by Molecular Dynamic methodologies. The two new radiation damage processes here considered in the framework of high brightness and particle fluency irradiation conditions are: 1) The radiation induced atom displacement processes due to a single primary knockout atom excitation in a defective target crystal matrix increasing its defect concentrations (vacancies, interstitials and Frenkel pairs) as a result of a severe and progressive material radiation damage and 2) The occurrence of atom displacements related to multiple primary knockout atom excitations for the same or different atomic species in an perfect target crystal matrix due to subsequent electron elastic atomic scattering in the same atomic neighborhood during a crystal lattice relaxation time. In the present work a review numeral simulation attempts of these two new radiation damage processes are presented, starting from the former developed algorithms and codes for Monte Carlo simulation of atom displacements induced by electron and gamma in

Energy efficiency of engines and appliances for transport on land, water, and in air.

PubMed

Furfari, Samuele

2016-01-01

The transport sector is fundamental for the economy but also for personal life. With a growing population and the globalization process, it is not surprising that the demand of transport is set to grow in the near future and certainly until 2050. This paper focuses on the huge potential of progress in the sector of technology for transport. As the principal sector for transport will remain on roads, the paper emphasizes the progress in the automotive sector. Since car manufacturers are investing massively into research and technology development to offer ever more efficient cars--not only energy efficient but also efficient in terms of safety and comfort--the car of tomorrow will be very different from the present one. The increasing role of electronics in cars will synergistically cooperate with that of so-called smart cities. The potential development of methane in the transport sector, mainly used for heavy transportation is discussed.

Influence of energy band alignment in mixed crystalline TiO2 nanotube arrays: good for photocatalysis, bad for electron transfer

NASA Astrophysics Data System (ADS)

Mohammadpour, Raheleh

2017-12-01

Despite the wide application ranges of TiO2, the precise explanation of the charge transport dynamic through a mixed crystal phase of this semiconductor has remained elusive. Here, in this research, mixed-phase TiO2 nanotube arrays (TNTAs) consisting of anatase and 0-15% rutile phases has been formed through various annealing processes and employed as a photoelectrode of a photovoltaic cell. Wide ranges of optoelectronic experiments have been employed to explore the band alignment position, as well as the depth and density of trap states in TNTAs. Short circuit potential, as well as open circuit potential measurements specified that the band alignment of more than 0.2 eV exists between the anatase and rutile phase Fermi levels, with a higher electron affinity for anatase; this can result in a potential barrier in crystallite interfaces and the deterioration of electron mobility through mixed phase structures. Moreover, a higher density of shallow localized trap states below the conduction band with more depth (133 meV in anatase to 247 meV in 15% rutile phase) and also deep oxygen vacancy traps have been explored upon introducing the rutile phase. Based on our results, employing TiO2 nanotubes as just the electron transport medium in mixed crystalline phases can deteriorate the charge transport mechanism, however, in photocatalytic applications when both electrons and holes are present, a robust charge separation in crystalline anatase/rutile interphases will result in better performances.

High Electron Mobility Thin‐Film Transistors Based on Solution‐Processed Semiconducting Metal Oxide Heterojunctions and Quasi‐Superlattices

PubMed Central

Lin, Yen‐Hung; Faber, Hendrik; Labram, John G.; Stratakis, Emmanuel; Sygellou, Labrini; Kymakis, Emmanuel; Hastas, Nikolaos A.; Li, Ruipeng; Zhao, Kui; Amassian, Aram; Treat, Neil D.; McLachlan, Martyn

2015-01-01

High mobility thin‐film transistor technologies that can be implemented using simple and inexpensive fabrication methods are in great demand because of their applicability in a wide range of emerging optoelectronics. Here, a novel concept of thin‐film transistors is reported that exploits the enhanced electron transport properties of low‐dimensional polycrystalline heterojunctions and quasi‐superlattices (QSLs) consisting of alternating layers of In2O3, Ga2O3, and ZnO grown by sequential spin casting of different precursors in air at low temperatures (180–200 °C). Optimized prototype QSL transistors exhibit band‐like transport with electron mobilities approximately a tenfold greater (25–45 cm2 V−1 s−1) than single oxide devices (typically 2–5 cm2 V−1 s−1). Based on temperature‐dependent electron transport and capacitance‐voltage measurements, it is argued that the enhanced performance arises from the presence of quasi 2D electron gas‐like systems formed at the carefully engineered oxide heterointerfaces. The QSL transistor concept proposed here can in principle extend to a range of other oxide material systems and deposition methods (sputtering, atomic layer deposition, spray pyrolysis, roll‐to‐roll, etc.) and can be seen as an extremely promising technology for application in next‐generation large area optoelectronics such as ultrahigh definition optical displays and large‐area microelectronics where high performance is a key requirement. PMID:27660741

Towards green high capacity optical networks

NASA Astrophysics Data System (ADS)

Glesk, I.; Mohd Warip, M. N.; Idris, S. K.; Osadola, T. B.; Andonovic, I.

2011-09-01

The demand for fast, secure, energy efficient high capacity networks is growing. It is fuelled by transmission bandwidth needs which will support among other things the rapid penetration of multimedia applications empowering smart consumer electronics and E-businesses. All the above trigger unparallel needs for networking solutions which must offer not only high-speed low-cost "on demand" mobile connectivity but should be ecologically friendly and have low carbon footprint. The first answer to address the bandwidth needs was deployment of fibre optic technologies into transport networks. After this it became quickly obvious that the inferior electronic bandwidth (if compared to optical fiber) will further keep its upper hand on maximum implementable serial data rates. A new solution was found by introducing parallelism into data transport in the form of Wavelength Division Multiplexing (WDM) which has helped dramatically to improve aggregate throughput of optical networks. However with these advancements a new bottleneck has emerged at fibre endpoints where data routers must process the incoming and outgoing traffic. Here, even with the massive and power hungry electronic parallelism routers today (still relying upon bandwidth limiting electronics) do not offer needed processing speeds networks demands. In this paper we will discuss some novel unconventional approaches to address network scalability leading to energy savings via advance optical signal processing. We will also investigate energy savings based on advanced network management through nodes hibernation proposed for Optical IP networks. The hibernation reduces the network overall power consumption by forming virtual network reconfigurations through selective nodes groupings and by links segmentations and partitionings.

Gamma-ray emission and electron acceleration in solar flares

NASA Technical Reports Server (NTRS)

Petrosian, Vahe; Mctiernan, James M.; Marschhauser, Holger

1994-01-01

Recent observations have extended the spectra of the impulsive phase of flares to the GeV range. Such high-energy photons can be produced either by electron bremsstrahlung or by decay of pions produced by accelerated protons. In this paper we investigate the effects of processes which become important at high energies. We examine the effects of synchrotron losses during the transport of electrons as they travel from the acceleration region in the corona to the gamma-ray emission sites deep in the chromosphere and photosphere, and the effects of scattering and absorption of gamma rays on their way from the photosphere to space instruments. These results are compared with the spectra from so-called electron-dominated flares, observed by GRS on the Solar Maximum Mission, which show negligible or no detectable contribution from accelerated protons. The spectra of these flares show a distinct steepening at energies below 100 keV and a rapid falloff at energies above 50 MeV. Following our earlier results based on lower energy gamma-ray flare emission we have modeled these spectra. We show that neither the radiative transfer effects, which are expected to become important at higher energies, nor the transport effects (Coulomb collisions, synchrotron losses, or magnetic field convergence) can explain such sharp spectral deviations from a simple power law. These spectral deviations from a power law are therefore attributed to the acceleration process. In a stochastic acceleration model the low-energy steepening can be attributed to Coulomb collision and the rapid high-energy steepening can result from synchrotron losses during the acceleration process.

Significant enhancement of power conversion efficiency for dye sensitized solar cell using 1D/3D network nanostructures as photoanodes

PubMed Central

Wang, Hao; Wang, Baoyuan; Yu, Jichao; Hu, Yunxia; Xia, Chen; Zhang, Jun; Liu, Rong

2015-01-01

The single–crystalline TiO2 nanorod arrays with rutile phase have attracted much attention in the dye sensitized solar cells (DSSCs) applications because of their superior chemical stability, better electron transport properties, higher refractive index and low production cost. However, it suffers from a low surface area as compared with TiO2 nanoparticle films. In order to enlarge the surface area of TiO2 nanorod arrays, the 1D nanorods/3D nanotubes sample was synthesized using a facile two-step hydrothermal process involving hydrothermal growth 1D/3D nanorods and followed by post-etching treatment. In such bi-layer structure, the oriented TiO2 nanorods layer could provide direct pathway for fast electron transportation, and the 3D nanotubes layer offers a higher surface area for dye loading, therefore, the 1D nanorods/3D nanotubes photoanode exhibited faster electron transport and higher surface area than either 1D or 3D nanostructures alone, and an highest efficiency of 7.68% was achieved for the DSSCs based on 1D nanorods/3D nanotubes photoanode with further TiCl4 treatment. PMID:25800933

Effect of Noise on DNA Sequencing via Transverse Electronic Transport

PubMed Central

Krems, Matt; Zwolak, Michael; Pershin, Yuriy V.; Di Ventra, Massimiliano

2009-01-01

Abstract Previous theoretical studies have shown that measuring the transverse current across DNA strands while they translocate through a nanopore or channel may provide a statistically distinguishable signature of the DNA bases, and may thus allow for rapid DNA sequencing. However, fluctuations of the environment, such as ionic and DNA motion, introduce important scattering processes that may affect the viability of this approach to sequencing. To understand this issue, we have analyzed a simple model that captures the role of this complex environment in electronic dephasing and its ability to remove charge carriers from current-carrying states. We find that these effects do not strongly influence the current distributions due to the off-resonant nature of tunneling through the nucleotides—a result we expect to be a common feature of transport in molecular junctions. In particular, only large scattering strengths, as compared to the energetic gap between the molecular states and the Fermi level, significantly alter the form of the current distributions. Since this gap itself is quite large, the current distributions remain protected from this type of noise, further supporting the possibility of using transverse electronic transport measurements for DNA sequencing. PMID:19804730

Microwave processes in the SPD-ATON stationary plasma thruster

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kirdyashev, K. P., E-mail: kpk@ms.ire.rssi.ru

2016-09-15

Results of experimental studies of microwave processes accompanying plasma acceleration in the SPD-ATON stationary plasma thruster are presented. Specific features of the generation of microwave oscillations in both the acceleration channel and the plasma flow outgoing from the thruster are analyzed on the basis of local measurements of the spectra of the plasma wave fields. Mechanisms for generation of microwave oscillations are considered with allowance for the inhomogeneity of the electron density and magnetic field behind the edge of the acceleration channel. The effect of microwave oscillations on the electron transport and the formation of the discharge current in themore » acceleration channel is discussed.« less

What Is Moving in Hybrid Halide Perovskite Solar Cells?

PubMed Central

2016-01-01

Conspectus Organic–inorganic semiconductors, which adopt the perovskite crystal structure, have perturbed the landscape of contemporary photovoltaics research. High-efficiency solar cells can be produced with solution-processed active layers. The materials are earth abundant, and the simple processing required suggests that high-throughput and low-cost manufacture at scale should be possible. While these materials bear considerable similarity to traditional inorganic semiconductors, there are notable differences in their optoelectronic behavior. A key distinction of these materials is that they are physically soft, leading to considerable thermally activated motion. In this Account, we discuss the internal motion of methylammonium lead iodide (CH3NH3PbI3) and formamidinium lead iodide ([CH(NH2)2]PbI3), covering: (i) molecular rotation-libration in the cuboctahedral cavity; (ii) drift and diffusion of large electron and hole polarons; (iii) transport of charged ionic defects. These processes give rise to a range of properties that are unconventional for photovoltaic materials, including frequency-dependent permittivity, low electron–hole recombination rates, and current–voltage hysteresis. Multiscale simulations, drawing from electronic structure, ab initio molecular dynamic and Monte Carlo computational techniques, have been combined with neutron diffraction measurements, quasi-elastic neutron scattering, and ultrafast vibrational spectroscopy to qualify the nature and time scales of the motions. Electron and hole motion occurs on a femtosecond time scale. Molecular libration is a sub-picosecond process. Molecular rotations occur with a time constant of several picoseconds depending on the cation. Recent experimental evidence and theoretical models for simultaneous electron and ion transport in these materials has been presented, suggesting they are mixed-mode conductors with similarities to fast-ion conducting metal oxide perovskites developed for battery and fuel cell applications. We expound on the implications of these effects for the photovoltaic action. The temporal behavior displayed by hybrid perovskites introduces a sensitivity in materials characterization to the time and length scale of the measurement, as well as the history of each sample. It also poses significant challenges for accurate materials modeling and device simulations. There are large differences between the average and local crystal structures, and the nature of charge transport is too complex to be described by common one-dimensional drift-diffusion models. Herein, we critically discuss the atomistic origin of the dynamic processes and the associated chemical disorder intrinsic to crystalline hybrid perovskite semiconductors. PMID:26859250

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gallego-Marcos, Fernando; Sánchez, Rafael; Platero, Gloria

We analyze long-range transport through an ac driven triple quantum dot with a single electron. Resonant transitions between separated and detuned dots are mediated by the exchange of n photons with the time-dependent field. An effective model is proposed in terms of second order (cotunneling) processes which dominate the long-range transport between the edge quantum dots. The ac field renormalizes the inter dot hopping, modifying the level hybridization. It results in a non-trivial behavior of the current with the frequency and amplitude of the external ac field.

Nanoscale patterning of electronic devices at the amorphous LaAlO3/SrTiO3 oxide interface using an electron sensitive polymer mask

NASA Astrophysics Data System (ADS)

Bjørlig, Anders V.; von Soosten, Merlin; Erlandsen, Ricci; Dahm, Rasmus Tindal; Zhang, Yu; Gan, Yulin; Chen, Yunzhong; Pryds, Nini; Jespersen, Thomas S.

