Sample records for charge transfer chemistry

  1. ChargeTransfer EAM Studies of Kinesin Molecular Motor

    E-print Network

    Maccabe, Barney

    of faithfully representing reactive interactions and charge transfer among constituent atomic and molecular of the CTEAM potential reveal remarkable agreement with theoretical quantum chemistry (UHF ChargeTransfer EAM Studies of Kinesin Molecular Motor Protein Mechanochemistry Vijay

  2. Mechanochemical Synthesis of Two Polymorphs of the Tetrathiafulvalene-Chloranil Charge Transfer Salt: An Experiment for Organic Chemistry

    ERIC Educational Resources Information Center

    Wixtrom, Alex; Buhler, Jessica; Abdel-Fattah, Tarek

    2014-01-01

    Mechanochemical syntheses avoid or considerably reduce the use of reaction solvents, thus providing green chemistry synthetic alternatives that are both environmentally friendly and economically advantageous. The increased solid-state reactivity generated by mechanical energy imparted to the reactants by grinding or milling can offer alternative…

  3. Charge Transfer Reactions Induce Born-Oppenheimer Breakdown in Surface Chemistry: Applications of Double Resonance Spectroscopy in Molecule-Surface Scattering

    NASA Astrophysics Data System (ADS)

    Wodtke, Alec M.

    2013-06-01

    Atomic and molecular interactions constitute a many-body quantum problem governed fundamentally only by the Coulomb forces between many electrons and nuclei. While simple to state, computers are simply not fast enough to solve this problem by brute force, except for the simplest examples. Combining the Born-Oppenheimer Approximation (BOA) with Density Functional Theory (DFT), however, allows theoretical simulations of extraordinarily complex chemical systems including molecular interactions at solid metal surfaces, the physical basis of surface chemistry. This lecture describes experiments demonstrating the limits of the BOA/DFT approximation as it relates to molecules interacting with solid metal surfaces. One of the most powerful experimental tools at our disposal is a form of double resonance spectroscopy, which allows us to define the quantum state of the molecule both before and after the collision with the surface, providing a complete picture of the resulting energy conversion processes. With such data, we are able to emphasize quantitative measurements that can be directly compared to first principles theories that go beyond the Born-Oppenheimer approximation. One important outcome of this work is the realization that Born-Oppenheimer breakdown can be induced by simple charge transfer reactions that are common in surface chemistry. J. D. White, J. Chen, D. Matsiev, D. J. Auerbach and A. M. Wodtke Nature {433}(7025), 503-505 (2005) Y. H. Huang, C. T. Rettner, D. J. Auerbach and A. M. Wodtke Science {290}(5489), 111-114 (2000) R. Cooper, I. Rahinov, Z. S. Li, D. Matsiev, D. J. Auerbach and A. M. Wodtke Chemical Science {1}(1), 55-61 (2010) J. Larue, T. Schäfer, D. Matsiev, L. Velarde, N. H. Nahler, D. J. Auerbach and A. M. Wodtke PCCP {13}(1), 97-99 (2011).

  4. Charge transfer and charge transport on the double helix

    NASA Astrophysics Data System (ADS)

    Armitage, N. P.; Briman, M.; Grüner, G.

    2004-01-01

    We present a short review of various experiments that measure charge transfer and charge transport in DNA. Some general comments are made on the possible connection between various chemistry-style charge transfer experiments that probe fluorescence quenching and remote oxidative damage and physics-style measurements that measure transport properties as defined typically in the solid-state. We then describe measurements performed by our group on the millimeter wave response of DNA. By measuring over a wide range of humidity conditions and comparing the response of single strand DNA and double strand DNA, we show that the appreciable AC conductivity of DNA is not due to photon assisted hopping between localized states, but instead due to dissipation from dipole motion in the surrounding water helix.

  5. Reorganization Parameters of Electronic Transitions in Electronically Delocalized Systems. 1. Charge Transfer Reactions

    E-print Network

    Matyushov, Dmitry

    . Charge Transfer Reactions Dmitry V. Matyushov*, and Gregory A. Voth* Department of Chemistry and Henry Eyring Center for Theoretical Chemistry, UniVersity of Utah, 315 South 1400 East, Salt Lake City, Utah

  6. Multiply-charged ions and interstellar chemistry.

    PubMed

    Böhme, Diethard Kurt

    2011-11-01

    Gaseous molecules and ions, and even dust grains, can accumulate charge in the interstellar medium (ISM) by harvesting the energy of UV photons, cosmic rays, helium ions and metastable atoms. This Perspective views the various modes of gas-phase formation of multiply-charged cations and the possible impact of their reactions on the chemical and ionization structure of the ISM, in the light of what is still very limited knowledge. Emphasis is given to gas-phase reactions of multiply-charged cations with atoms, molecules and electrons that lead to charge reduction, charge separation and chemical bond formation and these are examined for multiply-charged atoms, small molecules, hydrocarbons, polycyclic aromatic hydrocarbons and fullerenes, primarily as dications but also as a function of charge state. The increased electrostatic interaction due to multiple charge is seen to promote bonding to individual charge sites on large molecules (e.g. fullerenes) and allow ensuing "surface" chemistry under the influence of Coulomb repulsion. The unique ability of multiply charged cations to undergo charge separation reactions, either unimolecular or bimolecular, can feature in the production in the ISM of internally cold, but translationally hot, cations of lower charge state or hot atoms that may provide the driving force for subsequent chemical reactions in what is otherwise an ultracold environment. Available chemical kinetic models that account for the role of multiply-charged ions in the ISM are few and of limited scope and the observation of these ions in the ISM has remained elusive. PMID:21869973

  7. Contact charge-transfer lasers

    SciTech Connect

    Dharamsi, A.N.; Tulip, J.

    1981-07-01

    A mechanism for sustaining population inversions in contact charge-transfer complexes in which the ground electronic state is not bound is described. The mechanism relies on picosecond radiationless depletion of the lower laser state. This generates an inversion even when the ground-state potential curve, as plotted against the donor-acceptor distance, is not repulsive vertically below the excited state minimum. Contact charge-transfer lasers would offer high gain, high-energy density, and tunable sources of coherent radiation in the uv and visible. A method for pumping such a laser is examined and applied to the pyrrole-oxygen complex. A rate equation analysis is done and estimates for gain and energy density are presented.

  8. High performance charge transfer device detectors

    SciTech Connect

    Sweedler, J.V.; Bilhorn, R.B.; Epperson, P.M.; Sims, G.R.; Denton, M.B.

    1988-02-15

    There is great interest in replacing single-channel photomultiplier tubes (PMTs) with multichannel devices (1,2). Multichannel detectors such as vidicons, intensified target vidicons, image dissectors, and photodiode arrays (PDAs) do not offer the sensitivity, dynamic range, and noise performance necessary to be competitive with the PMT in many situations. Successful application of these multichannel detectors is limited to experimental conditions in which the multichannel advantage outweighs the noise, cross talk, and dynamic-range disadvantages. New multichannel alternatives to PMT detection are now capable of superior sensitivity and dynamic range when compared on a detector element by detector element basis. In fact, some of these devices exceed the sensitivity and dynamic range of all other available detectors. The performance of charge transfer devices (CTDs) has advanced to the point where the application of this technology to the field of analytical chemistry is appropriate. In the first of this two-part series, the theory, design, operation, and performance of CTD detectors are described. CTDs are solid-state multichannel detectors. These detectors integrate signal information as light strikes them, much like photographic film. The amount of charge generated in a CTD detector is measured either by moving the charge form the detector element where it is collected to a charge-sensing amplifier, or by moving it within the detector element and measuring the voltage change induced by this movement.

  9. Facilely and efficiently tuning metal-organic nanostructures of a charge-transfer complex based on a water controlled nanoreaction and the chemistry of 7,7,8,8-tetracyanoquinodimethane (TCNQ)

    NASA Astrophysics Data System (ADS)

    Song, Jingyi; Ji, Zhuoyu; Nie, Qiong; Hu, Wenping

    2014-02-01

    Metal-organic charge-transfer complexes based on 7,7,8,8-tetracyanoquinodimethane (TCNQ) have received considerable attention because of their unique solid-state physical properties for potential applications in nanoscale opto-electronic devices. To address the challenge in preparing novel metal-TCNQ (MTCNQ) nanostructures, here we introduce a facile and efficient way for synthesizing MTCNQ, taking Ni[TCNQ]2(H2O)2 as an example. By finely tuning the amount of water added into TCNQ solution, well-ordered and large-scale patterns of Ni[TCNQ]2(H2O)2 were successfully obtained in a controllable manner. This facile method will not only be beneficial for the tailored preparation of nanoscale MTCNQ complexes, but also enrich the chemistry of TCNQ.

  10. Charge transfer initiated nitroxyl chemistry on free silver clusters Ag{sub 2-5}{sup-} : size effects and magic complexes.

    SciTech Connect

    Hagen, J.; Socaciu-Sieberg, L. D.; LeRoux, J.; Popolan, D.; Vajda, S.; Bernhardt, T. M.; Woste, L.; Chemistry; Freie Univ.; Univ. Ulm

    2007-01-01

    The reactivity of small silver cluster anions Ag{sub 2--5}- toward nitric oxide and mixtures of nitric oxide with carbon monoxide is investigated under multi-collision conditions in a radio frequency octopole ion trap at temperatures of 100 and 300 K. A strongly cluster size dependent reaction behavior is observed, where reactive fragmentation dominates for clusters with four or fewer atoms and only Ag{sub 5}- is able to form reaction products without dissociation of the metal cluster. The decisive role of charge transfer in the NO bond breakage, NO oxidation, and the formation of free NO{sub 2}{sup -} and N{sub 2}O{sub 4}{sup -} ions, as well as NxO(y>x)-ligands on the silver clusters is discussed. The mass spectrometric data reveal the particular stability of the reaction products AgN{sub 2}O{sub 4}{sup -} and Ag{sub 3}NO{sup -}. The reaction product mass spectra obtained for Ag{sub 5}{sup -} in the presence of NO and CO show the depletion of the NxO(y>x)-ligands on the metal cluster possibly involving the oxidation of CO to CO2.

  11. Variationally consistent approximation scheme for charge transfer

    NASA Technical Reports Server (NTRS)

    Halpern, A. M.

    1978-01-01

    The author has developed a technique for testing various charge-transfer approximation schemes for consistency with the requirements of the Kohn variational principle for the amplitude to guarantee that the amplitude is correct to second order in the scattering wave functions. Applied to Born-type approximations for charge transfer it allows the selection of particular groups of first-, second-, and higher-Born-type terms that obey the consistency requirement, and hence yield more reliable approximation to the amplitude.

  12. Charge Transfer during Alkali-Surface Collisions

    NASA Astrophysics Data System (ADS)

    Weare, Christopher Bruce

    The transfer of electrons between atoms and solid surfaces is the driving force behind ionic bond formation in adsorption and determines the final charge state in particle-surface collisions. Despite its importance, however, many aspects of charge transfer are not completely understood. The experiments presented in this dissertation use the scattering of ^7Li ^+ ions from surfaces to study several aspects of charge transfer. Primarily, the effects of alkali adsorption on the surface local electrostatic potential (LEP) are investigated via resonant charge transfer. In addition, the effects of charge promotion on the final charge state distributions of scattered ^7Li ^+ ions are determined. On metal surfaces, large differences in the final charge state distributions of ^7Li ^+ ions scattered from substrate and adsorbate sites are observed at low alkali coverages, which disappear at high coverages. The final charge state distribution of ^7Li^+ ions is determined primarily by resonant charge transfer, which is dependent on the LEP. Thus, there is a transition in the LEP from inhomogeneous to nearly homogeneous as the adsorbate coverage increases. The LEP is modeled as a collection of isolated dipoles positioned at the adsorbate sites. Calculations of the final charge state distributions of ions scattered from such model surfaces do an excellent job of reproducing the measured charge state distributions. From these calculations, it is shown that the inhomogeneous to homogeneous transition in the LEP is due to a coverage dependent depolarization of the adsorbate dipoles. For the alkali-covered Si(111)-7 x 7 surface, the final charge state distribution is independent of scattering site. This behavior is not attributed to a homogeneous LEP, rather, it is due to the dangling bonds of the Si(111) -7 x 7 surface, which allow resonant charge transfer to take place well above the surface. As a consequence, variations in the LEP near the adsorbate sites are not detected. During the Li-Al charge promotion process, a Li 1s hole is created, which later decays by electron emission. Because of this, the charge state distributions of promoted ions differ significantly from those of non-promoted ions. From a combination of charge state distributions and secondary electron spectra, it is shown that the lifetime of the hole is on the order of the ion-surface interaction time, i.e., 10 fs.

  13. Applications of charge transfer devices in spectroscopy

    SciTech Connect

    Epperson, P.M.; Sweedler, J.V.; Bilhorn, R.B.; Sims, G.R.; Denton, M.B.

    1988-03-01

    Charge transfer device (CTD) detectors consist of two closely related silicon integrated circuits: the charge-coupled device (CCD), invented in 1970, and the charge injection device (CID), invented in 1973. Initially, several applications were proposed for these integrated circuits, including use as shift registers, logic and memory devices, electronic delay lines, and imaging detectors. The last application has so dominated the design and use of CTDs that they are among the most common electronic imaging detectors manufactured today.

  14. A monolithic SAW-charge transfer device

    NASA Technical Reports Server (NTRS)

    Papanicolaou, N. A.; Lin, H. C.

    1978-01-01

    Surface acoustic waves excited in a Si-SiO2-ZnO layered structure can produce a traveling electric field in the silicon substrate. Charges stored in the traveling potential wells can be transferred at high speed and density and with less complexity. The monolithic structure under investigation for the SAW-charge transfer device consists of a silicon substrate, a thin silicon dioxide insulating layer on top of which a ZnO piezoelectric film is deposited by sputtering. The surface acoustic waves are excited by interdigital transducers. The signal charge is injected into traveling potential wells that travel with the velocity of sound. Conditions for the transfer of the charges by the traveling wells are analyzed. A surface acoustic wave program was used to determine the optimum structure dimensions and transducer configuration which will produce the highest coupling in the excitation of the piezoelectric waves.

  15. Building model systems to understand Proton-Coupled Electron Transfer in heme : spectroscopic investigation of charge transfer to axially bound diimide acceptors

    E-print Network

    Hanson, Christina J

    2013-01-01

    Proton-Coupled Electron Transfer (PCET) is an important mechanistic motif in chemistry, which allows for efficient charge transport in many biological systems. We seek to understand how the proton and electron motions are ...

  16. Spacecraft Charging in Geostationary Transfer Orbit

    NASA Astrophysics Data System (ADS)

    Parker, L. N.; Minow, J. I.

    2014-12-01

    The 700 km x 5.8 Re orbit of the two Van Allen Probes spacecraft provide a unique opportunity to investigate surface charging in geostationary transfer orbits. We use records from the Helium Oxygen Proton Electron (HOPE) plasma spectrometer to identify candidate surface charging events based on the "ion line" charging signature in the ion records. We summarize the energetic particle environment and the conditions necessary for charging to occur in this environment. We discuss the altitude, duration, and magnitude of events observed in the Van Allen Probes from the beginning of the mission to present time. In addition, we explore what information the dual satellites provide on the spatial and temporal variations in the charging environments.

  17. Dynamical Treatment of Charge Transfer through Duplex Nucleic Acids Containing Modified Adenines

    PubMed Central

    Brancolini, Giorgia; Migliore, Agostino; Corni, Stefano; Fuentes-Cabrera, Miguel; Luque, F. Javier; Di Felice, Rosa

    2014-01-01

    We address the issue of whether chemical alterations of nucleobases are an effective tool to modulate charge transfer through DNA molecules. Our investigation uses a multi-level computational approach based on classical molecular dynamics and quantum chemistry. We find yet another evidence that structural fluctuations are a key factor to determine the electronic structure of double-stranded DNA. We argue that the electronic structure and charge transfer ability of flexible polymers is the result of a complex intertwining of various structural, dynamical and chemical factors. Chemical intuition may be used to design molecular wires, but this is not the sole component in the complex charge transfer mechanism through DNA. PMID:24060008

  18. Simple charge-transfer model for metallic complexes.

    PubMed

    Ramírez-Ramírez, José-Zeferino; Vargas, Rubicelia; Garza, Jorge; Gázquez, José L

    2010-08-01

    In the chemistry of metallic complexes, two important concepts have been used to rationalize the recognition and selectivity of a host by a guest: preorganization and complementarity. Both of these concepts stem from geometrical features. Less explored in the literature has been the interactional complementarity, where mainly the electronic factors in the intermolecular forces are involved. Because the charge transfer between a species rich in electrons (ligand) and another deficient in them (cation) is one of the main intermolecular factors that control the binding energies in metallic complexes, for such systems, we propose a simple model based on density functional theory. We define an interactional energy in which the geometrical energy changes are subtracted from the binding energies and just the electronic factors are taken into account. The model is tested for the complexation between bidentate and cyclic ligands and Ca, Pb, and Hg metal dications. The charge-transfer energy described by our model fits nicely with the interactional energy. Thus, when the geometrical changes do not contribute in a significant way to the complexation energy, the interactional energy is dominated by charge-transfer effects. PMID:20666541

  19. Biological charge transfer via flickering resonance

    PubMed Central

    Zhang, Yuqi; Liu, Chaoren; Balaeff, Alexander; Skourtis, Spiros S.; Beratan, David N.

    2014-01-01

    Biological electron-transfer (ET) reactions are typically described in the framework of coherent two-state electron tunneling or multistep hopping. However, these ET reactions may involve multiple redox cofactors in van der Waals contact with each other and with vibronic broadenings on the same scale as the energy gaps among the species. In this regime, fluctuations of the molecular structures and of the medium can produce transient energy level matching among multiple electronic states. This transient degeneracy, or flickering electronic resonance among states, is found to support coherent (ballistic) charge transfer. Importantly, ET rates arising from a flickering resonance (FR) mechanism will decay exponentially with distance because the probability of energy matching multiple states is multiplicative. The distance dependence of FR transport thus mimics the exponential decay that is usually associated with electron tunneling, although FR transport involves real carrier population on the bridge and is not a tunneling phenomenon. Likely candidates for FR transport are macromolecules with ET groups in van der Waals contact: DNA, bacterial nanowires, multiheme proteins, strongly coupled porphyrin arrays, and proteins with closely packed redox-active residues. The theory developed here is used to analyze DNA charge-transfer kinetics, and we find that charge-transfer distances up to three to four bases may be accounted for with this mechanism. Thus, the observed rapid (exponential) distance dependence of DNA ET rates over distances of ?15 Å does not necessarily prove a tunneling mechanism. PMID:24965367

  20. Variable Charge Soils: Mineralogy and Chemistry

    SciTech Connect

    Qafoku, Nik; Van Ranst, Eric; Noble, Andrew; Baert, Geert

    2003-11-01

    Soils rich in particles with amphoteric surface properties in the Oxisols, Ultisols, Alfisols, Spodosols and Andisols orders (1) are considered variable charge soils (2). The term “variable charge” is used to describe organic and inorganic soil constituents with reactive surface groups whose charge varies with pH, ionic concentration and composition of the soil solution. Such groups are the surface carboxyl, phenolic and amino functional groups of organic materials in soils, and surface hydroxyl groups of Fe and Al oxides, allophane and imogolite. The hydroxyl surface groups are also present on edges of some phyllosilicate minerals such as kaolinite, mica, and hydroxyl-interlayered vermiculite. The variable charge is developed on the surface groups as a result of adsorption or desorption of ions that are constituents of the solid phase, i.e., H+, and the adsorption or desorption of solid-unlike ions that are not constituents of the solid. Highly weathered soils usually undergo isoeletric weathering and reach a “zero net charge” stage during their development. They have a slightly acidic to acidic soil solution pH, which is close to either point of zero net charge (PZNC) (3) or point of zero salt effect (PZSE) (3). They are characterized by high abundances of minerals with a point of zero net proton charge (PZNPC) (3) at neutral and slightly basic pHs; the most important being Fe and Al oxides and allophane. Under acidic conditions, the surfaces of these minerals are net positively charged. In contrast, the surfaces of permanent charge phyllosilicates are negatively charged regardless of ambient conditions. Variable charge soils therefore, are heterogeneous charge systems. The coexistence and interactions of oppositely charged surfaces or particles confers a different pattern of physical and chemical behavior on the soil, relatively to a homogeneously charged system of temperate regions. In some variable charge soils (Oxisols and some Ultisols developed on ferromagnesian-rich parent materials) the surfaces of phyllosilicates are coated to a lesser or greater extent by amorphous or crystalline, oppositely charged nanoparticles of Fe and Al oxides. These coatings exhibit a high reactive surface area and help cementing larger particles with one another. As a result of these electrostatic interactions, stable microaggregates that are difficult to disperse are formed in variable charge soils. Most of highly weathered soils have reached the “advanced stage” of Jackson-Sherman weathering sequence that is characterized by the removal of Na, K, Ca, Mg, and Fe(II), the presence of Fe and Al polymers, and very dilute soil solutions with an ionic strength (IS) of less than 1 mmol L-1. The inter-penetration or overlapping of the diffuse double layers on oppositely charged surfaces may occur in these dilute systems. These diffuse layer interactions may affect the magnitude of the effective charge, i.e., the counter-ion charge (4). In addition, salt adsorption, which is defined as the simultaneous adsorption in equivalent amounts of the cation and anion of an electrolyte with no net release of other ions into the soil solution, appears to be a common phenomenon in these soils. They act as cation- and anion-exchangers and as salt-sorbers. The magnitude of salt adsorption depends strongly on initial IS in the soil solution and the presence in appreciable amounts of oppositely charged surfaces. Among the authors that have made illustrious contributions towards a better understanding of these fascinating soil systems are S. Matson, R.K. Schofield, van Olphen, M.E. Sumner, G.W. Thomas, G.P. Gillman, G. Uehara, B.K.G. Theng, K. Wada, N.J. Barrow, J.W. Bowden, R.J. Hunter and G. Sposito. This entry is mainly based on publications by these authors.

  1. Charge transfer in tunnel-junction arrays

    NASA Astrophysics Data System (ADS)

    Kaplan, Daniel M. R.

    Numerical modeling was used to study charge transfer in tunnel junction arrays. The effects of various configurations of background charge were considered, with the ultimate goal of making predictions about the possibility of device design. First the uniform (no background charge) arrays were considered. In this case solitonantisoliton avalanches were observed. Though the time duration of any avalanche, and the total charge DeltaQ = ne transferred across the array during the avalanche, are always finite, in arrays with length N larger than certain critical value Lc and large width M >> f(N), the avalanche magnitude n may be exponentially large, resulting in particular in a giant increase of shot noise. Next a special distribution of background charge was found, such that the array's Coulomb blockade is completely suppressed and shot noise is reduced substantially at low applied voltages. In particular the Fano factor F can approach the minimum value Fmin = 1/N << 1 (where N is the array length). Finally, the effects of the fully random q = [-e/2; + e/2] background charge were studied. Density of states at zero energy was found to have a dramatically different dependence on the array size in 1D and 2D. Also, in 2D systems a soft Coulomb gap was observed, whit DoS value at low energy diminishing rapidly with the array size. The effects of background charge on shot noise were also studied. At zero temperature and low current in 2D systems a strong increase in shot noise was observed, while addition of moderately low (T < eVt/N) temperature suppresses the noise. Results are discussed in the context of their possible application to single-electron devices.

  2. Ultrafast holography using charge-transfer polymers

    NASA Astrophysics Data System (ADS)

    Maniloff, Eric S.; Vacar, Dan; McBranch, Duncan W.; Wang, Hsing-Lin; Mattes, Benjamin R.; Gao, Jun; Heeger, Alan J.

    1997-02-01

    Charge-transfer polymers are a new class of nonlinear optical materials which can be used for generating femtosecond holographic gratings. Using semiconducting polymers sensitized with varying concentrations of C 60, holographic gratings were recorded by individual ultrafast laser pulses; the diffraction efficiency and time decay of the gratings were measured using non-degenerate four-wave mixing. Using a figure of merit for dynamic data processing, the temporal diffraction efficiency, this new class of materials exhibits between two and 12 orders of magnitude higher response than any other class of material. The high quantum efficiency and metastability of the charge transfer enables tuning of the decay dynamics by controlling the concentration of acceptors in the blend.

  3. Pattern classification using Charge Transfer Devices

    NASA Technical Reports Server (NTRS)

    Snyder, W. E.; Reece, J. H.; Benz, H. F.

    1978-01-01

    The potential uses of Charge Transfer Devices (CTDs) in pattern classification operations are explored. The needs for a hardware-based pattern classifier are established, and a matrix multiplication subsystem based upon a sum of products CTD is presented. An evaluation process for sum of products devices (particularly analog-analog correlators) is developed, and the feasibility of employing a particular device in a pattern classifier is determined. Finally, the possible impact of future trends in technology is considered.

  4. Satellite pattern classification using charge transfer devices

    NASA Technical Reports Server (NTRS)

    Snyder, W. E.; Husson, C.; Benz, H. F.

    1979-01-01

    The potential uses of Charge Transfer Devices (CTDs) in pattern classification operations are explored. The needs for a hardware-based pattern classifier are established, and a matrix multiplication subsystem based upon a sum-of-products CTD is presented. Applications of the subsystem to the classification of multi-modal Gaussian distributions in general and to LANDSAT data processing in particular are discussed. Finally, the potential impact of this technology on satellite data processing methodologies is discussed.

  5. Ultrafast holography using charge-transfer polymers

    Microsoft Academic Search

    Eric S. Maniloff; Dan Vacar; Duncan W. McBranch; Hsing-Lin Wang; Benjamin R. Mattes; Jun Gao; Alan J. Heeger

    1997-01-01

    Charge-transfer polymers are a new class of nonlinear optical materials which can be used for generating femtosecond holographic gratings. Using semiconducting polymers sensitized with varying concentrations of C60, holographic gratings were recorded by individual ultrafast laser pulses; the diffraction efficiency and time decay of the gratings were measured using non-degenerate four-wave mixing. Using a figure of merit for dynamic data

  6. Experiments on charge transfer in cosmic dust grain collisions

    Microsoft Academic Search

    T. Poppe; R. Schraepler

    2004-01-01

    The transfer of electrical charge in grain-target collisions was investigated leading to conclusions on the nature of charge transfer and its ammount. Grains, targets, collision velocities, and target temperatures were varied. We found, that the cosmic dust analogues generally acquired hundreds or thousands of elementary charges in collisions between 38 and 106 m\\/s. Thermally-diffusive charge transfer plays an important role

  7. On the Acid-Base Chemistry of Permanently Charged Minerals

    E-print Network

    Morel, François M. M.

    On the Acid-Base Chemistry of Permanently Charged Minerals A N N E M . L . K R A E P I E L University, Princeton, New Jersey 08544 The acid-base properties of oxides are well described by the surface complexation model, which superposes a thermodynamic description of acid-base reactions

  8. Phase Transfer Catalytic Reactions: A Physical Chemistry Laboratory Experiment

    NASA Astrophysics Data System (ADS)

    Shabestary, Nahid; Khazaeli, Sadegh; Hickman, Richie

    1998-11-01

    This article describes the application of phase-transfer catalysis within an undergraduate physical chemistry laboratory. Phase-transfer catalysis has been covered extensively in various books, articles, and patents. Many important industrial products are manufactured using this technique. However, very little of the subject is reflected in current undergraduate curriculum. The kinetic experiment designed here introduces many important concepts in phase-transfer catalysis and nucleophilic displacement reactions involving both mechanism and kinetics. Since this laboratory exploration includes catalytic reactions, organic synthesis, and chemical analysis, it covers many areas of chemistry. Thus, we believe this can be an important contribution to the students' learning. In this experiment, we have demonstrated that the reactions of alkyl bromides with NaCl under phase-transfer conditions can be carried out replacing bromide with chloride via a nucleophilic displacement reaction within a three-hour physical chemistry laboratory period.

  9. Phase Transfer Catalysis in Phosphorus Chemistry

    Microsoft Academic Search

    Gheorghe Ilia; Lavinia Macarie; Erika Bálint; György Keglevich

    2011-01-01

    Phase-transfer catalysis (PTC) has been widely used for the synthesis of organic compounds for more than three decades. The scope and mechanistic features of PTC have been the aim of numerous studies. This review focuses on the application of phase transfer catalysis in synthesis of phosphorus compounds.

  10. Graphene\\/substrate charge transfer characterized by inverse photoelectron spectroscopy

    Microsoft Academic Search

    Lingmei Kong; Cameron Bjelkevig; Sneha Gaddam; Mi Zhou; Younghee Lee; Ganghee Han; Haekyung Jeong; Ning Wu; Zhengzheng Zhang; Jie Xiao; Peter Dowben; Jeffry Kelber

    2011-01-01

    Wave vector-resolved inverse photoelectron spectroscopy (IPES) measurements demonstrate that there is a large variation of interfacial charge transfer between graphene and various substrates. IPES measurements of CVD single layer graphene on BN(0001)\\/Ru(0001), Ru, Ni(poly), and Cu(poly) indicate a substrate-to-graphene charge transfer of approximately 0.07, 0.06, 0.03 e- per carbon atom respectively and a charge transfer of 0.02 e- from graphene

  11. Electrochemical charge transfer at a metallic electrode: a simulation study 

    E-print Network

    Pounds, Michael A.

    2010-01-01

    Part I Electrochemical charge transfer at a metallic electrode: a simulation study The factors which affect the rate of heterogeneous electron transfer at a metallic electrode in the context of Marcus theory are ...

  12. Charge Transfer-Mediated Singlet Fission

    NASA Astrophysics Data System (ADS)

    Monahan, N.; Zhu, X.-Y.

    2015-04-01

    Singlet fission, the splitting of a singlet exciton into two triplet excitons in molecular materials, is interesting not only as a model many-electron problem, but also as a process with potential applications in solar energy conversion. Here we discuss limitations of the conventional four-electron and molecular dimer model in describing singlet fission in crystalline organic semiconductors, such as pentacene and tetracene. We emphasize the need to consider electronic delocalization, which is responsible for the decisive role played by the Mott-Wannier exciton, also called the charge transfer (CT) exciton, in mediating singlet fission. At the strong electronic coupling limit, the initial excitation creates a quantum superposition of singlet, CT, and triplet-pair states, and we present experimental evidence for this interpretation. We also discuss the most recent attempts at translating this mechanistic understanding into design principles for CT state-mediated intramolecular singlet fission in oligomers and polymers.

  13. MIE experiments and simultaneous measurement of the transferred charge

    NASA Astrophysics Data System (ADS)

    Langer, T.; Gramse, G.; Möckel, D.; von Pidoll, U.; Beyer, M.

    2011-06-01

    Using the apparatus commonly utilized for the determination of the minimum ignition energy a series of experiments have been carried out in ethene/air as a representative of explosion group IIB. Thereby, the transferred charge as a criterion to judge the ignition potential is determined to verify the threshold of 30 nC of transferred charge given in the standard IEC 60079-0. The stored charge in a capacitance before the discharge is compared to the transferred charge in the spark. Furthermore, the correlation of ignition energy and transferred charge is examined. Based on the results presented here, the threshold of the transferred charge for explosion group IIB is discussed. Moreover, the MIE value of an ethene/air mixture is reviewed taking into account the measurement uncertainty.

  14. Transfer of Algebraic and Graphical Thinking between Mathematics and Chemistry

    ERIC Educational Resources Information Center

    Potgieter, Marietjie; Harding, Ansie; Engelbrecht, Johann

    2008-01-01

    Students in undergraduate chemistry courses find, as a rule, topics with a strong mathematical basis difficult to master. In this study we investigate whether such mathematically related problems are due to deficiencies in their mathematics foundation or due to the complexity introduced by transfer of mathematics to a new scientific domain. In the…

  15. Charge Transfer Model of Atomic Ordering in Complex Perovskite Alloys

    E-print Network

    Wu, Zhigang

    Charge Transfer Model of Atomic Ordering in Complex Perovskite Alloys Zhigang Wu and Henry Krakauer-based perovskite alloys. The model allows charge transfer between A sites and is a generalization of Bellaiche Pb-based and Ba-based complex perovskite alloys. It yields smaller structural energy differences

  16. MOLECULAR PHYSICS, 2000, VOL. 98, NO. 21, 1749 1762 Coupling by charge transfer: role in bond stabilization for open-shell

    E-print Network

    Pirani, Fernando

    , but as complementary to the development of the ab-initio and semiempirical methods [3, 4] of quantum chemistry: it canMOLECULAR PHYSICS, 2000, VOL. 98, NO. 21, 1749± 1762 Coupling by charge transfer: role in bond into account the role of the charge transfer interaction. Relevant information on this interaction is obtained

  17. The roles of the solute and solvent cavities in charge-transfer-to-solvent dynamics: Ultrafast studies of potasside and sodide in diethyl ether

    Microsoft Academic Search

    Molly C. Cavanagh; Ryan M. Young; Benjamin J. Schwartz

    2008-01-01

    Although electron transfer reactions are among the most fundamental in chemistry, it is still not clear how to isolate the roles of the solute and solvent in moving charge between reactants in solution. In this paper, we address this question by comparing the ultrafast charge-transfer-to-solvent (CTTS) dynamics of potasside (K-) in diethyl ether (DEE) to those of sodide (Na-) in

  18. Transfer in chemistry: a study of students’ abilities in transferring mathematical knowledge to chemistry

    Microsoft Academic Search

    Richard A. Hoban; Odilla E. Finlayson; Brien C. Nolan

    2012-01-01

    It is recognized that there is a mathematics problem in chemistry, whereby, for example, undergraduate students appear to be unable to utilize basic calculus knowledge in a chemistry context – calculus knowledge – which would have been taught to these students in a mathematics context. However, there appears to be a scarcity of literature addressing the possible reasons for this

  19. Imaging charge transfer in iodomethane upon x-ray photoabsorption.

    PubMed

    Erk, Benjamin; Boll, Rebecca; Trippel, Sebastian; Anielski, Denis; Foucar, Lutz; Rudek, Benedikt; Epp, Sascha W; Coffee, Ryan; Carron, Sebastian; Schorb, Sebastian; Ferguson, Ken R; Swiggers, Michele; Bozek, John D; Simon, Marc; Marchenko, Tatiana; Küpper, Jochen; Schlichting, Ilme; Ullrich, Joachim; Bostedt, Christoph; Rolles, Daniel; Rudenko, Artem

    2014-07-18

    Studies of charge transfer are often hampered by difficulties in determining the charge localization at a given time. Here, we used ultrashort x-ray free-electron laser pulses to image charge rearrangement dynamics within gas-phase iodomethane molecules during dissociation induced by a synchronized near-infrared (NIR) laser pulse. Inner-shell photoionization creates positive charge, which is initially localized on the iodine atom. We map the electron transfer between the methyl and iodine fragments as a function of their interatomic separation set by the NIR-x-ray delay. We observe signatures of electron transfer for distances up to 20 angstroms and show that a realistic estimate of its effective spatial range can be obtained from a classical over-the-barrier model. The presented technique is applicable for spatiotemporal imaging of charge transfer dynamics in a wide range of molecular systems. PMID:25035485

  20. Contributions of charge-density research to medicinal chemistry

    PubMed Central

    Dittrich, Birger; Matta, Chérif F.