2018-04-01

A simple approach is presented for designing complex oxide mesoscopic electronic devices based on the conducting interfaces of room temperature grown LaAlO3/SrTiO3 heterostructures. The technique is based entirely on methods known from conventional semiconductor processing technology, and we demonstrate a lateral resolution of ˜100 nm. We study the low temperature transport properties of nanoscale wires and demonstrate the feasibility of the technique for defining in-plane gates allowing local control of the electrostatic environment in mesoscopic devices.

Electronic structures of graphane with vacancies and graphene adsorbed with fluorine atoms

NASA Astrophysics Data System (ADS)

Wu, Bi-Ru; Yang, Chih-Kai

2012-03-01

We investigate the electronic structure of graphane with hydrogen vacancies, which are supposed to occur in the process of hydrogenation of graphene. A variety of configurations is considered and defect states are derived by density functional calculation. We find that a continuous chain-like distribution of hydrogen vacancies will result in conduction of linear dispersion, much like the transport on a superhighway cutting through the jungle of hydrogen. The same conduction also occurs for chain-like vacancies in an otherwise fully fluorine-adsorbed graphene. These results should be very useful in the design of graphene-based electronic circuits.

Electron transport and light-harvesting switches in cyanobacteria

PubMed Central

Mullineaux, Conrad W.

2014-01-01

Cyanobacteria possess multiple mechanisms for regulating the pathways of photosynthetic and respiratory electron transport. Electron transport may be regulated indirectly by controlling the transfer of excitation energy from the light-harvesting complexes, or it may be more directly regulated by controlling the stoichiometry, localization, and interactions of photosynthetic and respiratory electron transport complexes. Regulation of the extent of linear vs. cyclic electron transport is particularly important for controlling the redox balance of the cell. This review discusses what is known of the regulatory mechanisms and the timescales on which they occur, with particular regard to the structural reorganization needed and the constraints imposed by the limited mobility of membrane-integral proteins in the crowded thylakoid membrane. Switching mechanisms requiring substantial movement of integral thylakoid membrane proteins occur on slower timescales than those that require the movement only of cytoplasmic or extrinsic membrane proteins. This difference is probably due to the restricted diffusion of membrane-integral proteins. Multiple switching mechanisms may be needed to regulate electron transport on different timescales. PMID:24478787

Development and fabrication of a solar cell junction processing system

NASA Technical Reports Server (NTRS)

Kiesling, R.

1981-01-01

The major component fabrication program was completed. Assembly and system testing of the pulsed electron beam annealing machine are described. The design program for the transport reached completion, and the detailed drawings were released for fabrication and procurement of the long lead time components.

Low-Energy Electron Interactions with CF_4

NASA Astrophysics Data System (ADS)

Christophorou, Loucas G.; Olthoff, James K.; Rao, M. V. V. S.

1996-10-01

Carbon tetrafluoride is one of the most widely used components of feed gas mixtures employed for a variety of plasma assisted materials processing applications. In this presentation, we synthesize and assess the available information on the cross sections and rate coefficients of collisional interations of CF4 with electrons.(L. G. Christophorou, J. K. Olthoff, and M.V. V. S. Rao, J. Phys. Chem. Ref. Data, submitted (May 1996)) A ``recommended'' data set is presented, based upon available data for: (i) cross sections for electron scattering (total, elastic, momentum, differential, inelastic), electron impact ionization (total and partial), electron impact dissociation, and electron attachment; and (ii) coefficients for electron transport, electron attachment, and electron impact ionization. -Research sponsored in part by the U.S. Air Force Wright Laboratory under contract F33615-96-C-2600 with the University of Tennessee. Also, Department of Physics, The University of Tennessee, Knoxville, TN.

Convective and diffusive ULF wave driven radiation belt electron transport

NASA Astrophysics Data System (ADS)

Degeling, A. W.; Rankin, R.; Elkington, S. R.

2011-12-01

The process of magnetospheric radiation belt electron transport driven by ULF waves is studied using a 2-D ideal MHD model for ULF waves in the equatorial plane including day/night asymmetry and a magnetopause boundary, and a test kinetic model for equatorially mirroring electrons. We find that ULF wave disturbances originating along the magnetopause flanks in the afternoon sector can act to periodically inject phase space density from these regions into the magnetosphere. Closely spaced drift-resonant surfaces for electrons with a given magnetic moment in the presence of the ULF waves create a layer of stochastic dynamics for L-shells above 6.5-7 in the cases examined, extending to the magnetopause. The phase decorrelation time scale for the stochastic region is estimated by the relaxation time for the diffusion coefficient to reach a steady value. This is found to be of the order of 10-15 wave periods, which is commensurate with the typical duration of observed ULF wave packets in the magnetosphere. For L-shells earthward of the stochastic layer, transport is limited to isolated drift-resonant islands in the case of narrowband ULF waves. We examine the effect of increasing the bandwidth of the ULF wave driver by summing together wave components produced by a set of independent runs of the ULF wave model. The wave source spectrum is given a flat-top amplitude of variable width (adjusted for constant power) and random phase. We find that increasing bandwidth can significantly enhance convective transport earthward of the stochastic layer and extend the stochastic layer to lower L-shells.

Comparative phytotoxicity of usnic acid, salicylic acid, cinnamic acid and benzoic acid on photosynthetic apparatus of Chlamydomonas reinhardtii.

PubMed

Gao, Yazhi; Liu, Wei; Wang, Xiaoxiong; Yang, Lihua; Han, Su; Chen, Shiguo; Strasser, Reto Jörg; Valverde, Bernal E; Qiang, Sheng

2018-07-01

The effects of four phytotoxins usnic acid (UA), salicylic acid (SA), cinnamic acid (CA) and benzoic acid (BA) on photosynthesis of Chlamydomonas reinhardtii were studied in vivo to identify and localise their initial action sites on two photosystems. Our experimental evidence shows that the four phytotoxins have multiple targets in chloroplasts, which mainly lie in photosystem II (PSII), not photosystem I (PSI). They share an original action site by blocking electron transport beyond Q A (primary plastoquinone acceptor) at PSII acceptor side since a fast increase of the J-step level is the greatest change in chlorophyll a fluorescence induction kinetics OJIP in C. reinhardtii cells treated with the phytotoxins. UA decreases photosynthetic activity by reducing O 2 evolution rate, interrupting PSII electron transport at both the donor and acceptor sides, inactivating the PSII reaction centers (RCs), reducing the content of chlorophylls and carotenoids, destroying the conformation of antenna pigment assemblies, and casuing the degradation of D1/D2 proteins. SA damage to photosynthetic machinery is mainly attributed to inhibition of PSII electron transport beyond Q A at the acceptor side, inactivation of the PSII RCs, reduction of chlorophyll content, digestion of thylakoid ploypeptides and destabilization of thylakoid membranes. Both CA and BA affect the photosynthetic process by decreasing PSII electron transport efficiency at the acceptor side and the amount of active PSII RCs. Besides, the initial cause of BA-inhibiting photosynthesis is also assocaited with the O 2 evolution rate and the disconnection of some antenna molecules from PSII RCs. Copyright © 2018 Elsevier Masson SAS. All rights reserved.

Enhancing grain boundary ionic conductivity in mixed ionic–electronic conductors

DOE PAGES

Lin, Ye; Fang, Shumin; Su, Dong; ...

2015-04-10

Mixed ionic–electronic conductors are widely used in devices for energy conversion and storage. Grain boundaries in these materials have nanoscale spatial dimensions, which can generate substantial resistance to ionic transport due to dopant segregation. Here, we report the concept of targeted phase formation in a Ce 0.8Gd 0.2O 2₋δ–CoFe 2O 4 composite that serves to enhance the grain boundary ionic conductivity. Using transmission electron microscopy and spectroscopy approaches, we probe the grain boundary charge distribution and chemical environments altered by the phase reaction between the two constituents. The formation of an emergent phase successfully avoids segregation of the Gd dopantmore » and depletion of oxygen vacancies at the Ce 0.8Gd 0.2O 2₋δ–Ce 0.8Gd 0.2O 2₋δ grain boundary. This results in superior grain boundary ionic conductivity as demonstrated by the enhanced oxygen permeation flux. Lastly, this work illustrates the control of mesoscale level transport properties in mixed ionic–electronic conductor composites through processing induced modifications of the grain boundary defect distribution.« less

Enhancing grain boundary ionic conductivity in mixed ionic–electronic conductors

PubMed Central

Lin, Ye; Fang, Shumin; Su, Dong; Brinkman, Kyle S; Chen, Fanglin

2015-01-01

Mixed ionic–electronic conductors are widely used in devices for energy conversion and storage. Grain boundaries in these materials have nanoscale spatial dimensions, which can generate substantial resistance to ionic transport due to dopant segregation. Here, we report the concept of targeted phase formation in a Ce0.8Gd0.2O2−δ–CoFe2O4 composite that serves to enhance the grain boundary ionic conductivity. Using transmission electron microscopy and spectroscopy approaches, we probe the grain boundary charge distribution and chemical environments altered by the phase reaction between the two constituents. The formation of an emergent phase successfully avoids segregation of the Gd dopant and depletion of oxygen vacancies at the Ce0.8Gd0.2O2−δ–Ce0.8Gd0.2O2−δ grain boundary. This results in superior grain boundary ionic conductivity as demonstrated by the enhanced oxygen permeation flux. This work illustrates the control of mesoscale level transport properties in mixed ionic–electronic conductor composites through processing induced modifications of the grain boundary defect distribution. PMID:25857355

Enhancing grain boundary ionic conductivity in mixed ionic-electronic conductors.

PubMed

Lin, Ye; Fang, Shumin; Su, Dong; Brinkman, Kyle S; Chen, Fanglin

2015-04-10

Mixed ionic-electronic conductors are widely used in devices for energy conversion and storage. Grain boundaries in these materials have nanoscale spatial dimensions, which can generate substantial resistance to ionic transport due to dopant segregation. Here, we report the concept of targeted phase formation in a Ce0.8Gd0.2O2-δ-CoFe2O4 composite that serves to enhance the grain boundary ionic conductivity. Using transmission electron microscopy and spectroscopy approaches, we probe the grain boundary charge distribution and chemical environments altered by the phase reaction between the two constituents. The formation of an emergent phase successfully avoids segregation of the Gd dopant and depletion of oxygen vacancies at the Ce0.8Gd0.2O2-δ-Ce0.8Gd0.2O2-δ grain boundary. This results in superior grain boundary ionic conductivity as demonstrated by the enhanced oxygen permeation flux. This work illustrates the control of mesoscale level transport properties in mixed ionic-electronic conductor composites through processing induced modifications of the grain boundary defect distribution.

A novel analytical model for scattering limited electron transport in nano-dimensional InAlAs/InGaAs heterostructure for cryogenic applications

NASA Astrophysics Data System (ADS)

Sharma, Neetika; Verma, Neha; Jogi, Jyotika

2017-11-01

This paper models the scattering limited electron transport in a nano-dimensional In0.52Al0.48As/In0.53Ga0.47As/InP heterostructure. An analytical model for temperature dependent sheet carrier concentration and carrier mobility in a two dimensional electron gas, confined in a triangular potential well has been developed. The model accounts for all the major scattering process including ionized impurity scattering and lattice scattering. Quantum mechanical variational technique is employed for studying the intrasubband scattering mechanism in the two dimensional electron gas. Results of various scattering limited structural parameters such as energy band-gap and functional parameters such as sheet carrier concentration, scattering rate and mobility are presented. The model corroborates the dominance of ionized impurity scattering mechanism at low temperatures and that of lattice scattering at high temperatures, both in turn limiting the carrier mobility. Net mobility obtained taking various scattering mechanisms into account has been found in agreement with earlier reported results, thus validating the model.

Enhancing grain boundary ionic conductivity in mixed ionic–electronic conductors

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lin, Ye; Fang, Shumin; Su, Dong

Mixed ionic–electronic conductors are widely used in devices for energy conversion and storage. Grain boundaries in these materials have nanoscale spatial dimensions, which can generate substantial resistance to ionic transport due to dopant segregation. Here, we report the concept of targeted phase formation in a Ce 0.8Gd 0.2O 2₋δ–CoFe 2O 4 composite that serves to enhance the grain boundary ionic conductivity. Using transmission electron microscopy and spectroscopy approaches, we probe the grain boundary charge distribution and chemical environments altered by the phase reaction between the two constituents. The formation of an emergent phase successfully avoids segregation of the Gd dopantmore » and depletion of oxygen vacancies at the Ce 0.8Gd 0.2O 2₋δ–Ce 0.8Gd 0.2O 2₋δ grain boundary. This results in superior grain boundary ionic conductivity as demonstrated by the enhanced oxygen permeation flux. Lastly, this work illustrates the control of mesoscale level transport properties in mixed ionic–electronic conductor composites through processing induced modifications of the grain boundary defect distribution.« less

Electronic transport properties of single-crystal bismuth nanowire arrays

NASA Astrophysics Data System (ADS)

Zhang, Zhibo; Sun, Xiangzhong; Dresselhaus, M. S.; Ying, Jackie Y.; Heremans, J.