    2014-01-01

    This article reviews efforts in accurate experimental charge-density studies with relevance to medicinal chemistry. Initially, classical charge-density studies that measure electron density distribution via least-squares refinement of aspherical-atom population parameters are summarized. Next, interaction density is discussed as an idealized situation resembling drug–receptor interactions. Scattering-factor databases play an increasing role in charge-density research, and they can be applied both to small-molecule and macromolecular structures in refinement and analysis; software development facilitates their use. Therefore combining both of these complementary branches of X-ray crystallography is recommended, and examples are given where such a combination already proved useful. On the side of the experiment, new pixel detectors are allowing rapid measurements, thereby enabling both high-throughput small-molecule studies and macromolecular structure determination to higher resolutions. Currently, the most ambitious studies compute intermolecular interaction energies of drug–receptor complexes, and it is recommended that future studies benefit from recent method developments. Selected new developments in theoretical charge-density studies are discussed with emphasis on its symbiotic relation to crystallography. PMID:25485126

  1. A surface acoustic wave /SAW/ charge transfer imager

    NASA Technical Reports Server (NTRS)

    Papanicolauo, N. A.; Lin, H. C.

    1981-01-01

    An 80 MHz, 2-microsecond surface acoustic wave charge transfer device (SAW-CTD) has been fabricated in which surface acoustic waves are used to create traveling longitudinal electric fields in the silicon substrate and to replace the multiphase clocks of charge coupled devices. The traveling electric fields create potential wells which will carry along charges that may be stored in the wells; the charges may be injected into the wells by light. An optical application is proposed where the SAW-CTD structure is used in place of a conventional interline transfer design.

  2. Marcus wins nobel prize in chemistry for electron transfer theory

    SciTech Connect

    Levi, B.G.

    1993-01-01

    This article describes the work of Rudolf Marcus of Caltech leading to his receipt of the 1992 Nobel Prize in Chemistry [open quotes]for his contributions to the theory of electron transfer reactions in chemical systems.[close quotes] Applications of Marcus' theory include such diverse phenomena as photosynthesis, electrically conducting polymers, chemiluminescence, and corrosion. Historical aspects of his career are given. 10 refs., 1 fig.

  3. How intermolecular charge transfer influences the air-water interface.

    PubMed

    Wick, Collin D; Lee, Alexis J; Rick, Steven W

    2012-10-21

    The interfacial properties of three water models that allow for intermolecular charge rearrangement were examined with molecular dynamics simulations. They included the TIP4P water model, the TIP4P-FQ water model, which recently were modified to include intermolecular charge transfer [A. J. Lee and S. W. Rick, J. Chem. Phys. 134, 184507 (2011)]. Furthermore, another model with intermolecular charge transfer was developed for this work that was both flexible and polarizable. The effect of including intermolecular charge transfer is modest on most interfacial properties, including surface tension, electrostatic potential, interfacial dipole, and structure. However, a negative charge was found to build up at the air-water interface, but much smaller than has been measured experimentally. PMID:23083178

  4. Femtochemistry of Intramolecular Charge and Proton Transfer Reactions in Solution

    SciTech Connect

    Douhal, Abderrazzak; Sanz, Mikel; Carranza, Maria Angeles; Organero, Juan Angel; Tormo, Laura [Departamento de Quimica Fisica, Seccion de Quimicas, Facultad de Ciencias del Medio Ambiente, Universidad de Castilla-La Mancha, Avda. Carlos III, S.N., 45071, Toledo (Spain)

    2005-03-17

    We report on the first observation of ultrafast intramolecular charge- and proton-transfer reactions in 4'-dimethylaminoflavonol (DAMF) in solution. Upon femtosecond excitation of a non-planar structure of DMAF in apolar medium, the intramolecular charge transfer (ICT) does not occur, and a slow (2 ps) proton motion takes place. However, in polar solvents, the ICT is very fast (100-200 fs) and the produced structure is stabilized that proton motion takes place in few or tens of ps.

  5. MIE experiments and simultaneous measurement of the transferred charge

    Microsoft Academic Search

    T. Langer; G. Gramse; D. Möckel; U. von Pidoll; M. Beyer

    2011-01-01

    Using the apparatus commonly utilized for the determination of the minimum ignition energy a series of experiments have been carried out in ethene\\/air as a representative of explosion group IIB. Thereby, the transferred charge as a criterion to judge the ignition potential is determined to verify the threshold of 30 nC of transferred charge given in the standard IEC 60079-0.

  6. Induced-charge errors in charge-transfer measurement: Brush discharges between charged, insulating discs and earthed, conductive spheres

    Microsoft Academic Search

    Harold L. Walmsley

    2010-01-01

    Charge-transfer measurements made with fast-response, unshielded probes will, in principle, underestimate charge-transfers because of induced-charge errors. It is, however, difficult to know when the degree of underestimation is significant or to allow for it quantitatively because information on the magnitude of these errors is fragmented. Consequently, when measurements are done for electrostatic hazard assessment, unsafe equipment could wrongly be classified

  7. Phonons and charge-transfer excitations in HTS superconductors

    SciTech Connect

    Bishop, A.R.

    1989-01-01

    Some of the experimental and theoretical evidence implicating phonons and charge-transfer excitations in HTS superconductors is reviewed. It is suggested that superconductivity may be driven by a synergistic interplay of (anharmonic) phonons and electronic degrees of freedom (e.g., charge fluctuations, excitons). 47 refs., 5 figs.

  8. Controlled transfer of single charge carriers

    SciTech Connect

    Urbina, C.; Pothier, H.; Lafarge, P.; Orfila, P.F.; Esteve, D.; Devoret, M. (SPSRM, Centre d'Etudes Nucleaires de Saclay, 91191 Gif-sur-Yvette (FR)); Geerlings, L.J.; Anderegg, V.F.; Holweg, P.A.M.; Nooij, J.E. (Dept. of Applied Physics, Delft Univ. of Technology, P.O. Box 5046, 2600 GA Delft (NL))

    1991-03-01

    This paper reports on the design and operation of two devices, the turnstile and the pump, that transfer electrons one by one. They are both based on the existence of stable electrostatic configurations in arrays of ultrasmall tunnel junctions. While the turnstile only works in the normal state the pump could in principle achieve the transfer of single Cooper pairs.

  9. Charge transfer during individual collisions in ice growing by riming

    NASA Technical Reports Server (NTRS)

    Avila, Eldo E.; Caranti, Giorgio M.

    1991-01-01

    The charging of a target by riming in the wind was studied in the temperature range of (-10, -18 C). For each temperature, charge transfers of both signs are observed and, according to the environmental conditions, one of them prevails. The charge is more positive as the liquid water concentration is increased at any particular temperature. It is found that even at the low impact velocities used (5 m/s) there is abundant evidence of fragmentation following the collision.

  10. Theoretical treatment of charge transfer processes of relevance to astrophysics

    SciTech Connect

    Krstic, P.S.; Stancil, P.C.; Schultz, D.R.

    1997-12-01

    Charge transfer is an important process in many astrophysical and atmospheric environments. While numerous experimental and theoretical studies exist for H and He targets, data on other targets, particularly metals and molecules, are sparse. Using a variety of theoretical methods and computational techniques the authors are developing methods to estimate the cross sections for electron capture (charge transfer) in slow collisions of low charge state ions with heavy (Mg, Ca, Fe, Co, Ni and Zn) neutrals. In this ongoing work particular attention is paid to ascertaining the importance of double electron capture.

  11. Charge transfer reactions in nematic liquid crystals

    SciTech Connect

    Wiederrecht, G.P. [Argonne National Lab., IL (United States). Chemistry Div.; Wasielewski, M.R. [Argonne National Lab., IL (United States). Chemistry Div.; [Northwestern Univ., Evanston, IL (United States). Dept. of Chemistry; Galili, T.; Levanon, H. [Hebrew Univ. of Jerusalem (Israel). Dept. of Physical Chemistry

    1998-07-01

    Ultrafast transient absorption studies of intramolecular photoinduced charge separation and thermal charge recombination were carried out on a molecule consisting of a 4-(N-pyrrolidino)naphthalene-1,8-imide donor (PNI) covalently attached to a pyromellitimide acceptor (PI) dissolved in the liquid crystal 4{prime}-(n-pentyl)-4-cyanobiphenyl (5CB). The temperature dependencies of the charge separation and recombination rates were obtained at temperatures above the nematic-isotropic phase transition of 5CB, where ordered microdomains exist and scattering of visible light by these domains is absent. The authors show that excited state charge separation is dominated by molecular reorientation of 5CB perpendicular to the director within the liquid crystal microdomains. They also show that charge recombination is adiabatic and is controlled by the comparatively slow collective reorientation of the liquid crystal microdomains relative to the orientation of PNI{sup +}-PI{sup {minus}}. They also report the results of time resolved electron paramagnetic resonance (TREPR) studies of photoinduced charge separation in a series of supramolecular compounds dissolved in oriented liquid crystal solvents. These studies permit the determination of the radical pair energy levels as the solvent reorganization energy increases from the low temperature crystalline phase, through the soft glass phase, to the nematic phase of the liquid crystal.

  12. Coherent ultrafast charge transfer in an organic photovoltaic blend.

    PubMed

    Falke, Sarah Maria; Rozzi, Carlo Andrea; Brida, Daniele; Maiuri, Margherita; Amato, Michele; Sommer, Ephraim; De Sio, Antonietta; Rubio, Angel; Cerullo, Giulio; Molinari, Elisa; Lienau, Christoph

    2014-05-30

    Blends of conjugated polymers and fullerene derivatives are prototype systems for organic photovoltaic devices. The primary charge-generation mechanism involves a light-induced ultrafast electron transfer from the light-absorbing and electron-donating polymer to the fullerene electron acceptor. Here, we elucidate the initial quantum dynamics of this process. Experimentally, we observed coherent vibrational motion of the fullerene moiety after impulsive optical excitation of the polymer donor. Comparison with first-principle theoretical simulations evidences coherent electron transfer between donor and acceptor and oscillations of the transferred charge with a 25-femtosecond period matching that of the observed vibrational modes. Our results show that coherent vibronic coupling between electronic and nuclear degrees of freedom is of key importance in triggering charge delocalization and transfer in a noncovalently bound reference system. PMID:24876491

  13. The study of surface acoustic wave charge transfer device

    NASA Technical Reports Server (NTRS)

    Papanicolaou, N.; Lin, H. C.

    1978-01-01

    A surface acoustic wave-charge transfer device, consisting of an n-type silicon substrate, a thermally grown silicon dioxide layer, and a sputtered film of piezoelectric zinc oxide is proposed as a means of circumventing problems associated with charge-coupled device (CCD) applications in memory, signal processing, and imaging. The proposed device creates traveling longitudinal electric fields in the silicon and replaces the multiphase clocks in CCD's. The traveling electric fields create potential wells which carry along charges stored there. These charges may be injected into the wells by light or by using a p-n junction as in conventional CCD's.

  14. Assessment of atomic partial charge schemes for polarisation and charge transfer effects in ionic liquids.

    PubMed

    Rigby, Jason; Izgorodina, Ekaterina I

    2013-02-01

    In this work, we assess several popular atomic partial charge schemes with the view of accurately quantifying charge distribution, dipole moments and charge transfer in routinely used ionic liquids (ILs). We investigated a series of ion pairs of imidazolium-based ILs such as [C((1-4))mim]X (where X = Cl, BF(4) and NTf(2)) and ionic clusters of [NMe(4)][BF(4)], [C(1)mim][BF(4)] and [C(1)mim]Cl that were composed of two, four and eight ion pairs. Assessed partial charge schemes include restrained electrostatic potentials (RESP) employing ChelpG, Connolly and Geodesic point selection algorithms, as well as density matrix partitioning schemes including Mulliken, Löwdin and Natural Population Analysis (NPA). The quality of charge distribution was analysed using the following criteria: (1) treatment of symmetry identical atoms, (2) invariance of charge in the imidazolium ring with increasing alkyl chain and (3) recalculation to dipole moments as a measure of electronic polarisation. The RESP schemes such as Connolly and Geodesic clearly outperform the ChelpG scheme as well as the density matrix-based schemes for these three criteria. Calculated partial charges reveal that dipole moments were best represented by the RESP schemes and confirmed the presence of charge transfer in ILs to a various degree. The degree of charge transfer was dependent on anions as well as cluster size. In the ion pairs, the chloride anion showed the largest charge transfer, followed by the NTf(2) and BF(4) anions. In ionic clusters the charge transfer was shown to gradually converge from two to eight ion pairs in the case of the [NMe(4)][BF(4)] and [C(1)mim][BF(4)] ILs to a value, close to that for corresponding ion pairs. In contrast, charge transfer in the [C(1)mim]Cl clusters converges to a lower value, showing an unusually strong inter-ionic bond with the chloride anion. NPA charges were found to perform poorly, with near-unity charges being retained on the anions and cations in ion pairs and ionic clusters. Mulliken and Löwdin charges were shown to be highly basis set dependent and unpredictable with marked fluctuations in partial charges and therefore their use for ILs is particularly discouraged. Ability of the partial charge schemes to capture fluctuations in the dipole moment within the ionic clusters was also examined. The Connolly and Geodesic RESP schemes were found to slightly outperform ChelpG. Evidence to suggest that chloride-based ILs might be poor model systems for ILs is also presented. PMID:23247883

  15. Imaging charge and energy transfer in molecules using free-electron lasers

    NASA Astrophysics Data System (ADS)

    Rudenko, Artem

    2014-05-01

    Charge and energy transfer reactions drive numerous important processes in physics, chemistry and biology, with applications ranging from X-ray astrophysics to artificial photosynthesis and molecular electronics. Experimentally, the central goal in studies of transfer phenomena is to trace the spatial localization of charge at a given time. Because of their element and site sensitivity, ultrafast X-rays provide a promising tool to address this goal. In this talk I will discuss several experiments where free-electron lasers were employed to study charge and energy transfer dynamics in fragmenting molecules. In a first example, we used intense, 70 femtosecond 1.5 keV pulses from the Linac Coherent Light Source (LCLS) to study distance dependence of electron transfer in laser-dissociated methyl iodide molecules. Inducing well-localized positive charge on the heavy iodine atom, we observe signature of electron transition from the separated methyl group up to the distances of 35 atomic units. In a complementary experiment, we studied charge exchange between two partners in a dissociating molecular iodine employing a pump-probe arrangement with two identical 90 eV pulses from the Free-Electron LASer in Hamburg (FLASH). In both cases, the effective spatial range of the electron transfer can be reasonably described by a classical over-the-barrier model developed for ion-atom collisions. Finally, I will discuss a time-resolved measurement on non-local relaxation mechanism based on a long-range energy transfer, the so-called interatomic Coulombic decay. This work was supported by Chemical Sciences, Geosciences, and Biosciences Division, Office of Basic Energy Sciences, Office of Science, US Department of Energy and by the Kansas NSF ``First Award'' program.

  16. Photodissociation and charge transfer dynamics of negative ions studied with femtosecond photoelectron spectroscopy

    SciTech Connect

    Zanni, Martin T.

    1999-12-17

    This dissertation presents studies aimed at understanding the potential energy surfaces and dynamics of isolated negative ions, and the effects of solvent on each. Although negative ions play important roles in atmospheric and solution phase chemistry, to a large extent the ground and excited state potential energy surfaces of gas phase negative ions are poorly characterized, and solvent effects even less well understood. In an effort to fill this gap, the author's coworkers and the author have developed a new technique, anion femtosecond photoelectron spectroscopy, and applied it to gas phase photodissociation and charge transfer processes. Studies are presented that (1) characterize the ground and excited states of isolated and clustered anions, (2) monitor the photodissociation dynamics of isolated and clustered anions, and (3) explore the charge-transfer-to-solvent states of atomic iodide clustered with polar and non-polar solvents.

  17. Charge separation and energy transfer in carotenopyropheophorbide-quinone triads

    SciTech Connect

    Liddell, P.A.; Barrett, D.; Makings, L.R.; Pessiki, P.J.; Gust, D.; Moore, T.A.

    1986-08-20

    In natural photosynthesis membranes, chlorophyll molecules serve as the site of the initial photodriven charge separation. In addition, they play a role in subsequent electron-transfer steps, accept singlet excitation energy from carotenoid antenna molecules, and transfer triplet energy to carotenoid acceptors (thereby preventing sensitized singlet oxygen production and subsequent photodamage to the organism). The authors report herein the synthesis and study of chlorophyll-based carotenopyropheophorbide-quinone triad molecules which mimic all of these natural processes.

  18. Valence topological charge-transfer indices for dipole moments

    Microsoft Academic Search

    Francisco Torrens

    2003-01-01

    New topological valence charge-transfer (CT) indices are applied to the calculation of dipole moments. The dipole moments calculated by algebraic and vector semisums of the CT indices are defined. The combination of the CT indices allows the estimation of the dipole moments. The model is generalized for molecules with heteroatoms. The ability of the indices for the description of the

  19. Layered charge transfer complex cathodes or solid electrolyte cells

    Microsoft Academic Search

    Louzos

    1981-01-01

    Layered charge transfer complex cathodes for use in solid electrolyte cells are described wherein one layer of the cathode contains an electronic conductor which is isolated from the cell's solid electrolyte by a second layer of the cathode that does not contain an electronic conductor.

  20. CORRELATING ELECTRONIC AND VIBRATIONAL MOTIONS IN CHARGE TRANSFER SYSTEMS

    SciTech Connect

    Khalil, Munira

    2014-06-27

    The goal of this research program was to measure coupled electronic and nuclear motions during photoinduced charge transfer processes in transition metal complexes by developing and using novel femtosecond spectroscopies. The scientific highlights and the resulting scientific publications from the DOE supported work are outlined in the technical report.

  1. Laser studies of energy-and charge-transfer dynamics

    E-print Network

    Mazur, Eric

    of 800, 400, and 266 nm. We observe a highly nonlinear desorption and reaction yield fluence dependence:1, 12:1 and 3:1 at 800, 400, and 266 nm respectively. At 800 nm, the desorption and reactionLaser studies of energy- and charge-transfer dynamics A thesis presented by Jay Robert Goldman

  2. PHOTOSENSITIVE CENTERS AND CHARGE TRANSFER PROCESSES IN BARIUM CALCIUM TITANATE

    E-print Network

    Malovichko, Galina

    PHOTOSENSITIVE CENTERS AND CHARGE TRANSFER PROCESSES IN BARIUM CALCIUM TITANATE G.MALOVICHKO, V calcium titanate crystals, Ba0.77Ca0.23TiO3, in the temperature range between 4.2 K and 300 K are reported of crystals from barium titanate (BT) family make them promising candidates for various applications

  3. Primary cells utilize halogen-organic charge transfer complex

    NASA Technical Reports Server (NTRS)

    Gutmann, F.; Hermann, A. M.; Rembaum, A.

    1966-01-01

    Electrochemical cells with solid state components employ charge transfer complexes or donor-acceptor complexes in which the donor component is an organic compound and the acceptor component is a halogen. A minor proportion of graphite added to these composition helps reduce the resistivity.

  4. Space-charge transfer in hybrid inorganic-organic systems.

    PubMed

    Xu, Yong; Hofmann, Oliver T; Schlesinger, Raphael; Winkler, Stefanie; Frisch, Johannes; Niederhausen, Jens; Vollmer, Antje; Blumstengel, Sylke; Henneberger, Fritz; Koch, Norbert; Rinke, Patrick; Scheffler, Matthias

    2013-11-27

    We discuss density functional theory calculations of hybrid inorganic-organic systems that explicitly include the global effects of doping (i.e., position of the Fermi level) and the formation of a space-charge layer. For the example of tetrafluoro-tetracyanoquinodimethane on the ZnO(0001[over ¯]) surface we show that the adsorption energy and electron transfer depend strongly on the ZnO doping. The associated work function changes are large, for which the formation of space-charge layers is the main driving force. The prominent doping effects are expected to be quite general for charge-transfer interfaces in hybrid inorganic-organic systems and important for device design. PMID:24329464

  5. Charge transfer in collisions of doubly charged ions of iron and nickel with hydrogen atoms

    SciTech Connect

    Neufeld, D.A.; Dalgarno, A.

    1987-04-01

    The Landau-Zener approximation is used to compute the charge-transfer recombination rate coefficients of Fe/sup 2+/ and Ni/sup 2+/ in hydrogen at thermal energies. The energy separations of the adiabatic potential-energy curves of the quasimolecules FeH/sup 2+/ and NiH/sup 2+/ are obtained from one-electron calculations. The rate coefficients are of the order of 10/sup -9/ cm/sup 3/X sup -1: or greater. Charge transfer of Fe/sup 2+/ occurs preferentially into the ground state of Fe/sup +/ so that the reverse process of charge-transfer ionization of Fe/sup +/ in collision with H/sup +/ also occurs rapidly above the reaction threshold.

  6. Photoinduced charge and energy transfer in molecular wires.

    PubMed

    Gilbert, Mélina; Albinsson, Bo

    2015-02-21

    Exploring charge and energy transport in donor-bridge-acceptor systems is an important research field which is essential for the fundamental knowledge necessary to develop future applications. These studies help creating valuable knowledge to respond to today's challenges to develop functionalized molecular systems for artificial photosynthesis, photovoltaics or molecular scale electronics. This tutorial review focuses on photo-induced charge/energy transfer in covalently linked donor-bridge-acceptor (D-B-A) systems. Of utmost importance in such systems is to understand how to control signal transmission, i.e. how fast electrons or excitation energy could be transferred between the donor and acceptor and the role played by the bridge (the "molecular wire"). After a brief description of the electron and energy transfer theory, we aim to give a simple yet accurate picture of the complex role played by the bridge to sustain donor-acceptor electronic communication. Special emphasis is put on understanding bridge energetics and conformational dynamics effects on the distance dependence of the donor-acceptor electronic coupling and transfer rates. Several examples of donor-bridge-acceptor systems from the literature are described as a support to the discussion. Finally, porphyrin-based molecular wires are introduced, and the relationship between their electronic structure and photophysical properties is outlined. In strongly conjugated porphyrin systems, limitations of the existing electron transfer theory to interpret the distance dependence of the transfer rates are also discussed. PMID:25212903

  7. Relationship between surface chemistry, biofilm structure, and electron transfer in Shewanella anodes.

    PubMed

    Artyushkova, Kateryna; Cornejo, Jose A; Ista, Linnea K; Babanova, Sofia; Santoro, Carlo; Atanassov, Plamen; Schuler, Andrew J

    2015-03-01

    A better understanding of how anode surface properties affect growth, development, and activity of electrogenic biofilms has great potential to improve the performance of bioelectrochemical systems such as microbial fuel cells. The aim of this paper was to determine how anodes with specific exposed functional groups (-N(CH3)3 (+), -COOH, -OH, and -CH3), created using ?-substituted alkanethiolates self-assembled monolayers attached to gold, affect the surface properties and functional performance of electrogenic Shewanella oneidensis MR-1 biofilms. A combination of spectroscopic, microscopic, and electrochemical techniques was used to evaluate how electrode surface chemistry influences morphological, chemical, and functional properties of S. oneidensis MR-1 biofilms, in an effort to develop improved electrode materials and structures. Positively charged, highly functionalized, hydrophilic surfaces were beneficial for growth of uniform biofilms with the smallest cluster sizes and intercluster diffusion distances, and yielding the most efficient electron transfer. The authors derived these parameters based on 3D morphological features of biofilms that were directly linked to functional properties of the biofilm during growth and that, during polarization, were directly connected to the efficiency of electron transfer to the anode. Our results indicate that substratum chemistry affects not only primary attachment, but subsequent biofilm development and bacterial physiology. PMID:25743616

  8. Active pixel sensor with intra-pixel charge transfer

    NASA Technical Reports Server (NTRS)

    Fossum, Eric R. (Inventor); Mendis, Sunetra (Inventor); Kemeny, Sabrina E. (Inventor)

    1995-01-01

    An imaging device formed as a monolithic complementary metal oxide semiconductor integrated circuit in an industry standard complementary metal oxide semiconductor process, the integrated circuit including a focal plane array of pixel cells, each one of the cells including a photogate overlying the substrate for accumulating photo-generated charge in an underlying portion of the substrate, a readout circuit including at least an output field effect transistor formed in the substrate, and a charge coupled device section formed on the substrate adjacent the photogate having a sensing node connected to the output transistor and at least one charge coupled device stage for transferring charge from the underlying portion of the substrate to the sensing node.

  9. Multistep hopping and extracellular charge transfer in microbial redox chains.

    PubMed

    Pirbadian, Sahand; El-Naggar, Mohamed Y

    2012-10-28

    Dissimilatory metal-reducing bacteria are microorganisms that gain energy by transferring respiratory electrons to extracellular solid-phase electron acceptors. In addition to its importance for physiology and natural environmental processes, this form of metabolism is being investigated for energy conversion and fuel production in bioelectrochemical systems, where microbes are used as biocatalysts at electrodes. One proposed strategy to accomplish this extracellular charge transfer involves forming a conductive pathway to electrodes by incorporating redox components on outer cell membranes and along extracellular appendages known as microbial nanowires within biofilms. To describe extracellular charge transfer in microbial redox chains, we employed a model based on incoherent hopping between sites in the chain and an interfacial treatment of electrochemical interactions with the surrounding electrodes. Based on this model, we calculated the current-voltage (I-V) characteristics and found the results to be in good agreement with I-V measurements across and along individual microbial nanowires produced by the bacterium Shewanella oneidensis MR-1. Based on our analysis, we propose that multistep hopping in redox chains constitutes a viable strategy for extracellular charge transfer in microbial biofilms. PMID:22797729

  10. Anharmonic metastable charge transfer vibronic exciton in potassium tantalate

    NASA Astrophysics Data System (ADS)

    Liu, G. K.; Vikhnin, V. S.; Kapphan, S. E.

    2006-03-01

    This study provides an experimental evidence of a non-linear state of charge transfer vibronic excitons (CTVE) and its well-defined metastable behaviors in KTaO 3. An IR source could induce the same green CTVE-recombination luminescence band as that by a UV pumping. This up-conversion luminescence is characterized by a relaxation time ? ( ? ˜ 60 s at 3 K), and theoretically explained as a result of IR-induced transfer of occupation of a metastable anharmonic CTVE state into a harmonic luminescent CTVE state. The observed temperature dependence of ? suggests that the relaxation is controlled by resonant and phonon-induced tunneling processes.

  11. Theoretical study of charge transfer dynamics in collisions of C6+ carbon ions with pyrimidine nucleobases

    NASA Astrophysics Data System (ADS)

    Bacchus-Montabonel, M. C.

    2012-07-01

    A theoretical approach of the charge transfer dynamics induced by collision of C6+ ions with biological targets has been performed in a wide collision energy range by means of ab-initio quantum chemistry molecular methods. The process has been investigated for the target series thymine, uracil and 5-halouracil corresponding to similar molecules with different substituent on carbon C5. Such a study may be related to hadrontherapy treatments by C6+carbon ions and may provide, in particular, information on the radio-sensitivity of the different bases with regard to ion-induced radiation damage. The results have been compared to a previous analysis concerning the collision of C4+ carbon ions with the same biomolecular targets and significant charge effects have been pointed out.

  12. Visible Light Photorelease of Carboxylic Acids via Charge-Transfer Excitation of N-Methylpyridinium Iodide Esters.

    PubMed

    Kunsberg, David J; Kipping, Allison H; Falvey, Daniel E

    2015-07-17

    Iodide contrast sensitization to direct irradiation of charge transfer salts incurs carboxylic acid release via visible light absorption. The photochemical reduction of N-methyl-4-pyridinium iodide esters to release carboxylic acids is examined using (1)H NMR analysis. Photolysis reactions are carried out under mild, biphasic solvent conditions using a household LED lamp. Carboxylic acid release is reported in high yields, and the viability of this method for synthetic chemistry is demonstrated through a macroscale reaction. PMID:26120927

  13. Charge Transfer Plasmons: Optical Frequency Conductances and Tunable Infrared Resonances.

    PubMed

    Wen, Fangfang; Zhang, Yue; Gottheim, Samuel; King, Nicholas S; Zhang, Yu; Nordlander, Peter; Halas, Naomi J

    2015-06-23

    A charge transfer plasmon (CTP) appears when an optical-frequency conductive pathway between two metallic nanoparticles is established, enabling the transfer of charge between nanoparticles when the plasmon is excited. Here we investigate the properties of the CTP in a nanowire-bridged dimer geometry. Varying the junction geometry controls its conductance, which modifies the resonance energies and scattering intensities of the CTP while also altering the other plasmon modes of the nanostructure. Reducing the junction conductance shifts this resonance to substantially lower energies in the near- and mid-infrared regions of the spectrum. The CTP offers both a high-information probe of optical frequency conductances in nanoscale junctions and a new, unique approach to controllably engineering tunable plasmon modes at infrared wavelengths. PMID:25986388

  14. Charge transfer magnetoexciton formation at vertically coupled quantum dots

    PubMed Central

    2012-01-01

    A theoretical investigation is presented on the properties of charge transfer excitons at vertically coupled semiconductor quantum dots in the presence of electric and magnetic fields directed along the growth axis. Such excitons should have two interesting characteristics: an extremely long lifetime and a permanent dipole moment. We show that wave functions and the low-lying energies of charge transfer exciton can be found exactly for a special morphology of quantum dots that provides a parabolic confinement inside the layers. To take into account a difference between confinement potentials of an actual structure and of our exactly solvable model, we use the Galerkin method. The density of energy states is calculated for different InAs/GaAs quantum dots’ dimensions, the separation between layers, and the strength of the electric and magnetic fields. A possibility of a formation of a giant dipolar momentum under external electric field is predicted. PMID:23092373

  15. Modelling charge transfer reactions with the frozen density embedding formalism

    SciTech Connect

    Pavanello, Michele [Gorlaeus Laboratories, Leiden Institute of Chemistry, Leiden University, P.O. Box 9502, 2300 RA Leiden (Netherlands); Neugebauer, Johannes [Institute for Physical and Theoretical Chemistry, Technische Universitaet Braunschweig, Hans-Sommer-Strasse 10, 38106 Braunschweig (Germany)

    2011-12-21

    The frozen density embedding (FDE) subsystem formulation of density-functional theory is a useful tool for studying charge transfer reactions. In this work charge-localized, diabatic states are generated directly with FDE and used to calculate electronic couplings of hole transfer reactions in two {pi}-stacked nucleobase dimers of B-DNA: 5{sup '}-GG-3{sup '} and 5{sup '}-GT-3{sup '}. The calculations rely on two assumptions: the two-state model, and a small differential overlap between donor and acceptor subsystem densities. The resulting electronic couplings agree well with benchmark values for those exchange-correlation functionals that contain a high percentage of exact exchange. Instead, when semilocal GGA functionals are used the electronic couplings are grossly overestimated.

  16. The driving forces for twisted or planar intramolecular charge transfer.

    PubMed

    Zhong, Cheng

    2015-04-14

    A D-A (donor-acceptor)-type chromophore may twist or flatten in its excited state to form a TICT (twisted intramolecular charge transfer) state or a PICT (planar intramolecular charge transfer) state, respectively. What is the driving force behind this twisting or planarization? Which geometry will occur for a certain D-A chromophore? To answer these questions, both fragment orbital interaction and excited state energy decomposition analyses were performed on several classical TICT/PICT molecules. Three driving forces were identified, namely, energy gap, hole-electron interactions, and excited state relaxation. The contributions of these driving forces in various types of molecules were analyzed to determine how the molecular structure affects them. The energy gap difference between the twisted and planar geometries was found to play a decisive role in most situations. Thus, evaluating the frontier orbital interactions between the donor and acceptor effectively predicts whether chromophores planarize or twist in the excited state. PMID:25759940

  17. Charge transfer and atomic-level pressure in metallic glasses

    SciTech Connect

    Ding, Jun, E-mail: ding@jhu.edu [Department of Materials Science and Engineering, Johns Hopkins University, Baltimore, Maryland 21218 (United States); Cheng, Yongqiang [Chemical and Engineering Materials Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831 (United States)

    2014-02-03

    This paper presents a systematic study on the charge transfer and ionicity in various metallic-glass forming systems, as well as its relationship with other atomic-level structure indicators, using the Bader analysis method and molecular dynamics simulation. It is shown that in a binary or multicomponent system, the chemical effects (when more than one elements present) appear to play a more important role in setting the absolute level of the atomic-level pressure, compared to the topological fluctuation.

  18. Optical properties of charge transfer salts of tetracyanoquinodimethane (TCNQ)

    NASA Astrophysics Data System (ADS)

    Torrance, J. B.; Scott, B. A.; Kaufman, F. B.

    1993-12-01

    A unified interpretation is given for the infrared and optical spectra of many TCNQ compounds which exhibit a wide variety of physical properties. Inter- and intra-molecular transitions are distinguished by polarization measurements on single crystals of several TCNQ salts. It is suggested that there is incomplete charge transfers in both tetrathiofulvalinium (TTF)- and N-methylphenazinium (NMP)-TCNQ and that the electron-electron interactions are not appreciably screened by the excitonic polarizability of the cations.