2000-02-01

We present here a detailed study of the electrical transport properties of single-crystal bismuth nanowire arrays embedded in a dielectric matrix. Measurements of the resistance of Bi nanowire arrays with different wire diameters (60-110 nm) have been carried out over a wide range of temperatures (2.0-300 K) and magnetic fields (0-5.4 T). The transport properties of a heavily Te-doped Bi nanowire array have also been studied. At low temperatures, we show that the wire boundary scattering is the dominant scattering process for carriers in the undoped single-crystal Bi nanowires, while boundary scattering is less important for a heavily Te-doped sample, consistent with general theoretical considerations. The temperature dependences of the zero-field resistivity and of the longitudinal magneto-coefficient of the Bi nanowires were also studied and were found to be sensitive to the wire diameter. The quantum confinement of carriers is believed to play an important role in determining the overall temperature dependence of the zero-field resistivity. Theoretical considerations of the quantum confinement effects on the electronic band structure and on the transport properties of Bi nanowires are discussed. Despite the evidence for localization effects and diffusive electron interactions at low temperatures (T<=4.0 K), localization effects are not the dominant mechanisms affecting the resistivity or the magnetoresistance in the temperature range of this study.

Stable p-i-n FAPbBr 3 devices with improved efficiency using sputtered ZnO as electron transport layer [Stable p-i-n FAPbBr 3 devices with improved efficiency using sputtered inorganic electron transport layer

DOE PAGES

Subbiah, Anand S.; Agarwal, Sumanshu; Mahuli, Neha; ...

2017-02-10

Here, radio-frequency magnetron sputtering is demonstrated as an effective tool to deposit highly crystalline thin zinc oxide (ZnO) layer directly on perovskite absorber as an electron transport layer (ETL). As an absorber, formamidinium lead tribromide (FAPbBr 3) is fabricated through a modified single-step solution process using hydrogen bromide (HBr) as an additive resulting in complete surface coverage and highly crystalline material. A planar p-i-n device architecture with spin-coated poly-(3,4-ethylenedioxythiophene):poly-styrenesulfonic acid (PEDOT:PSS) as hole transport material (HTM) and sputtered ZnO as ETL results in a short circuit current density of 9.5 mA cm -2 and an open circuit potential of 1.19more » V. Numerical simulations are performed to validate the underlying loss mechanisms. The use of phenyl C 60 butyric acid methyl ester (PCBM) interface layer between FAPbBr 3 and sputter-coated ZnO offers shielding from potential plasma-related interface damage. The modified interface results in a better device efficiency of 8.3% with an open circuit potential of 1.35 V. Such devices offer better stability under continuous illumination under ambient conditions in comparison with the conventional organic ETL (PCBM)-based devices.« less

Stable p-i-n FAPbBr 3 devices with improved efficiency using sputtered ZnO as electron transport layer [Stable p-i-n FAPbBr 3 devices with improved efficiency using sputtered inorganic electron transport layer

DOE Office of Scientific and Technical Information (OSTI.GOV)

Subbiah, Anand S.; Agarwal, Sumanshu; Mahuli, Neha

Here, radio-frequency magnetron sputtering is demonstrated as an effective tool to deposit highly crystalline thin zinc oxide (ZnO) layer directly on perovskite absorber as an electron transport layer (ETL). As an absorber, formamidinium lead tribromide (FAPbBr 3) is fabricated through a modified single-step solution process using hydrogen bromide (HBr) as an additive resulting in complete surface coverage and highly crystalline material. A planar p-i-n device architecture with spin-coated poly-(3,4-ethylenedioxythiophene):poly-styrenesulfonic acid (PEDOT:PSS) as hole transport material (HTM) and sputtered ZnO as ETL results in a short circuit current density of 9.5 mA cm -2 and an open circuit potential of 1.19more » V. Numerical simulations are performed to validate the underlying loss mechanisms. The use of phenyl C 60 butyric acid methyl ester (PCBM) interface layer between FAPbBr 3 and sputter-coated ZnO offers shielding from potential plasma-related interface damage. The modified interface results in a better device efficiency of 8.3% with an open circuit potential of 1.35 V. Such devices offer better stability under continuous illumination under ambient conditions in comparison with the conventional organic ETL (PCBM)-based devices.« less

Alkali Salt-Doped Highly Transparent and Thickness-Insensitive Electron-Transport Layer for High-Performance Polymer Solar Cell.

PubMed

Xu, Rongguo; Zhang, Kai; Liu, Xi; Jin, Yaocheng; Jiang, Xiao-Fang; Xu, Qing-Hua; Huang, Fei; Cao, Yong

2018-01-17

Solution-processable highly transparent and thickness-insensitive hybrid electron-transport layer (ETL) with enhanced electron-extraction and electron-transport properties for high-performance polymer solar cell was reported. With the incorporation of Cs 2 CO 3 into the poly[(9,9-bis(6'-((N,N-diethyl)-N-ethylammonium)-hexyl)-2,7-fluorene)-alt-1,4-diphenylsulfide]dibromide (PF6NPSBr) ETL, the power conversion efficiency (PCE) of resulted polymer solar cells (PSCs) was significantly enhanced due to the favorable interfacial contact, energy-level alignment, and thus facile electron transport in the PSC device. These organic-inorganic hybrid ETLs also exhibited high transparency and high electron mobility. All of these combined properties ensured us to design novel thickness-insensitive ETLs that avoid the parasitic absorption of ETL itself simultaneously. With the conventional device structure with poly{4,8-bis[5-(2-ethylhexyl)thiophen-2-yl]benzo[1,2-b:4,5-b']dithiophene-2,6-diyl-alt-3-fluoro-2-[(2-ethylhexyl)carbonyl]thieno[3,4-b]thiophene-4,6-diyl} (PTB7-Th) as a donor and [6,6]-phenyl-C71-butyric acid methyl ester (PC 71 BM) as an acceptor, devices with hybrid ETLs exhibited PCE of 8.30-9.45% within a wide range of ETL thickness. A notable PCE of 10.78% was achieved with the thick active layer poly(2,5-thiophene-alt-5,5'-(5,10-bis(4-(2-octyldodecyl)thiophen-2-yl)naphtho[1,2-c:5,6-c']bis([1,2,5]thiadiazole)) (PTNT812):PC 71 BM. These findings indicated that doping alkali salt into the organic interfacial materials can be a promising strategy to design highly efficient and thickness-insensitive ETL, which may be suitable for large-area PSC modules device fabrication with roll-to-roll printing technique.

The space shuttle payload planning working groups: Volume 9: Materials processing and space manufacturing

NASA Technical Reports Server (NTRS)

1973-01-01

The findings and recommendations of the Materials Processing and Space Manufacturing group of the space shuttle payload planning activity are presented. The effects of weightlessness on the levitation processes, mixture stability, and control over heat and mass transport in fluids are considered for investigation. The research and development projects include: (1) metallurgical processes, (2) electronic materials, (3) biological applications, and (4)nonmetallic materials and processes. Additional recommendations are provided concerning the allocation of payload space, acceptance of experiments for flight, flight qualification, and private use of the space shuttle.

Short-range contacts govern the performance of industry-relevant battery cathodes

NASA Astrophysics Data System (ADS)

Morelly, Samantha L.; Alvarez, Nicolas J.; Tang, Maureen H.

2018-05-01

Fundamental understanding of how processing affects composite battery electrode structure and performance is still lacking, especially for industry-relevant electrodes with low fractions of inactive material. This work combines rheology, electronic conductivity measurements, and battery rate capability tests to prove that short-range electronic contacts are more important to cathode rate capability than either ion transport or long-range electronic conductivity. LiNi0.33Mn0.33Co0.33O2, carbon black, and polyvinylidene difluoride in 1-methyl-2-pyrrolidinone represent a typical commercial electrode with <5.5 wt% inactive material. Dry-mixing carbon black with active material decreases the relative fraction of bulk (free) carbon, as shown by small angle oscillatory shear and microscopy. More free carbon leads to a stronger gel network (more long-range particle contacts) and higher electronic conductivity of the dried films. Improvements in battery rate capability at constant electrode porosity do not correlate to electronic conductivity, but rather show an optimum fraction of free carbon. Simple comparison of rate capability in electrodes with increased total carbon loading (3 wt%) shows improvement for all fractions of free carbon. These results clearly indicate that ion transport cannot be limiting and highlight the critical importance of short-range electronic contacts for controlling battery performance.

Simulation of electron beam formation and transport in a gas-filled electron-optical system with a plasma emitter

DOE Office of Scientific and Technical Information (OSTI.GOV)

Grishkov, A. A.; Kornilov, S. Yu., E-mail: kornilovsy@gmail.com; Rempe, N. G.

2016-07-15

The results of computer simulations of the electron-optical system of an electron gun with a plasma emitter are presented. The simulations are performed using the KOBRA3-INP, XOOPIC, and ANSYS codes. The results describe the electron beam formation and transport. The electron trajectories are analyzed. The mechanisms of gas influence on the energy inhomogeneity of the beam and its current in the regions of beam primary formation, acceleration, and transport are described. Recommendations for optimizing the electron-optical system with a plasma emitter are presented.

Tracking Electron Uptake from a Cathode into Shewanella Cells: Implications for Energy Acquisition from Solid-Substrate Electron Donors

PubMed Central

Rajeev, Pournami; Jain, Abhiney; Pirbadian, Sahand; Okamoto, Akihiro; Gralnick, Jeffrey A.; El-Naggar, Mohamed Y.; Nealson, Kenneth H.

2018-01-01

ABSTRACT While typically investigated as a microorganism capable of extracellular electron transfer to minerals or anodes, Shewanella oneidensis MR-1 can also facilitate electron flow from a cathode to terminal electron acceptors, such as fumarate or oxygen, thereby providing a model system for a process that has significant environmental and technological implications. This work demonstrates that cathodic electrons enter the electron transport chain of S. oneidensis when oxygen is used as the terminal electron acceptor. The effect of electron transport chain inhibitors suggested that a proton gradient is generated during cathode oxidation, consistent with the higher cellular ATP levels measured in cathode-respiring cells than in controls. Cathode oxidation also correlated with an increase in the cellular redox (NADH/FMNH2) pool determined with a bioluminescence assay, a proton uncoupler, and a mutant of proton-pumping NADH oxidase complex I. This work suggested that the generation of NADH/FMNH2 under cathodic conditions was linked to reverse electron flow mediated by complex I. A decrease in cathodic electron uptake was observed in various mutant strains, including those lacking the extracellular electron transfer components necessary for anodic-current generation. While no cell growth was observed under these conditions, here we show that cathode oxidation is linked to cellular energy acquisition, resulting in a quantifiable reduction in the cellular decay rate. This work highlights a potential mechanism for cell survival and/or persistence on cathodes, which might extend to environments where growth and division are severely limited. PMID:29487241

Brillouin light scattering as a probe for low frequency quasiparticles in solids

NASA Astrophysics Data System (ADS)

Klimovich, Nikita; Olson, Kevin; An, Kyongmo; Sullivan, Sean; Weathers, Annie; Shi, Li; Li, Xiaoqin

2015-03-01

In increasingly small electronic and spintronic devices, electrons, optical phonons, acoustic phonons, and magnons are often driven out of local thermal equilibrium. Thermal transport based on equilibrium dynamics does not adequately describe these systems necessitating a better understanding of non-equilibrium transport processes. Measuring the specific temperatures of the different energy carriers is therefore crucial in understanding the thermal transport. Brillouin light scattering (BLS) has recently been explored as a temperature sensor for low frequency acoustic phonons in glass, and also magnons in metallic and insulating ferromagnetic materials. We report the measured BLS spectra of acoustic phonons in Silicon at different temperatures. The temperature dependence of the BLS peak frequency, linewidth, and integrated intensity are examined to evaluate their potential uses as temperature sensors of acoustic phonons. We also observe a large nonequilibrium in phonon-magnon temperature in YIG under the effects of laser heating and thereby extract a value for the phonon-magnon coupling coefficient. This work is funded by the National Science Foundation and the Army Research Office.

Donor-acceptor cocrystal based on hexakis(alkoxy)triphenylene and perylenediimide derivatives with an ambipolar transporting property.

PubMed

Su, Yajun; Li, Yan; Liu, Jiangang; Xing, Rubo; Han, Yanchun

2015-02-07

An organic donor-acceptor cocrystal with an ambipolar transporting property was constructed based on N,N'-bis(1-ethylpropyl)-perylene-3,4,9,10-tetracarboxylic diimide (EP-PDI) and 2,3,6,7,10,11-hexakis-(hexyloxy)-triphenylene (H6TP). The cocrystal with an alternating stacking of H6TP and EP-PDI molecules was formed through both drop-casting and spin-coating processes, especially at the optimized ratios of H6TP/EP-PDI (2/1, 1/1). The formation of the cocrystal was driven by the strong π-π interaction and the weaker steric hindrance, resulting from the smaller side groups, between the donor and acceptor molecules. Field effect transistors (FETs) based on the H6TP/EP-PDI cocrystal exhibited relatively balanced hole/electron transport, with a hole mobility of 1.14 × 10(-3) cm(2) V(-1) s(-1) and an electron mobility of 1.40 × 10(-3) cm(2) V(-1) s(-1).

DOE Office of Scientific and Technical Information (OSTI.GOV)

Liu, Chang; Fox, William; Bhattacharjee, Amitava

Recent theory has demonstrated a novel physics regime for magnetic reconnection in high-energy-density plasmas where the magnetic field is advected by heat flux via the Nernst effect. In this paper, we elucidate the physics of the electron dissipation layer in this regime. Through fully kinetic simulation and a generalized Ohm's law derived from first principles, we show that momentum transport due to a nonlocal effect, the heat-flux-viscosity, provides the dissipation mechanism for magnetic reconnection. Scaling analysis, and simulations show that the reconnection process comprises a magnetic field compression stage and quasisteady reconnection stage, and the characteristic width of the currentmore » sheet in this regime is several electron mean-free paths. Finally, these results show the important interplay between nonlocal transport effects and generation of anisotropic components to the distribution function.« less

Current at Metal-Organic Interfaces

NASA Astrophysics Data System (ADS)

Kern, Klaus

2012-02-01

Charge transport through atomic and molecular constrictions greatly affects the operation and performance of organic electronic devices. Much of our understanding of the charge injection and extraction processes in these systems relays on our knowledge of the electronic structure at the metal-organic interface. Despite significant experimental and theoretical advances in studying charge transport in nanoscale junctions, a microscopic understanding at the single atom/molecule level is missing. In the present talk I will present our recent results to probe directly the nanocontact between single molecules and a metal electrode using scanning probe microscopy and spectroscopy. The experiments provide unprecedented microscopic details of single molecule and atom junctions and open new avenues to study quantum critical and many body phenomena at the atomic scale. Implications for energy conversion devices and carbon based nanoelectronics will also be discussed.