  19. Energy and charge transfer in nanoscale hybrid materials.

    PubMed

    Basché, Thomas; Bottin, Anne; Li, Chen; Müllen, Klaus; Kim, Jeong-Hee; Sohn, Byeong-Hyeok; Prabhakaran, Prem; Lee, Kwang-Sup

    2015-06-01

    Hybrid materials composed of colloidal semiconductor quantum dots and ?-conjugated organic molecules and polymers have attracted continuous interest in recent years, because they may find applications in bio-sensing, photodetection, and photovoltaics. Fundamental processes occurring in these nanohybrids are light absorption and emission as well as energy and/or charge transfer between the components. For future applications it is mandatory to understand, control, and optimize the wide parameter space with respect to chemical assembly and the desired photophysical properties. Accordingly, different approaches to tackle this issue are described here. Simple organic dye molecules (Dye)/quantum dot (QD) conjugates are studied with stationary and time-resolved spectroscopy to address the dynamics of energy and ultra-fast charge transfer. Micellar as well as lamellar nanostructures derived from diblock copolymers are employed to fine-tune the energy transfer efficiency of QD donor/dye acceptor couples. Finally, the transport of charges through organic components coupled to the quantum dot surface is discussed with an emphasis on functional devices. PMID:25761127

  20. Charge Transfer Excitons at van der Waals Interfaces.

    PubMed

    Zhu, Xiaoyang; Monahan, Nicholas R; Gong, Zizhou; Zhu, Haiming; Williams, Kristopher W; Nelson, Cory A

    2015-07-01

    The van der Waals interfaces of molecular donor/acceptor or graphene-like two-dimensional (2D) semiconductors are central to concepts and emerging technologies of light-electricity interconversion. Examples include, among others, solar cells, photodetectors, and light emitting diodes. A salient feature in both types of van der Waals interfaces is the poorly screened Coulomb potential that can give rise to bound electron-hole pairs across the interface, i.e., charge transfer (CT) or interlayer excitons. Here we address common features of CT excitons at both types of interfaces. We emphasize the competition between localization and delocalization in ensuring efficient charge separation. At the molecular donor/acceptor interface, electronic delocalization in real space can dictate charge carrier separation. In contrast, at the 2D semiconductor heterojunction, delocalization in momentum space due to strong exciton binding may assist in parallel momentum conservation in CT exciton formation. PMID:26001297

  1. Spin-dependent charge transfer state design rules in organic photovoltaics.

    PubMed

    Chang, Wendi; Congreve, Daniel N; Hontz, Eric; Bahlke, Matthias E; McMahon, David P; Reineke, Sebastian; Wu, Tony C; Bulovi?, Vladimir; Van Voorhis, Troy; Baldo, Marc A

    2015-01-01

    Charge transfer states play a crucial role in organic photovoltaics, mediating both photocurrent generation and recombination losses. In this work, we examine recombination losses as a function of the electron-hole spacing in fluorescent charge transfer states, including direct monitoring of both singlet and triplet charge transfer state dynamics. Here we demonstrate that large donor-acceptor separations minimize back transfer from the charge transfer state to a low-lying triplet exciton 'drain' or the ground state by utilizing external pressure to modulate molecular spacing. The triplet drain quenches triplet charge transfer states that would otherwise be spin protected against recombination, and switches the most efficient origin of the photocurrent from triplet to singlet charge transfer states. Future organic solar cell designs should focus on raising the energy of triplet excitons to better utilize triplet charge transfer mediated photocurrent generation or increasing the donor-acceptor spacing to minimize recombination losses. PMID:25762410

  2. Spin-dependent charge transfer state design rules in organic photovoltaics

    NASA Astrophysics Data System (ADS)

    Chang, Wendi; Congreve, Daniel N.; Hontz, Eric; Bahlke, Matthias E.; McMahon, David P.; Reineke, Sebastian; Wu, Tony C.; Bulovi?, Vladimir; van Voorhis, Troy; Baldo, Marc A.

    2015-03-01

    Charge transfer states play a crucial role in organic photovoltaics, mediating both photocurrent generation and recombination losses. In this work, we examine recombination losses as a function of the electron-hole spacing in fluorescent charge transfer states, including direct monitoring of both singlet and triplet charge transfer state dynamics. Here we demonstrate that large donor–acceptor separations minimize back transfer from the charge transfer state to a low-lying triplet exciton ‘drain’ or the ground state by utilizing external pressure to modulate molecular spacing. The triplet drain quenches triplet charge transfer states that would otherwise be spin protected against recombination, and switches the most efficient origin of the photocurrent from triplet to singlet charge transfer states. Future organic solar cell designs should focus on raising the energy of triplet excitons to better utilize triplet charge transfer mediated photocurrent generation or increasing the donor–acceptor spacing to minimize recombination losses.

  3. Metastable charge-transfer state of californium(iii) compounds.

    PubMed

    Liu, Guokui; Cary, Samantha K; Albrecht-Schmitt, Thomas E

    2015-06-28

    Among a series of anomalous physical and chemical properties of Cf(iii) compounds revealed by recent investigations, the present work addresses the characteristics of the optical spectra of An(HDPA)3·H2O (An = Am, Cm, and Cf), especially the broadband photoluminescence from Cf(HDPA)3·H2O induced by ligand-to-metal charge transfer (CT). As a result of strong ion-ligand interactions and the relative ease of reducing Cf(iii) to Cf(ii), a CT transition occurs at low energy (<3 eV) via the formation of a metastable Cf(ii) state. It is shown that the systematic trend in CT transitions of the lanthanide series is not paralleled by actinide elements lighter than Cf(iii), and californium represents a turning point in the periodicity of the actinide series. Analyses and modeling of the temperature-dependent luminescence dynamics indicate that the metastable Cf(ii) charge-transfer state undergoes radiative and non-radiative relaxations. Broadening of the CT transition arises from strong vibronic coupling and hole-charge interactions in the valence band. The non-radiative relaxation of the metastable CT state results from a competition between phonon-relaxation and thermal tunneling that populates the excited states of Cf(iii). PMID:26032575

  4. XAFS study of charge transfer in intercalation compounds

    NASA Astrophysics Data System (ADS)

    Ouvrard, Guy; Wu, Ziyu

    1997-12-01

    An intercalation process is a reversible topotactic reaction in which a guest species occupies empty sites in a solid structure. A charge transfer is always observed between the guest and the host. An accurate knowledge of this electronic exchange, i.e. how many electrons are transferred and on which electronic level, can only be obtained from precise electronic band structure calculations. Such calculations have to be supported by experimental data. For this purpose we have compared X-ray absorption spectroscopy (XAS) data with edge simulations in the multiple scattering formalism and band structure calculations in using the Tight Binding Linear Muffin Tin Orbitals method in the Atomic Spheres Approximation (TB-LMTO-ASA) method. This approach is first illustrated by a study of sulfur K edge on the two modifications (1T and 2H) of tantalum disulfide TaS 2. It is then applied for an accurate characterization of the charge transfer in the case of lithium intercalation into TiS 2, from XAFS experiments at the sulfur K edge. It is concluded that sulfur atoms are largely taking part in the intercalation process.

  5. Highly Twisted Triarylamines for Photoinduced Intramoleculer ChargeTransfer

    SciTech Connect

    Chudomel, J. M.; Yang, B. Q.; Barnes, M. D.; Achermann, M.; Mague, J. T.; Lahti, P. M.

    2011-08-04

    9-(N,N-Dianisylamino)anthracene (9DAAA), 9-(N,N-dianisylamino)dinaphth([1,2-a:2'-1'-j]-anthracene (9DAAH), and 9,10-bis(N,N-dianisylamino)anthracene (910BAA) were synthesized as highly twisted triarylamines with potential for photoexcited internal charge transfer. Crystallography of 9DAAA shows its dianisylamino group to be twisted nearly perpendicular to its anthracene unit, similar to a report for 910BAA. The solution fluorescence spectra show strong bathochromic shifts for each of the three molecular systems with strongly decreased quantum efficiency in higher polarity solvents. Solution-phase (ensemble) time-resolved photoluminescence measurements show up to 4-fold decreases in fluorescence lifetime in acetonitrile compared to hexane. The combined results are consistent with photoinduced, transient intramolecular charge-transfer from the bis-anisylamine unit to the polycyclic aromatic unit. Computational modeling is in accord with intramolecular transfer of electron density from the bis-anisylamino unit to the anthracene, based on in comparisons of HOMO and LUMO.

  6. Coupled electron-nuclear dynamics: Charge migration and charge transfer initiated near a conical intersection

    NASA Astrophysics Data System (ADS)

    Mendive-Tapia, David; Vacher, Morgane; Bearpark, Michael J.; Robb, Michael A.

    2013-07-01

    Coupled electron-nuclear dynamics, implemented using the Ehrenfest method, has been used to study charge migration with fixed nuclei, together with charge transfer when nuclei are allowed to move. Simulations were initiated at reference geometries of neutral benzene and 2-phenylethylamine (PEA), and at geometries close to potential energy surface crossings in the cations. Cationic eigenstates, and the so-called sudden approximation, involving removal of an electron from a correlated ground-state wavefunction for the neutral species, were used as initial conditions. Charge migration without coupled nuclear motion could be observed if the Ehrenfest simulation, using the sudden approximation, was started near a conical intersection where the states were both strongly coupled and quasi-degenerate. Further, the main features associated with charge migration were still recognizable when the nuclear motion was allowed to couple. In the benzene radical cation, starting from the reference neutral geometry with the sudden approximation, one could observe sub-femtosecond charge migration with a small amplitude, which results from weak interaction with higher electronic states. However, we were able to engineer large amplitude charge migration, with a period between 10 and 100 fs, corresponding to oscillation of the electronic structure between the quinoid and anti-quinoid cationic electronic configurations, by distorting the geometry along the derivative coupling vector from the D6h Jahn-Teller crossing to lower symmetry where the states are not degenerate. When the nuclear motion becomes coupled, the period changes only slightly. In PEA, in an Ehrenfest trajectory starting from the D2 eigenstate and reference geometry, a partial charge transfer occurs after about 12 fs near the first crossing between D1, D2 (N+-Phenyl, N-Phenyl+). If the Ehrenfest propagation is started near this point, using the sudden approximation without coupled nuclear motion, one observes an oscillation of the spin density - charge migration - between the N atom and the phenyl ring with a period of 4 fs. When the nuclear motion becomes coupled, this oscillation persists in a damped form, followed by an effective charge transfer after 30 fs.

  7. Coupled electron-nuclear dynamics: Charge migration and charge transfer initiated near a conical intersection

    SciTech Connect

    Mendive-Tapia, David; Vacher, Morgane; Bearpark, Michael J.; Robb, Michael A. [Department of Chemistry, Imperial College London, London SW7 2AZ (United Kingdom)] [Department of Chemistry, Imperial College London, London SW7 2AZ (United Kingdom)

    2013-07-28

    Coupled electron-nuclear dynamics, implemented using the Ehrenfest method, has been used to study charge migration with fixed nuclei, together with charge transfer when nuclei are allowed to move. Simulations were initiated at reference geometries of neutral benzene and 2-phenylethylamine (PEA), and at geometries close to potential energy surface crossings in the cations. Cationic eigenstates, and the so-called sudden approximation, involving removal of an electron from a correlated ground-state wavefunction for the neutral species, were used as initial conditions. Charge migration without coupled nuclear motion could be observed if the Ehrenfest simulation, using the sudden approximation, was started near a conical intersection where the states were both strongly coupled and quasi-degenerate. Further, the main features associated with charge migration were still recognizable when the nuclear motion was allowed to couple. In the benzene radical cation, starting from the reference neutral geometry with the sudden approximation, one could observe sub-femtosecond charge migration with a small amplitude, which results from weak interaction with higher electronic states. However, we were able to engineer large amplitude charge migration, with a period between 10 and 100 fs, corresponding to oscillation of the electronic structure between the quinoid and anti-quinoid cationic electronic configurations, by distorting the geometry along the derivative coupling vector from the D{sub 6h} Jahn-Teller crossing to lower symmetry where the states are not degenerate. When the nuclear motion becomes coupled, the period changes only slightly. In PEA, in an Ehrenfest trajectory starting from the D{sub 2} eigenstate and reference geometry, a partial charge transfer occurs after about 12 fs near the first crossing between D{sub 1}, D{sub 2} (N{sup +}-Phenyl, N-Phenyl{sup +}). If the Ehrenfest propagation is started near this point, using the sudden approximation without coupled nuclear motion, one observes an oscillation of the spin density – charge migration – between the N atom and the phenyl ring with a period of 4 fs. When the nuclear motion becomes coupled, this oscillation persists in a damped form, followed by an effective charge transfer after 30 fs.

  8. Interpretation of charge transfer measurements of brush discharges

    NASA Astrophysics Data System (ADS)

    Chowdhury, Kanchan; von Pidoll, Ulrich; Moeckel, Dieter; Langer, Tim; Beyer, Michael

    2011-06-01

    In the present work, experimental results on the measurement of the total charge on a charged insulating sheet before and after a provoked brush discharge, their difference "C", the induced charge "A" when approaching an earthed microprocessor operated hand-Coulombmeter, and the transferred charge "B" at the instance of the discharge are presented. "B" is identical with the value measured by the hand-Coulombmeter within the expected measurement uncertainty. Due to observed corona losses and multiple brush discharges independent of each other, "B" correlates better with the incendivity than "C". The quotient B/C was closer to 1 than calculated in the literature but shows all predicted trends. The results obtained can be used for correct estimation of the incendivity of brush discharges between 10 nC and 90 nC. There is no need to change the existing threshold limits of 60 nC, 30 nC and 10 nC for the explosion groups IIA, IIB and IIC hitherto used in standards for zone 1.

  9. Charge transfer between acenes and PbS nanocrystals.

    PubMed

    Dissanayake, D M N M; Hatton, R A; Lutz, T; Curry, R J; Silva, S R P

    2009-05-13

    Organic-inorganic hybrid heterojunctions have potential as the basis for future photovoltaic devices. Herein, we report the results of investigations exploring the possibility of using pentacene and tetracene as photoelectron donors in conjunction with PbS nanocrystals (PbS-NCs). Photoinduced charge transfer was probed using external quantum efficiency measurements on acene:PbS-NC hybrid photovoltaic devices in conjunction with photoluminescence studies of the corresponding bilayer films. It is shown that photoelectron transfer from pentacene to the PbS-NCs is inefficient as compared to that between tetracene and PbS-NCs. The latter case can be rationalized in terms of the energy level alignment at the heterojunction assuming a common vacuum level. However, in the case of pentacene:PbS-NC junctions an interfacial energy level shift must be considered in order to explain the observations. PMID:19420636

  10. Photoinduced charge-transfer materials for nonlinear optical applications

    DOEpatents

    McBranch, Duncan W.

    2006-10-24

    A method using polyelectrolyte self-assembly for preparing multi-layered organic molecular materials having individual layers which exhibit ultrafast electron and/or energy transfer in a controlled direction occurring over the entire structure. Using a high molecular weight, water-soluble, anionic form of poly-phenylene vinylene, self-assembled films can be formed which show high photoluminescence quantum efficiency (QE). The highest emission QE is achieved using poly(propylene-imine) (PPI) dendrimers as cationic binders. Self-quenching of the luminescence is observed as the solid polymer film thickness is increased and can be reversed by inserting additional spacer layers of transparent polyelectrolytes between each active conjugated layer, such that the QE grows with thickness. A red shift of the luminescence is also observed as additional PPV layers are added. This effect persists as self-quenching is eliminated. Charge transfer superlattices can be formed by additionally incorporating C.sub.60 acceptor layers.

  11. Energy transfer and charge separation kinetics in photosystem I

    PubMed Central

    Holzwarth, Alfred R.; Schatz, Günther; Brock, Helmuth; Bittersmann, Edith

    1993-01-01

    The energy transfer and charge separation kinetics of a photosystem I (PS I) core particle of an antenna size of 100 chlorophyll/P700 has been studied by combined fluorescence and transient absorption kinetics with picosecond resolution. This is the first combined picosecond study of transient absorption and fluorescence carried out on a PS I particle and the results are consistent with each other. The data were analyzed by both global lifetime and global target analysis procedures. In fluorescence major lifetime components were found to be 12 and 36 ps. The shorter-lived one shows a negative amplitude at long wavelengths and is attributed to an energy transfer process between pigments in the main antenna Chl pool and a small long-wavelength Chl pool emitting around 720 nm whereas the longer-lived component is assigned to the overall charge separation lifetime. The lifetimes resolved in transient absorption are 7-8 ps, 33 ps, and [unk]1 ns. The shortest-lived one is assigned to energy transfer between the same pigment pools as observed also in fluorescence kinetics, the middle component of 33 ps to the overall charge separation, and the long-lived component to the lifetime of the oxidized primary donor P700+. The transient absorption data indicate an even faster, but kinetically unresolved energy transfer component in the main Chl pool with a lifetime <3 ps. Several kinetic models were tested on both the fluorescence and the picosecond absorption data by global target analysis procedures. A model where the long-wave pigments are spatially and kinetically connected with the reaction center P700 is favored over a model where P700 is connected more closely with the main Chl pool. Our data show that the charge separation kinetics in these PS I particles is essentially trap limited. The relevance of our data with respect to other time-resolved studies on PS I core particles is discussed, in particular with respect to the nature and function of the long-wave pigments. From the transient absorption data we do not see any evidence for the occurrence of a reduced Chl primary electron acceptor, but we also can not exclude that possibility, provided that reoxidation of that acceptor should occur within a time <40 ps. PMID:19431900

  12. Investigation of structural charge transfer in zeolites by ultraviolet spectroscopy

    SciTech Connect

    Garbowski, E.D.; Mirodatos, C.

    1982-01-07

    Charge-transfer processes in various zeolites (faujasite, mordenite, ZSM5, erionite, and offretite) are evidenced by means of UV spectroscopy. UV bands at 240 and 320 nm are assigned to two different Al-O units. The band at 240 nm, present whatever the zeolite and whatever the chemical or thermal treatment, is related to framework Al-O units which are ''inert'' toward catalysis and easily removed by dealumination or dehydroxylation. The band at 320 nm, more stable toward dealumination and dehydroxylation, is specifically detected or significantly enhanced for catalytically active samples (methanol conversion, hydrocarbon cracking, and disproportionation). This band could be related to oxoaluminum structures inside the zeolite matrix.

  13. Negative thermal expansion induced by intermetallic charge transfer

    NASA Astrophysics Data System (ADS)

    Azuma, Masaki; Oka, Kengo; Nabetani, Koichiro

    2015-06-01

    Suppression of thermal expansion is of great importance for industry. Negative thermal expansion (NTE) materials which shrink on heating and expand on cooling are therefore attracting keen attention. Here we provide a brief overview of NTE induced by intermetallic charge transfer in A-site ordered double perovskites SaCu3Fe4O12 and LaCu3Fe4?xMnxO12, as well as in Bi or Ni substituted BiNiO3. The last compound shows a colossal dilatometric linear thermal expansion coefficient exceeding ?70 × 10?6 K?1 near room temperature, in the temperature range which can be controlled by substitution.

  14. Effect of solution physico-chemistry on the charge property of nanofiltration membranes

    Microsoft Academic Search

    Joo-Hwa Tay; Jianlin Liu; Darren Delai Sun

    2002-01-01

    Electrokinetic phenomenon is an important factor in pressure-driven membrane water filtration process. Zeta potential is a measurable and reliable parameter to characterize the charge property of membranes. This study investigated the effects of solution physico-chemistry on the zeta potential of nanofiltration membranes. A comprehensive semi-empirical mathematical model based on the Poisson–Boltzmann equation, Membrane Surface Charge model, was established. The correlations

  15. Radiative charge transfer and radiative association in He++ Ne collisions

    NASA Astrophysics Data System (ADS)

    Liu, X. J.; Qu, Y. Z.; Xiao, B. J.; Liu, C. H.; Zhou, Y.; Wang, J. G.; Buenker, R. J.

    2010-02-01

    A fully quantum-mechanical approach is utilized to study the collision process of He+ with neutral neon, and the radiative charge transfer (RCT) and radiative association (RA) cross sections are presented in the energy range from 0.08 meV to 1 eV, while the optical potential and semiclassical methods are adopted to calculate the total radiative decay cross sections for energies from 0.08 meV to 5 keV. The potential energy curves and dipole transition matrix elements are obtained by an ab initio multireference configuration interaction package. For the related three lowest X 2?+, A 2?, and B 2?+ states, the spectroscopic data are in good agreement with other theoretical calculations and experimental measurements. Our results indicate that the RCT cross section is much larger than the nonradiative charge transfer cross section for collision energy E < 20 eV, and when E > 40 eV, the nonradiative process becomes dominant. Especially, we found that in the present collision system the RA process is more important than the RCT process when E < 1 meV. The RCT and RA rate coefficients are also given for temperatures from 1 to 4 ×103 K.

  16. Charge transfer during alkali-surface adsorbate collisions

    NASA Astrophysics Data System (ADS)

    Yang, Ye

    The study of charge transfer process between atomic particles and surface adsorbates is important, from both fundamental and practical points of view. Resonant charge transfer (RCT) process during the scattering of low-energy alkali ions from surfaces is proven to depend on the surface local electrostatic potential (LEP). This dissertation investigates the surface electronic environment around halogen and hydrogen adatoms on transition metal and silicon surfaces by using alkali ion scattering. Charge transfer in 7Li+ scattering from clean Si surfaces was shown to involve RCT between the Li 2s level and the Si dangling bonds. Hydrogen adsorption decreases the neutralization because it ties up the dangling bonds. The neutral fractions in 7Li + scattering from Cs/Si are also determined primarily by the dangling bond states, so that the surface LEP cannot be directly probed. Hydrogen adsorption on Cs/Si ties up the dangling bonds, thereby revealing the local potentials. The neutralization probabilities of Li+ backscattered from the hydrogen- and iodine-covered Ni(100) surface were measured. The neutral fraction does not change significantly on H-adsorbed surface. For iodine adsorption, however, unexpected high neutralization probabilities were found for Li scattered directly from iodine sites. Similar behavior were observed for Li+ scattering from I- and Br-covered Fe(100) and Fe(110). The neutralization of Li+ was measured as a function of the incident energy, adatom charge and coverage, and exit angle. It was found that the larger neutral fractions of Li scattered from the halogen sites are caused by a lower potential directly above the adatoms due to internal polarization. As the exit beam moves off-normal, the neutral fraction of Li scattered from iodine decreases. This is in contrast to Cs and Ag adsorbates where the neutral fractions increase for glancing exit trajectories. These angular-dependences are verified by a semi-quantitative theoretical analysis. To further understand the role of local bonding in inducing halogen adatom polarization, neutralization of alkalis backscattered from I-adsorbed clean and oxidized Si(111) was measured. The results suggests that I adatoms are polarized on Si(111), but the polarization strength is greatly quenched for I adatoms on pre-oxidized Si(111), which are directly bonded to oxygen.

  17. Circumstellar disk chemistry: 2D UV radiative transfer and effects of stellar UV

    E-print Network

    Zadelhoff, Gerd-Jan van

    Circumstellar disk chemistry: 2D UV radiative transfer and effects of stellar UV G.J. van Zadelhoff interstellar abundances are modified. Photodissociation by UV radiation in the upper layers and freeze radiative transfer for a correct abundance determination If CO can be photodissociated by the stellar UV

  18. A nanocomposite superstructure of metal oxides with effective charge transfer interfaces

    NASA Astrophysics Data System (ADS)

    Bian, Zhenfeng; Tachikawa, Takashi; Zhang, Peng; Fujitsuka, Mamoru; Majima, Tetsuro

    2014-01-01

    The alignment of nanoparticle building blocks into ordered superstructures is one of the key topics in modern colloid and material chemistry. Metal oxide mesocrystals are superstructures of assembled nanoparticles of metal oxides and have potentially tunable electronic, optical and magnetic properties, which would be useful for applications ranging from catalysis to optoelectronics. Here we report a facile and general approach for synthesizing metal oxide mesocrystals and developing them into new nanocomposite materials containing two different metals. The surface and internal structures of the mesocrystals were fully characterized by electron microscopy techniques. Single-particle confocal fluorescence spectroscopy, electron paramagnetic resonance spectroscopy and time-resolved diffuse reflectance spectroscopy measurements revealed that efficient charge transfer occurred between n-type and p-type semiconductor nanoparticles in the composite mesocrystals. This behaviour is desirable for their applications ranging from catalysis, optoelectronics and sensing, to energy storage and conversion.

  19. Is dipole moment a valid descriptor of excited state's charge-transfer character?

    PubMed

    Petelenz, Piotr; Pac, Barbara

    2013-11-20

    In the ongoing discussion on excited states of the pentacene crystal, dipole moment values have been recently invoked to gauge the CT admixture to excited states of Frenkel parentage in a model cluster. In the present paper, a simple dimer model is used to show that, in general, the dipole moment is not a valid measure of the CT contribution. This finding eliminates some apparent disagreement between the computational results published by different research groups. The implications of our results and other related aspects of cluster-type quantum chemistry calculations are discussed in the context of the standing literature dispute concerning the mechanism of singlet fission in the pentacene crystal, notably the role of charge transfer contributions vs the involvement of an excimer-like doubly excited intermediate (D state). PMID:24138489

  20. Nanocrystal/J-aggregate constructs : chemistry, energy transfer, and applications

    E-print Network

    Walker, Brian J. (Brian Jacob)

    2011-01-01

    The interaction of light with matter is one of the most central subjects to modern chemistry. Two types of materials, semiconductor nanocrystals and J-aggregates of cyanine dyes, have been developed chiefly due to their ...

  1. Effect of solution chemistry on the surface charge of polymeric reverse osmosis and nanofiltration membranes

    Microsoft Academic Search

    Amy E. Childress; Menachem Elimelech

    1996-01-01

    A streaming potential analyzer has been used to investigate the effect of solution chemistry on the surface charge of four commercial reverse osmosis and nanofiltration membranes. Zeta potentials of these membranes were analyzed for aqueous solutions of various chemical compositions over a pH range of 2 to 9. In the presence of an indifferent electrolyte (NaCl), the isoelectric points of

  2. Charge transfer at metal\\/solid polymer interfaces in the presence of liquids

    Microsoft Academic Search

    Joe Wasem; Steve Langford; Tom Dickinson

    2002-01-01

    Physical and chemical interactions can transfer charge between liquids and insulating surfaces with important consequences. We examine charge transfer across a metal stylus\\/solid polymer interface in the presence of liquid (here a perfluoropolyether lubricant, Fomblin Z-DOL--a common lubricant for magnetic hard disks--and water). Observations of transient currents to\\/from the metal stylus, near-surface bound charge, and free charge escaping from the

  3. Charge transfer and electric strength of thin silicon oxynitride films

    SciTech Connect

    Kubrin, V.I.; Dorofeeva, E.G.; Kacharava, M.V.; Korzo, V.F.

    1984-05-01

    The charge transfer mechanism in thin silicon oxynitride films of various oxygen and nitrogen content is investigated. The measurements are carried out in the temperature range 77-500/sup 0/K and frequency interval 20 Hz to 10 MHz for specimens 10 nm to 20 ..mu..m thick, prepared by activation decomposition of tetramethoxylene in nitrogen atmosphere under the action of 220-280 nm UV radiation of 5-25 klx intensity with a substrate temperature of 100-450/sup 0/C. It is shown that at low frequencies the conductivity has mainly a 2-center hopping while at higher frequencies it has a multicenter phonon-stimulated character with an activation energy of 0.32-0.56 eV and the predominance of a trapping level of an energy up to 2.2 eV.

  4. Charge-transfer complexes of some linear conjugated polyenes.

    PubMed Central

    Mallik, B; Jain, K M; Misra, T N

    1980-01-01

    On adsorption of some electron-acceptor molecules on the solid films of all-trans-beta-carotene, beta-apo-8'-carotenal, astacene and methylbixin a new absorption band appears on the longer-wavelength side of the spectrum in addition to the original bands. The position of this new band is dependent on the electron affinity (EA) of the acceptor molecules, and the intensity of this band increases with the amount of adsorbed acceptor molecules. A linear relationship between the vmax. of the new band and EA was observed. The value of the ionization potential of the polyenes estimated from such linear relationship agrees satisfactorily with the value obtained by other methods. It has been concluded that the polyenes behave as electron donor and first form molecular charge-transfer complexes (of type [polyene . I2] with iodine) with electron acceptors, these finally dissociating to yield ionic complexes (of type [polyene . I+] with iodine). PMID:7213346

  5. Photoinduced Charge Transfer from Titania to Surface Doping Site

    PubMed Central

    Inerbaev, Talgat; Hoefelmeyer, James D.; Kilin, Dmitri S.

    2013-01-01

    We evaluate a theoretical model in which Ru is substituting for Ti at the (100) surface of anatase TiO2. Charge transfer from the photo-excited TiO2 substrate to the catalytic site triggers the photo-catalytic event (such as water oxidation or reduction half-reaction). We perform ab-initio computational modeling of the charge transfer dynamics on the interface of TiO2 nanorod and catalytic site. A slab of TiO2 represents a fragment of TiO2 nanorod in the anatase phase. Titanium to ruthenium replacement is performed in a way to match the symmetry of TiO2 substrate. One molecular layer of adsorbed water is taken into consideration to mimic the experimental conditions. It is found that these adsorbed water molecules saturate dangling surface bonds and drastically affect the electronic properties of systems investigated. The modeling is performed by reduced density matrix method in the basis of Kohn-Sham orbitals. A nano-catalyst modeled through replacement defect contributes energy levels near the bottom of the conduction band of TiO2 nano-structure. An exciton in the nano-rod is dissipating due to interaction with lattice vibrations, treated through non-adiabatic coupling. The electron relaxes to conduction band edge and then to the Ru cite with faster rate than hole relaxes to the Ru cite. These results are of the importance for an optimal design of nano-materials for photo-catalytic water splitting and solar energy harvesting. PMID:23795229

  6. Interface charge transfer in polypyrrole coated perovskite manganite magnetic nanoparticles

    NASA Astrophysics Data System (ADS)

    Pana, O.; Soran, M. L.; Leostean, C.; Macavei, S.; Gautron, E.; Teodorescu, C. M.; Gheorghe, N.; Chauvet, O.

    2012-02-01

    Different hybrid structures were obtained by coating magnetic nanoparticles of perovskite type manganite at optimal doping (La0.67Sr0.33MnO3,LSMO) with different quantities of polypyrrole (PPy). The amorphous layer of polypyrrole surrounding the crystalline magnetic core was observed by high resolution transmission electron microscopy (HRTEM) and analyzed by using X-ray photoelectron spectroscopy (XPS) and X-ray absorption spectroscopy (XAS) measurements in near edge structure (XANES) techniques. By analyzing the magnetic behavior of the samples one can observe that the surface modification of magnetic nanoparticles by PPy results in an increase in the saturation magnetization of the composites. The process is ascribed to paired electrons transferred from the delocalized ? states of the PPy into the outer disordered layers of the manganite. The analysis of pre-edge peak of the Mn K-edge XANES spectra in the case of PPy coated LSMO nanoparticles indicates that the charge transfer between polymer and nanoparticles is (directed) going to missing or distorted oxygen positions, hence increasing the 3d electrons' mobility and orbital hybridization between the neighboring manganese ion. As a consequence, within the surface layers of LSMO nanoparticles, both energy bands disrupted the structure, and the double exchange process between Mn ions was reestablished determining the saturation magnetizations and pre-edge features increase, respectively.

  7. Doping graphene films via chemically mediated charge transfer.

    PubMed

    Ishikawa, Ryousuke; Bando, Masashi; Morimoto, Yoshitaka; Sandhu, Adarsh

    2011-01-01

    Transparent conductive films (TCFs) are critical components of a myriad of technologies including flat panel displays, light-emitting diodes, and solar cells. Graphene-based TCFs have attracted a lot of attention because of their high electrical conductivity, transparency, and low cost. Carrier doping of graphene would potentially improve the properties of graphene-based TCFs for practical industrial applications. However, controlling the carrier type and concentration of dopants in graphene films is challenging, especially for the synthesis of p-type films. In this article, a new method for doping graphene using the conjugated organic molecule, tetracyanoquinodimethane (TCNQ), is described. Notably, TCNQ is well known as a powerful electron accepter and is expected to favor electron transfer from graphene into TCNQ molecules, thereby leading to p-type doping of graphene films. Small amounts of TCNQ drastically improved the resistivity without degradation of optical transparency. Our carrier doping method based on charge transfer has a huge potential for graphene-based TCFs. PMID:21711624

  8. Charge Transfer Characteristics and Initiation Mechanisms of Long Delayed Sprites

    NASA Astrophysics Data System (ADS)

    Li, J.; Cummer, S. A.; Lyons, W. A.; Nelson, T. E.

    2007-12-01

    Simultaneous measurements of high altitude optical emissions and the magnetic field produced by sprite-associated lightning discharges enable a close examination of the link between low altitude lightning process and high altitude sprite process. In this work, we report results of the coordinated analysis of high speed (1000--10000 frames per second) sprite video and wideband (0.1 Hz to 30 kHz) magnetic field measurements made simultaneously at the Yucca Ridge Field Station and Duke University during the June through August 2005 campaign period. During the observation period, the high speed camera detected 83 sprite events in 67 TLE sequences, which are caused by the same number of +CGs. 46% of these sprite events are delayed more than 10 ms after the lightning return stroke. With the estimated lightning source current moment waveform, we computed the continuing current amplitude and total charge transfer characteristics of the long delayed sprites (>10 ms delay). Our calculation shows the total charge moment change of the long delayed sprites can vary from several hundred C km to more than ten thousand C km. All the long delayed sprites are related with intense continuing current bigger than 2 kA. This continuing current provides about 50% to 90% of the total charge transfer. However, a bigger continuing current does not necessarily mean a shorter time delay. This indicates that other processes also involved in the sprite initiation for long delayed sprites. In our observations, the sferic burst, a high frequency noise caused by intra-cloud activity, is always accompanied by a slow intensification in the lightning source current before the time of sprite initiation. Thus we used the lightning source current as an input and employed a 2-D FDTD model to numerically simulate the electric field at different altitudes and compare it with the breakdown field. Including the effect of the electron mobility dependence on electric field, the simulation results showed that the slow intensification itself plays an important role in sprite initiation. For events analyzed, the predicted altitude from the FDTD simulation agree well with the measurement from high speed video images. Both the measurements and the simulations indicate that sprites with long time delay tend to initiate at a lower altitude comparing to short delayed sprites.

  9. Reversible phase transfer of nanoparticles based on photoswitchable host-guest chemistry.

    PubMed

    Peng, Lu; You, Mingxu; Wu, Cuichen; Han, Da; Öçsoy, Ismail; Chen, Tao; Chen, Zhuo; Tan, Weihong

    2014-03-25

    An azobenzene-containing surfactant was synthesized for the phase transfer of ?-cyclodextrin (?-CD)-capped gold nanoparticles between water and toluene phases by host-guest chemistry. With the use of the photoisomerization of azobenzene, the reversible phase transfer of gold nanoparticles was realized by irradiation with UV and visible light. Furthermore, the phase transfer scheme was applied for the quenching of a reaction catalyzed by gold nanoparticles, as well as the recovery and recycling of the gold nanoparticles from aqueous solutions. This work will have significant impact on materials transfer and recovery in catalysis and biotechnological applications. PMID:24524295

  10. Reversible Phase Transfer of Nanoparticles Based on Photoswitchable Host–Guest Chemistry

    PubMed Central

    2015-01-01

    An azobenzene-containing surfactant was synthesized for the phase transfer of ?-cyclodextrin (?-CD)-capped gold nanoparticles between water and toluene phases by host–guest chemistry. With the use of the photoisomerization of azobenzene, the reversible phase transfer of gold nanoparticles was realized by irradiation with UV and visible light. Furthermore, the phase transfer scheme was applied for the quenching of a reaction catalyzed by gold nanoparticles, as well as the recovery and recycling of the gold nanoparticles from aqueous solutions. This work will have significant impact on materials transfer and recovery in catalysis and biotechnological applications. PMID:24524295

  11. Charge transfer inefficiency in the pre- and post-irradiated Swept Charge Device CCD236

    NASA Astrophysics Data System (ADS)

    Smith, P. H.; Gow, J. P. D.; Pool, P.; Holland, A. D.

    2015-03-01

    This paper describes the mapping of spectral response of an e2v technologies Swept Charge Device (SCD) CCD236 pre and post irradiation with a 10 MeV equivalent proton fluence of 5.0 × 108 protons cm?2. The CCD236 is a large area (4.4 cm2) X-ray detector which will be used in India's Chandrayaan-2 Large Soft X-ray Spectrometer (CLASS) and China's Hard X-ray Modulation Telescope (HXMT). To enable the suppression of surface dark current, clocking is performed continuously resulting in a linear readout. As such the flat field illumination used to measure any change in spectral response over a conventional Charge-Coupled Devices (CCDs) is not possible. An alternative masking technique has been used to expose pinpoint regions of the device to Mn-K? and Mn-K? X-rays, enabling a local map of spectral response to be built up over the device. This novel approach allows for an estimation of the Charge Transfer Inefficiency (CTI) of the device to be made by allowing the creation of a CTI scatter plot similar to that typically observed in conventional CCDs.

  12. Eliminating the Reverse Charge Sharing Effect in the Charge-Transfer-Switch (CTS) Converter

    NASA Astrophysics Data System (ADS)

    Shiau, Miin-Shyue; Liu, Don-Gey; Liao, Shry-Sann

    A novel voltage level controller for low-power charge pump converters will be presented in this paper. The proposed voltage level controller would react according to the pumped voltage in the charge-transfer-switch (CTS) converter. For the CTS circuit, the pumping operation would be degraded by the charge sharing effect in the auxiliary switch path. In this study, a voltage shifter was used as the voltage level controller to overcome this serious problem without consuming too much chip area. The simulation results showed that the converter can accept a rated input of 1.5V and generated an output up to 8V based on the TSMC 0.35-µm CMOS technology. The layout consumed an area of 125*160µm2. The highest output obtained in measuring the real chip was 5.5V which is primarily due to the limitation that the transistor could tolerated. The largest load was estimated as high as 6mW which is large enough for on-chip application.

  13. Exciton harvesting, charge transfer, and charge-carrier transport in amorphous-silicon nanopillar/polymer hybrid solar cells

    E-print Network

    McGehee, Michael

    Exciton harvesting, charge transfer, and charge-carrier transport in amorphous-silicon nanopillar/polymer hybrid solar cells Vignesh Gowrishankar,1,a Shawn R. Scully,1 Albert T. Chan,1 Michael D. McGehee,1,b Qi report on the device physics of nanostructured amorphous-silicon a-Si:H /polymer hybrid solar cells

  14. Bonding and charge transfer in nitrogen-donor uranyl complexes: insights from NEXAFS spectra.

    PubMed

    Pemmaraju, C D; Copping, Roy; Wang, Shuao; Janousch, Markus; Teat, Simon J; Tyliszcak, Tolek; Canning, Andrew; Shuh, David K; Prendergast, David

    2014-11-01

    We investigate the electronic structure of three newly synthesized nitrogen-donor uranyl complexes [(UO2)(H2bbp)Cl2], [(UO)2(Hbbp)(Py)Cl], and [(UO2)(bbp)(Py)2] using a combination of near-edge X-ray absorption fine structure (NEXAFS) spectroscopy experiments and simulations. The complexes studied feature derivatives of the tunable tridentate N-donor ligand 2,6-bis(2-benzimidazyl)pyridine (bbp) and exhibit discrete chemical differences in uranyl coordination. The sensitivity of the N K-edge X-ray absorption spectrum to local bonding and charge transfer is exploited to systematically investigate the evolution of structural as well as electronic properties across the three complexes. A thorough interpretation of the measured experimental spectra is achieved via ab initio NEXAFS simulations based on the eXcited electron and Core-Hole (XCH) approach and enables the assignment of spectral features to electronic transitions on specific absorbing sites. We find that ligand-uranyl bonding leads to a signature blue shift in the N K-edge absorption onset, resulting from charge displacement toward the uranyl, while changes in the equatorial coordination shell of the uranyl lead to more subtle modulations in the spectral features. Theoretical simulations show that the flexible local chemistry at the nonbinding imidazole-N sites of the bbp ligand is also reflected in the NEXAFS spectra and highlights potential synthesis strategies to improve selectivity. In particular, we find that interactions of the bbp ligand with solvent molecules can lead to changes in ligand-uranyl binding geometry while also modulating the K-edge absorption. Our results suggest that NEXAFS spectroscopy combined with first-principles interpretation can offer insights into the coordination chemistry of analogous functionalized conjugated ligands. PMID:25330350

  15. ARCHITECTURE OF A CHARGE-TRANSFER STATE REGULATING LIGHT HARVESTING IN A PLANT ANTENNA PROTEIN

    SciTech Connect

    Fleming, Graham; Ahn, Tae Kyu; Avenson, Thomas J.; Ballottari, Matteo; Cheng, Yuan-Chung; Niyogi, Krishna K.; Bassi, Roberto; Fleming, Graham R.

    2008-04-02

    Energy-dependent quenching of excess absorbed light energy (qE) is a vital mechanism for regulating photosynthetic light harvesting in higher plants. All of the physiological characteristics of qE have been positively correlated with charge-transfer between coupled chlorophyll and zeaxanthin molecules in the light-harvesting antenna of photosystem II (PSII). In this work, we present evidence for charge-transfer quenching in all three of the individual minor antenna complexes of PSII (CP29, CP26, and CP24), and we conclude that charge-transfer quenching in CP29 involves a de-localized state of an excitonically coupled chlorophyll dimer. We propose that reversible conformational changes in CP29 can `tune? the electronic coupling between the chlorophylls in this dimer, thereby modulating the energy of the chlorophylls-zeaxanthin charge-transfer state and switching on and off the charge-transfer quenching during qE.

  16. Laser driven hydrogen transfer reactions in atmospheric chemistry

    NASA Astrophysics Data System (ADS)

    Lester, Marsha I.

    2015-03-01

    Ozonolysis of alkenes, an important non-photolytic source of OH radicals in the troposphere, proceeds through energized Criegee intermediates that undergo unimolecular decay to produce OH radicals. In this work, infrared laser activation of cold methyl-substituted Criegee intermediates is utilized to drive hydrogen transfer from the methyl group to the terminal oxygen, followed by dissociation to OH radicals. State-selective excitation of the Criegee intermediates in the CH stretch overtone region combined with sensitive OH detection reveals the infrared spectra of CH3CHOO and (CH3)2 COO, effective barrier heights for the critical hydrogen transfer step, and rapid decay dynamics to OH products. Complementary theory provides insights on the infrared overtone spectra as well as vibrational excitations, structural changes, and energy required to move from the minimum energy configuration of the Criegee intermediates to the transition state for the hydrogen transfer reaction. Research supported by the National Science Foundation.

  17. Solvation-driven charge transfer and localization in metal complexes.

    PubMed

    Rondi, Ariana; Rodriguez, Yuseff; Feurer, Thomas; Cannizzo, Andrea

    2015-05-19

    In any physicochemical process in liquids, the dynamical response of the solvent to the solutes out of equilibrium plays a crucial role in the rates and products: the solvent molecules react to the changes in volume and electron density of the solutes to minimize the free energy of the solution, thus modulating the activation barriers and stabilizing (or destabilizing) intermediate states. In charge transfer (CT) processes in polar solvents, the response of the solvent always assists the formation of charge separation states by stabilizing the energy of the localized charges. A deep understanding of the solvation mechanisms and time scales is therefore essential for a correct description of any photochemical process in dense phase and for designing molecular devices based on photosensitizers with CT excited states. In the last two decades, with the advent of ultrafast time-resolved spectroscopies, microscopic models describing the relevant case of polar solvation (where both the solvent and the solute molecules have a permanent electric dipole and the mutual interaction is mainly dipole-dipole) have dramatically progressed. Regardless of the details of each model, they all assume that the effect of the electrostatic fields of the solvent molecules on the internal electronic dynamics of the solute are perturbative and that the solvent-solute coupling is mainly an electrostatic interaction between the constant permanent dipoles of the solute and the solvent molecules. This well-established picture has proven to quantitatively rationalize spectroscopic effects of environmental and electric dynamics (time-resolved Stokes shifts, inhomogeneous broadening, etc.). However, recent computational and experimental studies, including ours, have shown that further improvement is required. Indeed, in the last years we investigated several molecular complexes exhibiting photoexcited CT states, and we found that the current description of the formation and stabilization of CT states in an important group of molecules such as transition metal complexes is inaccurate. In particular, we proved that the solvent molecules are not just spectators of intramolecular electron density redistribution but significantly modulate it. Our results solicit further development of quantum mechanics computational methods to treat the solute and (at least) the closest solvent molecules including the nonperturbative treatment of the effects of local electrostatics and direct solvent-solute interactions to describe the dynamical changes of the solute excited states during the solvent response. PMID:25902015

  18. Heavy ion beam induced charge transfer in ArCs mixtures

    Microsoft Academic Search

    D. E. Murnick; R. Gernhauser; A. Ulrich; W. Krotz; J. Wieser

    1993-01-01

    In situ production of target ions in cold, dense matter by heavy ion collisions and subsequent selective charge transfer may provide an effective pumping scheme for heavy ion beam pumped lasers. Charge transfer from cesium atoms to doubly charged argon ions was used for selective population of 4d-levels in Ar II. The argon ions were produced in an argon-cesium gas

  19. Ultrafast charge transfer processes in ordered molecular systems

    NASA Astrophysics Data System (ADS)

    Olson, Eric James Crane

    1998-11-01

    Using ultrafast emission and absorption spectroscopies, rates of DNA-mediated electron-transfer reactions have been established between a series of metal complex donors and acceptors bound by intercalation to the DNA double helix. In the presence of intercalating rhodium(III) acceptors, a substantial fraction of photoexcited (M(phen)2dppz) 2+ (M = Ru, Os) exhibits fast oxidative quenching (k q > 3 × 1010 s-1), while the remaining excited-state species exhibit a range of quenching constants less than 108 s-1. Transient-absorption experiments on the picosecond timescale indicate that, for all donors bound to mixed sequence DNA, the majority of back electron transfer is also very fast (ca. 1010 s-1) and its rate constant is independent of the loading of Rh complexes on the helix. We report a Monte Carlo simulation combined with an electron-tunneling kinetics program to model transient- absorption and emission data monitoring reactions between a series of metallointercalators on a variety of DNA. Our simplistic model simulates sub-ns transient absorption, sub-ns TCSPC and ns luminescence spectroscopy remarkably well. The apparent simple first-order kinetics are reproduced by an electron tunneling mechanism with a ? value near 1.0 A-1. The extent of reaction is reproduced by assuming a preferential binding of acceptors near donors. (Ru(phen)2dppz) 2+ (phen = 1,10- phenanthroline, dppz = dipyridophenazine) and closely related complexes have previously been observed to have an undetectably small quantum yield of photoluminescence in water but a moderate emission yield when bound to DNA. This so-called 'light-switch' effect is a critical factor in the utility of these complexes as spectroscopic probes for DNA. Here we describe a detailed investigation of the photophysics of (Ru(phen)2dppz) 2+ in aqueous solution, and in mixtures of acetonitrile and water, by time-resolved absorption and emission spectroscopies. Atomic force microscopy (AFM) and near-field scanning optical microscopy (NSOM) are used in conjunction with bulk absorption and fluorescence measurements to correlate the morphological and photophysical properties of titanyl phthalocyanine/perylene phenethylimide (TiOPc/PPEI) bilayer systems. Steady-state fluorescence intensity and fluorescence lifetime measurements are used as a measure of interfacial charge-transfer quenching efficiencies.

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

    PubMed

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

    2015-06-24

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

  1. Quantum ferroelectricity in charge-transfer complex crystals

    PubMed Central

    Horiuchi, Sachio; Kobayashi, Kensuke; Kumai, Reiji; Minami, Nao; Kagawa, Fumitaka; Tokura, Yoshinori

    2015-01-01

    Quantum phase transition achieved by fine tuning the continuous phase transition down to zero kelvin is a challenge for solid state science. Critical phenomena distinct from the effects of thermal fluctuations can materialize when the electronic, structural or magnetic long-range order is perturbed by quantum fluctuations between degenerate ground states. Here we have developed chemically pure tetrahalo-p-benzoquinones of n iodine and 4–n bromine substituents (QBr4–nIn, n=0–4) to search for ferroelectric charge-transfer complexes with tetrathiafulvalene (TTF). Among them, TTF–QBr2I2 exhibits a ferroelectric neutral–ionic phase transition, which is continuously controlled over a wide temperature range from near-zero kelvin to room temperature under hydrostatic pressure. Quantum critical behaviour is accompanied by a much larger permittivity than those of other neutral–ionic transition compounds, such as well-known ferroelectric complex of TTF–QCl4 and quantum antiferroelectric of dimethyl–TTF–QBr4. By contrast, TTF–QBr3I complex, another member of this compound family, shows complete suppression of the ferroelectric spin-Peierls-type phase transition. PMID:26076656

  2. Dynamical excimer formation in rigid carbazolophane via charge transfer state.

    PubMed

    Tamai, Yasunari; Ohkita, Hideo; Shimada, Jiro; Benten, Hiroaki; Ito, Shinzaburo; Yamanaka, Sho; Hisada, Kenji; Tani, Keita; Kubono, Koji; Shinmyozu, Teruo

    2013-08-22

    Formation dynamics of intramolecular excimer in dioxa[3.3](3,6)carbazolophane (CzOCz) was studied by time-resolved spectroscopic methods and computational calculations. In the ground state, the most stable conformer in CzOCz is the anti-conformation where two carbazole rings are in antiparallel alignment. No other isomers were observed even after the solution was heated up to 150 °C, although three characteristic isomers were found by the molecular mechanics calculation: the first is the anti-conformer, the second is the syn-conformer where two carbazole rings are stacked in the same direction, and the third is the int-conformer where two carbazole rings are aligned in an edge-to-face geometry. Because of the anti-conformation, the interchromophoric interaction in CzOCz is negligible in the ground state. Nonetheless, the intramolecular excimer in CzOCz was dynamically formed in an acetonitrile (MeCN) solution, indicating strong interchromophoric interaction and the isomerization from the anti- to syn-conformation in the excited state. The excimer formation in CzOCz is more efficient in polar solvents than in less polar solvents, suggesting the contribution of the charge transfer (CT) state to the excimer formation. The stabilization in the excited state is discussed in terms of molecular orbital interaction between two carbazole rings. The solvent-polarity-induced excimer formation is discussed in terms of the CT character in the int-conformation. PMID:23905591

  3. Charge transfer vibronic transitions in uranyl tetrachloride compounds;

    SciTech Connect

    Liu, G. K.; Deifel, N. P.; Cahill, C. L. (Chemical Sciences and Engineering Division); (George Washington University)

    2012-01-01

    The electronic and vibronic interactions of uranyl (UO{sub 2}){sup 2+} in three tetrachloride crystals have been investigated with spectroscopic experiments and theoretical modeling. Analysis and simulation of the absorption and photoluminescence spectra have resulted in a quantitative understanding of the charge transfer vibronic transitions of uranyl in the crystals. The spectra obtained at liquid helium temperature consist of extremely narrow zero-phonon lines (ZPL) and vibronic bands. The observed ZPLs are assigned to the first group of the excited states formed by electronic excitation from the 3{sigma} ground state into the f{sub {delta}{phi}}, orbitals of uranyl. The Huang-Rhys theory of vibronic coupling is modified successfully for simulating both the absorption and luminescence spectra. It is shown that only vibronic coupling to the axially symmetric stretching mode is Franck-Condon allowed, whereas other modes are involved through coupling with the symmetric stretching mode. The energies of electronic transitions, vibration frequencies of various local modes, and changes in the O=U=O bond length of uranyl in different electronic states and in different coordination geometries are evaluated in empirical simulations of the optical spectra. Multiple uranyl sites derived from the resolution of a superlattice at low temperature are resolved by crystallographic characterization and time- and energy-resolved spectroscopic studies. The present empirical simulation provides insights into fundamental understanding of uranyl electronic interactions and is useful for quantitative characterization of uranyl coordination.

  4. Charge Transfer Vibronic Transitions in Uranyl Tetrachloride Compounds

    SciTech Connect

    Liu, Guokui [Argonne National Lab. (ANL), Argonne, IL (United States); Deifel, Nicholas P. [George Washington Univ., Washington, DC (United States); Cahill, Christopher L. [George Washington Univ., Washington, DC (United States); Zhurov, Vladimir V. [Univ. of Toledo, OH (United States); Pinkerton, A. Alan [Univ. of Toledo, OH (United States)

    2012-01-19

    The electronic and vibronic interactions of uranyl (UO?)2+ in three tetrachloride crystals have been investigated with spectroscopic experiments and theoretical modeling. Analysis and simulation of the absorption and photoluminescence spectra have resulted in a quantitative understanding of the charge transfer vibronic transitions of uranyl in the crystals. The spectra obtained at liquid helium temperature consist of extremely narrow zero-phonon lines (ZPL) and vibronic bands. The observed ZPLs are assigned to the first group of the excited states formed by electronic excitation from the 3? ground state into the f?,? orbitals of uranyl. The Huang–Rhys theory of vibronic coupling is modified successfully for simulating both the absorption and luminescence spectra. It is shown that only vibronic coupling to the axially symmetric stretching mode is Franck–Condon allowed, whereas other modes are involved through coupling with the symmetric stretching mode. The energies of electronic transitions, vibration frequencies of various local modes, and changes in the O?U?O bond length of uranyl in different electronic states and in different coordination geometries are evaluated in empirical simulations of the optical spectra. Multiple uranyl sites derived from the resolution of a superlattice at low temperature are resolved by crystallographic characterization and time- and energy-resolved spectroscopic studies. The present empirical simulation provides insights into fundamental understanding of uranyl electronic interactions and is useful for quantitative characterization of uranyl coordination.

  5. Quantum ferroelectricity in charge-transfer complex crystals.

    PubMed

    Horiuchi, Sachio; Kobayashi, Kensuke; Kumai, Reiji; Minami, Nao; Kagawa, Fumitaka; Tokura, Yoshinori

    2015-01-01

    Quantum phase transition achieved by fine tuning the continuous phase transition down to zero kelvin is a challenge for solid state science. Critical phenomena distinct from the effects of thermal fluctuations can materialize when the electronic, structural or magnetic long-range order is perturbed by quantum fluctuations between degenerate ground states. Here we have developed chemically pure tetrahalo-p-benzoquinones of n iodine and 4-n bromine substituents (QBr4-nIn, n=0-4) to search for ferroelectric charge-transfer complexes with tetrathiafulvalene (TTF). Among them, TTF-QBr2I2 exhibits a ferroelectric neutral-ionic phase transition, which is continuously controlled over a wide temperature range from near-zero kelvin to room temperature under hydrostatic pressure. Quantum critical behaviour is accompanied by a much larger permittivity than those of other neutral-ionic transition compounds, such as well-known ferroelectric complex of TTF-QCl4 and quantum antiferroelectric of dimethyl-TTF-QBr4. By contrast, TTF-QBr3I complex, another member of this compound family, shows complete suppression of the ferroelectric spin-Peierls-type phase transition. PMID:26076656

  6. Fostering Analogical Transfer: The Multiple Components Approach to Algebra Word Problem Solving in a Chemistry Context

    ERIC Educational Resources Information Center

    Ngu, Bing Hiong; Yeung, Alexander Seeshing

    2012-01-01

    Holyoak and Koh (1987) and Holyoak (1984) propose four critical tasks for analogical transfer to occur in problem solving. A study was conducted to test this hypothesis by comparing a multiple components (MC) approach against worked examples (WE) in helping students to solve algebra word problems in chemistry classes. The MC approach incorporated…

  7. Ionicity and paramagnetism of strong organic charge-transfer complexes

    NASA Astrophysics Data System (ADS)

    Soos, Z. G.; Keller, H. J.; Ludolf, K.; Queckbörner, J.; Wehe, D.; Flandrois, S.

    1981-05-01

    Ionic charge-transfer (CT) complexes were prepared by mixing neutral solutions of the potent electron acceptor TCNQF4 (7,7,8,8-tetracyano-2,3,5,6-tetrafluoroquinodimethane) with the strong donors M2P(5,10-dihydro-5,10-diemethylphenazine) and TMPD(N,N,N',N'-tetramethyl-p-phenylenediamine). M2P-TCNQF4 [complex (1)] and TMPD-TCNQF4 [complex (2)] were obtained as deep blue solids, the latter only in polycrystalline form. Complex (1) crystallizes in the triclinic space group P1¯ with a = 7.002 (2), b = 8.787(2), c = 9.551(3), ? = 108.53(2), ? = 99.68(2), ? = 91.88(2), and Z = 1. The planar M2P+? and TCNQF-4? radical ions form mixed regular stacks. The structure refinement gave R = 0.039 and Rw = 0.033 for 1044 counter data. The ionicity ? and structure of mixed ???D+?A-?D+?A-???? stacks are closely related to the paramagnetic susceptibility ?(T). The two TCNQF4 complexes are shown to be the first highly ionic (??0.9) systems. ?(T) for complex (1) follows a Heisenberg antiferromagnetic chain with J = 175 cm-1 for T?122 K, below which ?(T) decreases steeply as expected for a dimerization transition. ?(T) for complex (2) can be fit to a power law T-?, with ? = 0.75±0.10, and also indicates ??0.9. Both complexes (1) and (2) are on the paramagnetic side of the paramagnetic-diamagnetic interface, while the finite activation energy for paramagnetism in the less ionic M2P-TCNQ and TMPD-TCNQ complexes puts them on the diamagnetic side. The elementary excitations of these related CT complexes with different ionicities are modeled.

  8. Association function of conjugated polymer charge-transfer complex.

    PubMed

    Parashchuk, Olga D; Bruevich, Vladimir V; Paraschuk, Dmitry Yu

    2010-06-21

    The donor-acceptor ground-state charge-transfer complex (CTC) formed in solution between a conjugated polymer, poly[methoxy-5-(2'-ethylhexyloxy)-1,4-phenylene-vinylene] (MEH-PPV), and a low-molecular-weight organic acceptor, 2,4,7-trinitrofluorenone (TNF), is studied by optical absorption and Raman spectroscopy. The CTC absorption as a function of TNF content shows a threshold increase that is in conflict with the model commonly used for optical characterization of low-molecular-weight CTCs. The shift of MEH-PPV characteristic Raman band at 1585 cm(-1) also exhibits a threshold dependence upon TNF addition. We assign the threshold in both the absorption and Raman data to the CTC concentration. To describe the threshold in the terms of the common model, we extend it by introducing an association function instead of a constant. The association function of acceptor concentration has been calculated to be K(a) approximately 1.5-3 M(-1) below the threshold, to increase steeply up to K(a) approximately 6-7.5 M(-1) just after the threshold, and then to grow gradually up to K(a) approximately 40 M(-1). The CTC molar absorption coefficient has been found to be epsilon(CTC) = (12.7 +/- 0.6) x 10(3) M(-1) cm(-1) at 635 nm. We explain the threshold as a result of the positive feedback: the CTC formation induces planarizaton of conjugated polymer segments that in turn facilitates further CTC formation. PMID:20396825

  9. Ionic electrets: electrostatic charging of surfaces by transferring mobile ions upon contact.

    PubMed

    McCarty, Logan S; Winkleman, Adam; Whitesides, George M

    2007-04-01

    This paper describes the fabrication and characterization of ionic electrets-materials that bear a long-lived electrostatic charge because of an imbalance between the number of cationic and anionic charges in the material. Crosslinked polystyrene microspheres that contain covalently bound ions and mobile counterions transfer some of their mobile ions in air, in the absence of bulk liquid, to another material upon contact. According to the ion-transfer model of contact electrification, this selective transfer of mobile ions yields microspheres that have a net electrostatic charge. A tool that operates on the principle of electrostatic induction measures the charge on individual microspheres (50-450 microm in diameter). Microspheres with a variety of covalently bound ionic functional groups (tetraalkylammonium, alkyltriphenylphosphonium, alkylsulfonate, and arylsulfonate) acquire charges consistent with this ion-transfer mechanism. The charge on a microsphere is proportional to its surface area (ca. 1 elementary charge per 2000 nm2) and close to the theoretical limit imposed by the dielectric breakdown of air. The charge density in an atmosphere of SF6 is more than twice that in an atmosphere of N2. These observations suggest that the charge density of these ionic electret microspheres is limited by the dielectric breakdown of the surrounding gas. Functionalizing the surfaces of glass or silicon with covalently bound ions and mobile counterions generates ionic electrets from these inorganic substrates. Soft lithography can pattern charge on a planar silicon surface (with oxide) and on the surface of 250-mum glass microspheres. PMID:17311380

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

    NASA Astrophysics Data System (ADS)

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

    2015-05-01

    The electronic excitation spectra of charge transfer compounds built from the hydrocarbons picene and chrysene, and the strong electron acceptors F4TCNQ (2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane) and TCNQ (7,7,8,8-tetracyanoquinodimethan) have been investigated using electron energy-loss spectroscopy. The corresponding charge transfer compounds have been prepared by co-evaporation of the pristine constituents. We demonstrate that all investigated combinations support charge transfer, which results in new electronic excitation features at low energy. This might represent a way to synthesize low band gap organic semiconductors.

  11. Highly efficient nonradiative energy transfer using charged CdSe/ZnS nanocrystals for light-harvesting in solution

    E-print Network

    Demir, Hilmi Volkan

    Highly efficient nonradiative energy transfer using charged CdSe/ZnS nanocrystals for light energy transfer FRET facilitated by the use of positively charged CdSe/ZnS core-shell nanocrystals NCs Förster resonance energy transfer FRET , enabled with the use of light-harvesting, positively charged CdSe/ZnS

  12. Surface Science Letters Surface to bulk charge transfer at

    E-print Network

    and Chemistry Department, Manchester University, Oxford Road, Manchester M13 9PL, UK b Fritz-Haber-Institut der for the in- dustrially important process of styrene synthesis from ethylbenzene [1­3]. Such benefits have

  13. Chemistry and radiative transfer of water in cold, dense clouds

    NASA Astrophysics Data System (ADS)

    Keto, Eric; Rawlings, Jonathan; Caselli, Paola

    2014-05-01

    The Herschel Space Observatory's recent detections of water vapour in the cold, dense cloud L1544 allow a direct comparison between observations and chemical models for oxygen species in conditions just before star formation. We explain a chemical model for gas-phase water, simplified for the limited number of reactions or processes that are active in extreme cold (<15 K). In this model, water is removed from the gas phase by freezing on to grains and by photodissociation. Water is formed as ice on the surface of dust grains from O and OH and released into the gas phase by photodesorption. The reactions are fast enough with respect to the slow dynamical evolution of L1544 that the gas-phase water is in equilibrium for the local conditions throughout the cloud. We explain the paradoxical radiative transfer of the H2O (110-101) line. Despite discouragingly high optical depth caused by the large Einstein A coefficient, the subcritical excitation in the cold, rarefied H2 causes the line brightness to scale linearly with column density. Thus, the water line can provide information on the chemical and dynamical processes in the darkest region in the centre of a cold, dense cloud. The inverse P-Cygni profile of the observed water line generally indicates a contracting cloud. This profile is reproduced with a dynamical model of slow contraction from unstable quasi-static hydrodynamic equilibrium (an unstable Bonnor-Ebert sphere).

  14. The role of charge-transfer states in energy transfer and dissipation within natural and artificial bacteriochlorophyll-proteins

    PubMed Central

    Wahadoszamen, Md.; Margalit, Iris; Ara, Anjue Mane; van Grondelle, Rienk; Noy, Dror

    2014-01-01

    Understanding how specific protein environments affect the mechanisms of non-radiative energy dissipation within densely assembled chlorophylls in photosynthetic protein complexes is of great interest to the construction of bioinspired solar energy conversion devices. Mixing of charge-transfer and excitonic states in excitonically interacting chlorophylls was implicated in shortening excited states lifetimes but its relevance to active control of energy dissipation in natural systems is under considerable debate. Here we show that the degree of fluorescence quenching in two similar pairs of excitonically interacting bacteriochlorophyll derivatives is directly associated with increasing charge transfer character in the excited state, and that the protein environment may control non-radiative dissipation by affecting the mixing of charge transfer and excitonic states. The capability of local protein environments to determine the fate of excited states, and thereby to confer different functionalities to excitonically coupled dimers substantiates the dimer as the basic functional element of photosynthetic enzymes. PMID:25342121

  15. Charge transfer kinetics at the solid–solid interface in porous electrodes

    E-print Network

    Bai, Peng

    Interfacial charge transfer is widely assumed to obey the Butler–Volmer kinetics. For certain liquid–solid interfaces, the Marcus–Hush–Chidsey theory is more accurate and predictive, but it has not been applied to porous ...

  16. Charge transfer across transition-metal oxide interfaces: Emergent conductance and electronic structure

    NASA Astrophysics Data System (ADS)

    Chen, Hanghui; Park, Hyowon; Millis, Andrew J.; Marianetti, Chris A.

    2014-12-01

    We perform density functional theory plus dynamical mean-field theory calculations to investigate internal charge transfer in a superlattice composed of alternating layers of vanadate and manganite perovskite and Ruddlesden-Popper structure materials. We show that the electronegativity difference between vanadium and manganese causes moderate charge transfer from VO2 to MnO2 layers in both perovskite and Ruddlesden-Popper-based superlattices, leading to hole doping of the VO2 layer and electron doping of the MnO2 layer. Comparison of the perovskite and Ruddlesden-Popper-based heterostructures shows that apical oxygen motion in the perovskite superlattice enhances charge transfer. Our first principles simulations demonstrate that the combination of internal charge transfer and quantum confinement provided by heterostructuring is a powerful approach to engineering electronic structure and tailoring correlation effects in transition metal oxides.

  17. Laser-assisted charge-transfer reactions (Li3++H): Coupled dressed-quasimolecular-state approach

    E-print Network

    Ho, Tak-San; Laughlin, Cecil; Chu, Shih-I

    1985-07-01

    A semiclassical coupled dressed-quasimolecular-states (DQMS) approach is presented for nonperturbative treatment of multichannel charge-transfer reactions at low collision velocities and high laser intensities, incorporating ...

  18. Behavior of charge-transfer absorption upon passing through the neutral-ionic phase transition

    NASA Astrophysics Data System (ADS)

    Jacobsen, C. S.; Torrance, J. B.

    1983-01-01

    The charge-transfer band is determined from reflectance measurements on single crystals of TTF-chloranil from 300 to 45 K, passing through the neutral-ionic phase transition at 84 K. As the temperature is decreased from 300 K toward the transition, h?CT decreases slowly from 0.66 to 0.55 eV, perhaps the lowest energy observed for a charge-transfer band. Below this transition, h?CT increases slightly and a second band appears at higher energy. From the measured oscillator strength, the temperature dependence of the degree of charge transfer has been determined. It is found to increase from ˜0.20 to ˜0.30 as the temperature is lowered from 300 to 100 K. Below TC, the degree of charge transfer rises to a value near 0.70.

  19. Product distributions for some thermal energy charge transfer reactions of rare gas ions

    NASA Technical Reports Server (NTRS)

    Anicich, V. G.; Laudenslager, J. B.; Huntress, W. T., Jr.; Futrell, J. H.

    1977-01-01

    Ion cyclotron resonance methods were used to measure the product distributions for thermal-energy charge-transfer reactions of He(+), Ne(+), and Ar(+) ions with N2, O2, CO, NO, CO2, and N2O. Except for the He(+)-N2 reaction, no molecular ions were formed by thermal-energy charge transfer from He(+) and Ne(+) with these target molecules. The propensity for dissociative ionization channels in these highly exothermic charge-transfer reactions at thermal energies contrasts with the propensity for formation of parent molecular ions observed in photoionization experiments and in high-energy charge-transfer processes. This difference is explained in terms of more stringent requirements for energy resonance and favorable Franck-Condon factors at thermal ion velocities.

  20. Charge Transfer through Single-Stranded Peptide Nucleic Acid Composed of Thymine Nucleotides

    E-print Network

    Borguet, Eric

    Charge Transfer through Single-Stranded Peptide Nucleic Acid Composed of Thymine Nucleotides Amit; In Final Form: February 18, 2008 Self-assembled monolayers (SAMs) of single-stranded peptide nucleic acids. Peptide nucleic acid (PNA) is an analo

  1. Integer versus Fractional Charge Transfer at Metal(/Insulator)/Organic Interfaces: Cu(/NaCl)/TCNE.

    PubMed

    Hofmann, Oliver T; Rinke, Patrick; Scheffler, Matthias; Heimel, Georg

    2015-05-26

    Semilocal and hybrid density functional theory was used to study the charge transfer and the energy-level alignment at a representative interface between an extended metal substrate and an organic adsorbate layer. Upon suppressing electronic coupling between the adsorbate and the substrate by inserting thin, insulating layers of NaCl, the hybrid functional localizes charge. The laterally inhomogeneous charge distribution resulting from this spontaneous breaking of translational symmetry is reflected in observables such as the molecular geometry, the valence and core density of states, and the evolution of the work function with molecular coverage, which we discuss for different growth modes. We found that the amount of charge transfer is determined, to a significant extent, by the ratio of the lateral spacing of the molecules and their distance to the metal. Therefore, charge transfer does not only depend on the electronic structure of the individual components but, just as importantly, on the interface geometry. PMID:25905769

  2. Crystallography and Ellipsometry of Organic Charge Transfer Systems.

    NASA Astrophysics Data System (ADS)

    Lee, Wan-Jin

    Five crystal structures were determined. In the orange 1:1 complex between methyl-2-(2,4 -dinitroanilino)propanoate (MAP) and 2-methyl-4-nitroaniline (MNA) (space group P2_1, NR = 1783 unique reflections, reliability factor R = 4.1%, NP = 346 parameters), the MAP and MNA molecules stack above each other along (010) at van der Waals separations; there is a hydrogen bond between MAP and MNA. MNA, whose monoclinic structure MNA(M) is known (space group Ia), has a new triclinic polymorph, MNA(T) (P1, NR = 715, R = 6.5%, NP = 196): this structure is almost superimposable to MNA(M); three significant reflections are the difference between the structures. In the 1:1 complex between DPA and MNA (P2 _1, NR = 463, R = 13.9%, NP = 116) the DPA and MNA molecules do not overlap well, but are H-bonded. In bis-(N-methylene-2,5-bis-(2-thienyl)pyrrole) (P1, = 1583, R = 7.8%, NP = 145), half the molecule is unique; the two thiophenes have large dihedral angles with the middle pyrrole. Bis-(dimethylthienotetratellurafulvalene) (BDMT -TTeF) forms a black insulating 1:1 complex with buckminsterfullerene, C_{60}, and CS _2; (C2/c, NR = 1552, NP = 166, R = 9.8%). The C_{60} is disordered; BDMT-TTeF is bent. The complex index of refraction of MAP:MNA (ellipsometry, lambda = 632.8 nm) has principal values n_1-ik_1 = 1.5310-0.01959i; n_2-ik _2 = 1.7090-0.06752i; n_3 -ik_3 = 1.9561-0.02465i; {bf n_3}-i {bf k_3} is almost parallel to the c axis, and n1-i {bf k_1 } is along a. Disordered Langmuir-Blodgett multilayer films of C_{60} have (ellipsometry) n = 1.80(6) and a thickness of 19.0(1.2) A per "monolayer", i.e. about 2 C_{60} molecules per "monolayer". From published crystal structures of 179 TCNQ, 71 TTF + TMTTF, and 89 BEDT-TTF complexes and salts (electrical insulators, semiconductors, metals, or superconductors), one needs to know the degree of charge transfer rho, to understand their electrical conductivity. Eighty -two "reference" structures, with known rho , yield linear least-squares equations for rho as a function of molecular length, bond length ratio and bond length difference (coefficient of determination R^2 > 90%). These equations can then predict rho from bond length data for other structures.