Balanced electron-hole transport in spin-orbit semimetal SrIrO3 heterostructures

NASA Astrophysics Data System (ADS)

Manca, Nicola; Groenendijk, Dirk J.; Pallecchi, Ilaria; Autieri, Carmine; Tang, Lucas M. K.; Telesio, Francesca; Mattoni, Giordano; McCollam, Alix; Picozzi, Silvia; Caviglia, Andrea D.

2018-02-01

Relating the band structure of correlated semimetals to their transport properties is a complex and often open issue. The partial occupation of numerous electron and hole bands can result in properties that are seemingly in contrast with one another, complicating the extraction of the transport coefficients of different bands. The 5 d oxide SrIrO3 hosts parabolic bands of heavy holes and light electrons in gapped Dirac cones due to the interplay between electron-electron interactions and spin-orbit coupling. We present a multifold approach relying on different experimental techniques and theoretical calculations to disentangle its complex electronic properties. By combining magnetotransport and thermoelectric measurements in a field-effect geometry with first-principles calculations, we quantitatively determine the transport coefficients of different conduction channels. Despite their different dispersion relationships, electrons and holes are found to have strikingly similar transport coefficients, yielding a holelike response under field-effect and thermoelectric measurements and a linear electronlike Hall effect up to 33 T.

Scientific Computation Application Partnerships in Materials and Chemical Sciences, Charge Transfer and Charge Transport in Photoactivated Systems, Developing Electron-Correlated Methods for Excited State Structure and Dynamics in the NWChem Software Suite

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cramer, Christopher J.

Charge transfer and charge transport in photoactivated systems are fundamental processes that underlie solar energy capture, solar energy conversion, and photoactivated catalysis, both organometallic and enzymatic. We developed methods, algorithms, and software tools needed for reliable treatment of the underlying physics for charge transfer and charge transport, an undertaking with broad applicability to the goals of the fundamental-interaction component of the Department of Energy Office of Basic Energy Sciences and the exascale initiative of the Office of Advanced Scientific Computing Research.

Magnetosphere-ionosphere coupling during active aurora

NASA Astrophysics Data System (ADS)

Grubbs, Guy, II

In this work, processes which couple the Earth's magnetosphere and ionosphere are examined using observations of aurora from ground-based imaging, in situ electron measurements, and electron transport modeling. The coupling of these regions relies heavily on the energy transport between the two and the ionospheric conductances, which regulate the location and magnitude of the transport. The combination of the datasets described are used to derive the conductances and electron energy populations at the upper boundary of the ionosphere. These values are constrained using error analysis of the observation and measurement techniques and made available to the global magnetosphere modeling community for inclusion as boundary conditions at the magnetosphere and ionosphere coupling region. A comparative study of the active aurora and incident electron distributions was conducted using ground-based measurements and in-situ sounding rocket data. Three narrow-field (47 degree field-of-view) electron-multiplying charge-coupled device (EMCCD) imagers were located at Venetie, AK which took high spatio-temporal resolution measurements of the aurora using different wavelength filters (427.8 nm, 557.7 nm, and 844.6 nm). The measured emission line ratios were combined with atmospheric modeling in order to predict the total electron energy flux and characteristic electron energy incident on the atmosphere. These predictions were compared with in-situ measurements made by the Ground-to-Rocket Electrodynamics-Electrons Correlative Experiment (GREECE) sounding rocket launched in early 2014. The GREECE particle instruments were modeled using a ray-tracing program, SIMION, in order to predict the instrument responses for different incident particles. Each instrument model was compared with data taken in the lab in order to compare and update the models appropriately. A rocket emulation system was constructed for lab testing prior to and during instrument integration into the rocket and used throughout the project to test instrument response and output. EMCCD imagers were calibrated using known light sources in order to find the imager response at each pixel prior to and during deployment. Electron transport models were modified to use the most recent versions of empirical atmospheric models and chemical reaction rates. The electron transport models showed less than 20% and 50% error for intensity measurements 10 degrees and 20 degrees from magnetic zenith, respectively. An inversion technique was developed in order to derive the characteristics of the in situ electron populations using only the spectral ground-based imaging. The electron populations and atmospheric conductances were characterized, using the inversion technique and the modified Robinson relation, during the St. Patrick's Day storm on 18 March 2015. Discrete arcs contained the most energetic electrons and highest conductances, followed by pulsating aurora and then diffuse aurora. These techniques can be used to constrain the electrons and ionospheric conductances responsible for different types of aurora using imaging data taken over long time periods, when in situ measurements are unavailable.

49 CFR Appendix C to Part 599 - Electronic Transaction Screen

Code of Federal Regulations, 2010 CFR

2010-10-01

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2012-10-01

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2013-10-01

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2014-10-01

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2011-10-01

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Enhanced efficiency and stability of inverted perovskite solar cells using highly crystalline SnO 2 nanocrystals as the robust electron-transporting layer

DOE PAGES

Zhu, Zonglong; Bai, Yang; Liu, Xiao; ...

2016-05-11

Here highly crystalline SnO 2 is demonstrated to serve as a stable and robust electron-transporting layer for high-performance perovskite solar cells. Benefiting from its high crystallinity, the relatively thick SnO 2 electron-transporting layer (≈120 nm) provides a respectable electron-transporting property to yield a promising power conversion efficiency (PCE)(18.8%) Over 90% of the initial PCE can be retained after 30 d storage in ambient with ≈70% relative humidity.

Color stable white phosphorescent organic light emitting diodes with red emissive electron transport layer

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wook Kim, Jin; Yoo, Seung Il; Sung Kang, Jin

2015-06-28

We analyzed the performance of multi-emissive white phosphorescent organic light-emitting diodes (PHOLEDs) in relation to various red emitting sites of hole and electron transport layers (HTL and ETL). The shift of the recombination zone producing stable white emission in PHOLEDs was utilized as luminance was increased with red emission in its electron transport layer. Multi-emissive white PHOLEDs including the red light emitting electron transport layer yielded maximum external quantum efficiency of 17.4% with CIE color coordinates (−0.030, +0.001) shifting only from 1000 to 10 000 cd/m{sup 2}. Additionally, we observed a reduction of energy loss in the white PHOLED via Ir(piq){submore » 3} as phosphorescent red dopant in electron transport layer.« less

Anomalous Transport in High Beta Poloidal DIII-D Discharges

NASA Astrophysics Data System (ADS)

Pankin, A.; Garofalo, A.; Kritz, A.; Rafiq, T.; Weiland, J.

2016-10-01

Dominant instabilities that drive anomalous transport in high beta poloidal DIII-D discharges are investigated using the MMM7.1, and TGLF models in the predictive integrated modeling TRANSP code. The ion thermal transport is found to be strongly reduced in these discharges, but turbulence driven by the ITG modes along with the neoclassical transport still play a role in determining the ion temperature profiles. The electron thermal transport driven by the ETG modes impact the electron temperature profiles. The E × B flow shear is found to have a small effect in reducing the electron thermal transport. The Shafranov shift is found to strongly reduce the anomalous transport in the high beta poloidal DIII-D discharges. The reduction of Shafranov shift can destroy the ion internal transport barrier and can result in significantly lower core temperatures. The MMM7.1 model predicts electron and ion temperature profiles reasonably well, but it fails to accurately predict the properties of electron internal transport barrier, which indicates that the ETG model in MMM7.1 needs to be improved in the high beta poloidal operational regime. Research supported by the Office of Science, US DOE.

Electronic Versus Manual Data Processing: Evaluating the Use of Electronic Health Records in Out-of-Hospital Clinical Research

PubMed Central

Newgard, Craig D.; Zive, Dana; Jui, Jonathan; Weathers, Cody; Daya, Mohamud

2011-01-01

Objectives To compare case ascertainment, agreement, validity, and missing values for clinical research data obtained, processed, and linked electronically from electronic health records (EHR), compared to “manual” data processing and record abstraction in a cohort of out-ofhospital trauma patients. Methods This was a secondary analysis of two sets of data collected for a prospective, population-based, out-of-hospital trauma cohort evaluated by 10 emergency medical services (EMS) agencies transporting to 16 hospitals, from January 1, 2006 through October 2, 2007. Eighteen clinical, operational, procedural, and outcome variables were collected and processed separately and independently using two parallel data processing strategies, by personnel blinded to patients in the other group. The electronic approach included electronic health record data exports from EMS agencies, reformatting and probabilistic linkage to outcomes from local trauma registries and state discharge databases. The manual data processing approach included chart matching, data abstraction, and data entry by a trained abstractor. Descriptive statistics, measures of agreement, and validity were used to compare the two approaches to data processing. Results During the 21-month period, 418 patients underwent both data processing methods and formed the primary cohort. Agreement was good to excellent (kappa 0.76 to 0.97; intraclass correlation coefficient 0.49 to 0.97), with exact agreement in 67% to 99% of cases, and a median difference of zero for all continuous and ordinal variables. The proportions of missing out-of-hospital values were similar between the two approaches, although electronic processing generated more missing outcomes (87 out of 418, 21%, 95% CI = 17% to 25%) than the manual approach (11 out of 418, 3%, 95% CI = 1% to 5%). Case ascertainment of eligible injured patients was greater using electronic methods (n = 3,008) compared to manual methods (n = 629). Conclusions In this sample of out-of-hospital trauma patients, an all-electronic data processing strategy identified more patients and generated values with good agreement and validity compared to traditional data collection and processing methods. PMID:22320373

77 FR 47692 - Notice of Transportation Services' Transition From Paper to Electronic Fare Media Comments...

Federal Register 2010, 2011, 2012, 2013, 2014

2012-08-09

... limited to, system activity monitoring, data mining, anomaly reporting, etc. In order to reduce or... situations. Comment: Commenters asked about transaction monitoring, the restriction process developed for monitoring compliance, and how the TRANServe card would be protected to reduce fraudulent use. Response: The...

Significant modulation of mitochondrial electron transport system by nicotine in various rat brain regions

USDA-ARS?s Scientific Manuscript database

The mitochondrion is the organelle responsible for generation of most usable energy in a cell. It also plays an important role in a series of physiological processes such as apoptosis and proliferation. Although previous studies have demonstrated that nicotine modulates the morphology and function ...

75 FR 29568 - Extension of Agency Information Collection Activity Under OMB Review: Aircraft Operator Security

Federal Register 2010, 2011, 2012, 2013, 2014

2010-05-26

... Act (PRA) Officer, Office of Information Technology (OIT), TSA-11, Transportation Security..., electronic, mechanical, or other technological collection techniques or other forms of information technology... criminal history records check (CHRC). As part of the CHRC process, the individual must provide identifying...

Bias Voltage-Dependent Impedance Spectroscopy Analysis of Hydrothermally Synthesized ZnS Nanoparticles

NASA Astrophysics Data System (ADS)

Dey, Arka; Dhar, Joydeep; Sil, Sayantan; Jana, Rajkumar; Ray, Partha Pratim

2018-04-01

In this report, bias voltage-dependent dielectric and electron transport properties of ZnS nanoparticles were discussed. ZnS nanoparticles were synthesized by introducing a modified hydrothermal process. The powder XRD pattern indicates the phase purity, and field emission scanning electron microscope image demonstrates the morphology of the synthesized sample. The optical band gap energy (E g = 4.2 eV) from UV measurement explores semiconductor behavior of the synthesized material. The electrical properties were performed at room temperature using complex impedance spectroscopy (CIS) technique as a function of frequency (40 Hz-10 MHz) under different forward dc bias voltages (0-1 V). The CIS analysis demonstrates the contribution of bulk resistance in conduction mechanism and its dependency on forward dc bias voltages. The imaginary part of the impedance versus frequency curve exhibits the existence of relaxation peak which shifts with increasing dc forward bias voltages. The dc bias voltage-dependent ac and dc conductivity of the synthesized ZnS was studied on thin film structure. A possible hopping mechanism for electrical transport processes in the system was investigated. Finally, it is worth to mention that this analysis of bias voltage-dependent dielectric and transport properties of as-synthesized ZnS showed excellent properties for emerging energy applications.

Doping and electronic properties of GaAs grown by close-spaced vapor transport from powder sources for scalable III–V photovoltaics

DOE PAGES

Ritenour, Andrew J.; Boucher, Jason W.; DeLancey, Robert; ...

2014-09-01

The high balance-of-system costs of photovoltaic (PV) installations indicate that reductions in cell $/W costs alone are likely insufficient for PV electricity to reach grid parity unless energy conversion efficiency is also increased. Technologies which yield both high-efficiency cells (>25%) and maintain low costs are needed. GaAs and related III-V semiconductors are used in the highest-efficiency single- and multi-junction photovoltaics, but the technology is too expensive for non-concentrated terrestrial applications. This is due in part to the difficulty of scaling the metal-organic chemical vapor deposition (MOCVD) process, which relies on expensive reactors and employs toxic and pyrophoric gas-phase precursors suchmore » as arsine and trimethyl gallium, respectively. In this study, we describe GaAs films made by an alternative close-spaced vapor transport (CSVT) technique which is carried out at atmospheric pressure and requires only bulk GaAs, water vapor, and a temperature gradient in order to deposit crystalline films with similar electronic properties to that of GaAs deposited by MOCVD. CSVT is similar to the vapor transport process used to deposit CdTe thin films and is thus a potentially scalable low-cost route to GaAs thin films.« less

Fabrication and ab initio study of downscaled graphene nanoelectronic devices

NASA Astrophysics Data System (ADS)

Mizuta, Hiroshi; Moktadir, Zakaria; Boden, Stuart A.; Kalhor, Nima; Hang, Shuojin; Schmidt, Marek E.; Cuong, Nguyen Tien; Chi, Dam Hieu; Otsuka, Nobuo; Muruganathan, Manoharan; Tsuchiya, Yoshishige; Chong, Harold; Rutt, Harvey N.; Bagnall, Darren M.