  3. Laser-plasma ion beams-experiments towards charge transfer x-ray laser

    SciTech Connect

    Crespo Lopez-Urrutia, J.R.; Fill, E.E. (Max-Planck-Institut fuer Quantenoptik, D-8046 Garching (Germany)); Bruch, R. (University of Nevada Reno, Nevada 89557 (United States)); Schneider, D. (Lawrence Livermore National Laboratory, California 94550 (United States))

    1993-06-05

    Laser plasmas produced at intensities of up to 10[sup 14] W/cm[sup 2] expand towards a secondary target a few millimeters away. The intense x-ray emission during the interaction plasma-target was recorded spectrally, spatially and time-resolved. A number of processes, like recombination and charge transfer may account for this strong radiation. The implications of these experiments to the design of a charge transfer x-ray laser are discussed.

  4. Modeling Charge Transfer in Fullerene Collisions via Real-Time Electron Dynamics

    SciTech Connect

    Jakowski, Jacek [ORNL; Irle, Stephan [ORNL; Morokuma, Keiji [ORNL; Sumpter, Bobby G [ORNL

    2012-01-01

    An approach for performing real-time dynamics of electron transfer in a prototype redox reaction that occurs in reactive collisions between neutral and ionic fullerenes is discussed. The quantum dynamical simulations show that the electron transfer occurs within 60 fs directly preceding the collision of the fullerenes, followed by structural changes and relaxation of electron charge. The consequences of real-time electron dynamics are fully elucidated for the far from equilibrium processes of collisions between neutral and multiply charged fullerenes.

  5. N+ charge transfer and N+2 dissociation in N2 at swarm energies

    Microsoft Academic Search

    E. Basurto; J. de Urquijo; C. Cisneros; I. Alvarez

    2001-01-01

    This paper reports a drift-tube-mass-spectrometer measurement of the relative abundances of N+ and N+2 in pure nitrogen, over a ratio of electric field to gas density, E\\/N, from 800 to 7200 Td [1 townsend (Td)=10-17 V cm2]. A proposed charge transfer dissociation scheme between the above two ions and N2 allowed us to obtain spatial rate coefficients for charge transfer

  6. Charge Transfer Excited State Contributions to Polarity Dependent Ferromagnetism in ZnO Diluted Magnetic Semiconductors

    Microsoft Academic Search

    Kevin R. Kittilstved; William K. Liu; Daniel R. Gamelin

    2005-01-01

    A close link between the charge transfer electronic structures and polarity dependent high-TC ferromagnetism of TM2+:ZnO DMSs (TM2+ = 3d ions) is demonstrated. Trends in ferromagnetism across the 3d series of TM2+:ZnO DMSs predicted from their charge transfer energies reproduce experimental trends well. These results provide a unified basis for understanding both n- and p-type ferromagnetic oxide DMSs.

  7. Modulation of terrestrial ion escape flux composition /by low-altitude acceleration and charge exchange chemistry/

    NASA Technical Reports Server (NTRS)

    Moore, T. E.

    1980-01-01

    Motivated by recent observations of highly variable hot plasma composition in the magnetosphere, control of the ionospheric escape flux composition by low-altitude particle dynamics and ion chemistry has been investigated for an e(-), H(+), O(+) ionosphere. It is found that the fraction of the steady state escape flux which is O(+) can be controlled very sensitively by the occurrence of parallel or transverse ion acceleration at altitudes below the altitude where the neutral oxygen density falls rapidly below the neutral hydrogen density and the ionospheric source of O(+) tends to be rapidly converted by charge exchange to H(+). The acceleration is required both to overcome the gravitational confinement of O(+) and to violate charge exchange equilibrium so that the neutral hydrogen atmosphere appears 'optically' thin to escaping O(+). Constraints are placed on the acceleration processes, and it is shown that O(+) escape is facilitated by observed ionospheric responses to magnetic activity.

  8. Charge Transfer Efficiency modeling/measurements as function of CCD pixel rate

    SciTech Connect

    Yates, G.J.; Gallegos, R.; Pena, C. [Los Alamos National Lab., NM (United States); Zagarino, P. [Sharpenit, Ellwood, CA (United States)

    1995-09-01

    We have developed a charge transport model for predicting the effects on Charge Transfer Efficiency (CTE) of Charge Coupled Devices (CCDs) as functions of number of transfers, pixel charge flow rate, and magnitude in the CCD`s vertical and horizontal charge transport mediums. The model uses carrier lifetime an mobility criteria to establish pixel speed arguments and limitations for various CCD architectures. The model is compared with experimental measurements obtained using strobed single pixel illumination and a variant of the deferred charge tail technique while independently varying the CCD pixel rates for both the vertical and horizontal readout phases. The generic model is discussed and applied to specific real CCDs. Agreement between predicted performance and actual measured performance is presented.

  9. Valence Topological Charge-Transfer Indices for Dipole Moments: Percutaneous Enhancers

    Microsoft Academic Search

    Francisco Torrens

    2004-01-01

    Valence topological charge-transfer (CT) indices are applied to the calculation of dipole moments. The algebraic and vector semisum CT indices are defined. The combination of CT indices allows the estimation of the dipole moments. The model is generalized for molecules with heteroatoms. The ability of the indices for the description of the molecular charge distribution is established by comparing them

  10. Charge transfer from delocalized excited states in a bulk heterojunction material

    NASA Astrophysics Data System (ADS)

    Kaake, Loren G.; Moses, Daniel; Heeger, Alan J.

    2015-02-01

    Charge generation in an organic photovoltaic blend was investigated using transient absorption spectroscopy. In films of pure electron donating material, subpicosecond spectral oscillations were observed and assigned to torsional modes associated with excited state relaxation and localization. These modes are systematically suppressed in the presence of fullerene, indicating that a significant fraction of charge transfer occurs prior to excited state localization.

  11. Monovalent counterion distributions at highly charged water interfaces: Proton-transfer and Poisson-Boltzmann theory

    E-print Network

    Vakni, David

    Monovalent counterion distributions at highly charged water interfaces: Proton-transfer and Poisson sensitive synchrotron­x-ray scattering studies reveal the distributions of monovalent ions next to highly charged interfaces. A lipid phosphate dihexadecyl hydrogen phosphate was spread as a monolayer at the air-water

  12. Electronic and Nuclear Factors in Charge and Excitation Transfer

    SciTech Connect

    Piotr Piotrowiak

    2004-09-28

    We report the and/or state of several subprojects of our DOE sponsored research on Electronic and Nuclear Factors in Electron and Excitation Transfer: (1) Construction of an ultrafast Ti:sapphire amplifier. (2) Mediation of electronic interactions in host-guest molecules. (3) Theoretical models of electrolytes in weakly polar media. (4) Symmetry effects in intramolecular excitation transfer.

  13. Intrinsic charge trapping in organic and polymeric semiconductors: a physical chemistry perspective

    SciTech Connect

    Zhu, Xiaoyang; Barbara, Paul F.; Kaake, Loren

    2010-01-01

    We aim to understand the origins of intrinsic charge carrier traps in organic and polymeric semiconductor materials from a physical chemistry perspective. In crystalline organic semiconductors, we point out some of the inadequacies in the description of intrinsic charge traps using language and concepts developed for inorganic semiconductors. In ?-conjugated polymeric semiconductors, we suggest the presence of a two-tier electronic energy landscape, a bimodal majority landscape due to two dominant structural motifs and a minority electronic energy landscape from intrinsic charged defects. The bimodal majority electronic energy landscape results from a combination of amorphous domains and microcrystalline or liquid-crystalline domains. The minority tier of the electronic density of states is comprised of deep Coulomb traps embedded in the majority electronic energy landscape. This minority electronic energy landscape may dominate transport properties at low charge carrier densities, such as those expected for organic photovoltaic devices, while the bimodal majority electronic energy landscape becomes significant at high carrier densities, that is, in organic field effect transistors.

  14. Incorporation of charge transfer into the explicit polarization fragment method by grand canonical density functional theory

    PubMed Central

    Isegawa, Miho; Gao, Jiali; Truhlar, Donald G.

    2011-01-01

    Molecular fragmentation algorithms provide a powerful approach to extending electronic structure methods to very large systems. Here we present a method for including charge transfer between molecular fragments in the explicit polarization (X-Pol) fragment method for calculating potential energy surfaces. In the conventional X-Pol method, the total charge of each fragment is preserved, and charge transfer between fragments is not allowed. The description of charge transfer is made possible by treating each fragment as an open system with respect to the number of electrons. To achieve this, we applied Mermin's finite temperature method to the X-Pol wave function. In the application of this method to X-Pol, the fragments are open systems that partially equilibrate their number of electrons through a quasithermodynamics electron reservoir. The number of electrons in a given fragment can take a fractional value, and the electrons of each fragment obey the Fermi–Dirac distribution. The equilibrium state for the electrons is determined by electronegativity equalization with conservation of the total number of electrons. The amount of charge transfer is controlled by re-interpreting the temperature parameter in the Fermi–Dirac distribution function as a coupling strength parameter. We determined this coupling parameter so as to reproduce the charge transfer energy obtained by block localized energy decomposition analysis. We apply the new method to ten systems, and we show that it can yield reasonable approximations to potential energy profiles, to charge transfer stabilization energies, and to the direction and amount of charge transferred. PMID:21895159

  15. Adsorbed Mass of Polymers on Self-Assembled Monolayers: Effect of Surface Chemistry and Polymer Charge.

    PubMed

    Maroni, Plinio; Montes Ruiz-Cabello, Francisco Javier; Cardoso, Catia; Tiraferri, Alberto

    2015-06-01

    The adsorbed mass of polymers on surfaces with different chemistry is presented, and the related adsorption mechanism is discussed. Strong and weak polyelectrolytes of negative and positive charge are studied, as well as an uncharged polymer. Self-assembled monolayers of alkanethiols on gold are used in reflectometry and quartz crystal microbalance (QCM-D) experiments as adsorbing substrates bearing different terminal moieties, namely, methyl, hydroxyl, carboxyl, and amine groups. The various polymer-surface combinations allow the systematic investigation of the role of surface chemistry and polymer charge on adsorbed amount. Interactions of different nature and range drive polymer adsorption: the measured adsorbed amounts reveal information about their relative contribution. When electrostatic chain-surface attraction is present, the largest adsorbed masses are observed. However, significant mass is measured even when an electrostatic barrier to adsorption is present, suggesting the importance of forces of nonelectrostatic origin, which include both hydrophobic interactions and specific forces acting at short distances. This mechanism results in large adsorbed amounts for the adsorption of weak polyelectrolytes, and it is apparent especially in the adsorption behavior of a neutral polymer. PMID:25993382

  16. Charge transfer at metal/solid polymer interfaces in the presence of liquids

    NASA Astrophysics Data System (ADS)

    Wasem, Joe; Langford, Steve; Dickinson, Tom

    2002-03-01

    Physical and chemical interactions can transfer charge between liquids and insulating surfaces with important consequences. We examine charge transfer across a metal stylus/solid polymer interface in the presence of liquid (here a perfluoropolyether lubricant, Fomblin Z-DOL--a common lubricant for magnetic hard disks--and water). Observations of transient currents to/from the metal stylus, near-surface bound charge, and free charge escaping from the surface provide direct evidence for the transfer of negative charge (electrons) from the metal (Al) to both the polymer (e.g., polyfluoroethylene--Teflon^TM) and the liquid. We report measurements of the resulting charge densities on the solid polymer surface and in the liquid, as well as the energy distributions of negative charge emitted into vacuum above the liquid layer. Finally, we discuss the potential impact of this charge on the physical manipulation of these liquids on the polymer surface as well as the possible role of negative charge in the decomposition of perfluoropolyether lubricants via electron attachment.

  17. An abnormally slow proton transfer reaction in a simple HBO derivative due to ultrafast intramolecular-charge transfer events.

    PubMed

    Alarcos, Noemí; Gutierrez, Mario; Liras, Marta; Sánchez, Félix; Douhal, Abderrazzak

    2015-07-01

    We report on the steady-state, picosecond and femtosecond time-resolved studies of a charge and proton transfer dye 6-amino-2-(2'-hydroxyphenyl)benzoxazole (6A-HBO) and its methylated derivative 6-amino-2-(2'-methoxyphenyl)benzoxazole (6A-MBO), in different solvents. With femtosecond resolution and comparison with the photobehaviour of 6A-MBO, we demonstrate for 6A-HBO in solution, the photoproduction of an intramolecular charge-transfer (ICT) process at S1 taking place in ?140 fs or shorter, followed by solvent relaxation in the charge transferred species. The generated structure (syn-enol charge transfer conformer) experiences an excited-state intramolecular proton-transfer (ESIPT) reaction to produce a keto-type tautomer. This subsequent proton motion occurs in 1.2 ps (n-heptane), 14 ps (DCM) and 35 ps (MeOH). In MeOH, it is assisted by the solvent molecules and occurs through tunneling for which we got a large kinetic isotope effect (KIE) of about 13. For the 6A-DBO (deuterated sample in CD3OD) the global proton-transfer reaction takes place in 200 ps, showing a remarkable slow KIE regime. The slow ESIPT reaction in DCM (14 ps), not through tunnelling as it is not sensitive to OH/OD exchange, has however to overcome an energy barrier using intramolecular as well as solvent coordinates. The rich ESIPT dynamics of 6A-HBO in the used solutions is governed by an ICT reaction, triggered by the amino group, and it is solvent dependent. Thus, the charge injection to a 6A-HBO molecular frame makes the ICT species more stable, and the phenol group less acidic, slowing down the subsequent ESIPT reaction. Our findings bring new insights into the coupling between ICT and ESIPT reactions on the potential-energy surfaces of several barriers. PMID:25870162

  18. Transferring the heterogeneity of surface emissions to variability in pollutant concentrations over urban areas through a chemistry-transport model

    E-print Network

    Menut, Laurent

    -quality Chemistry-transport models Subgrid scale variability Heterogeneous emissions a b s t r a c t HorizontalTransferring the heterogeneity of surface emissions to variability in pollutant concentrations over urban areas through a chemistry-transport model Myrto Valari a,b,*, Laurent Menut a a Laboratoire de

  19. A parametric study of shock jump chemistry, electron temperature, and radiative heat transfer models in hypersonic flows

    E-print Network

    Greendyke, Robert Brian

    1988-01-01

    A PARAMETRIC STUDY OF SHOCK JUMP CHEMISTRY, ELECTRON TEMPERATURE, AND RADIATIVE HEAT TRANSFER MODELS IN HYPERSONIC FLOWS A Thesis by ROBERT BRIAN GREENDYKE Submitted to the Graduate College of Texas A&M University in partial fulfillment... of the requirements for the degree of MASTER OF SCIENCE August 1988 Major Subject: Aerospace Engineering A PARAMETRIC STUDY OF SHOCK JUMP CHEMISTRY, ELECTRON TEMPERATURE, AND RADIATIVE HEAT TRANSFER MODELS IN HYPERSONIC FLOWS A Thesis by ROBERT BRIAN...

  20. Single and double charge transfer of He(2+) ions with molecules at near-thermal energies

    NASA Technical Reports Server (NTRS)

    Tosh, R. E.; Johnsen, R.

    1993-01-01

    Rate coefficients were measured for charge-transfer reactions of He(2+) ions with H2, N2, O2, CO, CO2, and H2O. The experiments were carried out using a selected-ion drift-tube mass spectrometer. Total rate coefficients are found to be very large and are generally close to the limiting Langevin capture rate coefficients or the corresponding ADO-model (Su and Bowers, 1973) coefficients. The product-ion spectra indicate that both single and double charge transfer and possibly transfer ionization occur in these reactions.

  1. The effects of charge transfer on the aqueous solvation of ions

    SciTech Connect

    Soniat, Marielle; Rick, Steven W. [Department of Chemistry, University of New Orleans, New Orleans, Louisiana 70148 (United States)

    2012-07-28

    Ab initio-based charge partitioning of ionic systems results in ions with non-integer charges. This charge-transfer (CT) effect alters both short- and long-range interactions. Until recently, the effects of CT have been mostly neglected in molecular dynamics (MD) simulations. The method presented in this paper for including charge transfer between ions and water is consistent with ab initio charge partitioning and does not add significant time to the simulation. The ions of sodium, potassium, and chloride are parameterized to reproduce dimer properties and aqueous structures. The average charges of the ions from MD simulations (0.900, 0.919, and -0.775 for Na{sup +}, K{sup +}, and Cl{sup -}, respectively) are consistent with quantum calculations. The hydration free energies calculated for these ions are in agreement with experimental estimates, which shows that the interactions are described accurately. The ions also have diffusion constants in good agreement with experiment. Inclusion of CT results in interesting properties for the waters in the first solvation shell of the ions. For all ions studied, the first shell waters acquire a partial negative charge, due to the difference between water-water and water-ion charge-transfer amounts. CT also reduces asymmetry in the solvation shell of the chloride anion, which could have important consequences for the behavior of chloride near the air-water interface.

  2. Bio-batteries and bio-fuel cells: leveraging on electronic charge transfer proteins.

    PubMed

    Kannan, A M; Renugopalakrishnan, V; Filipek, S; Li, P; Audette, G F; Munukutla, L

    2009-03-01

    Bio-fuel cells are alternative energy devises based on bio-electrocatalysis of natural substrates by enzymes or microorganisms. Here we review bio-fuel cells and bio-batteries based on the recent literature. In general, the bio-fuel cells are classified based on the type of electron transfer; mediated electron transfer and direct electron transfer or electronic charge transfer (ECT). The ECT of the bio-fuel cells is critically reviewed and a variety of possible applications are considered. The technical challenges of the bio-fuel cells, like bioelectrocatalysis, immobilization of bioelectrocatalysts, protein denaturation etc. are highlighted and future research directions are discussed leveraging on the use of electron charge transfer proteins. In addition, the packaging aspects of the bio-fuel cells are also analyzed and the found that relatively little work has been done in the engineering development of bio-fuel cells. PMID:19435024

  3. Ultrafast Charge- and Energy-Transfer Dynamics in Conjugated Polymer: Cadmium Selenide Nanocrystal Blends

    PubMed Central

    2014-01-01

    Hybrid nanocrystal–polymer systems are promising candidates for photovoltaic applications, but the processes controlling charge generation are poorly understood. Here, we disentangle the energy- and charge-transfer processes occurring in a model system based on blends of cadmium selenide nanocrystals (CdSe-NC) with poly[2-methoxy-5-(3?,7?-dimethyloctyloxy)-1,4-phenylene vinylene] (MDMO-PPV) using a combination of time-resolved absorption and luminescence measurements. The use of different capping ligands (n-butylamine, oleic acid) as well as thermal annealing allows tuning of the polymer–nanocrystal interaction. We demonstrate that energy transfer from MDMO-PPV to CdSe-NCs is the dominant exciton quenching mechanism in nonannealed blends and occurs on ultrafast time scales (<1 ps). Upon thermal annealing electron transfer becomes competitive with energy transfer, with a transfer rate of 800 fs independent of the choice of the ligand. Interestingly, we find hole transfer to be much less efficient than electron transfer and to extend over several nanoseconds. Our results emphasize the importance of tuning the organic–nanocrystal interaction to achieve efficient charge separation and highlight the unfavorable hole-transfer dynamics in these blends. PMID:24490650

  4. Quasi-continuous Charge Transfer via Electron A Dissertation Presented

    E-print Network

    - tuations of the current ("shot noise") with the Fano factor F SI (f) /2e I , iii #12;the shot noise I and the single-particle density of states, but also the statistics of site occupations and hop Charge Problem . . . . . . . . . . . 13 1.2.3 Shot Noise Suppression

  5. Ultrafast holography and transient absorption spectroscopy in charge-transfer polymers

    SciTech Connect

    McBranch, D.W.; Maniloff, E.S. [Los Alamos National Lab., NM (United States); Vacar, D.; Heeger, A.J. [Univ. of California, Santa Barbara, CA (United States). Institute for Polymers and Organic Solids

    1997-10-01

    Charge-transfer polymers are a new class of nonlinear optical materials which can be used for generating femtosecond holographic gratings. Using semiconducting polymers sensitized with varying concentrations of C{sub 60}, holographic gratings were recorded by individual ultrafast laser pulses; the diffraction efficiency and time decay of the gratings were measured using non-degenerate four-wave mixing. Using a figure of merit for dynamic data processing, the temporal diffraction efficiency, this new class of materials exhibits between two and 12 orders of magnitude higher response than previous reports. The charge transfer range at polymer/C{sub 60} interfaces was further studied using transient absorption spectroscopy. The fact that charge-transfer occurs in the picosecond-time scale in bilayer structures (thickness 200 {angstrom}) implies that diffusion of localized excitations to the interface is not the dominant mechanism; the charge transfer range is a significant fraction of the film thickness. From analysis of the excited state decay curves, we estimate the charge transfer range to be 80 {angstrom} and interpret that range as resulting from quantum delocalization of the photoexcitations.

  6. Simulating electron transfer attachment to a positively charged model peptide.

    PubMed

    Anusiewicz, Iwona; Berdys-Kochanska, Joanna; Skurski, Piotr; Simons, Jack

    2006-02-01

    Ab initio electronic structure methods, including stabilization method tools for handling electronically metastable states, are used to treat a model system designed to probe the electron-transfer event characterizing electron-transfer dissociation (ETD) mass spectroscopic studies of peptides. The model system consists of a cation H(3)C-(C=O)NH-CH(2)-CH(2)-NH(3)(+), containing a protonated amine site and an amide site, that undergoes collisions with a CH(3)(-) anion. Cross-sections for electron transfer from CH(3)(-) to the protonated amine site are shown to exceed those for transfer to the Coulomb-stabilized amide site by 2 orders of magnitude. Moreover, it is shown that the fates of the amine-attached and amide-attached species are similar in that both eventually lead to the same carbon-centered radical species H(3)C-((*)C-OH)NH-CH(2)-CH(2)-NH(2), although the reaction pathways by which the two species produce this radical are somewhat different. The implications for understanding peptide fragmentation patterns under ETD conditions are also discussed in light of this work's findings. PMID:16435786

  7. On the initial charge separation in bacterial reaction centers: Long-range electron transfer via an exciton-charge transfer (ECT) coupling mechanism

    NASA Astrophysics Data System (ADS)

    Scherer, P. O. J.; Fischer, Sighart F.

    1987-11-01

    The low-lying electronically excited states for the reaction center of Rps. viridis are investigated using PPP/CI calculations. The six pigments are treated as three interacting pairs, the symmetric special pair dimer BC MPBC LP and the two loosely coupledasymmetric dimers BC LABP L and BC MABP M. It is shown that the charge transfer state BC LA+BP L- can fall below the special pair excitation P* due to partial charge transfer from a histidine to BC LA and due to stabilization of BP L- by a glutamic acid residue. As a result P* can decay in 2.8 ps into BC LA+BP L- which goes over into the radical pair P + BP L- in less than 1 ps. The first step can be described as an excitonic interaction between P* and BC LA+ BP L-.

  8. Charge transfer and momentum exchange in exospheric D-H(+) and H-D(+) collisions

    NASA Technical Reports Server (NTRS)

    Hodges, R. R., Jr.; Breig, E. L.

    1993-01-01

    Mechanisms that control the escape of deuterium from planetary exospheres include the acceleration of D(+) in the polar wind, and the production of suprathermal D atoms through nonthermal collisions. In this paper we examine the effects of neutral-ion interactions involving deuterium and hydrogen on the velocity distribution of neutral D. A two-center scattering approximation is used as the basis for calculations of the differential cross sections for charge transfer and elastic scatter in collision of H with D(+) and of D with H(+) for ionosphere-exosphere collision energies below 10 e V. These data are used to derive temperature dependent rate coefficients for the charge transfer branches of these interactions, and to determine the effects of ion-neutral temperature differences on the rate of generation of suprathermal D through charge transfer and elastic scatter.

  9. Charge-transfer interactions in a multichromophoric hexaarylbenzene containing pyrene and triarylamines.

    PubMed

    Lambert, Christoph; Ehbets, Julia; Rausch, Dirk; Steeger, Markus

    2012-07-20

    Two different hexaarylbenzenes with three pyrene and three triarylamine substituents in different positions (trigonal symmetric and asymmetric arrangement) were synthesized, and their charge-transfer states were investigated by optical spectroscopy. In these multichromophoric systems triarylamine acts as the electron donor and pyrene as the electron acceptor. A reference chromophore with only one donor-acceptor pair was also investigated. All these chromophores form charge-transfer states upon photoexcitation which relax with a moderate fluorescence quantum yield to the ground state. The compounds do not differ significantly concerning most of their fluorescence properties, which shows that the fluorescent charge-transfer state is very similar in all chromophores. This observation indicates symmetry breaking for the symmetric chromophore within fluorescence lifetime of several tens of ns. This interpretation was substantiated by fluorescence excitation anisotropy measurements in a sucrose octaacetate matrix. PMID:22731634

  10. Charge transfer in strongly correlated systems: An exact diagonalization approach to model Hamiltonians

    SciTech Connect

    Schöppach, Andreas; Gnandt, David; Koslowski, Thorsten, E-mail: koslowsk@uni-freiburg.de [Institut für Physikalische Chemie, Universität Freiburg, Albertstraße 23a, D-79104 Freiburg im Breisgau (Germany)] [Institut für Physikalische Chemie, Universität Freiburg, Albertstraße 23a, D-79104 Freiburg im Breisgau (Germany)

    2014-04-07

    We study charge transfer in bridged di- and triruthenium complexes from a theoretical and computational point of view. Ab initio computations are interpreted from the perspective of a simple empirical Hamiltonian, a chemically specific Mott-Hubbard model of the complexes' ? electron systems. This Hamiltonian is coupled to classical harmonic oscillators mimicking a polarizable dielectric environment. The model can be solved without further approximations in a valence bond picture using the method of exact diagonalization and permits the computation of charge transfer reaction rates in the framework of Marcus' theory. In comparison to the exact solution, the Hartree-Fock mean field theory overestimates both the activation barrier and the magnitude of charge-transfer excitations significantly. For triruthenium complexes, we are able to directly access the interruthenium antiferromagnetic coupling strengths.

  11. Emergent conductance and magnetism at metal oxide interfaces via internal charge transfer

    NASA Astrophysics Data System (ADS)

    Chen, Hanghui; Millis, Andrew; Marianetti, Chris

    2015-03-01

    Internal charge transfer across the interface of transition metal oxides is proven to be a powerful approach to induce new electronic structure in metamaterials (PRL 111, 116403 (2013); arXiv:1408.0217 (2014)). Here we use ab initio calculations to demonstrate that while SrVO3 is a paramagnetic metal and SrMnO3 is an antiferromagetic insulator, charge transfer in a SrVO3/SrMnO3 superlattice leads to both electronic and magnetic reconstructions on the Mn sites: the Mn eg states are electron doped and the Mn t2 g core spins are ferromagnetically aligned. As a result, net magnetic moments are expected to emerge in the superlattice. Our work shows that charge transfer is a robust route to the design of novel two dimensional half metallic ferromagnets. This research was supported by National Science Foundation under Grant No. DMR-1120296.

  12. Evidences For Charge Transfer-Induced Conformational Changes In Carbon Nanostructure-Protein Corona

    PubMed Central

    Podila, R.; Vedantam, P.; Ke, P. C.; Brown, J. M.; Rao, A. M.

    2012-01-01

    The binding of proteins to a nanostructure often alters protein secondary and tertiary structures. However, the main physical mechanisms that elicit protein conformational changes in the presence of the nanostructure have not yet been fully established. Here we performed a comprehensive spectroscopic study to probe the interactions between bovine serum albumin (BSA) and carbon-based nanostructures of graphene and single-walled carbon nanotubes (SWNTs). Our results showed that the BSA “corona” acted as a weak acceptor to facilitate charge transfer from the carbon nanostructures. Notably, we observed that charge transfer occurred only in the case of SWNTs but not in graphene, resulting from the sharp and discrete electronic density of states of the former. Furthermore, the relaxation of external ?–helices in BSA secondary structure increased concomitantly with the charge transfer. These results may help guide controlled nanostructure-biomolecular interactions and prove beneficial for developing novel drug delivery systems, biomedical devices and engineering of safe nanomaterials. PMID:23243478

  13. Note: Charge transfer in a hydrated peptide group is determined mainly by its intrinsic hydrogen-bond energetics

    SciTech Connect

    Mirkin, Noemi G.; Krimm, Samuel [LSA Biophysics, University of Michigan, 930 N. University Ave., Ann Arbor, Michigan 48109-1055 (United States)] [LSA Biophysics, University of Michigan, 930 N. University Ave., Ann Arbor, Michigan 48109-1055 (United States)

    2014-01-28

    Charge transfer in a hydrogen-bonded N-methylacetamide(H{sub 2}O){sub 3} system is obtained from ?B97X-D/6-31++G** and CHelpG atomic charge calculations of individual peptide-water interactions as well as that of the entire complex. In the latter, the electron transfer to water is 0.19 e, influenced primarily by the hydrogen bonds to the C=O group. The values of such charge transfer are paralleled by the corresponding intrinsic hydrogen-bond energies. These results support the desirability of incorporating charge transfer in molecular mechanics energy functions.

  14. Charge Transfer and Triplet States in High Efficiency OPV Materials and Devices

    NASA Astrophysics Data System (ADS)

    Dyakonov, Vladimir

    2013-03-01

    The advantage of using polymers and molecules in electronic devices, such as light-emitting diodes (LED), field-effect transistors (FET) and, more recently, solar cells (SC) is justified by the unique combination of high device performance and processing of the semiconductors used. Power conversion efficiency of nanostructured polymer SC is in the range of 10% on lab scale, making them ready for up-scaling. Efficient charge carrier generation and recombination in SC are strongly related to dissociation of the primary singlet excitons. The dissociation (or charge transfer) process should be very efficient in photovoltaics. The mechanisms governing charge carrier generation, recombination and transport in SC based on the so-called bulk-heterojunctions, i.e. blends of two or more semiconductors with different electron affinities, appear to be very complex, as they imply the presence of the intermediate excited states, neutral and charged ones. Charge transfer states, or polaron pairs, are the intermediate states between free electrons/holes and strongly bound excitons. Interestingly, the mostly efficient OLEDs to date are based on the so-called triplet emitters, which utilize the triplet-triplet annihilation process. In SC, recent investigations indicated that on illumination of the device active layer, not only mobile charges but also triplet states were formed. With respect to triplets, it is unclear how these excited states are generated, via inter-system crossing or via back transfer of the electron from acceptor to donor. Triplet formation may be considered as charge carrier loss channel; however, the fusion of two triplets may lead to a formation of singlet excitons instead. In such case, a generation of charges by utilizing of the so far unused photons will be possible. The fundamental understanding of the processes involving the charge transfer and triplet states and their relation to nanoscale morphology and/or energetics of blends is essential for the optimization of the performance of molecular photovoltaic devices. I will present the state of the art in this field and discuss the mechanisms of polaron pair generation and recombination in the novel low band gap polymer-fullerene blends as well as in high-efficiency SC. The advantage of using polymers and molecules in electronic devices, such as light-emitting diodes (LED), field-effect transistors (FET) and, more recently, solar cells (SC) is justified by the unique combination of high device performance and processing of the semiconductors used. Power conversion efficiency of nanostructured polymer SC is in the range of 10% on lab scale, making them ready for up-scaling. Efficient charge carrier generation and recombination in SC are strongly related to dissociation of the primary singlet excitons. The dissociation (or charge transfer) process should be very efficient in photovoltaics. The mechanisms governing charge carrier generation, recombination and transport in SC based on the so-called bulk-heterojunctions, i.e. blends of two or more semiconductors with different electron affinities, appear to be very complex, as they imply the presence of the intermediate excited states, neutral and charged ones. Charge transfer states, or polaron pairs, are the intermediate states between free electrons/holes and strongly bound excitons. Interestingly, the mostly efficient OLEDs to date are based on the so-called triplet emitters, which utilize the triplet-triplet annihilation process. In SC, recent investigations indicated that on illumination of the device active layer, not only mobile charges but also triplet states were formed. With respect to triplets, it is unclear how these excited states are generated, via inter-system crossing or via back transfer of the electron from acceptor to donor. Triplet formation may be considered as charge carrier loss channel; however, the fusion of two triplets may lead to a formation of singlet excitons instead. In such case, a generation of charges by utilizing of the so far unused photons will be possible. The fundamental understa

  15. Molecular ionic junction for enhanced electronic charge transfer.

    PubMed

    Bolink, Henk J; Baranoff, Etienne; Clemente-León, Miguel; Coronado, Eugenio; Lopéz-Muñoz, Angel; Repetto, Diego; Sessolo, Michele; Nazeeruddin, Md K

    2009-01-01

    We present the first evidence of charge injection improvement in an organic electroluminescent device provided by a single ionic molecular layer. A hole-dominated, hybrid organic-inorganic light-emitting device is used as a probe to verify the effectiveness of the ionic compound monolayer on modifying the metal oxide cathode. The rearrangement of ions under an applied bias induces a strong field at the electrode-organic interface resulting in an enhancement of the electron injection into the organic semiconductor. A strong decrease in turn-on voltage for electroluminescence is observed for the device containing the ionic molecular monolayer. PMID:19209442

  16. Observation of slow charge redistribution preceding excited-state proton transfer

    SciTech Connect

    Spry, D. B.; Fayer, M. D. [Department of Chemistry, Stanford University, Stanford, California 94305 (United States)

    2007-11-28

    The photoacid 8-hydroxy-N,N,N{sup '},N{sup '},N{sup '},N{sup '}-hexamethylpyrene-1,3,6-trisulfonamide (HPTA) and related compounds are used to investigate the steps involved in excited-state deprotonation in polar solvents using pump-probe spectroscopy and time correlated single photon counting fluorescence spectroscopy. The dynamics show a clear two-step process leading to excited-state proton transfer. The first step after electronic excitation is charge redistribution occurring on a tens of picoseconds time scale followed by proton transfer on a nanosecond time scale. The three states observed in the experiments (initial excited state, charge redistributed state, and proton transfer state) are recognized by distinct features in the time dependence of the pump-probe spectrum and fluorescence spectra. In the charge redistributed state, charge density has transferred from the hydroxyl oxygen to the pyrene ring, but the OH sigma bond is still intact. The experiments indicate that the charge redistribution step is controlled by a specific hydrogen bond donation from HPTA to the accepting base molecule. The second step is the full deprotonation of the photoacid. The full deprotonation is clearly marked by the growth of stimulated emission spectral band in the pump-probe spectrum that is identical to the fluorescence spectrum of the anion.