2012-09-01

In this paper we first present a new fabrication process of downscaled graphene nanodevices based on direct milling of graphene using an atomic-size helium ion beam. We address the issue of contamination caused by the electron-beam lithography process to pattern the contact metals prior to the ultrafine milling process in the helium ion microscope (HIM). We then present our recent experimental study of the effects of the helium ion exposure on the carrier transport properties. By varying the time of helium ion bombardment onto a bilayer graphene nanoribbon transistor, the change in the transfer characteristics is investigated along with underlying carrier scattering mechanisms. Finally we study the effects of various single defects introduced into extremely-scaled armchair graphene nanoribbons on the carrier transport properties using ab initio simulation.

Energy-filtered cold electron transport at room temperature

PubMed Central

Bhadrachalam, Pradeep; Subramanian, Ramkumar; Ray, Vishva; Ma, Liang-Chieh; Wang, Weichao; Kim, Jiyoung; Cho, Kyeongjae; Koh, Seong Jin

2014-01-01

Fermi-Dirac electron thermal excitation is an intrinsic phenomenon that limits functionality of various electron systems. Efforts to manipulate electron thermal excitation have been successful when the entire system is cooled to cryogenic temperatures, typically <1 K. Here we show that electron thermal excitation can be effectively suppressed at room temperature, and energy-suppressed electrons, whose energy distribution corresponds to an effective electron temperature of ~45 K, can be transported throughout device components without external cooling. This is accomplished using a discrete level of a quantum well, which filters out thermally excited electrons and permits only energy-suppressed electrons to participate in electron transport. The quantum well (~2 nm of Cr2O3) is formed between source (Cr) and tunnelling barrier (SiO2) in a double-barrier-tunnelling-junction structure having a quantum dot as the central island. Cold electron transport is detected from extremely narrow differential conductance peaks in electron tunnelling through CdSe quantum dots, with full widths at half maximum of only ~15 mV at room temperature. PMID:25204839

Experimental Studies of Lateral Electron Transport in Gallium Arsenide-Aluminum Gallium Arsenide Heterostructures.

DTIC Science & Technology

1982-12-01

AD-A125 858 EXPERIMENTAL STUDIES OF LATERAL ELECTRON TRANSPORT IN 1/3 GALLIUM ARSENIDE-RL..(U) ILLINOIS UNIV AT URBANA COORDINATED SCIENCE LAB N R...EXPERIMENTAL STUDIES OF LATERALXILECTRON TRANSPORT ,:g IN GALLIUM ARSENIDE -ALUMINUM GALLIUM ARSENIDE- -HETEROSTRUCTURES APRVE O PUBLICRLEAS.DSRBUINULMTE. 2...EXPERIMENTAL STUDIES OF LATERAL ELECTRON TRANSPORT IN GALLIUM ARSENIDE-ALUMINUM GALLIUM ARSENIDE Technical Report R-975 HETEROSTRUCTURES 6. PERFORMING ONG

Mixed conduction and grain boundary effect in lithium niobate under high pressure

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wang, Qinglin; Center for High Pressure Science and Technology Advanced Research, Changchun 130012; Liu, Cailong

2015-03-30

The charge transport behavior of lithium niobate has been investigated by in situ impedance measurement up to 40.6 GPa. The Li{sup +} ionic conduction plays a dominant role in the transport process. The relaxation process is described by the Maxwell-Wagner relaxation arising at the interfaces between grains and grain boundaries. The grain boundary microstructure rearranges after the phase transition, which improves the bulk dielectric performance. The theoretical calculations show that the decrease of bulk permittivity with increasing pressure in the Pnma phase is caused by the pressure-induced enhancement of electron localization around O atoms, which limits the polarization of Nb-O electricmore » dipoles.« less

Influence of electromagnetic field on soliton-mediated charge transport in biological systems.

PubMed

Brizhik, Larissa

2015-01-01

It is shown that electromagnetic fields affect dynamics of Davydov's solitons which provide charge transport processes in macromolecules during metabolism of the system. There is a resonant frequency of the field at which it can cause the transition of electrons from bound soliton states into delocalised states. Such decay of solitons reduces the effectiveness of charge transport, and, therefore, inhibits redox processes. Solitons radiate their own electromagnetic field of characteristic frequency determined by their average velocity. This self-radiated field leads to synchronization of soliton dynamics and charge transport processes, and is the source of the coherence in the system. Exposition of the system to the oscillating electromagnetic field of the frequency, which coincides with the eigen-frequency of solitons can enhance eigen-radiation of solitons, and, therefore, will enhance synchronization of charge transpor, stimulate the redox processes and increase coherence in the system. Electromagnetic oscillating field causes also ratchet phenomenon of solitons, i.e., drift of solitons in macromolecules in the presence of unbiased periodic field. Such additional drift enhances the charge transport processes. It is shown that temperature facilitates the ratchet drift. In particular, temperature fluctuations lead to the lowering of the critical value of the intensity and period of the field, above which the drift of solitons takes place. Moreover, there is a stochastic resonance in the soliton dynamics in external electromagnetic fields. This means, that there is some optimal temperature at which the drift of solitons is maximal.

49 CFR 220.305 - Use of personal electronic devices.

Code of Federal Regulations, 2010 CFR

2010-10-01

... ADMINISTRATION, DEPARTMENT OF TRANSPORTATION RAILROAD COMMUNICATIONS Electronic Devices § 220.305 Use of personal electronic devices. A railroad operating employee must have each personal electronic device turned off with... 49 Transportation 4 2010-10-01 2010-10-01 false Use of personal electronic devices. 220.305...

49 CFR 220.305 - Use of personal electronic devices.

Code of Federal Regulations, 2011 CFR

2011-10-01

... 49 Transportation 4 2011-10-01 2011-10-01 false Use of personal electronic devices. 220.305... ADMINISTRATION, DEPARTMENT OF TRANSPORTATION RAILROAD COMMUNICATIONS Electronic Devices § 220.305 Use of personal electronic devices. A railroad operating employee must have each personal electronic device turned off with...

49 CFR 220.305 - Use of personal electronic devices.

Code of Federal Regulations, 2012 CFR

2012-10-01

... 49 Transportation 4 2012-10-01 2012-10-01 false Use of personal electronic devices. 220.305... ADMINISTRATION, DEPARTMENT OF TRANSPORTATION RAILROAD COMMUNICATIONS Electronic Devices § 220.305 Use of personal electronic devices. A railroad operating employee must have each personal electronic device turned off with...

Solution-Processed Metal Oxides as Efficient Carrier Transport Layers for Organic Photovoltaics.

PubMed

Choy, Wallace C H; Zhang, Di

2016-01-27

Carrier (electron and hole) transport layers (CTLs) are essential components for boosting the performance of various organic optoelectronic devices such as organic solar cells and organic light-emitting diodes. Considering the drawbacks of conventional CTLs (easily oxidized/unstable, demanding/costly fabrication, etc.), transition metal oxides with good carrier transport/extraction and superior stability have drawn extensive research interest as CTLs for next-generation devices. In recent years, many research efforts have been made toward the development of solution-based metal oxide CTLs with the focus on low- or even room-temperature processes, which can potentially be compatible with the deposition processes of organic materials and can significantly contribute to the low-cost and scale-up of organic devices. Here, the recent progress of different types of solution-processed metal oxide CTLs are systematically reviewed in the context of organic photovoltaics, from synthesis approaches to device performance. Different approaches for further enhancing the performance of solution-based metal oxide CTLs are also discussed, which may push the future development of this exciting field. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Electrical response of electron selective atomic layer deposited TiO2‑x heterocontacts on crystalline silicon substrates

NASA Astrophysics Data System (ADS)

Ahiboz, Doğuşcan; Nasser, Hisham; Aygün, Ezgi; Bek, Alpan; Turan, Raşit

2018-04-01

Integration of oxygen deficient sub-stoichiometric titanium dioxide (TiO2‑x) thin films as the electron transporting-hole blocking layer in solar cell designs are expected to reduce fabrication costs by eliminating high temperature processes while maintaining high conversion efficiencies. In this paper, we conducted a study to reveal the electrical properties of TiO2‑x thin films grown on crystalline silicon (c-Si) substrates by atomic layer deposition (ALD) technique. Effect of ALD substrate temperature, post deposition annealing, and doping type of the c-Si substrate on the interface states and TiO2‑x bulk properties were extracted by performing admittance (C-V, G-V) and current-voltage (J-V) measurements. Moreover, the asymmetry in C-V and J-V measurements between the p-n type and n-n TiO2‑x-c-Si heterojunction types were examined and the electron transport selectivity of TiO2‑x was revealed.

Crucial role of decoherence for electronic transport in molecular wires: Polyaniline as a case study

NASA Astrophysics Data System (ADS)

Cattena, Carlos J.; Bustos-Marún, Raúl A.; Pastawski, Horacio M.

2010-10-01

In this work we attempt to elucidate the nature of conductivity in polymers by taking the acid-base doped polyaniline (PAni) polymer. We evaluate the PAni conductance by using realistic ab initio parameters and including decoherent processes within the minimal parametrization model of D’Amato-Pastawski. In contrast to general wisdom, which associates the conducting state with coherent propagation in a periodic polaronic lattice, we show that decoherence can account for high conductance in the strongly disordered bipolaronic lattice. Hence, according to our results, there is no need of considering a mix model of “conducting” polaronic lattice islands separated by “insulating” bipolaronic lattice strands as is usually assumed for PAni. We find that without dephasing events, even very short strands of bipolaronic lattices are not able to sustain electronic transport. We also include a discussion of specific mechanisms that should be involved in decoherence rates of PAni and relate them with Marcus-Hush theory of electron transfer.

Electron transport limitation in P3HT:CdSe nanorods hybrid solar cells.

PubMed

Lek, Jun Yan; Xing, Guichuan; Sum, Tze Chien; Lam, Yeng Ming

2014-01-22

Hybrid solar cells have the potential to be efficient solar-energy-harvesting devices that can combine the benefits of solution-processable organic materials and the extended absorption offered by inorganic materials. In this work, an understanding of the factors limiting the performance of hybrid solar cells is explored. Through photovoltaic-device characterization correlated with transient absorption spectroscopy measurements, it was found that the interfacial charge transfer between the organic (P3HT) and inorganic (CdSe nanorods) components is not the factor limiting the performance of these solar cells. The insulating original ligands retard the charge recombination between the charge-transfer states across the CdSe-P3HT interface, and this is actually beneficial for charge collection. These cells are, in fact, limited by the subsequent electron collection via CdSe nanoparticles to the electrodes. Hence, the design of a more continuous electron-transport pathway should greatly improve the performance of hybrid solar cells in the future.

Limitations for current production in Geobacter sulfurreducens biofilms.

PubMed

Bonanni, P Sebastian; Bradley, Dan F; Schrott, Germán D; Busalmen, Juan Pablo

2013-04-01

Devices that exploit electricity produced by electroactive bacteria such as Geobacter sulfurreducens have not yet been demonstrated beyond the laboratory scale. The current densities are far from the maximum that the bacteria can produce because fundamental properties such as the mechanism of extracellular electron transport and factors limiting cell respiration remain unclear. In this work, a strategy for the investigation of electroactive biofilms is presented. Numerical modeling of the response of G. sulfurreducens biofilms cultured on a rotating disk electrode has allowed for the discrimination of different limiting steps in the process of current production within a biofilm. The model outputs reveal that extracellular electron transport limits the respiration rate of the cells furthest from the electrode to the extent that cell division is not possible. The mathematical model also demonstrates that recent findings such as the existence of a redox gradient in actively respiring biofilms can be explained by an electron hopping mechanism but not when considering metallic-like conductivities. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Fluid theory and simulations of instabilities, turbulent transport and coherent structures in partially-magnetized plasmas of \\mathbf{E}\\times \\mathbf{B} discharges

NASA Astrophysics Data System (ADS)

Smolyakov, A. I.; Chapurin, O.; Frias, W.; Koshkarov, O.; Romadanov, I.; Tang, T.; Umansky, M.; Raitses, Y.; Kaganovich, I. D.; Lakhin, V. P.

2017-01-01

Partially-magnetized plasmas with magnetized electrons and non-magnetized ions are common in Hall thrusters for electric propulsion and magnetron material processing devices. These plasmas are usually in strongly non-equilibrium state due to presence of crossed electric and magnetic fields, inhomogeneities of plasma density, temperature, magnetic field and beams of accelerated ions. Free energy from these sources make such plasmas prone to various instabilities resulting in turbulence, anomalous transport, and appearance of coherent structures as found in experiments. This paper provides an overview of instabilities that exist in such plasmas. A nonlinear fluid model has been developed for description of the Simon-Hoh, lower-hybrid and ion-sound instabilities. The model also incorporates electron gyroviscosity describing the effects of finite electron temperature. The nonlinear fluid model has been implemented in the BOUT++ framework. The results of nonlinear simulations are presented demonstrating turbulence, anomalous current and tendency toward the formation of coherent structures.

Simulation of the effects of sub-breakdown electric fields on the chemical kinetics in nonpremixed counterflow methane/air flames

NASA Astrophysics Data System (ADS)

Belhi, Memdouh; Im, Hong; Computational Reacting Flows Laboratory, Clean Combustion Research Center Team

2017-11-01

The effects of an electric field on the combustion kinetics in nonpremixed counterflow methane/air flames were investigated via one-dimensional numerical simulations. A classical fluid model coupling Poison's equation with transport equations for combustion species and electric field-induced particles was used. A methane-air reaction mechanism accounting for the natural ionization in flames was combined with a set of reactions that describe the formation of active particles induced by the electric field. Kinetic parameters for electron-impact reactions and transport coefficients of electrons were modeled as functions of reduced electric field via solutions to the Boltzmann kinetic equation using the BOLSIG code. Mobility of ions was computed based on the (n,6,4) and coulomb interaction potentials, while the diffusion coefficient was approximated from the mobility using Einstein relation. Contributions of electron dissociation, excitation and ionization processes were characterized quantitatively. An analysis to identify the plasma regime where the electric field can alter the combustion kinetic was proposed.

Unraveling Massive Crocins Transport and Accumulation through Proteome and Microscopy Tools during the Development of Saffron Stigma

PubMed Central

Gómez-Gómez, Lourdes; Parra-Vega, Verónica; Rivas-Sendra, Alba; Seguí-Simarro, Jose M.; Molina, Rosa Victoria; Pallotti, Claudia; Rubio-Moraga, Ángela; Diretto, Gianfranco; Prieto, Alicia; Ahrazem, Oussama

2017-01-01

Crocins, the glucosides of crocetin, are present at high concentrations in saffron stigmas and accumulate in the vacuole. However, the biogenesis of the saffron chromoplast, the changes during the development of the stigma and the transport of crocins to the vacuole, are processes that remain poorly understood. We studied the process of chromoplast differentiation in saffron throughout stigma development by means of transmission electron microscopy. Our results provided an overview of a massive transport of crocins to the vacuole in the later developmental stages, when electron dense drops of a much greater size than plastoglobules (here defined “crocinoplast”) were observed in the chromoplast, connected to the vacuole with a subsequent transfer of these large globules inside the vacuole. A proteome analysis of chromoplasts from saffron stigma allowed the identification of several well-known plastid proteins and new candidates involved in crocetin metabolism. Furthermore, expressions throughout five developmental stages of candidate genes responsible for carotenoid and apocarotenoid biogenesis, crocins transport to the vacuole and starch metabolism were analyzed. Correlation matrices and networks were exploited to identify a series of transcripts highly associated to crocetin (such as 1-Deoxy-d-xylulose 5-phosphate synthase (DXS), 1-Deoxy-d-xylulose 5-phosphate reductoisomerase (DXR), carotenoid isomerase (CRTISO), Crocetin glucosyltransferase 2 (UGT2), etc.) and crocin (e.g., ζ-carotene desaturase (ZDS) and plastid-lipid-associated proteins (PLAP2)) accumulation; in addition, candidate aldehyde dehydrogenase (ADH) genes were highlighted. PMID:28045431

Lead Halide Perovskites as Charge Generation Layers for Electron Mobility Measurement in Organic Semiconductors.

PubMed

Love, John A; Feuerstein, Markus; Wolff, Christian M; Facchetti, Antonio; Neher, Dieter

2017-12-06

Hybrid lead halide perovskites are introduced as charge generation layers (CGLs) for the accurate determination of electron mobilities in thin organic semiconductors. Such hybrid perovskites have become a widely studied photovoltaic material in their own right, for their high efficiencies, ease of processing from solution, strong absorption, and efficient photogeneration of charge. Time-of-flight (ToF) measurements on bilayer samples consisting of the perovskite CGL and an organic semiconductor layer of different thickness are shown to be determined by the carrier motion through the organic material, consistent with the much higher charge carrier mobility in the perovskite. Together with the efficient photon-to-electron conversion in the perovskite, this high mobility imbalance enables electron-only mobility measurement on relatively thin application-relevant organic films, which would not be possible with traditional ToF measurements. This architecture enables electron-selective mobility measurements in single components as well as bulk-heterojunction films as demonstrated in the prototypical polymer/fullerene blends. To further demonstrate the potential of this approach, electron mobilities were measured as a function of electric field and temperature in an only 127 nm thick layer of a prototypical electron-transporting perylene diimide-based polymer, and found to be consistent with an exponential trap distribution of ca. 60 meV. Our study furthermore highlights the importance of high mobility charge transporting layers when designing perovskite solar cells.

Performance of regional oxygen saturation monitoring by near-infrared spectroscopy (NIRS) in pediatric inter-hospital transports with special reference to air ambulance transports: a methodological study.

PubMed

Hamrin, Tova Hannegård; Radell, Peter J; Fläring, Urban; Berner, Jonas; Eksborg, Staffan

2017-12-28

The aim of the present study was to evaluate the performance of regional oxygen saturation (rSO 2 ) monitoring with near infrared spectroscopy (NIRS) during pediatric inter-hospital transports and to optimize processing of the electronically stored data. Cerebral (rSO 2 -C) and abdominal (rSO 2 -A) NIRS sensors were used during transport in air ambulance and connecting ground ambulance. Data were electronically stored by the monitor during transport, extracted and analyzed off-line after the transport. After removal of all zero and floor effect values, the Savitzky-Golay algorithm of data smoothing was applied on the NIRS-signal. The second order of smoothing polynomial was used and the optimal number of neighboring points for the smoothing procedure was evaluated. NIRS-data from 38 pediatric patients was examined. Reliability, defined as measurements without values of 0 or 15%, was acceptable during transport (> 90% of all measurements). There were, however, individual patients with < 90% reliable measurements during transport, while no patient was found to have < 90% reliable measurements in hospital. Satisfactory noise reduction of the signal, without distortion of the underlying information, was achieved when 20-50 neighbors ("window-size") were used. The use of NIRS for measuring rSO 2 in clinical studies during pediatric transport in ground and air-ambulance is feasible but hampered by unreliable values and signal interference. By applying the Savitzky-Golay algorithm, the signal-to-noise ratio was improved and enabled better post-hoc signal evaluation.

Homoepitaxial graphene tunnel barriers for spin transport (Presentation Recording)

NASA Astrophysics Data System (ADS)

Friedman, Adam L.

2015-09-01

Tunnel barriers are key elements for both charge-and spin-based electronics, offering devices with reduced power consumption and new paradigms for information processing. Such devices require mating dissimilar materials, raising issues of heteroepitaxy, interface stability, and electronic states that severely complicate fabrication and compromise performance. Graphene is the perfect tunnel barrier. It is an insulator out-of-plane, possesses a defect-free, linear habit, and is impervious to interdiffusion. Nonetheless, true tunneling between two stacked graphene layers is not possible in environmental conditions (magnetic field, temperature, etc.) usable for electronics applications. However, two stacked graphene layers can be decoupled using chemical functionalization. Here, we demonstrate homoepitaxial tunnel barrier devices in which graphene serves as both the tunnel barrier and the high mobility transport channel. Beginning with multilayer graphene, we fluorinate or hydrogenate the top layer to decouple it from the bottom layer, so that it serves as a single monolayer tunnel barrier for both charge and spin injection into the lower graphene transport channel. We demonstrate successful tunneling by measuring non-linear IV curves, and a weakly temperature dependent zero bias resistance. We perform lateral transport of spin currents in non-local spin-valve structures and determine spin lifetimes with the non-local Hanle effect to be commensurate with previous studies (~200 ps). However, we also demonstrate the highest spin polarization efficiencies (~45%) yet measured in graphene-based spin devices [1]. [1] A.L. Friedman, et al., Homoepitaxial tunnel barriers with functionalized graphene-on-graphene for charge and spin transport, Nat. Comm. 5, 3161 (2014).

Ionic-Electronic Ambipolar Transport in Metal Halide Perovskites: Can Electronic Conductivity Limit Ionic Diffusion?

PubMed

Kerner, Ross A; Rand, Barry P

2018-01-04

Ambipolar transport describes the nonequilibrium, coupled motion of positively and negatively charged particles to ensure that internal electric fields remain small. It is commonly invoked in the semiconductor community where the motion of excess electrons and holes drift and diffuse together. However, the concept of ambipolar transport is not limited to semiconductor physics. Materials scientists working on ion conducting ceramics understand ambipolar transport dictates the coupled diffusion of ions and the rate is limited by the ion with the lowest diffusion coefficient. In this Perspective, we review a third application of ambipolar transport relevant to mixed ionic-electronic conducting materials for which the motion of ions is expected to be coupled to electronic carriers. In this unique situation, the ambipolar diffusion model has been successful at explaining the photoenhanced diffusion of metal ions in chalcogenide glasses and other properties of materials. Recent examples of photoenhanced phenomena in metal halide perovskites are discussed and indicate that mixed ionic-electronic ambipolar transport is similarly important for a deep understanding of these emerging materials.

49 CFR 220.303 - General use of electronic devices.

Code of Federal Regulations, 2010 CFR

2010-10-01

... ADMINISTRATION, DEPARTMENT OF TRANSPORTATION RAILROAD COMMUNICATIONS Electronic Devices § 220.303 General use of electronic devices. A railroad operating employee shall not use an electronic device if that use would... 49 Transportation 4 2010-10-01 2010-10-01 false General use of electronic devices. 220.303 Section...

49 CFR 220.303 - General use of electronic devices.

Code of Federal Regulations, 2011 CFR

2011-10-01

... 49 Transportation 4 2011-10-01 2011-10-01 false General use of electronic devices. 220.303 Section... ADMINISTRATION, DEPARTMENT OF TRANSPORTATION RAILROAD COMMUNICATIONS Electronic Devices § 220.303 General use of electronic devices. A railroad operating employee shall not use an electronic device if that use would...

49 CFR 220.303 - General use of electronic devices.

Code of Federal Regulations, 2012 CFR

2012-10-01

... 49 Transportation 4 2012-10-01 2012-10-01 false General use of electronic devices. 220.303 Section... ADMINISTRATION, DEPARTMENT OF TRANSPORTATION RAILROAD COMMUNICATIONS Electronic Devices § 220.303 General use of electronic devices. A railroad operating employee shall not use an electronic device if that use would...

Investigations into the formation of nanocrystalline quantum dot thin films by mist deposition process

NASA Astrophysics Data System (ADS)

Kshirsagar, Aditya

Semiconductor nanocrystalline quantum dots (NQDs) have material properties remarkably different compared to bulk semiconductors with the same material composition. These NQDs have various novel applications in the electronic and photonic industry, such as light emitting diodes (LEDs) and flat-panel displays. In these applications, ultra-thin films of NQDs in the monolayer regime are needed to ensure optimal current transport properties and device efficiency. There is ongoing search to find a suitable method to deposit and pattern such ultra-thin films of quantum dots with few monolayer thicknesses. Several competing approaches are available, each with its pros and cons. This study explores mist deposition as the technique to fill this void. In this study, ultra-thin films of quantum dots are deposited on diverse substrates and are characterized to understand the mechanics of mist deposition. Various applications of blanket deposited and patterned quantum dot films are studied. The results discussed here include atomic force microscopy analysis of the films to study surface morphology, fluorescence microscopy to study light emission and optical microscope images to study patterning techniques. These results demonstrate the ability of mist deposition to form 1-4 monolayers thick, uniform, defect-free patterned films with root mean square (RMS) surface roughness less than 2 nm. LEDs fabricated using mist deposition show a peak luminescence greater than 500 cd/m2 for matched red, yellow and green devices using Alq3 as the electron transport layer, and over 9000 cd/m2 for red devices using ZnO as the electron transport layer, respectively. In addition to the experimental approach to study the process and explore potential applications, simulation and modeling are carried out to understand the various aspects of mist deposition. A mathematical model is presented which discusses the atomization process of the precursor solution, the physics involved during the deposition process, and the mechanics of film formation. Results of film morphology simulation using Monte Carlo techniques and process simulation using multi-physics approach are discussed. Problems in pattern transfer due to electrostatic effects when using shadow masks are presented in a separate chapter.

Study on the Electronic Transport Properties of Zigzag GaN Nanotubes

NASA Astrophysics Data System (ADS)

Li, Enling; Wang, Xiqiang; Hou, Liping; Zhao, Danna; Dai, Yuanbin; Wang, Xuewen

2011-02-01

The electronic transport properties of zigzag GaN nanotubes (n, 0) (4 <= n <= 9) have been calculated using the density functional theory and non-equilibrium Green's functions method. Firstly, the density functional theory (DFT) is used to optimize and calculate the electronic structure of GaNNTs (n, 0) (4<=n<=9). Secondly, DFT and non-equilibrium Green function (NEGF) method are also used to predict the electronic transport properties of GaNNTs two-probe system. The results showed: there is a corresponding relation between the electronic transport properties and the valley of state density of each GaNNT. In addition, the volt-ampere curve of GaNNT is approximately linear.

Phase-breaking effect on polaron transport in organic conjugated polymers

DOE PAGES

Meng, Ruixuan; Yin, Sun; Zheng, Yujun; ...

2017-06-15

Despite intense investigations and many accepted viewpoints on theory and experiment, the coherent and incoherent carrier transport in organic semiconductors remains an unsettled topic due to the strong electron-phonon coupling. Based on the tight-binding Su-Schrieffer-Heeger (SSH) model combined with a non-adiabatic dynamics method, we study the effect of phase-breaking on polaron transport by introducing a group of phase-breaking factors into π-electron wave-functions in organic conjugated polymers. Two approaches are applied: the modification of the transfer integral and the phase-breaking addition to the wave-function. Within the former, it is found that a single site phase-breaking can trap a polaron. However, withmore » a larger regular phase-breaking a polaron becomes more delocalized and lighter. Additionally, a group of disordered phase-breaking factors can make the polaron disperse in transport process. Within the latter approach, we show that the phase-breaking can render the delocalized state in valence band discrete and the state in the gap more localized. Consequently, the phase-breaking frequency and intensity can reduce the stability of a polaron. Furthermore, the phase-breaking in organic systems is the main factor that degrades the coherent transport and destroys the carrier stability.« less

Extremely Low Operating Current Resistive Memory Based on Exfoliated 2D Perovskite Single Crystals for Neuromorphic Computing.