  17. New Light Shed on Charge Transfer in Fundamental H++H2 Collisions

    NASA Astrophysics Data System (ADS)

    Urbain, X.; de Ruette, N.; Andrianarijaona, V. M.; Martin, M. F.; Menchero, L. Fernández; Errea, L. F.; Méndez, L.; Rabadán, I.; Pons, B.

    2013-11-01

    There is no consensus on the magnitude and shape of the charge transfer cross section in low-energy H++H2 collisions, in spite of the fundamental importance of these collisions. Experiments have thus been carried out in the energy range 15?E?5000eV. The measurements invalidate previous recommended data for E?200eV and confirm the existence of a local maximum around 45 eV, which was predicted theoretically. Additionally, vibrationally resolved cross sections allow us to investigate the evolution of the underlying charge transfer mechanism as a function of E.

  18. Charge transfer and excitation in high-energy ion-atom collisions

    SciTech Connect

    Schlachter, A.S.; Berkner, K.H.; McDonald, R.J.; Stearns, J.W.; Bernstein, E.M.; Clark, M.W.; Tanis, J.A.; Graham, W.G.; McFarland, R.H.; Stockli, M.P.

    1986-11-01

    Coincidence measurements of charge transfer and simultaneous projectile electron excitation provide insight into correlated two-electron processes in energetic ion-atom collisions. Projectile excitation and electron capture can occur simultaneously in a collision of a highly charged ion with a target atom; this process is called resonant transfer and excitation (RTE). The intermediate excited state which is thus formed can subsequently decay by photon emission or by Auger-electron emission. Results are shown for RTE in both the K shell of Ca ions and the L shell of Nb ions, for simultaneous projectile electron loss and excitation, and for the effect of RTE on electron capture.

  19. Enhanced charge transfer by phenyl groups at a rubrene/C{sub 60} interface

    SciTech Connect

    Mou Weiwei; Hattori, Shinnosuke; Nomura, Ken-ichi; Nakano, Aiichiro [Collaboratory for Advanced Computing and Simulations, Department of Physics and Astronomy, Department of Computer Science, Department of Chemical Engineering and Materials Science, University of Southern California, Los Angeles, California 90089-0242 (United States); Ohmura, Satoshi; Shimojo, Fuyuki [Collaboratory for Advanced Computing and Simulations, Department of Physics and Astronomy, Department of Computer Science, Department of Chemical Engineering and Materials Science, University of Southern California, Los Angeles, California 90089-0242 (United States); Department of Physics, Kumamoto University, Kumamoto 860-8555 (Japan)

    2012-05-14

    Exciton dynamics at an interface between an electron donor, rubrene, and a C{sub 60} acceptor is studied by nonadiabatic quantum molecular dynamics simulation. Simulation results reveal an essential role of the phenyl groups in rubrene in increasing the charge-transfer rate by an order-of-magnitude. The atomistic mechanism of the enhanced charge transfer is found to be the amplification of aromatic breathing modes by the phenyl groups, which causes large fluctuations of electronic excitation energies. These findings provide insight into molecular structure design for efficient solar cells, while explaining recent experimental observations.

  20. Infrared, Optical, and Luminescent Properties of Quasi-One Organic Charge Transfer Salts and Polymers

    Microsoft Academic Search

    Janice Lynn Musfeldt

    1992-01-01

    Polarized infrared and optical reflectance spectroscopies were used to study the structural phase transitions in two quarter-filled semiconducting organic charge transfer salts, N-propylquinolinium(TCNQ)_2 and N-dimethyl thiomorpholinium(TCNQ)_2 ; and two half-filled salts, Potassium-TCNQ and Rubidium-TCNQ. The spectra of NPrQn(TCNQ)_2 display characteristics common to quarter-filled charge transfer salts. Various cluster models were applied to describe the electron-phonon coupling at 300 K. The

  1. Charge Transfer Excited State Contributions to Polarity Dependent Ferromagnetism in ZnO Diluted Magnetic Semiconductors

    Microsoft Academic Search

    Kevin R. Kittilstved; William K. Liu; Daniel R. Gamelin

    2005-01-01

    A close link between the charge transfer electronic structures and polarity\\u000adependent high-TC ferromagnetism of TM2+:ZnO DMSs (TM2+ = 3d ions) is\\u000ademonstrated. Trends in ferromagnetism across the 3d series of TM2+:ZnO DMSs\\u000apredicted from their charge transfer energies reproduce experimental trends\\u000awell. These results provide a unified basis for understanding both n- and\\u000ap-type ferromagnetic oxide DMSs.

  2. Ultrafast Charge-Transfer-to-Solvent Dynamics of Iodide in Tetrahydrofuran. 2. Photoinduced Electron Transfer to Counterions in Solution

    Microsoft Academic Search

    Arthur E. Bragg; Benjamin J. Schwartz

    2008-01-01

    The excited states of atomic anions in liquids are bound only by the polarization of the surrounding solvent. Thus, the electron-detachment process following excitation to one of these solvent-bound states, known as charge-transfer-to-solvent (CTTS) states, provides a useful probe of solvent structure and dynamics. These transitions and subsequent relaxation dynamics also are influenced by other factors that alter the solution

  3. Evaluation of Bulk Charging in Geostationary Transfer Orbit and Earth Escape Trajectories Using the Numit 1-D Charging Model

    NASA Technical Reports Server (NTRS)

    Minow, Joseph I.; Coffey, Victoria N.; Parker, Linda N.; Blackwell, William C., Jr.; Jun, Insoo; Garrett, Henry B.

    2007-01-01

    The NUMIT 1-dimensional bulk charging model is used as a screening to ol for evaluating time-dependent bulk internal or deep dielectric) ch arging of dielectrics exposed to penetrating electron environments. T he code is modified to accept time dependent electron flux time serie s along satellite orbits for the electron environment inputs instead of using the static electron flux environment input originally used b y the code and widely adopted in bulk charging models. Application of the screening technique ts demonstrated for three cases of spacecraf t exposure within the Earth's radiation belts including a geostationa ry transfer orbit and an Earth-Moon transit trajectory for a range of orbit inclinations. Electric fields and charge densities are compute d for dielectric materials with varying electrical properties exposed to relativistic electron environments along the orbits. Our objectiv e is to demonstrate a preliminary application of the time-dependent e nvironments input to the NUMIT code for evaluating charging risks to exposed dielectrics used on spacecraft when exposed to the Earth's ra diation belts. The results demonstrate that the NUMIT electric field values in GTO orbits with multiple encounters with the Earth's radiat ion belts are consistent with previous studies of charging in GTO orb its and that potential threat conditions for electrostatic discharge exist on lunar transit trajectories depending on the electrical proper ties of the materials exposed to the radiation environment.

  4. Structure-property relationships for three indoline dyes used in dye-sensitized solar cells: TDDFT study of visible absorption and photoinduced charge-transfer processes.

    PubMed

    Li, Huixing; Chen, Maodu

    2013-12-01

    The electronic structures of three D-A-?-A indoline dyes (WS-2, WS-6, and WS-11) used in dye-sensitized solar cells (DSSCs) were studied by performing quantum chemistry calculations. The coplanarity of the A-?-A segment and distinct noncoplanarity of the indoline donor part of each dye were confirmed by checking the calculated geometric parameters. The relationships between molecular modifications and the optical properties of the dyes were derived in terms of the partial density of states, absorption spectrum, frontier molecular orbital, and excited-state charge transfer. 3D real-space analysis of the transition density (TD) and charge difference density (CDD) was also performed to further investigate the excited-state features of the molecular systems, as they provide visualized physical pictures of the charge separation and transfer. It was found that modifying the alkyl chain of the bridge unit near the acceptor unit is an efficient way to decrease dye aggregation and improve DSSC efficiency. Inserting a hexylthiophene group next to the donor unit leads to a complicated molecular structure and a decrease in the charge-transfer ability of the system, which has an unfavorable impact on DSSC performance. PMID:24154611

  5. Interpenetrating network hydrogels via simultaneous "click chemistry" and atom transfer radical polymerization.

    PubMed

    Xu, L Q; Yao, F; Fu, G D; Kang, E T

    2010-07-12

    Simultaneous interpenetrating polymer networks (sIPNs) from concurrent copper(I)-catalyzed azide-alkyne cycloaddition "click chemistry" and atom transfer radical polymerization (ATRP) are described. Semi-sIPN of poly(ethylene glycol)/poly(2-hydroxyethyl methacrylate) (semi-PEG/PHEMA-sIPN) was first prepared via simultaneous "click chemistry" and ATRP from a mixture of poly(ethylene glycol)-diazide (N3-PEG-N3, Mn=4000 g/mol), tetrakis(2-propynyloxymethyl)methane (TPOM), ethyl-2-bromobutyrate (EBB), CuBr, pentamethyldiethylenetriamine (PMDETA), and 2-hydroxyethyl methacrylate (HEMA) in dimethylformamide (DMF). Full sIPN of PEG/PHEMA (full-PEG/PHEMA-sIPN) was then prepared via simultaneous "click chemistry" and ATRP from a mixture of N3-PEG-N3 (Mn=4000 g/mol), TPOM, EBB, CuBr, PMDETA, HEMA, and poly(ethylene glycol) diacrylate) (PEGDA, Mn=575) in DMF. Both the semi- and full-sIPNs exhibit a fast gelation rate and high gel yield. The sIPNs also exhibit high swelling ratios and good mechanical and antifouling properties. The morphology and thermal behavior of the sIPNs were studied by scanning electron microscopy (SEM), thermogravimetric analysis (TGA), and differential scanning calorimetry (DSC). These sIPNs could find applications as biomaterials for contact lenses, biomedical materials, artificial organs, and drug delivery systems. PMID:20518556

  6. Charge-transfer energy in closed-shell ion-atom interactions. [for H and Li ions in He

    NASA Technical Reports Server (NTRS)

    Alvarez-Rizzatti, M.; Mason, E. A.

    1975-01-01

    The importance of charge-transfer energy in the interactions between closed-shell ions and atoms is investigated. Ab initio calculations on H(plus)-He and Li(plus)-He are used as a guide for the construction of approximate methods for the estimation of the charge-transfer energy for more complicated systems. For many alkali ion-rate gas systems the charge-transfer energy is comparable to the induction energy in the region of the potential minimum, although for doubly charged alkaline-earth ions in rare gases the induction energy always dominates. Surprisingly, an empirical combination of repulsion energy plus asymptotic induction energy plus asymptotic dispersion energy seems to give a fair representation of the total interaction, especially if the repulsion energy is parameterized, despite the omission of any explicit charge-transfer contribution. More refined interaction models should consider the charge-transfer energy contribution.

  7. New parameterization of non-inductive charge transfer based on previous laboratory experiments

    NASA Astrophysics Data System (ADS)

    Tsenova, B. D.; Mitzeva, R. P.

    2009-01-01

    Empirical equations for the sign and magnitude of the separated non-inductive charge during rebounding collisions of ice-crystal and graupel are obtained using discriminant and regression analyses. The original source of data is Takahashi's laboratory experiment [Takahashi, T., 1978. Riming electrification as a charge generation mechanism in thunderstorms. J. Atmos. Sci. 35. 1536-1548], who presented measured charge transfer values as isolines, function of cloud temperature and cloud water content. The simulations show that the use of these equations in a numerical cloud model gives similar values for the total charge density in a simulated thundercloud to those obtained using the lookup table of Takahashi's data as implemented by many authors. Tests reveal that the use of the proposed equations is computationally more efficient for numerical simulations of thunderstorm electrification comparing to the use of the look-up table. In addition, the results show that the different parameterization schemes for the charge transfer to a graupel particle due to a single ice crystal interaction proposed by Takahashi [Takahashi, T., 1984. Thunderstorm electrification — a numerical study. J. Atmos. Sci., 41. 2541-2558] and Saunders et al. [Saunders, C.P.R., Keith, W.D. and Mitzeva, R.P., 1991. The effect of liquid water on thunderstorm charging. J. Geophys. Res. 96. 11007-11017], may affect significantly the total charge density in the simulated cloud case.

  8. Delocalization and dielectric screening of charge transfer states in organic photovoltaic cells.

    PubMed

    Bernardo, B; Cheyns, D; Verreet, B; Schaller, R D; Rand, B P; Giebink, N C

    2014-01-01

    Charge transfer (CT) states at a donor-acceptor heterojunction have a key role in the charge photogeneration process of organic solar cells, however, the mechanism by which these states dissociate efficiently into free carriers remains unclear. Here we explore the nature of these states in small molecule-fullerene bulk heterojunction photovoltaics with varying fullerene fraction and find that the CT energy scales with dielectric constant at high fullerene loading but that there is a threshold C60 crystallite size of ~4?nm below which the spatial extent of these states is reduced. Electroabsorption measurements indicate an increase in CT polarizability when C60 crystallite size exceeds this threshold, and that this change is correlated with increased charge separation yield supported by CT photoluminescence transients. These results support a model of charge separation via delocalized CT states independent of excess heterojunction offset driving energy and indicate that local fullerene crystallinity is critical to the charge separation process. PMID:24488203

  9. Electronically and ionically conductive gels of ionic liquids and charge-transfer tetrathiafulvalene-tetracyanoquinodimethane.

    PubMed

    Mei, Xiaoguang; Ouyang, Jianyong

    2011-09-01

    Electronically and ionically conductive gels were fabricated by mixing and mechanically grinding neutral tetrathiafulvalene (TTF) and tetracyanoquinodimethane (TCNQ) in ionic liquids (ILs) like 3-ethyl-1-methylimidazolium dicyanoamide (EMIDCA), 1-ethyl-3-methylimidazolium thiocyanate (EMISCN), 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (EMITf(2)N), trihexyltetradecylphosphonium bis(trifluoromethylsulfonyl)imide (P(14,6,6,6)Tf(2)N), and methyl-trioctylammonium bis(trifluoromethylsulfonyl)imide (MOATf(2)N). Charge-transfer TTF-TCNQ crystallites were generated during the mechanical grinding as indicated by the UV-visibile-near-infrared (UV-vis-NIR) absorption spectroscopy, Fourier transform infrared (FTIR) spectroscopy, and X-ray diffraction. The charge-transfer TTF-TCNQ crystallites have a needle-like shape. They form solid networks to gelate the ILs. The gel behavior is confirmed by the dynamic mechanical measurements. It depends on both the anions and cations of the ILs. In addition, when 1-methyl-3-butylimidazolium tetrafluoroborate (BMIBF(4)) and 1-methyl-3-propylimidazolium iodide (PMII) were used, the TTF-TCNQ/IL mixtures did not behave as gels. The TTF-TCNQ/IL gels are both electronically and ionically conductive, because the solid phase formed by the charge-transfer TTF-TCNQ crystallites is electronically conductive, while the ILs are ionically conductive. The gel formation is related to needle-like charge-transfer TTF-TCNQ cyrstallites and the ?-? and Coulombic interactions between TTF-TCNQ and ILs. PMID:21800893

  10. Elastic, excitation, ionization and charge transfer cross sections of current interest in fusion energy research

    SciTech Connect

    Schultz, D.R.; Krstic, P.S.

    1996-12-31

    Due to the present interest in modeling and diagnosing the edge and divertor plasma regions in magnetically confined fusion devices, we have sought to provide new calculations regarding the elastic, excitation, ionization, and charge transfer cross sections in collisions among relevant ions, neutrals, and isotopes in the low- to intermediate-energy regime. We summarize here some of our recent work.

  11. Time-dependent picture of the charge-transfer contributions to surface enhanced Raman spectroscopy

    NASA Astrophysics Data System (ADS)

    Lombardi, John R.; Birke, Ronald L.

    2007-06-01

    We reexamine the Herzberg-Teller theory of charge-transfer contributions to the theory of surface enhanced Raman scattering (SERS). In previous work, the Kramers-Heisenberg-Dirac framework was utilized to explain many of the observed features in SERS. However, recent experimental and theoretical developments suggest that we revise the theory to take advantage of the time-dependent picture of Raman scattering. Results are obtained for molecular adsorption on nanoparticles in both the strong confinement limit and the weak confinement limit. We show that the Herzberg-Teller contributions to the charge-transfer effect in SERS display a resonance at the molecule-to-metal or metal-to-molecule transition while retaining the selection rules associated with normal Raman spectroscopy (i.e., harmonic oscillator, as opposed to Franck-Condon overlaps). The charge-transfer contribution to the enhancement factor scales as ?-4, where ? is the homogeneous linewidth of the charge-transfer transition, and thus is extremely sensitive to the magnitude of this parameter. We show that the Herzberg-Teller coupling term may be associated with the polaron-coupling constant of the surface phonon-electron interaction. A time-dependent expression for the Raman amplitude is developed, and we discuss the implications of these results for both metal and semiconductor nanoparticle surfaces.

  12. Radical cation salts and charge transfer complexes based on functionalized TTF derivatives

    Microsoft Academic Search

    J.-P. Legros; F. Dahan; L. Binet; J.-M. Fabre

    1999-01-01

    A series of new donors based on unsymmetrical tetrachalcogenofulvalenes bearing one or two NH2 or OH groups have been synthetized in order to help promoting extended H-bonding networks in potentially conductive compounds based on radical cation salts (RCS) and charge transfer complexes (CTC) systems. The synthesis route of these donors, designed to increase selectivity and yield, is described. Preparation, stoichiometry,

  13. Charge transfer and association of Li+ colliding with Na from very low to intermediate energies

    NASA Astrophysics Data System (ADS)

    Li, T. C.; Qu, Y. Z.; Wu, Y.; Liu, L.; Wang, J. G.; Liebermann, H.-P.; Buenker, R. J.

    2015-05-01

    The nonradiative charge-transfer processes of Li++Na (3 s ) collisions have been investigated by using the fully quantum-mechanical molecular-orbital close-coupling method and the two-center atomic-orbital close-coupling method for the energy range of 10-4-2 keV /u and 0.2 -10 keV /u , respectively. The radiative charge-transfer, radiative decay, and radiative-association processes have been studied by employing the fully quantum, optical-potential, and semiclassical methods for the energy range of 2 ×10-10-110 eV /u . The nonradiative charge-transfer processes dominate the collisions for energies above 0.2 eV/u while radiative decay processes dominate in the lower-energy region. Especially, we found that the radiative-association process is more important than the radiative charge-transfer process when E <2 ×10-2eV /u . The rate coefficients of nonradiative and radiative processes are also given for the temperature range of 3 ×104-2 ×109K and 10-6-103K , respectively.

  14. Charge Transfer and Bonding in Endohedral Fullerenes from High-Energy Spectroscopy

    Microsoft Academic Search

    Mark S. Golden; Thomas Pichler; Petra Rudolf

    2004-01-01

    This contribution deals with the investigation of charge transfer and bonding in endohedral fullerenes in the solid state using high-energy spectroscopies such as photoemission and x-ray absorption. An overview is given of the detailed and direct information that can be won as regards the valence state of the encapsulated species, the degree of hybridisation between the electronic states of the

  15. Laboratory Measurements of Charge Transfer on Atomic Hydrogen at Thermal Energies

    NASA Technical Reports Server (NTRS)

    Havener, C. C.; Vane, C. R.; Krause, H. F.; Stancil, P. C.; Mroczkowski, T.; Savin, D. W.

    2002-01-01

    We describe our ongoing program to measure velocity dependent charge transfer (CT) cross sections for selected ions on atomic hydrogen using the ion-aloin merged-beams apparatus at Oak Ridge Natioiial Laboralory. Our focus is on those ions for which CT plays an important role in determining the ionization structure, line emis sion, and thermal structure of observed cosmic photoionized plasmas.

  16. CHARGE TRANSFER REACTIONS OF NITRIC OXIDE WITH ATOMIC AND MOLECULAR IONS OF OXYGEN AND NITROGEN

    Microsoft Academic Search

    B. R. Turner; J. A. Rutherford; R. F. Stebbings

    1966-01-01

    The cross sections for charge transfer in collisions between nitric oxide and atomic and molecular positive ions of oxygen and nitrogen have been measured in the energy range from 3 to 200 ev in a crossed-beam experiment. A smooth interpolation is made between these resuits and the rate coefficients obtained at thermal energy by the afterglow technique. The dependence of

  17. Charge transfer induced local Frenkel exciton states in naphthalene crystals heavily doped with durene

    NASA Astrophysics Data System (ADS)

    Brovchenko, Ivan V.; Eilmes, Andrzej; Petelenz, Piotr

    1995-02-01

    Absorption and luminescence spectra of durene-doped naphthalene crystals are reported for different dopant concentrations. New impurity-induced absorption bands are interpreted as charge transfer induced local Frenkel exciton states. The results of theoretical calculations, performed (without invoking any adjustable parameters) for a series of finite model clusters are in very good agreement with experiment and support this interpretation.

  18. Estimation of instantaneous heat transfer coefficients for a direct-injection stratified-charge rotary engine

    Microsoft Academic Search

    C. M. Lee; H. E. Addy; T. H. Bond; K. S. Chun

    1987-01-01

    The main objective of this report was to derive equations to estimate neat transfer coefficients in both the combustion chamber and coolant passage of a rotary engine. This was accomplished by making detailed temperature and pressure measurements in a direct-injection stratified-charge rotary engine under a range of conditions. For each specific measurement point, the local physical properties of the fluids

  19. PHYSICAL REVIEW B 86, 115417 (2012) Pseudoparticle approach for charge-transferring molecule-surface collisions

    E-print Network

    Fehske, Holger

    2012-01-01

    to treat resonant charge-transfer and Auger processes on an equal footing, as it is necessary when both percent to the secondary electron emission. DOI: 10.1103/PhysRevB.86.115417 PACS number(s): 34.35.+a, 34 of surface reactions is of fundamental interest. It represents a quantum impurity problem where a finite many

  20. Synthesis and properties of charge-transfer complexes based on quaternary salts of amines and tetracyanoquinodimethane

    Microsoft Academic Search

    V. A. Bondarenko; É. Lazar; K. I. Pokhodnya; M. A. Tanatar

    1986-01-01

    The electrical and optical properties of four charge-transfer complexes based on a molecule of tetracyanoquinodimethane (an acceptor) and donor molecules of quaternary salts of amines have been studied. It has been shown that the conductivity of the complexes has a semiconductor character and is determined by conduction along stacks of tetracyanoquinodimethane molecules.

  1. Synthesis and properties of charge-transfer complexes based on quaternary salts of amines and tetracyanoquinodimethane

    SciTech Connect

    Bondarenko, V.A.; Lazar, E.; Pokhodnya, K.I.; Tanatar, M.A.

    1986-07-01

    The electrical and optical properties of four charge-transfer complexes based on a molecule of tetracyanoquinodimethane (an acceptor) and donor molecules of quaternary salts of amines have been studied. It has been shown that the conductivity of the complexes has a semiconductor character and is determined by conduction along stacks of tetracyanoquinodimethane molecules.

  2. Interaction between cation and anion sublattices in molecular charge transfer salts: structural conditions for ferrimagnetism

    Microsoft Academic Search

    S. S. Turner; D. Le Pévelen; P. Day

    2003-01-01

    Many molecular charge transfer salts with organo-chalcogen donors and transition-metal complex anions have been synthesised in recent years in an effort to find lattices that combine conductivity with long range magnetic order, but in most cases interaction between the donor and anion sublattices is very weak. We have approached this issue by selecting anions that contain S or Se atoms

  3. Structure of Charge Transfer Reaction Complexes Formed in Anionic Polymerization of Isoprene

    Microsoft Academic Search

    K. K. Kalninsh; A. F. Podolskii

    2003-01-01

    A new mechanism is suggested for the anionic polymerization of isoprene. The key moment of this mechanism is thermal electron excitation of the complex of a “living” polymer with a monomer to the low lying S1 (T1) state involving a charge (electron) and (Li+) cation transfer from the terminal unit to the monomer molecule. It is stated that the probability

  4. Photoinduced Charge Transfer within Polyaniline-Encapsulated Quantum Dots Decorated on Graphene

    E-print Network

    Xiong, Qihua

    limitations such as low efficiency of organic solar cell,7 as well as short lifetime of some metal oxides in optoelectronic devices. KEYWORDS: charge transfer, graphene, quantum dots, photovoltaic devices, polyaniline, responsive hybrid materials for photovoltaic devices are currently drawing immense attention on account

  5. Charge transfer type excitons at donor/acceptor interfaces of organic solar cells

    NASA Astrophysics Data System (ADS)

    Muraoka, Azusa; Yamashita, Koichi

    2015-03-01

    The conversion of excitons into charge within organic solar cells is complicated by bound electronhole pairs, or charge transfer states at donor/acceptor interfaces. The solar cell requires generating an efficient current. Thus it is necessary that charge transfer is further separated into free charge carriers to be transported to electrode. We focus on the improved the conversion efficiency of Bulk-heterojunction organic solar cells. We use dependent density functional theory with CAM-B3LYP/6-31G(d) to study the oscillator strengths, electronic structure, HOMO-LUMO band gap and energy level in several polymer (donor) : fullerene (acceptor) blends, such as MDMO-PPV, PCDTBT, PCPDTBT, PBB3, PTB7 and PTBF2 with PC70BM. To determine the effective physical factor in light energy conversion, we consider ,(i) charge transfer type excitation generated directly by photoinduced electron transition in the donor/acceptor interface (ii) the factors for controlling the conversion efficiency such as short-circuit current density and closed circuit voltage.

  6. Computing intramolecular charge and energy transfer rates using optimal modes.

    PubMed

    Yang, Xunmo; Bittner, Eric R

    2015-06-28

    In our recent work [X. Yang and E. R. Bittner, J. Phys. Chem. A 118, 5196 (2014)], we showed how to construct a reduced set of nuclear motions that capture the coupling between electronic and nuclear degrees of freedom over the course of an electronic transition. We construct these modes, referred to as "Lanczos modes," by applying a search algorithm to find linear combinations of vibrational normal modes that optimize the electronic/nuclear coupling operator. Here, we analyze the irreducible representations of the dominant contributions of these modes and find that for the cases considered here, these belong to totally symmetric irreducible representations of the donor and acceptor moieties. Upon investigating the molecular geometry changes following the transition, we propose that the electronic transition process can be broken into two steps, in the agreement of Born-Oppenheimer approximation: a fast excitation transfer occurs, facilitated by the "primary Lanczos mode," followed by slow nuclear relaxation on the final electronic diabatic surface. PMID:26133417

  7. Spectroscopy of Equilibrium and Non-Equilibrium Charge Transfer in Semiconductor Quantum Structures

    E-print Network

    Clemens Rössler; Simon Burkhard; Tobias Krähenmann; Marc Röösli; Peter Märki; Julien Basset; Thomas Ihn; Klaus Ensslin; Christian Reichl; Werner Wegscheider

    2014-08-22

    We investigate equilibrium and non-equilibrium charge-transfer processes by performing high-resolution transport spectroscopy. Using electrostatically defined quantum dots for energy-selective emission and detection, we achieved unprecedented spectral resolution and a high degree of tunability of relevant experimental parameters. Most importantly, we observe that the spectral width of elastically transferred electrons can be substantially smaller than the linewidth of a thermally broadened Coulomb peak. This finding indicates that the charge-transfer process is fast compared to the electron--phonon interaction time. By drawing an analogy to double quantum dots, we argue that the spectral width of the elastic resonance is determined by the lifetime broadening $h\\it{\\Gamma}$ of the emitter and detector states. Good agreement with the model is found also in an experiment in which the charge transfer is in the regime $h\\it{\\Gamma}\\gg k_{\\rm{B}}T$. By performing spectroscopy below the Fermi energy, we furthermore observe elastic and inelastic transfer of holes.

  8. Chemistry

    NSDL National Science Digital Library

    K-12 Outreach,

    Chemistry is the scientific study of matter and its interaction with other matter and with energy. It is the branch of natural science that deals with the composition of substances and their properties and reactions.

  9. Charge transfer dynamics from adsorbates to surfaces with single active electron and configuration interaction based approaches

    NASA Astrophysics Data System (ADS)

    Ramakrishnan, Raghunathan; Nest, Mathias

    2015-01-01

    We employ wavepacket simulations based on many-body time-dependent configuration interaction (TD-CI), and single active electron theories, to predict the ultrafast molecule/metal electron transfer time scales, in cyano alkanethiolates bonded to model gold clusters. The initial states represent two excited states where a valence electron is promoted to one of the two virtual ?? molecular orbitals localized on the cyanide fragment. The ratio of the two time scales indicate the efficiency of one charge transfer channel over the other. In both our one-and many-electron simulations, this ratio agree qualitatively with each other as well as with the previously reported experimental time scales (Blobner et al., 2012), measured for a macroscopic metal surface. We study the effect of cluster size and the description of electron correlation on the charge transfer process.

  10. On charge transfer in the adsorbed molecules-graphene monolayer-SiC substrate system

    SciTech Connect

    Davydov, S. Yu., E-mail: sergei_davydov@mail.ru [Russian Academy of Sciences, Ioffe Physical Technical Institute (Russian Federation)

    2011-05-15

    A step-by-step consideration of charge transfer in the molecule-single-layer graphene-SiC substrate system is presented. At the first step, a simple model of the density of states of a single graphene monolayer adsorbed on silicon carbide (the graphene-SiC system) is suggested, which allows the calculation of the corresponding occupation numbers of graphene atoms. It is shown that the graphene monolayer accumulates a negative charge. At the second step, the graphene-SiC system is considered as a substrate that adsorbs molecules with a high electron affinity. The charge of these molecules as a function of their surface concentration is calculated. It is shown that, in the case of a monolayer coating, the negative surface charge density of molecules in the molecule-graphene monolayer-SiC substrate system is considerably higher than the surface charge density transferring from the SiC substrate to the graphene layer. This suggests that it is possible to neutralize the excess charge in the graphene layer via adsorption of proper particles on the layer.

  11. Suppression of electron transfer to dioxygen by charge transfer and electron transfer complexes in the FAD-dependent reductase component of toluene dioxygenase.

    PubMed

    Lin, Tzong-Yuan; Werther, Tobias; Jeoung, Jae-Hun; Dobbek, Holger

    2012-11-01

    The three-component toluene dioxygenase system consists of an FAD-containing reductase, a Rieske-type [2Fe-2S] ferredoxin, and a Rieske-type dioxygenase. The task of the FAD-containing reductase is to shuttle electrons from NADH to the ferredoxin, a reaction the enzyme has to catalyze in the presence of dioxygen. We investigated the kinetics of the reductase in the reductive and oxidative half-reaction and detected a stable charge transfer complex between the reduced reductase and NAD(+) at the end of the reductive half-reaction, which is substantially less reactive toward dioxygen than the reduced reductase in the absence of NAD(+). A plausible reason for the low reactivity toward dioxygen is revealed by the crystal structure of the complex between NAD(+) and reduced reductase, which shows that the nicotinamide ring and the protein matrix shield the reactive C4a position of the isoalloxazine ring and force the tricycle into an atypical planar conformation, both factors disfavoring the reaction of the reduced flavin with dioxygen. A rapid electron transfer from the charge transfer complex to electron acceptors further reduces the risk of unwanted side reactions, and the crystal structure of a complex between the reductase and its cognate ferredoxin shows a short distance between the electron-donating and -accepting cofactors. Attraction between the two proteins is likely mediated by opposite charges at one large patch of the complex interface. The stability, specificity, and reactivity of the observed charge transfer and electron transfer complexes are thought to prevent the reaction of reductase(TOL) with dioxygen and thus present a solution toward conflicting requirements. PMID:22992736

  12. Suppression of Electron Transfer to Dioxygen by Charge Transfer and Electron Transfer Complexes in the FAD-dependent Reductase Component of Toluene Dioxygenase*

    PubMed Central

    Lin, Tzong-Yuan; Werther, Tobias; Jeoung, Jae-Hun; Dobbek, Holger

    2012-01-01

    The three-component toluene dioxygenase system consists of an FAD-containing reductase, a Rieske-type [2Fe-2S] ferredoxin, and a Rieske-type dioxygenase. The task of the FAD-containing reductase is to shuttle electrons from NADH to the ferredoxin, a reaction the enzyme has to catalyze in the presence of dioxygen. We investigated the kinetics of the reductase in the reductive and oxidative half-reaction and detected a stable charge transfer complex between the reduced reductase and NAD+ at the end of the reductive half-reaction, which is substantially less reactive toward dioxygen than the reduced reductase in the absence of NAD+. A plausible reason for the low reactivity toward dioxygen is revealed by the crystal structure of the complex between NAD+ and reduced reductase, which shows that the nicotinamide ring and the protein matrix shield the reactive C4a position of the isoalloxazine ring and force the tricycle into an atypical planar conformation, both factors disfavoring the reaction of the reduced flavin with dioxygen. A rapid electron transfer from the charge transfer complex to electron acceptors further reduces the risk of unwanted side reactions, and the crystal structure of a complex between the reductase and its cognate ferredoxin shows a short distance between the electron-donating and -accepting cofactors. Attraction between the two proteins is likely mediated by opposite charges at one large patch of the complex interface. The stability, specificity, and reactivity of the observed charge transfer and electron transfer complexes are thought to prevent the reaction of reductaseTOL with dioxygen and thus present a solution toward conflicting requirements. PMID:22992736

  13. Substituent and Solvent Effects on Excited State Charge Transfer Behavior of Highly Fluorescent Dyes Containing Thiophenylimidazole-Based Aldehydes

    NASA Technical Reports Server (NTRS)

    Santos, Javier; Bu, Xiu R.; Mintz, Eric A.