PubMed

Tian, He; Zhao, Lianfeng; Wang, Xuefeng; Yeh, Yao-Wen; Yao, Nan; Rand, Barry P; Ren, Tian-Ling

2017-12-26

Extremely low energy consumption neuromorphic computing is required to achieve massively parallel information processing on par with the human brain. To achieve this goal, resistive memories based on materials with ionic transport and extremely low operating current are required. Extremely low operating current allows for low power operation by minimizing the program, erase, and read currents. However, materials currently used in resistive memories, such as defective HfO x , AlO x , TaO x , etc., cannot suppress electronic transport (i.e., leakage current) while allowing good ionic transport. Here, we show that 2D Ruddlesden-Popper phase hybrid lead bromide perovskite single crystals are promising materials for low operating current nanodevice applications because of their mixed electronic and ionic transport and ease of fabrication. Ionic transport in the exfoliated 2D perovskite layer is evident via the migration of bromide ions. Filaments with a diameter of approximately 20 nm are visualized, and resistive memories with extremely low program current down to 10 pA are achieved, a value at least 1 order of magnitude lower than conventional materials. The ionic migration and diffusion as an artificial synapse is realized in the 2D layered perovskites at the pA level, which can enable extremely low energy neuromorphic computing.

Phase-breaking effect on polaron transport in organic conjugated polymers

DOE Office of Scientific and Technical Information (OSTI.GOV)

Meng, Ruixuan; Yin, Sun; Zheng, Yujun

Despite intense investigations and many accepted viewpoints on theory and experiment, the coherent and incoherent carrier transport in organic semiconductors remains an unsettled topic due to the strong electron-phonon coupling. Based on the tight-binding Su-Schrieffer-Heeger (SSH) model combined with a non-adiabatic dynamics method, we study the effect of phase-breaking on polaron transport by introducing a group of phase-breaking factors into π-electron wave-functions in organic conjugated polymers. Two approaches are applied: the modification of the transfer integral and the phase-breaking addition to the wave-function. Within the former, it is found that a single site phase-breaking can trap a polaron. However, withmore » a larger regular phase-breaking a polaron becomes more delocalized and lighter. Additionally, a group of disordered phase-breaking factors can make the polaron disperse in transport process. Within the latter approach, we show that the phase-breaking can render the delocalized state in valence band discrete and the state in the gap more localized. Consequently, the phase-breaking frequency and intensity can reduce the stability of a polaron. Furthermore, the phase-breaking in organic systems is the main factor that degrades the coherent transport and destroys the carrier stability.« less

Electron heat transport measured in a stochastic magnetic field.

PubMed

Biewer, T M; Forest, C B; Anderson, J K; Fiksel, G; Hudson, B; Prager, S C; Sarff, J S; Wright, J C; Brower, D L; Ding, W X; Terry, S D

2003-07-25

New profile measurements have allowed the electron thermal diffusivity profile to be estimated from power balance in the Madison Symmetric Torus where magnetic islands overlap and field lines are stochastic. The measurements show that (1) the electron energy transport is conductive not convective, (2) the measured thermal diffusivities are in good agreement with numerical simulations of stochastic transport, and (3) transport is greatly reduced near the reversal surface where magnetic diffusion is small.

Hot-electron-mediated surface chemistry: toward electronic control of catalytic activity.

PubMed

Park, Jeong Young; Kim, Sun Mi; Lee, Hyosun; Nedrygailov, Ievgen I

2015-08-18

Energy dissipation at surfaces and interfaces is mediated by excitation of elementary processes, including phonons and electronic excitation, once external energy is deposited to the surface during exothermic chemical processes. Nonadiabatic electronic excitation in exothermic catalytic reactions results in the flow of energetic electrons with an energy of 1-3 eV when chemical energy is converted to electron flow on a short (femtosecond) time scale before atomic vibration adiabatically dissipates the energy (in picoseconds). These energetic electrons that are not in thermal equilibrium with the metal atoms are called "hot electrons". The detection of hot electron flow under atomic or molecular processes and understanding its role in chemical reactions have been major topics in surface chemistry. Recent studies have demonstrated electronic excitation produced during atomic or molecular processes on surfaces, and the influence of hot electrons on atomic and molecular processes. We outline research efforts aimed at identification of the intrinsic relation between the flow of hot electrons and catalytic reactions. We show various strategies for detection and use of hot electrons generated by the energy dissipation processes in surface chemical reactions and photon absorption. A Schottky barrier localized at the metal-oxide interface of either catalytic nanodiodes or hybrid nanocatalysts allows hot electrons to irreversibly transport through the interface. We show that the chemicurrent, composed of hot electrons excited by the surface reaction of CO oxidation or hydrogen oxidation, correlates well with the turnover rate measured separately by gas chromatography. Furthermore, we show that hot electron flows generated on a gold thin film by photon absorption (or internal photoemission) can be amplified by localized surface plasmon resonance. The influence of hot charge carriers on the chemistry at the metal-oxide interface are discussed for the cases of Au, Ag, and Pt nanoparticles on oxide supports and Pt-CdSe-Pt nanodumbbells. We show that the accumulation or depletion of hot electrons on metal nanoparticles, in turn, can also influence catalytic reactions. Mechanisms suggested for hot-electron-induced chemical reactions on a photoexcited plasmonic metal are discussed. We propose that the manipulation of the flow of hot electrons by changing the electrical characteristics of metal-oxide and metal-semiconductor interfaces can give rise to the intriguing capability of tuning the catalytic activity of hybrid nanocatalysts.

Protein bioelectronics: a review of what we do and do not know

NASA Astrophysics Data System (ADS)

Bostick, Christopher D.; Mukhopadhyay, Sabyasachi; Pecht, Israel; Sheves, Mordechai; Cahen, David; Lederman, David

2018-02-01

We review the status of protein-based molecular electronics. First, we define and discuss fundamental concepts of electron transfer and transport in and across proteins and proposed mechanisms for these processes. We then describe the immobilization of proteins to solid-state surfaces in both nanoscale and macroscopic approaches, and highlight how different methodologies can alter protein electronic properties. Because immobilizing proteins while retaining biological activity is crucial to the successful development of bioelectronic devices, we discuss this process at length. We briefly discuss computational predictions and their connection to experimental results. We then summarize how the biological activity of immobilized proteins is beneficial for bioelectronic devices, and how conductance measurements can shed light on protein properties. Finally, we consider how the research to date could influence the development of future bioelectronic devices.

49 CFR 229.20 - Electronic recordkeeping.

Code of Federal Regulations, 2014 CFR

2014-10-01

... 49 Transportation 4 2014-10-01 2014-10-01 false Electronic recordkeeping. 229.20 Section 229.20..., DEPARTMENT OF TRANSPORTATION RAILROAD LOCOMOTIVE SAFETY STANDARDS General § 229.20 Electronic recordkeeping... part through electronic transmission, storage, and retrieval provided that all of the requirements...

49 CFR 229.20 - Electronic recordkeeping.

Code of Federal Regulations, 2013 CFR

2013-10-01

... 49 Transportation 4 2013-10-01 2013-10-01 false Electronic recordkeeping. 229.20 Section 229.20..., DEPARTMENT OF TRANSPORTATION RAILROAD LOCOMOTIVE SAFETY STANDARDS General § 229.20 Electronic recordkeeping... part through electronic transmission, storage, and retrieval provided that all of the requirements...

Dispersive electron transport in tris(8-hydroxyquinoline) aluminum (Alq3) probed by impedance spectroscopy.

PubMed

Berleb, Stefan; Brütting, Wolfgang

2002-12-31

Electron transport in tris(8-hydroxyquinoline) aluminum (Alq3) is investigated by impedance spectroscopy under conditions of space-charge limited conduction (SCLC). Existing SCLC models are extended to include the field dependence of the charge carrier mobility and energetically distributed trap states. The dispersive nature of electron transport is revealed by a frequency-dependent mobility with a dispersion parameter alpha in the range 0.4-0.5, independent of temperature. This indicates that positional rather than energetic disorder is the dominant mechanism for the dispersive transport of electrons in Alq3.

The steady-state and transient electron transport within bulk zinc-blende indium nitride: The impact of crystal temperature and doping concentration variations

DOE Office of Scientific and Technical Information (OSTI.GOV)

Siddiqua, Poppy; O'Leary, Stephen K., E-mail: stephen.oleary@ubc.ca

2016-03-07

Within the framework of a semi-classical three-valley Monte Carlo electron transport simulation approach, we analyze the steady-state and transient aspects of the electron transport within bulk zinc-blende indium nitride, with a focus on the response to variations in the crystal temperature and the doping concentration. We find that while the electron transport associated with zinc-blende InN is highly sensitive to the crystal temperature, it is not very sensitive to the doping concentration selection. The device consequences of these results are then explored.

Spin-polarized electron transport in hybrid graphene-BN nanoribbons

NASA Astrophysics Data System (ADS)

Gao, Song; Lu, Wei; Zheng, Guo-Hui; Jia, Yalei; Ke, San-Huang

2017-05-01

The experimental realization of hybrid graphene and h-BN provides a new way to modify the electronic and transport properties of graphene-based materials. In this work, we investigate the spin-polarized electron transport in hybrid graphene-BN zigzag nanoribbons by performing first-principles nonequilibrium Green’s function method calculations. A 100% spin-polarized electron transport in a large energy window around the Fermi level is found and this behavior is independent of the ribbon width as long as there contain 3 zigzag carbon chains. This behavior may be useful in making perfect spin filters.

Fluctuations, Electron Transport, and Flow Shear in 2D Axial, Azimuthal (z-θ) Hybrid Hall Thruster Simulations.

NASA Astrophysics Data System (ADS)

Fernandez, Eduardo; Gascon, Nicolas; Knoll, Aaron; Scharfe, Michelle; Cappelli, Mark

2007-11-01

Motivated by the inability of radial-axial (r-z) simulations to properly treat cross-field electron transport in Hall thrusters, a novel 2D z-θ model has been implemented. In common with many r-z descriptions, the simulation is hybrid in nature and assumes quasi-neutrality. Unlike r-z models, electron transport is not enhanced with an ad-hoc mobility coefficient; instead it is given by collisional or ``classical'' terms as well as ``anomalous'' contributions associated with azimuthal electric field fluctuations. Results indicate that anomalous transport dominates classical transport for most of the channel and near field, except in a strong electron flow shear region near the channel exit. The correlation between flow shear, fluctuation behavior, and electron transport will be examined, along with experimental data from the Stanford Hall Thruster. Our findings make a strong link to the turbulent transport suppression mechanism by flow shear seen in fusion devices. The scheme for combining the r-z and z-θ descriptions into an upcoming 3D hybrid model will be presented.

[Regulation effects of short sunlight on two electron transport pathways in nectarine flower bud during dormancy induction].

PubMed

Li, Dong-Mei; Zhang, Hai-Sen; Tan, Qiu-Ping; Li, Ling; Yu, Qin; Gao, Dong-Sheng

2011-11-01

Taking the nectarine variety 'Shuguang' (Prunus persica var. nectariana cv. Shuguang) as test material, and by using respiration inhibitors KCN and SHAM, this paper studied the cytochrome electron transport pathway and the alternative respiration pathway in nectarine flower bud during dormancy induction under the effects of short sunlight. Both the total respiration rate (V(t)) and the cytochrome electron transport pathway respiration rate (rho' V(cyt)) presented double hump-shaped variation. Short sunlight brought the first-hump of V(t) and rho' V(cyt), forward and delayed the second-hump synchronously, inhibited the rho' V(cyt), but had no significant effects on the V(t). The capacity (V(alt)) and activity (rho V (alt)) of alternative respiration pathway also varied in double hump-shape, and the variation was basically in synchronous. Short sunlight made the first climax of V(alt) and rhoV(alt) advanced, but had little effects on the later period climax. The inhibition of cytochrome electron transport pathway and the enhancement of alternative respiration pathway were the important features of nectarine flower bud during dormancy induction, and according to the respective contributions of the two electron transport pathways to the total respiration rate, the cytochrome electron transport pathway was still the main pathway of electron transport, whereas the alternative respiration pathway played an auxiliary and branched role.

Influence of Reactive Transport on the Reduction of U(VI) in the Presence of Fe(III) and Nitrate: Implications for U(VI) Immobilization by Bioremediation / Biobarriers- Final Report

DOE Office of Scientific and Technical Information (OSTI.GOV)

B.D. Wood

2007-01-01

Subsurface contamination by metals and radionuclides represent some of the most challenging remediation problems confronting the Department of Energy (DOE) complex. In situ remediation of these contaminants by dissimilatory metal reducing bacteria (DMRB) has been proposed as a potential cost effective remediation strategy. The primary focus of this research is to determine the mechanisms by which the fluxes of electron acceptors, electron donors, and other species can be controlled to maximize the transfer of reductive equivalents to the aqueous and solid phases. The proposed research is unique in the NABIR portfolio in that it focuses on (i) the role ofmore » flow and transport in the initiation of biostimulation and the successful sequestration of metals and radionuclides [specifically U(VI)], (ii) the subsequent reductive capacity and stability of the reduced sediments produced by the biostimulation process, and (iii) the potential for altering the growth of biomass in the subsurface by the addition of specific metabolic uncoupling compounds. A scientifically-based understanding of these phenomena are critical to the ability to design successful bioremediation schemes. The laboratory research will employ Shewanella putrefaciens (CN32), a facultative DMRB that can use Fe(III) oxides as a terminal electron acceptor. Sediment-packed columns will be inoculated with this organism, and the reduction of U(VI) by the DMRB will be stimulated by the addition of a carbon and energy source in the presence of Fe(III). Separate column experiments will be conducted to independently examine: (1) the importance of the abiotic reduction of U(VI) by biogenic Fe(II); (2) the influence of the transport process on Fe(III) reduction and U(VI) immobilization, with emphasis on methods for controlling the fluxes of aqueous species to maximize uranium reduction; (3) the reductive capacity of biologically-reduced sediments (with respect to re-oxidation by convective fluxes of O2 and NO3-) and the long-term stability of immobilized uranium mineral phases after bioremediation processes are complete, and (4) the ability for metabolic uncoupling compounds to maintain microbial growth while limiting biomass production. The results of the laboratory experiments will be used to develop mathematical descriptive models for the coupled transport and reduction processes.« less

Plasmonic tunnel junctions for single-molecule redox chemistry.