    2001-01-01

    The excited state charge transfer for a series of highly fluorescent dyes containing thiophenylimidazole moiety was investigated. These systems follow the Twisted Intramolecular Charge Transfer (TICT) model. Dual fluorescence was observed for each substituted dye. X-ray structures analysis reveals a twisted ground state geometry for the donor substituted aryl on the 4 and 5 position at the imidazole ring. The excited state charge transfer was modeled by a linear solvation energy relationship using Taft's pi and Dimroth's E(sub T)(30) as solvent parameters. There is linear relation between the energy of the fluorescence transition and solvent polarity. The degree of stabilization of the excited state charge transfer was found to be consistent with the intramolecular molecular charge transfer. Excited dipole moment was studied by utilizing the solvatochromic shift method.

  14. Charge transfer and coherent charge propagation in metal-insulator junctions

    Microsoft Academic Search

    Moichiro Nagae

    1987-01-01

    In a metal-insulator-metal junction, electron transfer from the inside of the barrier to one metal side, or vice versa, due to the change in height and shape of the potential barrier is calculated by means of the linear-response theory. A step-type potential model with a single interface is used as an electron potential in the junction. One of the results

  15. Temperature-dependent kinetics of charge transfer, hydrogen-atom transfer, and hydrogen-atom expulsion in the reaction of CO+ with CH4 and CD4.

    PubMed

    Melko, Joshua J; Ard, Shaun G; Johnson, Ryan S; Shuman, Nicholas S; Guo, Hua; Viggiano, Albert A

    2014-09-18

    We have determined the rate constants and branching ratios for the reactions of CO(+) with CH4 and CD4 in a variable-temperature selected ion flow tube. We find that the rate constants are collisional for all temperatures measured (193-700 K for CH4 and 193-500 K for CD4). For the CH4 reaction, three product channels are identified, which include charge transfer (CH4(+) + CO), H-atom transfer (HCO(+) + CH3), and H-atom expulsion (CH3CO(+) + H). H-atom transfer is slightly preferred to charge transfer at low temperature, with the charge-transfer product increasing in contribution as the temperature is increased (H-atom expulsion is a minor product for all temperatures). Analogous products are identified for the CD4 reaction. Density functional calculations on the CO(+) + CH4 reaction were also conducted, revealing that the relative temperature dependences of the charge-transfer and H-atom transfer pathways are consistent with an initial charge transfer followed by proton transfer. PMID:24588097

  16. Monovalent counterion distributions at highly charged water interfaces: Proton-transfer and Poisson-Boltzmann theory

    E-print Network

    Wei Bu; David Vaknin; Alex Travesset

    2005-10-30

    Surface sensitive synchrotron-X-ray scattering studies reveal the distributions of monovalent ions next to highly charged interfaces. A lipid phosphate (dihexadecyl hydrogen-phosphate) was spread as a monolayer at the air-water interface, containing CsI at various concentrations. Using anomalous reflectivity off and at the $L_3$ Cs$^+$ resonance, we provide, for the first time, spatial counterion distributions (Cs$^+$) next to the negatively charged interface over a wide range of ionic concentrations. We argue that at low salt concentrations and for pure water the enhanced concentration of hydroniums H$_3$O$^+$ at the interface leads to proton-transfer back to the phosphate group by a high contact-potential, whereas high salt concentrations lower the contact-potential resulting in proton-release and increased surface charge-density. The experimental ionic distributions are in excellent agreement with a renormalized-surface-charge Poisson-Boltzmann theory without fitting parameters or additional assumptions.

  17. Enhanced Electron Transfer Dissociation of Peptides Modified at C-terminus with Fixed Charges

    NASA Astrophysics Data System (ADS)

    Ko, Byoung Joon; Brodbelt, Jennifer S.

    2012-11-01

    The impact of the conversion of carboxylates in peptides to basic or fixed charge sites on the outcome of electron transfer dissociation (ETD) is evaluated with respect to ETD efficiency and the number of diagnostic sequence ions. Four reagents, including benzylamine (BA), 1-benzylpiperazine (BZP), carboxymethyl trimethylammonium chloride hydrazide (GT), and (2-aminoethyl)trimethylammonium chloride hydrochloride (AETMA), were used for the carboxylate derivatization, with the first two replacing the acidic carboxylate groups with basic functionalities and the latter two introducing fixed charge sites. The ETD efficiencies and Xcorr scores were compared for both nonderivatized and derivatized tryptic and Glu-C peptides from cytochrome c. Derivatization of the carboxylate increases the average charge states, the number of fragment ions, and the dissociation efficiencies of peptides, especially for the fixed charge reagent, AETMA.

  18. Lead methylammonium triiodide perovskite-based solar cells: an interfacial charge-transfer investigation.

    PubMed

    Xu, Xiaobao; Zhang, Hua; Cao, Kun; Cui, Jin; Lu, Jianfeng; Zeng, Xianwei; Shen, Yan; Wang, Mingkui

    2014-11-01

    This work reports on an investigation into interfacial charge transfer in CH3NH3PbI3 perovskite solar cells by using anatase TiO2 nanocuboids enclosed by active {100} and {001} facets. The devices show 6.0 and 8.0% power conversion efficiency with and without hole-transport material. Transient photovoltage/photocurrent decay and charge extraction, as well as impedance spectroscopy measurements, reveal that carbon materials are effective counter electrodes in perovskite solar cells. The photogenerated charges are observed to be stored in mesoporous TiO2 film under illumination and in the CH3NH3PbI3 layer in the dark. The use of 2,2',7,7'-tetrakis(N,N-di-p-methoxyphenylamine)-9,9-spirobifluorene (spiro-MeOTAD) as a hole-transport material accelerates interfacial charge recombination between the photogenerated electrons and holes. PMID:25213607

  19. Active pixel sensor having intra-pixel charge transfer with analog-to-digital converter

    NASA Technical Reports Server (NTRS)

    Fossum, Eric R. (Inventor); Mendis, Sunetra K. (Inventor); Pain, Bedabrata (Inventor); Nixon, Robert H. (Inventor); Zhou, Zhimin (Inventor)

    2000-01-01

    An imaging device formed as a monolithic complementary metal oxide semiconductor Integrated circuit in an industry standard complementary metal oxide semiconductor process, the integrated circuit including a focal plane array of pixel cells, each one of the cells including a photogate overlying the substrate for accumulating photo-generated charge in an underlying portion of the substrate, a readout circuit including at least an output field effect transistor formed in the substrate, and a charge coupled device section formed on the substrate adjacent the photogate having a sensing node connected to the output transistor and at least one charge coupled device stage for transferring charge from the underlying portion of the substrate to the sensing node and an analog-to-digital converter formed in the substrate connected to the output of the readout circuit.

  20. Impact of a single base pair substitution on the charge transfer rate along short DNA hairpins

    PubMed Central

    Renaud, Nicolas; Berlin, Yuri A.; Ratner, Mark A.

    2013-01-01

    Numerical studies of hole migration along short DNA hairpins were performed with a particular emphasis on the variations of the rate and quantum yield of the charge separation process with the location of a single guanine:cytosine (G:C) base pair. Our calculations show that the hole arrival rate increases as the position of the guanine:cytosine base pair shifts from the beginning to the end of the sequence. Although these results are in agreement with recent experimental findings, the mechanism governing the charge migration along these sequences is revisited here. Instead of the phenomenological two-step hopping mechanism via the guanine base, the charge propagation occurs through a delocalization of the hole density along the base pair stack. Furthermore, the variations of the charge transfer with the position of the guanine base are explained by the impact of the base pair substitutions on the delocalized conduction channels. PMID:23980166

  1. DNA-assisted photoinduced charge transfer between a cationic poly(phenylene vinylene) and a cationic fullerene.

    PubMed

    Park, Youngil; Liu, Zhongwei; Routh, Prahlad K; Kuo, Cheng-Yu; Park, Young-Shin; Tsai, Hsinhan; Martinez, Jennifer S; Shreve, Andrew P; Cotlet, Mircea; Wang, Hsing-Lin

    2015-06-28

    Water-soluble cationic conjugated poly(phenylene vinylene) (PPV) and cationic fullerene were complexed with negatively charged single stranded DNA and double stranded DNA via electrostatic interactions to achieve photoinduced charge transfer with efficiencies as high as those observed from oppositely charged, cationic PPV and anionic fullerene but with distinctly different quenching mechanisms. PMID:25894733

  2. Mass transfer within electrostatic precipitators: in-flight adsorption of mercury by charged suspended particulates.

    PubMed

    Clack, Herek L

    2006-06-01

    Electrostatic precipitation is the dominant method of particulate control used for coal combustion, and varying degrees of mercury capture and transformation have been reported across ESPs. Nevertheless, the fate of gas-phase mercury within an ESP remains poorly understood. The present analysis focuses on the gas-particle mass transfer that occurs within a charged aerosol in an ESP. As a necessary step in gas-phase mercury adsorption or transformation, gas-particle mass transfer-particularly in configurations other than fixed beds-has received far less attention than studies of adsorption kinetics. Our previous analysis showed that only a small fraction of gas-phase mercury entering an ESP is likelyto be adsorbed by collected particulate matter on the plate electrodes. The present simplified analysis provides insight into gas-particle mass transfer within an ESP under two limiting conditions: laminar and turbulent fluid flows. The analysis reveals that during the process of particulate collection, gas-particle mass transfer can be quite high, easily exceeding the mass transfer to ESP plate electrodes in most cases. Decreasing particle size, increasing particle mass loading, and increasing temperature all result in increased gas-particle mass transfer. The analysis predicts significantly greater gas-particle mass transfer in the laminar limitthan in the turbulent limit; however, the differences become negligible under conditions where other factors, such as total mass of suspended particulates, are the controlling mass transfer parameters. Results are compared to selected pilot- and full-scale sorbent injection data. PMID:16786702

  3. Ion-pair charge-transfer complexes of a dithiooxalate zinc donor component with viologens. Synthesis, structural and electronic characterization

    Microsoft Academic Search

    Matthias Hofbauer; Mario Möbius; Falk Knoch; Roland Benedix

    1996-01-01

    Bipyridinium and phenanthrolinium acceptors of different reduction potentials form with zinc 1,2-dithiooxalates (dto) ion-pair charge-transfer complexes of the general formula {A2+[Zn(dto)2]2?}. The contact ion pairs exhibit absorptions in the range 390–490 nm which can be attributed to the ion-pair charge-transfer (IPCT) type. On the base of spectroscopic, electrochemical and quantum-chemical investigations the relation between optical and thermal electron transfer within

  4. Charge Transfer Induced Multifunctional Transitions with Sensitive Pressure Manipulation in a Metal-Organic Framework.

    PubMed

    Yang, Junye; Zhou, Long; Cheng, Jinguang; Hu, Zhiwei; Kuo, Changyang; Pao, Chih-Wen; Jang, Lingyun; Lee, Jyh-Fu; Dai, Jianhong; Zhang, Sijia; Feng, Shaomin; Kong, Panpan; Yuan, Zhen; Yuan, Jie; Uwatoko, Yoshiya; Liu, Tao; Jin, Changqing; Long, Youwen

    2015-07-01

    The metal-organic framework {[Fe(2,2'-bipyridine)(CN)4]2Co(4,4'-bipyridine)}·4H2O (Fe2Co-MOF) with single-chain magnetism undergoes an intermetallic charge transfer that converts the Fe2Co charge/spin configurations from Fe(3+)LS-Co(2+)HS-Fe(3+)LS to Fe(2+)LS-Co(3+)LS-Fe(3+)LS (LS = low spin, HS = high spin) around 220 K under ambient pressure. A series of coherent phase transitions in structure, magnetism, permittivity and ferroelectricity are found to take place accompanying with the charge transfer, making Fe2Co-MOF a unique ferroelectric single-chain magnet at low temperature. Moreover, our detailed measurements of magnetization, dielectric constant, and Raman scattering under high pressures illustrate that the charge transfer as well as the resulting multifunctional transitions can be readily induced to occur at room temperature by applying a tiny external pressure of about 0.5 kbar. The present study thus provides a pressure well-controllable multifunctional material with potential applications in a broad temperature region across room temperature. PMID:26083272

  5. Problems of Rate Chemistry in the Flight Regimes of Aeroassisted Orbital Transfer Vehicles

    NASA Technical Reports Server (NTRS)

    Park, Chul

    1985-01-01

    The dissociating and ionizing nonequilibrium flows behind a normal shock wave are calculated for the density and vehicle regimes appropriate for aeroassisted orbital transfer vehicles; the departure of vibrational and electron temperatures from the gas temperature as well as viscous transport phenomena are accounted for. From the thermodynamic properties so determined, radiative power emission is calculated using an existing code. The resulting radiation characteristics are compared with the available experimental data. Chemical parameters are varied to Investigate their effect on the radiation characteristics. It is concluded that the current knowledge of rate chemistry leads to a factor-of-4 uncertainty In nonequilibrium radiation intensities. The chemical parameters that must be studied to Improve the accuracy are identified.

  6. Problems of rate chemistry in the flight regimes of aeroassisted orbital transfer vehicles

    NASA Technical Reports Server (NTRS)

    Park, C.

    1984-01-01

    The dissociating and ionizing nonequilibrium flows behind a normal shock wave are calculated for the density and vehicle regimes appropriate for aeroassisted orbital transfer vehicles; the departure of vibrational and electron temperatures from the gas temperature as well as viscous transport phenomena are accounted for. From the thermodynamic properties so determined, radiative power emission is calculated using an existing code. The resulting radiation characteristics are compared with the available experimental data. Chemical parameters are varied to investigate their effect on the radiation characteristics. It is concluded that the current knowledge of rate chemistry leads to a factor-of-4 uncertainty in nonequilibrium radiation intensities. The chemical parameters that must be studied to improve the accuracy are identified.

  7. Ultrafast spectroscopic signature of charge transfer between single-walled carbon nanotubes and C60.

    PubMed

    Dowgiallo, Anne-Marie; Mistry, Kevin S; Johnson, Justin C; Blackburn, Jeffrey L

    2014-08-26

    The time scales for interfacial charge separation and recombination play crucial roles in determining efficiencies of excitonic photovoltaics. Near-infrared photons are harvested efficiently by semiconducting single-walled carbon nanotubes (SWCNTs) paired with appropriate electron acceptors, such as fullerenes (e.g., C60). However, little is known about crucial photochemical events that occur on femtosecond to nanosecond time scales at such heterojunctions. Here, we present transient absorbance measurements that utilize a distinct spectroscopic signature of charges within SWCNTs, the absorbance of a trion quasiparticle, to measure both the ultrafast photoinduced electron transfer time (?pet) and yield (?pet) in photoexcited SWCNT–C60 bilayer films. The rise time of the trion-induced absorbance enables the determination of the photoinduced electron transfer (PET) time of ?pet ? 120 fs, while an experimentally determined trion absorbance cross section reveals the yield of charge transfer (?pet ? 38 ± 3%). The extremely fast electron transfer times observed here are on par with some of the best donor:acceptor pairs in excitonic photovoltaics and underscore the potential for efficient energy harvesting in SWCNT-based devices. PMID:25019648

  8. Charge transfer from first principles: self-consistent GW applied to donor-acceptor systems

    NASA Astrophysics Data System (ADS)

    Atalla, Viktor; Caruso, Fabio; Rubio, Angel; Scheffler, Matthias; Rinke, Patrick

    2015-03-01

    Charge transfer in donor-acceptor systems (DAS) is determined by the relative alignment between the frontier orbitals of the donor and the acceptor. Semi-local approximations to density functional theory (DFT) may give a qualitatively wrong level alignment in DAS, leading to unphysical fractional electron transfer in weakly bound donor-acceptor pairs. GW calculations based on first-order perturbation theory (G0W0) correct the level alignment, but leave unaffected the electron density. We demonstrate that self-consistent GW (sc GW) provides an ideal framework for the description of charge transfer in DAS. Moreover, sc GW seamlessly accounts for many-body correlations and van der Waals interactions. As in G0W0 , the sc GW level alignment is in agreement with experimental reference data. However in sc GW , also the electron density is treated at the GW level and, therefore, it is consistent with the level alignment between donor and acceptor leading to a qualitatively correct description of charge-transfer properties.

  9. Brookhaven National Laboratory: Chemistry Department

    NSDL National Science Digital Library

    At this website, the Brookhaven National Laboratory presents its chemistry research dealing primarily with imaging and neuroscience, charge transfer for energy conversion, chemistry with ionizing radiation, catalysis and surface science, nanoscience, combustion, and nuclear chemistry. Within each category, users can find instructive text and supportive images about the specific projects and the leading researchers. Visitors can learn about the Beamline U7A at the National Synchrotron Light Source, the Laser-Electron Accelerator Facility (LEAF), the Positron Emission Tomography (PET) Facility, and other exceptional research facilities. The website features histories of the chemistry department and of the Brookhaven National Laboratory.

  10. Metal-organic charge transfer can produce biradical states and is mediated by conical intersections.

    PubMed

    Tishchenko, Oksana; Li, Ruifang; Truhlar, Donald G

    2010-11-01

    The present paper illustrates key features of charge transfer between calcium atoms and prototype conjugated hydrocarbons (ethylene, benzene, and coronene) as elucidated by electronic structure calculations. One- and two-electron charge transfer is controlled by two sequential conical intersections. The two lowest electronic states that undergo a conical intersection have closed-shell and open-shell dominant configurations correlating with the 4s(2) and 4s(1)3d(1) states of Ca, respectively. Unlike the neutral-ionic state crossing in, for example, hydrogen halides or alkali halides, the path from separated reactants to the conical intersection region is uphill and the charge-transferred state is a biradical. The lowest-energy adiabatic singlet state shows at least two minima along a single approach path of Ca to the ? system: (i) a van der Waals complex with a doubly occupied highest molecular orbital, denoted ?(2)(1), and a small negative charge on Ca and (ii) an open-shell singlet (biradical) at intermediate approach (Ca...C ?2.5-2.7 ?) with molecular orbital structure (1)(2), where (2) is an orbital showing significant charge transfer form Ca to the ?-system, leading to a one-electron multicentered bond. A third minimum (iii) at shorter distances along the same path corresponding to a closed-shell state with molecular orbital structure has also been found; however, it does not necessarily represent the ground state at a given CaC distance in all three systems. The topography of the lowest adiabatic singlet potential energy surface is due to the one- and two-electron bonding patterns in Ca-? complexes. PMID:21037111

  11. Metal-Organic Charge Transfer Can Produce Biradical States and is Mediated by Conical Intersections

    SciTech Connect

    Tishchenko, Oksana; Li, Ruifang; Truhlar, Donald G.

    2010-11-09

    The present paper illustrates key features of charge transfer between calcium atoms and prototype conjugated hydrocarbons (ethylene, benzene, and coronene) as elucidated by electronic structure calculations. One- and two-electron charge transfer is controlled by two sequential conical intersections. The two lowest electronic states that undergo a conical intersection have closedshell and open-shell dominant configurations correlating with the 4s2 and 4s13d1 states of Ca, respectively. Unlike the neutralionic state crossing in, for example, hydrogen halides or alkali halides, the path from separated reactants to the conical intersection region is uphill and the charge-transferred state is a biradical. The lowest-energy adiabatic singlet state shows at least two minima along a single approach path of Ca to the ? system: (i) a van der Waals complex with a doubly occupied highest molecular orbital, denoted ?21 , and a small negative charge on Ca and (ii) an open-shell singlet (biradical) at intermediate approach (Ca?C distance ?2.5–2.7 Å) with molecular orbital structure ?1?2, where ?2 is an orbital showing significant charge transfer form Ca to the ?-system, leading to a one-electron multicentered bond. A third minimum (iii) at shorter distances along the same path corresponding to a closed-shell state with molecular orbital structure ?22 has also been found; however, it does not necessarily represent the ground state at a given Ca?C distance in all three systems. The topography of the lowest adiabatic singlet potential energy surface is due to the one- and two-electron bonding patterns in Ca-? complexes.

  12. Charge transfer excitations from excited state Hartree-Fock subsequent minimization scheme

    SciTech Connect

    Theophilou, Iris, E-mail: i.theophilou@fz-juelich.de [Peter Grunberg Institut (PGI) Forschungszentrum Jülich, D-52425 Jülich (Germany)] [Peter Grunberg Institut (PGI) Forschungszentrum Jülich, D-52425 Jülich (Germany); Tassi, M.; Thanos, S. [Institute for Advanced Materials, Physicochemical Processes, Nanotechnology and Microsystems, ‘Demokritos’ National Center for Scientific Research, 15310 Athens (Greece)] [Institute for Advanced Materials, Physicochemical Processes, Nanotechnology and Microsystems, ‘Demokritos’ National Center for Scientific Research, 15310 Athens (Greece)

    2014-04-28

    Photoinduced charge-transfer processes play a key role for novel photovoltaic phenomena and devices. Thus, the development of ab initio methods that allow for an accurate and computationally inexpensive treatment of charge-transfer excitations is a topic that nowadays attracts a lot of scientific attention. In this paper we extend an approach recently introduced for the description of single and double excitations [M. Tassi, I. Theophilou, and S. Thanos, Int. J. Quantum Chem. 113, 690 (2013); M. Tassi, I. Theophilou, and S. Thanos, J. Chem. Phys. 138, 124107 (2013)] to allow for the description of intermolecular charge-transfer excitations. We describe an excitation where an electron is transferred from a donor system to an acceptor one, keeping the excited state orthogonal to the ground state and avoiding variational collapse. These conditions are achieved by decomposing the space spanned by the Hartree-Fock (HF) ground state orbitals into four subspaces: The subspace spanned by the occupied orbitals that are localized in the region of the donor molecule, the corresponding for the acceptor ones and two more subspaces containing the virtual orbitals that are localized in the neighborhood of the donor and the acceptor, respectively. Next, we create a Slater determinant with a hole in the subspace of occupied orbitals of the donor and a particle in the virtual subspace of the acceptor. Subsequently we optimize both the hole and the particle by minimizing the HF energy functional in the corresponding subspaces. Finally, we test our approach by calculating the lowest charge-transfer excitation energies for a set of tetracyanoethylene-hydrocarbon complexes that have been used earlier as a test set for such kind of excitations.

  13. Nonadiabatic dynamics of charge transfer and singlet fission at the pentacene/C60 interface.

    PubMed

    Akimov, Alexey V; Prezhdo, Oleg V

    2014-01-29

    Charge carrier multiplication in organic heterojunction systems, a process known as singlet fission (SF), holds promise for development of solar cells with enhanced photon-to-electron yields, and therefore it is of substantial fundamental interest. The efficiency of photovoltaic devices based on this principle is determined by complex dynamics involving key electronic states coupled to particular nuclear motions. Extensive experimental and theoretical studies are dedicated to this topic, generating multiple opinions on the nature of such states and motions, their properties, and mechanisms of the competing processes, including electron-phonon relaxation, SF, and charge separation. Using nonadiabatic molecular dynamics, we identify the key steps and mechanisms involved in the SF and subsequent charge separation, and build a comprehensive kinetic scheme that is consistent with the existing experimental and theoretical results. The ensuing model provides time scales that are in excellent agreement with the experimental observations. We demonstrate that SF competes with the traditional photoinduced electron transfer between pentacene and C60. Efficient SF relies on the presence of intermediate dark states within the pentacene subsystem. Having multiexciton and charge transfer character, these states play critical roles in the dynamics, and should be considered explicitly when explaining the entire process from the photoexcitation to the final charge separation. PMID:24397723

  14. Photocurrent Generation through Charge-Transfer Processes in Noncovalent Perylenediimide/DNA Complexes.

    PubMed

    Takada, Tadao; Ido, Misa; Ashida, Akane; Nakamura, Mitsunobu; Fujitsuka, Mamoru; Kawai, Kiyohiko; Majima, Tetsuro; Yamana, Kazushige

    2015-04-27

    The charge-transfer process in noncovalent perylenediimide (PDI)/DNA complexes has been investigated by using nanosecond laser flash photolysis (LFP) and photocurrent measurements. The PDI/DNA complexes were prepared by inclusion of cationic PDI molecules into the artificial cavities created inside DNA. The LFP experiments showed that placement of the PDI chromophore at a specific site and included within the base stack of DNA led to the efficient generation of a charge-separated state with a long lifetime by photoexcitation. When two PDI chromophores were separately placed at different positions in DNA, the yield of the charge-separated state with a long lifetime was dependent upon the number of A-T base pairs between the PDIs, which was explained by electron hopping from one PDI to another. Photocurrent generation of the DNA-modified electrodes with the complex was also dependent upon the arrangement of the PDI chromophores. A good correlation was obtained between observed charge separation and photocurrent generation on the PDI/DNA-modified electrodes, which demonstrated the importance of the defined arrangement and assembly of organic chromophores in DNA for efficient charge separation and transfer in multichromophore arrays. PMID:25784217

  15. Mixed regular stack charge-transfer crystals: Fundamental microscopic parameters from optical spectra

    NASA Astrophysics Data System (ADS)

    Painelli, A.; Girlando, A.

    1987-08-01

    Diagrammatic valence bond calculations are applied to the study of the charge-transfer (CT) excitation spectrum and of the electron-molecular vibration (emv) coupling in mixed regular stack CT crystals. The intersite electrostatic interactions are treated by both mean-field and unscreened point-charge potential approaches, obtaining quite similar results. The evaluation of microscopic parameters through optical spectra is critically discussed, and a new method is proposed to estimate the parameters relevant to the long-range Coulomb interaction from the analysis of the emv perturbation on the Raman spectra.

  16. Resonant transfer and excitation: Dependence on projectile charge state and target-electron momentum distribution

    SciTech Connect

    Tanis, J.A.; Bernstein, E.M.; Clark, M.W.; Graham, W.G.; McFarland, R.H.; Morgan, T.J.; Mowat, J.R.; Mueller, D.W.; Mueller, A.; Stockli, M.P.

    1986-09-01

    Resonant transfer and excitation (RTE) involving simultaneous electron capture and projectile K-shell excitation has been measured for calcium ions in charge states ranging from neon-like to hydrogen-like incident on molecular hydrogen over an energy range 100--370 MeV. The results establish a projectile charge-state dependence for RTE and provide a detailed test of theoretical calculations. The effect of the target-electron momentum distribution on the RTE process is demonstrated by comparing with previous results for calcium ions incident on helium.

  17. Fermi level density of states modulation without charge transfer in nickelate superlattices.

    PubMed

    Han, Myung Joon; van Veenendaal, Michel

    2014-04-01

    By using first-principles density functional theory calculations for (LaNiO3)m/(SrTiO3)n superlattices, we report a systematic electronic response to the interface geometry. It is found that the density of states at the Fermi level of metallic nickelate layers is significantly reduced without charge transfer in the vicinity of the interface to the insulating SrTiO3. This type of electronic state redistribution is clearly distinctive from other interface phenomena such as charge and orbital reconstruction. Our result sheds new light on the understanding of the nickelates and other transition-metal oxide heterostructures. PMID:24637347

  18. Inner-Shell Charge-Transfer in Asymmetric Ion-Atom Collisions 

    E-print Network

    Reading, John F.; Ford, A. Lewis; Swafford, G. L.; Fitchard, A.

    1979-01-01

    Station, Texas 77843 (Received 10 February 1978) A method used previously for inner-shell ionization in asymmetric ion-atom collisions is extended to include charge transfer between the target inner shells and projectile E shell. We work in the energy... rangeq'" = Rv/Z?e' & 1 and use an independent-electron model (Hartree-Pock) for the target. We treat the interaction with the projectile as a time-dependent perturbation due to a bare charge moving on a straight- line path. Our method, as for ionization...

  19. Molecular control of photoexcited charge transfer and recombination at a quaterthiophene/zinc oxide interface

    SciTech Connect

    Mou Weiwei; Nakano, Aiichiro [Collaboratory for Advanced Computing and Simulations, Department of Physics and Astronomy, Department of Computer Science, Department of Chemical Engineering and Materials Science, University of Southern California, Los Angeles, California 90089-0242 (United States); Ohmura, Satoshi; Shimojo, Fuyuki [Collaboratory for Advanced Computing and Simulations, Department of Physics and Astronomy, Department of Computer Science, Department of Chemical Engineering and Materials Science, University of Southern California, Los Angeles, California 90089-0242 (United States); Department of Physics, Kumamoto University, Kumamoto 860-8555 (Japan)

    2012-05-14

    Nonadiabatic quantum molecular dynamics simulations are performed to study photoexcited charge transfer (CT) and charge recombination (CR) at an interface between a conjugated oligomer donor, quaterthiophene (QT), and an inorganic acceptor (ZnO). Simulations reveal a detrimental effect of static disorder in QT conformation on the efficiency of hybrid QT/ZnO solar cells due to increased CR. On the contrary, dynamic disorder (i.e., fluctuation of carbon-hydrogen bonds in QT) is essential for high efficiency by assisting CT. The separate controllability of CT and CR at the molecular level has impacts on molecular design for efficient solar cells and explains recent experimental observations.

  20. Forster Resonance Energy Transfer and Conformational Stability of Proteins: An Advanced Biophysical Module for Physical Chemistry Students

    ERIC Educational Resources Information Center

    Sanchez, Katheryn M.; Schlamadinger, Diana E.; Gable, Jonathan E.; Kim, Judy E.

    2008-01-01

    Protein folding is an exploding area of research in biophysics and physical chemistry. Here, we describe the integration of several techniques, including absorption spectroscopy, fluorescence spectroscopy, and Forster resonance energy transfer (FRET) measurements, to probe important topics in protein folding. Cytochrome c is used as a model…

  1. Excitation of the ligand-to-metal charge transfer band induces electron tunnelling in azurin

    SciTech Connect

    Baldacchini, Chiara [Biophysics and Nanoscience Centre, DEB-CNISM, Università della Tuscia, I-01100 Viterbo (Italy); Institute of Agro-environmental and Forest Biology, National Research Council, I-05010 Porano (Italy); Bizzarri, Anna Rita; Cannistraro, Salvatore, E-mail: cannistr@unitus.it [Biophysics and Nanoscience Centre, DEB-CNISM, Università della Tuscia, I-01100 Viterbo (Italy)

    2014-03-03

    Optical excitation of azurin blue copper protein immobilized on indium-tin oxide, in resonance with its ligand-to-metal charge transfer absorption band, resulted in a light-induced current tunnelling within the protein milieu. The related electron transport rate is estimated to be about 10{sup 5}?s{sup ?1}. A model based on resonant tunnelling through an azurin excited molecular state is proposed. The capability of controlling electron transfer processes through light pulses opens interesting perspectives for implementation of azurin in bio-nano-opto-electronic devices.

  2. Resonant hot charge-transfer excitations in fullerene-porphyrin complexes: Many-body Bethe-Salpeter study

    NASA Astrophysics Data System (ADS)

    Duchemin, Ivan; Blase, Xavier

    2013-06-01

    We study the neutral singlet excitations of the zinc-tetraphenylporphyrin and C70-fullerene donor-acceptor complex within the many-body Green's-function GW and Bethe-Salpeter approaches. The lowest transition is a charge-transfer excitation between the donor and the acceptor with an energy in excellent agreement with recent constrained density functional theory calculations. Beyond the lowest charge-transfer state, which can be determined with simple electrostatic models that we validate, the Bethe-Salpeter approach provides the full excitation spectrum. We evidence the existence of hot electron-hole states which are resonant in energy with the lowest donor intramolecular excitation and show a hybrid intramolecular and charge-transfer character, favoring the transition towards charge separation. Such findings, and the ability to describe accurately both low-lying and excited charge-transfer states, are important steps in the process of discriminating “cold” versus “hot” exciton dissociation processes.

  3. Chemistry control and corrosion mitigation of heat transfer salts for the fluoride salt reactor (FHR)

    SciTech Connect

    Kelleher, B. C.; Sellers, S. R.; Anderson, M. H.; Sridharan, K.; Scheele, R. D. [Dept. of Engineering Physics, Univ.of Wisconsin - Madison, 1500 Engineering Drive, Madison, WI 53706 (United States)

    2012-07-01

    The Molten Salt Reactor Experiment (MSRE) was a prototype nuclear reactor which operated from 1965 to 1969 at Oak Ridge National Laboratory. The MSRE used liquid fluoride salts as a heat transfer fluid and solvent for fluoride based {sup 235}U and {sup 233}U fuel. Extensive research was performed in order to optimize the removal of oxide and metal impurities from the reactor's heat transfer salt, 2LiF-BeF{sub 2} (FLiBe). This was done by sparging a mixture of anhydrous hydrofluoric acid and hydrogen gas through the FLiBe at elevated temperatures. The hydrofluoric acid reacted with oxides and hydroxides, fluorinating them while simultaneously releasing water vapor. Metal impurities such as iron and chromium were reduced by hydrogen gas and filtered out of the salt. By removing these impurities, the corrosion of reactor components was minimized. The Univ. of Wisconsin - Madison is currently researching a new chemical purification process for fluoride salts that make use of a less dangerous cleaning gas, nitrogen trifluoride. Nitrogen trifluoride has been predicted as a superior fluorinating agent for fluoride salts. These purified salts will subsequently be used for static and loop corrosion tests on a variety of reactor materials to ensure materials compatibility for the new FHR designs. Demonstration of chemistry control methodologies along with potential reduction in corrosion is essential for the use of a fluoride salts in a next generator nuclear reactor system. (authors)

  4. Enhanced charge transfer to molecular ions by electronic excitation of the target

    SciTech Connect

    Bruckmeier, R.; Wunderlich, C.; Figger, H. [Max-Planck-Institut fuer Quantenoptik, 85748 Garching (Germany)] [Max-Planck-Institut fuer Quantenoptik, 85748 Garching (Germany)

    1995-07-01

    A beam of molecular ions (ArH{sup +}, ArD{sup +}, or D{sub 3}{sup +}) was neutralized by passage through an excited cesium vapor; two single-mode diode lasers were used to populate the 6 {sup 2}{ital P}{sub 3/2} state of the cesium atoms. The charge-transfer cross section could be increased by laser excitation of the Cs target, in some cases by orders of magnitude. This was established by observing the intensity of the luminescence from the neutralized molecules, which was enhanced by a factor of up to 10. The enhancement factors are in qualitative agreement with results of computations that follow the theoretical treatment for atoms introduced by Rapp and Francis [J. Chem. Phys. 37, 2631 (1962)]. This experimental technique is a generally applicable method for any molecular-beam technique that relies on charge transfer.

  5. Primary Side Power Flow Control of Wireless Power Transfer for Electric Vehicle Charging

    SciTech Connect

    Miller, John M [ORNL; Onar, Omer C [ORNL; Chinthavali, Madhu Sudhan [ORNL

    2015-01-01

    Various noncontacting methods of plug-in electric vehicle charging are either under development or now deployed as aftermarket options in the light-duty automotive market. Wireless power transfer (WPT) is now the accepted term for wireless charging and is used synonymously for inductive power transfer and magnetic resonance coupling. WPT technology is in its infancy; standardization is lacking, especially on interoperability, center frequency selection, magnetic fringe field suppression, and the methods employed for power flow regulation. This paper proposes a new analysis concept for power flow in WPT in which the primary provides frequency selection and the tuned secondary, with its resemblance to a power transmission network having a reactive power voltage control, is analyzed as a transmission network. Analysis is supported with experimental data taken from Oak Ridge National Laboratory s WPT apparatus. This paper also provides an experimental evidence for frequency selection, fringe field assessment, and the need for low-latency communications in the feedback path.