PubMed

de Nijs, Bart; Benz, Felix; Barrow, Steven J; Sigle, Daniel O; Chikkaraddy, Rohit; Palma, Aniello; Carnegie, Cloudy; Kamp, Marlous; Sundararaman, Ravishankar; Narang, Prineha; Scherman, Oren A; Baumberg, Jeremy J

2017-10-20

Nanoparticles attached just above a flat metallic surface can trap optical fields in the nanoscale gap. This enables local spectroscopy of a few molecules within each coupled plasmonic hotspot, with near thousand-fold enhancement of the incident fields. As a result of non-radiative relaxation pathways, the plasmons in such sub-nanometre cavities generate hot charge carriers, which can catalyse chemical reactions or induce redox processes in molecules located within the plasmonic hotspots. Here, surface-enhanced Raman spectroscopy allows us to track these hot-electron-induced chemical reduction processes in a series of different aromatic molecules. We demonstrate that by increasing the tunnelling barrier height and the dephasing strength, a transition from coherent to hopping electron transport occurs, enabling observation of redox processes in real time at the single-molecule level.

Temperature dependence of Brillouin light scattering spectra of acoustic phonons in silicon

NASA Astrophysics Data System (ADS)

Olsson, Kevin S.; Klimovich, Nikita; An, Kyongmo; Sullivan, Sean; Weathers, Annie; Shi, Li; Li, Xiaoqin

2015-02-01

Electrons, optical phonons, and acoustic phonons are often driven out of local equilibrium in electronic devices or during laser-material interaction processes. The need for a better understanding of such non-equilibrium transport processes has motivated the development of Raman spectroscopy as a local temperature sensor of optical phonons and intermediate frequency acoustic phonons, whereas Brillouin light scattering (BLS) has recently been explored as a temperature sensor of low-frequency acoustic phonons. Here, we report the measured BLS spectra of silicon at different temperatures. The origins of the observed temperature dependence of the BLS peak position, linewidth, and intensity are examined in order to evaluate their potential use as temperature sensors for acoustic phonons.

Imaging of nonlocal hot-electron energy dissipation via shot noise.

PubMed

Weng, Qianchun; Komiyama, Susumu; Yang, Le; An, Zhenghua; Chen, Pingping; Biehs, Svend-Age; Kajihara, Yusuke; Lu, Wei

2018-05-18

In modern microelectronic devices, hot electrons accelerate, scatter, and dissipate energy in nanoscale dimensions. Despite recent progress in nanothermometry, direct real-space mapping of hot-electron energy dissipation is challenging because existing techniques are restricted to probing the lattice rather than the electrons. We realize electronic nanothermometry by measuring local current fluctuations, or shot noise, associated with ultrafast hot-electron kinetic processes (~21 terahertz). Exploiting a scanning and contact-free tungsten tip as a local noise probe, we directly visualize hot-electron distributions before their thermal equilibration with the host gallium arsenide/aluminium gallium arsenide crystal lattice. With nanoconstriction devices, we reveal unexpected nonlocal energy dissipation at room temperature, which is reminiscent of ballistic transport of low-temperature quantum conductors. Copyright © 2018 The Authors, some rights reserved; exclusive licensee American Association for the Advancement of Science. No claim to original U.S. Government Works.

First principles studies of electron tunneling in proteins

PubMed Central

Hayashi, Tomoyuki; Stuchebrukhov, Alexei A.

2014-01-01

A first principles study of electronic tunneling along the chain of seven Fe/S clusters in respiratory complex I, a key enzyme in the respiratory electron transport chain, is described. The broken-symmetry states of the Fe/S metal clusters calculated at both DFT and semi-empirical ZINDO levels were utilized to examine both the extremely weak electronic couplings between Fe/S clusters and the tunneling pathways, which provide a detailed atomistic-level description of the charge transfer process in the protein. One-electron tunneling approximation was found to hold within a reasonable accuracy, with only a moderate induced polarization of the core electrons. The method is demonstrated to be able to calculate accurately the coupling matrix elements as small as 10−4 cm−1. A distinct signature of the wave properties of electrons is observed as quantum interferences of multiple tunneling pathways. PMID:25383312

Experimental Characterization of Plasma Detachment from Magnetic Nozzles

NASA Astrophysics Data System (ADS)

Olsen, Christopher Scott

Magnetic nozzles, like Laval nozzles, are observed in several natural systems and have application in areas such as electric propulsion and plasma processing. Plasma flowing through these nozzles is inherently tied to the field lines and must separate for momentum redirection or particle transport to occur. Plasma detachment and associated mechanisms from a magnetic nozzle are investigated. Experimental results are presented from the plume of the VASIMRRTM VX-200 device flowing along an axisymmetric magnetic nozzle and operated at two ion energies to explore momentum dependent detachment. The argon plume expanded into a 150m3 vacuum chamber where the background pressure was low enough that charge-exchange mean-free-paths were longer than experiment scale lengths. This magnetic nozzle system is demonstrated to hydrodynamically scale up to astrophysical plasmas, particularly the solar chromosphere, implying general relevance to many systems. Plasma parameters were mapped over a large spatial range using measurements from multiple plasma diagnostics. The data show that the plume does not follow the magnetic field lines. A mapped integration of the ion flux shows the plume may be divided into three regions where 1) the plume briefly follows the magnetic flux, 2) diverges quadratically before 3) expanding with linear trajectories. Transitioning from region 1→2, the ion flux departs from the magnetic flux suggesting ion detachment. An instability forms in region 2 driving an oscillating electric field that causes ions to expand before enhancing electron cross-field transport through anomalous resistivity. Transitioning from region 2→3 the electric field dissipates, the trajectories linearize, and the plume effectively detaches. A delineation of sub-to-super Alfvenic flow aligns well with the inflection points of the linearization without a change in magnetic topology. The detachment process is best described as a two part process: First, ions detach by a breakdown of the magnetic moment when the quantity |v/fcLB| becomes of order unity. Second, the turbulent electric field enhances electron transport up to a factor of 4+/-1 above collisional diffusion; electron cross-field velocities approximate that of the ions and depart on more centralized field lines. Electrons are believed to detach by breakdown of magnetic moment further downstream in the weaker magnetic field.

Laser-driven strong magnetostatic fields with applications to charged beam transport and magnetized high energy-density physics

NASA Astrophysics Data System (ADS)

Santos, J. J.; Bailly-Grandvaux, M.; Ehret, M.; Arefiev, A. V.; Batani, D.; Beg, F. N.; Calisti, A.; Ferri, S.; Florido, R.; Forestier-Colleoni, P.; Fujioka, S.; Gigosos, M. A.; Giuffrida, L.; Gremillet, L.; Honrubia, J. J.; Kojima, S.; Korneev, Ph.; Law, K. F. F.; Marquès, J.-R.; Morace, A.; Mossé, C.; Peyrusse, O.; Rose, S.; Roth, M.; Sakata, S.; Schaumann, G.; Suzuki-Vidal, F.; Tikhonchuk, V. T.; Toncian, T.; Woolsey, N.; Zhang, Z.

2018-05-01

Powerful nanosecond laser-plasma processes are explored to generate discharge currents of a few 100 kA in coil targets, yielding magnetostatic fields (B-fields) in excess of 0.5 kT. The quasi-static currents are provided from hot electron ejection from the laser-irradiated surface. According to our model, which describes the evolution of the discharge current, the major control parameter is the laser irradiance Ilasλlas2 . The space-time evolution of the B-fields is experimentally characterized by high-frequency bandwidth B-dot probes and proton-deflectometry measurements. The magnetic pulses, of ns-scale, are long enough to magnetize secondary targets through resistive diffusion. We applied it in experiments of laser-generated relativistic electron transport through solid dielectric targets, yielding an unprecedented 5-fold enhancement of the energy-density flux at 60 μm depth, compared to unmagnetized transport conditions. These studies pave the ground for magnetized high-energy density physics investigations, related to laser-generated secondary sources of radiation and/or high-energy particles and their transport, to high-gain fusion energy schemes, and to laboratory astrophysics.

Fringe-controlled biodegradation under dynamic conditions: Quasi 2-D flow-through experiments and reactive-transport modeling

NASA Astrophysics Data System (ADS)

Eckert, Dominik; Kürzinger, Petra; Bauer, Robert; Griebler, Christian; Cirpka, Olaf A.

2015-01-01

Biodegradation in contaminated aquifers has been shown to be most pronounced at the fringe of contaminant plumes, where mixing of contaminated water and ambient groundwater, containing dissolved electron acceptors, stimulates microbial activity. While physical mixing of contaminant and electron acceptor by transverse dispersion has been shown to be the major bottleneck for biodegradation in steady-state plumes, so far little is known on the effect of flow and transport dynamics (caused, e.g., by a seasonally fluctuating groundwater table) on biodegradation in these systems. Towards this end we performed experiments in quasi-two-dimensional flow-through microcosms on aerobic toluene degradation by Pseudomonas putida F1. Plume dynamics were simulated by vertical alteration of the toluene plume position and experimental results were analyzed by reactive-transport modeling. We found that, even after disappearance of the toluene plume for two weeks, the majority of microorganisms stayed attached to the sediment and regained their full biodegradation potential within two days after reappearance of the toluene plume. Our results underline that besides microbial growth, also maintenance and dormancy are important processes that affect biodegradation performance under transient environmental conditions and therefore deserve increased consideration in future reactive-transport modeling.

Electronic transport close to semi-infinite 2D systems and their interfaces

NASA Astrophysics Data System (ADS)

Xia, Fanbing; Wang, Jian; Jian Wang's research Group Team

Transport properties of 2D materials especially close to their boundary has received much attention after the successful fabrication of Graphene. While most previous work is devoted to the conventional lead-device-lead setup with a finite size center area, this project investigates real space transport properties of infinite and semi-infinite 2D systems under the framework of Non-equilibrium Green's function. The commonly used method of calculating Green's function by inverting matrices in the real space can be unstable in dealing with large systems as sometimes it gives non-converging result. By transforming from the real space to momentum space, the author managed to replace the matrix inverting process by Brillouin Zone integral which can be greatly simplified by the application of contour integral. Combining this methodology with Dyson equations, we are able to calculate transport properties of semi-infinite graphene close to its zigzag boundary and its combination with other material including s-wave superconductor. Interference pattern of transmitted and reflected electrons, Graphene lensing effects and difference between Specular Andreev reflection and normal Andreev reflection are verified. We also generalize how to apply this method to a broad range of 2D materials. The University of Hong Kong.

HZETRN: Description of a free-space ion and nucleon transport and shielding computer program

NASA Technical Reports Server (NTRS)

Wilson, John W.; Badavi, Francis F.; Cucinotta, Francis A.; Shinn, Judy L.; Badhwar, Gautam D.; Silberberg, R.; Tsao, C. H.; Townsend, Lawrence W.; Tripathi, Ram K.

1995-01-01

The high-charge-and energy (HZE) transport computer program HZETRN is developed to address the problems of free-space radiation transport and shielding. The HZETRN program is intended specifically for the design engineer who is interested in obtaining fast and accurate dosimetric information for the design and construction of space modules and devices. The program is based on a one-dimensional space-marching formulation of the Boltzmann transport equation with a straight-ahead approximation. The effect of the long-range Coulomb force and electron interaction is treated as a continuous slowing-down process. Atomic (electronic) stopping power coefficients with energies above a few A MeV are calculated by using Bethe's theory including Bragg's rule, Ziegler's shell corrections, and effective charge. Nuclear absorption cross sections are obtained from fits to quantum calculations and total cross sections are obtained with a Ramsauer formalism. Nuclear fragmentation cross sections are calculated with a semiempirical abrasion-ablation fragmentation model. The relation of the final computer code to the Boltzmann equation is discussed in the context of simplifying assumptions. A detailed description of the flow of the computer code, input requirements, sample output, and compatibility requirements for non-VAX platforms are provided.

Quantum transport through disordered 1D wires: Conductance via localized and delocalized electrons

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gopar, Víctor A.

Coherent electronic transport through disordered systems, like quantum wires, is a topic of fundamental and practical interest. In particular, the exponential localization of electron wave functions-Anderson localization-due to the presence of disorder has been widely studied. In fact, Anderson localization, is not an phenomenon exclusive to electrons but it has been observed in microwave and acoustic experiments, photonic materials, cold atoms, etc. Nowadays, many properties of electronic transport of quantum wires have been successfully described within a scaling approach to Anderson localization. On the other hand, anomalous localization or delocalization is, in relation to the Anderson problem, a less studiedmore » phenomenon. Although one can find signatures of anomalous localization in very different systems in nature. In the problem of electronic transport, a source of delocalization may come from symmetries present in the system and particular disorder configurations, like the so-called Lévy-type disorder. We have developed a theoretical model to describe the statistical properties of transport when electron wave functions are delocalized. In particular, we show that only two physical parameters determine the complete conductance distribution.« less