  6. Investigations of the kinetics of charge-transfer reactions in photoelectrochemical solar cells

    NASA Astrophysics Data System (ADS)

    Memming, Ruediger; Reineke, Rolf; Meissner, Dieter

    1992-12-01

    Photoelectrochemical solar cells can be made on the basis of majority and minority carrier devices. Since the forward dark current limits the photovoltage, the kinetics of the charge transfer across the interface has been studied in detail. It is shown that the exchange current, and consequently the forward current, can be kinetically or diffusion controlled, depending on the charge transfer rate at the interface. In the case of a majority carrier device, the forward current is usually much smaller than that predicted from the thermionic emission model, leading to higher photovoltages in a photoelectrochemical cell. It is further shown that the forward current of a minority carrier device is mainly governed by the injection and recombination of minority carriers. Here the conversion efficiency is limited by the quality of the semiconductor, similarly as in pure solid state devices.

  7. Charge-transfer complexes of Cu(II)/HD analogue in sol gel sensors

    NASA Astrophysics Data System (ADS)

    Brinkley, J. F.; Kirkey, M. L.; Marques, A. D. S.; Lin, C. T.

    2003-01-01

    An optically transparent xerogel encapsulating Cu(II) acetate is fabricated to detect mustard gas (HD) analogues via a charge-transfer mechanism. A fast response (color change from sky blue to canary yellow) is observed for the chlorinated sulfide, and is accompanied by an absorption band at 370-420 nm. MO calculations revealed that the chlorinated HD analogue displays a charge-transfer transition extended from sulfur to chlorine atom. A 1:1 complex of Cu(II)/HD analogue is preferred. For a colorimetric sol-gel detector prepared at pH 3, the detection limit of HD analogue is calibrated at 0.03 ?l per 1.5 ml sensor volume.

  8. Charge transfer in gas surface scattering: the three electronic state system

    NASA Astrophysics Data System (ADS)

    Guan, Daren; Yi, Xizhang; Ding, Shiliang; Gu, Lichuan; Olson, John A.

    1998-07-01

    A general theoretical treatment for near-resonant charge exchange in gas-surface scattering is presented for a coupled three electronic state system. Specifically, the quadratic form method in linear algebra is used to solve a coupled set of differential equations within the framework of Micha's common eikonal formalism to determine evolution of nuclear transition amplitudes. The electron transfer probability was thus given analytically. It is also found that if the diabatic potentials Vd for the system satisfy the condition that D>0, where D is the discriminant of characteristic polynomial of eigenvalue equation of the matrix Vd, the charge transfer will be forbidden due to the hermicity of Vd. Comparison with a previous calculation of the ionization probability for a sodium atom scattering from a W(110) surface shows quite good agreement. The results demonstrate that the method appears to have a wide range of validity for the description of a variety of nonadiabatic phenomena in gas-surface scattering.

  9. Low Energy Charge Transfer between C5+ and Atomic Hydrogen

    SciTech Connect

    Draganic, Ilija N [ORNL; Seely, D. G. [Albion College; Havener, Charles C [ORNL

    2011-01-01

    Charge transfer (CT) with carbon ions has been identified for a long time as important in both magnetic fusion plasma devices and more recently in solar wind interactions with comets, planets, or neutrals in the heliosphere. A merged-beams technique is used to measure the absolute total charge transfer cross section for C5+ and atomic H over four orders of magnitude in collision energy, from 12,000 eV/u to 0.64 eV/u. The present measurements are compared with previous measurements using an atomic hydrogen target and benchmark available classical trajectory Monte-Carlo and molecular-orbital close-coupling calculations. An increasing cross section below 10 eV/u is attributed to trajectory effects due to the ion-induced dipole attraction between reactants.

  10. Low-energy charge transfer between C5+ and atomic hydrogen

    SciTech Connect

    Draganic, Ilija N [ORNL; Havener, Charles C [ORNL; Seely, D. G. [Albion College

    2011-01-01

    Charge transfer with carbon ions has been identified as important in both magnetic fusion plasma devices and, more recently, in solar wind interactions with comets, planets, or neutrals in the heliosphere. A merged-beams technique is used to measure the absolute total charge-transfer cross section for C{sup 5+} and atomic H over four orders of magnitude in collision energy, from 12,000 to 0.64 eV/u. The present measurements are compared with previous measurements using an atomic hydrogen target and benchmark available classical trajectory Monte Carlo and molecular-orbital close-coupling calculations. An observed increasing cross section below 10 eV/u is attributed to trajectory effects due to the ion-induced dipole attraction between reactants.

  11. Intermolecular interactions and charge transfer in the 2:1 tetrathiafulvalene bromanil complex, (TTF)2-BA.

    PubMed

    García-Orduña, Pilar; Dahaoui, Slimane; Lecomte, Claude

    2011-06-01

    The crystal structure of the 2:1 charge-transfer complex of tetrathiafulvalene [2,2'-bis(1,3-dithiolylidene)] and bromanil (tetrabromo-1,4-benzoquinone) [(TTF)(2)-BA, (C(6)H(4)S(4))(2)-C(6)Br(4)O(2)] has been determined by X-ray diffraction at room temperature, 100 and 25 K. No structural phase transition occurs in the temperature range studied. The crystal is made of TTF-BA-TTF sandwich trimers. A charge-transfer estimation between donor and acceptor (0.2 e) molecules is proposed in comparison to the molecular geometries of TTF-BA and TTF and BA isolated molecules. Displacement parameters of the molecules have been modeled with the TLS formalism. PMID:21586832

  12. Cross sections for charge transfer between mercury ions and other metals

    NASA Technical Reports Server (NTRS)

    Vroom, D. A.; Rutherford, J. A.

    1977-01-01

    Cross sections for charge transfer between several ions and metals of interest to the NASA electro propulsion program have been measured. Specifically, the ions considered were Hg(+), Xe(+) and Cs(+) and the metals Mo, Fe, Al, Ti, Ta, and C. Measurements were made in the energy regime from 1 to 5,000 eV. In general, the cross sections for charge transfer were found to be less than 10 to the minus 15 power sq cm for most processes over the total energy range. Exceptions are Hg(+) in collision with Ti and Ta. The results obtained for each reaction are given in both graphical and numerical form in the text. For quick reference, the data at several ion velocities are condensed into one table given in the summary.

  13. A charge-transfer amplifier and an encoded-bus architecture for low-power SRAM's

    Microsoft Academic Search

    Shoichiro Kawashima; Toshihiko Mori; Ryuhei Sasagawa; Makoto Hamaminato; Shigetoshi Wakayama; Kazuo Sukegawa; Isao Fukushi

    1998-01-01

    This paper proposes and reports a low-power SRAM using a charge-transfer (CT) pre-sense amplifier and a bus signal encoding scheme. The CT amplifier overcomes the Vth relative difference between the pair MOS transistors, and thus reduces the input offset voltage. The encoded-bus scheme reduces the number of signals being switched to cut the capacitive load. These read-path dynamic circuits have

  14. A Sensitive Dissolved Oxygen Sensor Based on a Charge-Transfer Complex Modified Electrode

    Microsoft Academic Search

    TU Yifeng

    2006-01-01

    A charge-transfer complex was modified on the graphite paste electrode for making a sensitive dissolved oxygen sensor. It was composed of copper with two ligands of phenanthroline and 1,2-dicyano-1,2-dithiol- ethane. Because of the low redox potential of the core ion and the pull and repulsive effect from the ligands, the redox of modified complex toke place under lower potential and

  15. Charge-transfer gap closure in transition-metal halides under pressure

    SciTech Connect

    Chen, A.L.; Yu, P.Y.

    1995-01-01

    Insulator-to-metal transition induced by pressure has been studied in three transition metal iodides: NiI{sub 2}, CoI{sub 2} and FeI{sub 2} using optical absorption and resistivity measurements at room temperature. Comparisons between the results obtained by these two techniques suggested that the closure of the charge-transfer gap is the principal mechanism responsible for the insulator-to-metal transition in these materials.

  16. Charge-Transfer Excitations Steer the Davydov Splitting and Mediate Singlet Exciton Fission in Pentacene

    NASA Astrophysics Data System (ADS)

    Beljonne, D.; Yamagata, H.; Brédas, J. L.; Spano, F. C.; Olivier, Y.

    2013-05-01

    Quantum-chemical calculations are combined to a model Frenkel-Holstein Hamiltonian to assess the nature of the lowest electronic excitations in the pentacene crystal. We show that an admixture of charge-transfer excitations into the lowest singlet excited states form the origin of the Davydov splitting and mediate instantaneous singlet exciton fission by direct optical excitation of coherently coupled single and double exciton states, in agreement with recent experiments.

  17. Charge-transfer excitations steer the Davydov splitting and mediate singlet exciton fission in pentacene.

    PubMed

    Beljonne, D; Yamagata, H; Brédas, J L; Spano, F C; Olivier, Y

    2013-05-31

    Quantum-chemical calculations are combined to a model Frenkel-Holstein Hamiltonian to assess the nature of the lowest electronic excitations in the pentacene crystal. We show that an admixture of charge-transfer excitations into the lowest singlet excited states form the origin of the Davydov splitting and mediate instantaneous singlet exciton fission by direct optical excitation of coherently coupled single and double exciton states, in agreement with recent experiments. PMID:23767738

  18. Femtosecond dynamics of intramolecular charge transfer in 4-dimethylamino-4?-cyanostilbene in polar solvents

    Microsoft Academic Search

    Nina Eilers-König; Thomas Kühne; Dirk Schwarzer; Peter Vöhringer; Jörg Schroeder

    1996-01-01

    The femtosecond dynamics of 4-(N,N-dimethylamino)-4?-cyanostilbene (DCS) in acetonitrile and methanol solvent was studied by fluorescence upconversion and pump-probe absorption spectroscopy. The spectral evolution observed provides strong evidence for a fast internal charge-transfer (CT) process dominating the dynamics in the first few picoseconds, while Stokes shift dynamics seem to play only a minor role. The initially excited state seems to have

  19. Ultrafast Nonlinear Optical Properties of Charge-Transfer Polymers. Transient Holography and Transient Absorption Studies

    Microsoft Academic Search

    Duncan W. McBranch; Eric S. Maniloff; Dan Vacar; Alan J. Heeger

    1998-01-01

    Charge-transfer polymers are a new class of nonlinear optical materials which can be used for generating femtosecond holographic gratings. Using semiconducting polymers sensitized with varying concentrations of C60, holographic gratings were recorded by individual ultrafast laser pulses; the diffraction efficiency and time decay of the gratings were measured using nondegenerate four-wave mixing. Using a figure of merit for dynamic data

  20. Ab initio calculation of H+He{sup +} charge-transfer cross sections for plasma physics

    Microsoft Academic Search

    J. Loreau; N. Vaeck; K. Sodoga; D. Lauvergnat; M. Desouter-Lecomte

    2010-01-01

    The charge-transfer in low-energy (0.25 to 150 eV\\/amu) H(nl)+He{sup +}(1s) collisions is investigated using a quasimolecular approach for the n=2,3 as well as the first two n=4 singlet states. The diabatic potential energy curves of the HeH{sup +} molecular ion are obtained from the adiabatic potential energy curves and the nonadiabatic radial coupling matrix elements using a two-by-two diabatization method,

  1. Ab initio calculation of H+He+ charge-transfer cross sections for plasma physics

    Microsoft Academic Search

    J. Loreau; K. Sodoga; D. Lauvergnat; M. Desouter-Lecomte; N. Vaeck

    2010-01-01

    The charge-transfer in low-energy (0.25 to 150 eV\\/amu) H(nl)+He+(1s) collisions is investigated using a quasimolecular approach for the n=2,3 as well as the first two n=4 singlet states. The diabatic potential energy curves of the HeH+ molecular ion are obtained from the adiabatic potential energy curves and the nonadiabatic radial coupling matrix elements using a two-by-two diabatization method, and a

  2. Colossal negative thermal expansion in BiNiO3 induced by intermetallic charge transfer

    Microsoft Academic Search

    Masaki Azuma; Wei-Tin Chen; Hayato Seki; Michal Czapski; Smirnova Olga; Kengo Oka; Masaichiro Mizumaki; Tetsu Watanuki; Naoki Ishimatsu; Naomi Kawamura; Shintaro Ishiwata; Matthew G. Tucker; Yuichi Shimakawa; J. Paul Attfield

    2011-01-01

    The unusual property of negative thermal expansion is of fundamental interest and may be used to fabricate composites with zero or other controlled thermal expansion values. Here we report that colossal negative thermal expansion (defined as linear expansion <-10-4 K-1 over a temperature range ~100 K) is accessible in perovskite oxides showing charge-transfer transitions. BiNiO3 shows a 2.6% volume reduction

  3. Controlling the charge transfer in phenylene-bridged borylene-amine pi-conjugated systems.

    PubMed

    Pro?, Agnieszka; Zhou, Gang; Norouzi-Arasi, Hassan; Baumgarten, Martin; Müllen, Klaus

    2009-08-20

    Novel boron-nitrogen-containing pi-conjugated compounds 3,3'- and 4,4'-((2,4,6-triisopropylphenyl)borylene)bis(N,N-diarylbenzenamine) (1-2), m- and p-phenylene bridged to the boron center, respectively, have been synthesized and characterized. Optical studies by means of UV-vis absorption and emission measurements as well as DFT calculations reveal a different charge transfer behavior between the para series and the meta series at ground and excited states. PMID:19719198

  4. The effects of charge transfer inefficiency (CTI) on galaxy shape measurements

    SciTech Connect

    Rhodes, Jason; /Caltech, JPL /Caltech; Leauthaud, Alexie; /LBL, Berkeley; Stoughton, Chris; /Fermilab; Massey, Richard; /Royal Observ., Edinburgh; Dawson, Kyle; /Utah U.; Kolbe, William; Roe, Natalie; /LBL, Berkeley

    2010-02-01

    We examine the effects of charge transfer inefficiency (CTI) during CCD readout on the demanding galaxy shape measurements required by studies of weak gravitational lensing. We simulate a CCD readout with CTI such as that caused by charged particle radiation damage in space-based detectors. We verify our simulations on real data from fully depleted p-channel CCDs that have been deliberately irradiated in a laboratory. We show that only charge traps with time constants of the same order as the time between row transfers during readout affect galaxy shape measurements. We simulate deep astronomical images and the process of CCD readout, characterizing the effects of CTI on various galaxy populations. Our code and methods are general and can be applied to any CCDs, once the density and characteristic release times of their charge trap species are known. We baseline our study around p-channel CCDs that have been shown to have charge transfer efficiency up to an order of magnitude better than several models of n-channel CCDs designed for space applications. We predict that for galaxies furthest from the readout registers, bias in the measurement of galaxy shapes, {Delta}e, will increase at a rate of (2.65 {+-} 0.02) x 10{sup -4} yr{sup -1} at L2 for accumulated radiation exposure averaged over the solar cycle. If uncorrected, this will consume the entire shape measurement error budget of a dark energy mission surveying the entire extragalactic sky within about 4 yr of accumulated radiation damage. However, software mitigation techniques demonstrated elsewhere can reduce this by a factor of {approx}10, bringing the effect well below mission requirements. This conclusion is valid only for the p-channel CCDs we have modeled; CCDs with higher CTI will fare worse and may not meet the requirements of future dark energy missions. We also discuss additional ways in which hardware could be designed to further minimize the impact of CTI.

  5. Heme photolysis occurs by ultrafast excited state metal-to-ring charge transfer.

    PubMed Central

    Franzen, S; Kiger, L; Poyart, C; Martin, J L

    2001-01-01

    Ultrafast time-resolved resonance Raman spectra of carbonmonoxy hemoglobin (Hb), nitroxy Hb, and deoxy Hb are compared to determine excited state decay mechanisms for both ligated and unligated hemes. Transient absorption and Raman data provide evidence for a sequential photophysical relaxation pathway common to both ligated and unligated forms of Hb* (photolyzed heme), in which the excited state 1Q decays sequentially: 1Q-->Hb*I-->Hb*II-->Hb ground state. Consistent with the observed kinetics, the lifetimes of these states are <50 fs, approximately 300 fs, and approximately 3 ps for 1Q, Hb*I, and Hb*II, respectively. The transient absorption data support the hypothesis that the Hb*I state results from an ultrafast iron-to-porphyrin ring charge transfer process. The Hb*II state arises from porphyrin ring-to-iron back charge transfer to produce a porphyrin ground state configuration a nonequilibrium iron d-orbital population. Equatorial d-pi* back-bonding of the heme iron to the porphyrin during the lifetime of the Hb*II state accounts for the time-resolved resonance Raman shifts on the approximately 3 ps time scale. The proposed photophysical pathway suggests that iron-to-ring charge transfer is the key event in the mechanism of photolysis of diatomic ligands following a porphyrin ring pi-pi* transition. PMID:11325737

  6. Charge transfer and adsorption-desorption kinetics in carbon nanotube and graphene gas sensing

    NASA Astrophysics Data System (ADS)

    Liang, Sang-Zi; Chen, Gugang; Harutyunyan, Avetik; Cole, Milton; Sofo, Jorge

    2014-03-01

    Detection of molecules in the gas phase by carbon nanotube and graphene has great application potentials due to the high sensitivity and surface-to-volume ratio. In chemiresistor, the conductance of the materials has been proposed to change as a result of charge transfer from the adsorbed molecules. Due to self-interaction errors, calculations using LDA or GGA density functionals have an innate disadvantage in dealing with charge transfer situations. A model which takes into consideration the dielectric interaction between the graphene surface and the molecule is employed to estimate the distance where charge transfer becomes favorable. Adsorption-desorption kinetics is studied with a modified Langmuir model, including sites from which the molecules do not desorb within the experimental time. Assuming a constant mobility, the model reproduces existing experimental conductance data. Its parameters provide information about the microscopic process during the detection and varying them allows optimization of aspects of sensor performance, including sensitivity, detection limit and response time. This work is supported by Honda Research Institute USA, Inc.

  7. Charge transfer in photorechargeable composite films of TiO2 and polyaniline

    NASA Astrophysics Data System (ADS)

    Nomiyama, Teruaki; Sasabe, Kenichi; Sakamoto, Kenta; Horie, Yuji

    2015-07-01

    A photorechargeable battery (PRB) is a photovoltaic device having an energy storage function in a single cell. The photoactive electrode of PRB is a bilayer film consisting of bare porous TiO2 and a TiO2–polyaniline (PANi) mixture that work as a photovoltaic current generator and an electrochemical energy storage by ion dedoping, respectively. To study the charge transfer between TiO2 and PANi, the photorechargeable quantum efficiency QE ([electron count on discharge]/[incident photon count on photocharge]) was measured by varying the thickness LS of the TiO2–PANi mixture. The quantum efficiency QEuv for UV photons had a maximum of ?7% at LS ? 7 µm. The time constant ?TP for the charge transfer was about 10?1 s, which was longer ten times or more than the lifetime of excited electrons within TiO2. These facts reveal that the main rate-limiting factor in the photocharging process is the charge transfer between TiO2 and PANi.

  8. Ab initio calculation of H+He{sup +} charge-transfer cross sections for plasma physics

    SciTech Connect

    Loreau, J.; Vaeck, N. [Laboratoire de Chimie Quantique et Photophysique, Universite Libre de Bruxelles, CP 160/09 50, avenue F. D. Roosevelt, B-1050 Bruxelles (Belgium); Sodoga, K. [Laboratoire de Chimie Physique, Batiment 349, Universite de Paris-Sud, UMR8000, F-91405 Orsay (France); Faculte des Sciences, Departement de Physique, Universite de Lome, Boite Postale 1515 Lome (Togo); Lauvergnat, D. [Laboratoire de Chimie Physique, Batiment 349, Universite de Paris-Sud, UMR8000, F-91405 Orsay (France); Desouter-Lecomte, M. [Laboratoire de Chimie Physique, Batiment 349, Universite de Paris-Sud, UMR8000, F-91405 Orsay (France); Departement de Chimie, B6c, Universite de Liege, Sart-Tilman, B-4000 Liege 1 (Belgium)

    2010-07-15

    The charge-transfer in low-energy (0.25 to 150 eV/amu) H(nl)+He{sup +}(1s) collisions is investigated using a quasimolecular approach for the n=2,3 as well as the first two n=4 singlet states. The diabatic potential energy curves of the HeH{sup +} molecular ion are obtained from the adiabatic potential energy curves and the nonadiabatic radial coupling matrix elements using a two-by-two diabatization method, and a time-dependent wave-packet approach is used to calculate the state-to-state cross sections. We find a strong dependence of the charge-transfer cross section on the principal and orbital quantum numbers n and l of the initial or final state. We estimate the effect of the nonadiabatic rotational couplings, which is found to be important even at energies below 1 eV/amu. However, the effect is small on the total cross sections at energies below 10 eV/amu. We observe that to calculate charge-transfer cross sections in an n manifold, it is only necessary to include states with n{sup '{<=}}n, and we discuss the limitations of our approach as the number of states increases.

  9. Ab initio calculation of H + He$^+$ charge transfer cross sections for plasma physics

    E-print Network

    J. Loreau; K. Sodoga; D. Lauvergnat; M. Desouter-Lecomte; N. Vaeck

    2010-06-02

    The charge transfer in low energy (0.25 to 150 eV/amu) H($nl$) + He$^+(1s)$ collisions is investigated using a quasi-molecular approach for the $n=2,3$ as well as the first two $n=4$ singlet states. The diabatic potential energy curves of the HeH$^+$ molecular ion are obtained from the adiabatic potential energy curves and the non-adiabatic radial coupling matrix elements using a two-by-two diabatization method, and a time-dependent wave-packet approach is used to calculate the state-to-state cross sections. We find a strong dependence of the charge transfer cross section in the principal and orbital quantum numbers $n$ and $l$ of the initial or final state. We estimate the effect of the non-adiabatic rotational couplings, which is found to be important even at energies below 1 eV/amu. However, the effect is small on the total cross sections at energies below 10 eV/amu. We observe that to calculate charge transfer cross sections in a $n$ manifold, it is only necessary to include states with $n^{\\prime}\\leq n$, and we discuss the limitations of our approach as the number of states increases.

  10. Lock-arm supramolecular ordering: a molecular construction set for cocrystallizing organic charge transfer complexes.

    PubMed

    Blackburn, Anthea K; Sue, Andrew C-H; Shveyd, Alexander K; Cao, Dennis; Tayi, Alok; Narayanan, Ashwin; Rolczynski, Brian S; Szarko, Jodi M; Bozdemir, Ozgur A; Wakabayashi, Rie; Lehrman, Jessica A; Kahr, Bart; Chen, Lin X; Nassar, Majed S; Stupp, Samuel I; Stoddart, J Fraser

    2014-12-10

    Organic charge transfer cocrystals are inexpensive, modular, and solution-processable materials that are able, in some instances, to exhibit properties such as optical nonlinearity, (semi)conductivity, ferroelectricity, and magnetism. Although the properties of these cocrystals have been investigated for decades, the principal challenge that researchers face currently is to devise an efficient approach which allows for the growth of high-quality crystalline materials, in anticipation of a host of different technological applications. The research reported here introduces an innovative design, termed LASO-lock-arm supramolecular ordering-in the form of a modular approach for the development of responsive organic cocrystals. The strategy relies on the use of aromatic electronic donor and acceptor building blocks, carrying complementary rigid and flexible arms, capable of forming hydrogen bonds to amplify the cocrystallization processes. The cooperativity of charge transfer and hydrogen-bonding interactions between the building blocks leads to binary cocrystals that have alternating donors and acceptors extending in one and two dimensions sustained by an intricate network of hydrogen bonds. A variety of air-stable, mechanically robust, centimeter-long, organic charge transfer cocrystals have been grown by liquid-liquid diffusion under ambient conditions inside 72 h. These cocrystals are of considerable interest because of their remarkable size and stability and the promise they hold when it comes to fabricating the next generation of innovative electronic and photonic devices. PMID:25369425

  11. Ultrafast intramolecular charge transfer of formyl perylene observed using femtosecond transient absorption spectroscopy.

    PubMed

    Mohammed, Omar F

    2010-11-01

    The excited-state photophysics of formylperylene (FPe) have been investigated in a series of nonpolar, polar aprotic, and polar protic solvents. A variety of experimental and theoretical methods were employed including femtosecond transient absorption (fs-TA) spectroscopy with 130 fs temporal resolution. We report that the ultrafast intramolecular charge transfer from the perylene unit to the formyl (CHO) group can be facilitated drastically by hydrogen-bonding interactions between the carbonyl group oxygen of FPe and hydrogen-donating solvents in the electronically excited state. The excited-state absorption of FPe in methanol (MeOH) is close to the reported perylene radical cation produced by bimolecular quenching by an electron acceptor. This is a strong indication for a substantial charge transfer in the S(1) state in protic solvents. The larger increase of the dipole moment change in the protic solvents than that in aprotic ones strongly supports this observation. Relaxation mechanisms including vibrational cooling and solvation coupled to the charge-transfer state are also discussed. PMID:20886856

  12. Organic photovoltaics: A charge transfer perspective in the study of donor-acceptor systems

    NASA Astrophysics Data System (ADS)

    Olguin, Marco Augusto

    The present research involves the study of donor-acceptor (D/A) dyad complexes from a charge transfer energy perspective. The aim is to provide insight and predictive understanding into the charge transfer processes of the molecular-level components in donor-acceptor based organic solar cells using computational methods to describe photochemical processes at the quantum mechanical level within the Density Functional Theory (DFT) approximation. Predictive understanding is anchored in reproducing experimental results, wherein the present work a perturbative excited-state DFT method is described in detail and shown to give Charge Transfer (CT) energies in excellent agreement with benchmark experimental data. With an accurate excited state method for calculating CT excitation energies at hand, the present research applies the method to the study of D/A pairs employed in photovoltaic devices. An examination is made of the effect on the CT energetics of varying the donor and acceptor component in the dyad and the changes in the frontier orbital energy levels and CT energies with respect to a varying D/A distance and D/A relative orientation. The results of the perturbative excited state DFT calculations provide direct insight into photovoltaic device efficiency since the CT energy determines the achievable open circuit voltage of a donor-acceptor based organic solar cell device.

  13. Investigation of ground state charge transfer complex between paracetamol and p-chloranil through DFT and UV-visible studies

    NASA Astrophysics Data System (ADS)

    Shukla, Madhulata; Srivastava, Nitin; Saha, Satyen

    2012-08-01

    The present report deals with the theoretical investigation on ground state structure and charge transfer (CT) transitions in paracetamol (PA)/p-chloranil (CA) complex using Density Functional Theory (DFT) and Time Dependent Density Functional Theory (TD-DFT) method. It is found that Cdbnd O bond length of p-chloranil increases on complexation with paracetamol along with considerable amount of charge transfer from PA to CA. TD-DFT calculations have been performed to analyse the observed UV-visible spectrum of PA-CA charge transferred complex. Interestingly, in addition to expected CT transition, a weak symmetry relieved ?-?* transition in the chloranil is also observed.

  14. Tuning the entanglement between orbital reconstruction and charge transfer at a film surface

    PubMed Central

    Cui, B.; Song, C.; Li, F.; Wang, G. Y.; Mao, H. J.; Peng, J. J.; Zeng, F.; Pan, F.

    2014-01-01

    The interplay between orbital, charge, spin, and lattice degrees of freedom is at the core of correlated oxides. This is extensively studied at the interface of heterostructures constituted of two-layer or multilayer oxide films. Here, we demonstrate the interactions between orbital reconstruction and charge transfer in the surface regime of ultrathin (La,Sr)MnO3, which is a model system of correlated oxides. The interactions are manipulated in a quantitative manner by surface symmetry-breaking and epitaxial strain, both tensile and compressive. The established charge transfer, accompanied by the formation of oxygen vacancies, provides a conceptually novel vision for the long-term problem of manganites—the severe surface/interface magnetization and conductivity deterioration. The oxygen vacancies are then purposefully tuned by cooling oxygen pressure, markedly improving the performances of differently strained films. Our findings offer a broad opportunity to tailor and benefit from the entanglements between orbit, charge, spin, and lattice at the surface of oxide films. PMID:24569650

  15. Raman spectroscopy of charge transfer interactions between single wall carbon nanotubes and [FeFe] hydrogenase.

    PubMed

    Blackburn, Jeffrey L; Svedruzic, Drazenka; McDonald, Timothy J; Kim, Yong-Hyun; King, Paul W; Heben, Michael J

    2008-10-28

    We report a Raman spectroscopy study of charge transfer interactions in complexes formed by single-walled carbon nanotubes (SWNTs) and [FeFe] hydrogenase I (CaHydI) from Clostridium acetobutylicum. The choice of Raman excitation wavelength and sample preparation conditions allows differences to be observed for complexes involving metallic (m) and semiconducting (s) species. Adsorbed CaHydI can reversibly inject electronic charge into the LUMOs of s-SWNTs, while charge can be injected and removed from m-SWNTs at lower potentials just above the Fermi energy. Time-dependent enzymatic assays demonstrated that the reduced and oxidized forms of CaHydI are deactivated by oxygen, but at rates that varied by an order of magnitude. The time evolution of the oxidative decay of the CaHydI activity reveals different time constants when complexed with m-SWNTs and s-SWNTs. The correlation of enzymatic assays with time-dependent Raman spectroscopy provides a novel method by which the charge transfer interactions may be investigated in the various SWNT-CaHydI complexes. Surprisingly, an oxidized form of CaHydI is apparently more resistant to oxygen deactivation when complexed to m-SWNTs rather than s-SWNTs. PMID:19082027

  16. Photoinduced Electron Transfer in DNA: Charge Shift Dynamics Between 8-Oxo-Guanine Anion and Adenine.

    PubMed

    Zhang, Yuyuan; Dood, Jordan; Beckstead, Ashley A; Li, Xi-Bo; Nguyen, Khiem V; Burrows, Cynthia J; Improta, Roberto; Kohler, Bern

    2015-06-18

    Femtosecond time-resolved IR spectroscopy is used to investigate the excited-state dynamics of a dinucleotide containing an 8-oxoguanine anion at the 5'-end and neutral adenine at the 3'-end. UV excitation of the dinucleotide transfers an electron from deprotonated 8-oxoguanine to its ?-stacked neighbor adenine in less than 1 ps, generating a neutral 8-oxoguanine radical and an adenine radical anion. These species are identified by the excellent agreement between the experimental and calculated IR difference spectra. The quantum efficiency of this ultrafast charge shift reaction approaches unity. Back electron transfer from the adenine radical anion to the 8-oxguanine neutral radical occurs in 9 ps, or approximately 6 times faster than between the adenine radical anion and the 8-oxoguanine radical cation (Zhang, Y. et al. Proc. Natl. Acad. Sci. U.S.A. 2014, 111, 11612-11617). The large asymmetry in forward and back electron transfer rates is fully rationalized by semiclassical nonadiabatic electron transfer theory. Forward electron transfer is ultrafast because the driving force is nearly equal to the reorganization energy, which is estimated to lie between 1 and 2 eV. Back electron transfer is highly exergonic and takes place much more slowly in the Marcus inverted region. PMID:25660103

  17. Molecular orbital (SCF-X?-SW) theory of metal-metal charge transfer processes in minerals - II. Application to Fe2+ --> Ti4+ charge transfer transitions in oxides and silicates

    USGS Publications Warehouse

    Sherman, David M.

    1987-01-01

    A molecular orbital description, based on X?-Scattered wave calculations on a (FeTiO10)14? cluster, is given for Fe2+ ? Ti4+ charge transfer transitions in minerals. The calculated energy for the lowest Fe2+ ? Ti4+ metal-metal charge transfer transition is 18040 cm?1 in reasonable agreement with energies observed in the optical spectra of Fe-Ti oxides and silicates. As in the case of Fe2+ ? Fe3+ charge transfer in mixed-valence iron oxides and silicates, Fe2+ ? Ti4+ charge transfer is associated with Fe-Ti bonding across shared polyhedral edges. Such bonding results from the overlap of the Fe(t 2g ) and Ti(t 2g ) 3d orbitals.

  18. Energy transfer in binary collisions of two gyrating charged particles in a magnetic field

    NASA Astrophysics Data System (ADS)

    Nersisyan, H. B.; Zwicknagel, G.

    2010-08-01

    Binary collisions of the gyrating charged particles in an external magnetic field are considered within a classical second-order perturbation theory, i.e., up to contributions that are quadratic in the binary interaction, starting from the unperturbed helical motion of the particles. The calculations are done with the help of a binary collision treatment, which is valid for any strength of the magnetic field and involves all harmonics of the particles' cyclotron motion. The energy transfer is explicitly calculated for a regularized and screened potential, which is both of finite range and nonsingular at the origin. The validity of the perturbation treatment is evaluated by comparing with classical trajectory Monte Carlo (CTMC) calculations which also allow one to investigate the strong collisions with large energy and velocity transfer at low velocities. For large initial velocities, on the other hand, only small velocity transfers occur. There the nonperturbative numerical CTMC results agree excellently with the predictions of the perturbative treatment.

  19. Charge transfer by electronic excitation: Direct measurement by high resolution spectroscopy in the gas phase.

    PubMed

    Fleisher, A J; Morgan, P J; Pratt, D W

    2009-12-01

    We report a quantitative measurement of the amount of charge that is transferred when the single ammonia complex of the photoacid beta-naphthol (2HNA) is excited by light. The measurement was made by comparing the permanent electric dipole moments of cis-2HNA in its ground (S(0)) and excited (S(1)) states, determined by Stark-effect studies of its fully resolved S(1)<--S(0) electronic spectrum. While the increase in electron transfer from the donor (NH(3)) to the acceptor (2HN) upon excitation is small ( approximately 0.05e), it is sufficient to redshift the electronic spectrum of the complex by approximately 600 cm(-1) ( approximately 0.1 eV). Thereby explored is the incipient motion of the acid-base complex along the excited state (electron-coupled) proton transfer coordinate. PMID:19968329

  20. Mass transfer within electrostatic precipitators: in-flight adsorption of mercury by charged suspended particulates

    SciTech Connect

    Herek L. Clack [Illinois Institute of Technology, Chicago, IL (United States). Department of Mechanical, Materials and Aerospace Engineering

    2006-06-01

    Electrostatic precipitation is the dominant method of particulate control used for coal combustion, and varying degrees of mercury capture and transformation have been reported across ESPs. Nevertheless, the fate of gas-phase mercury within an ESP remains poorly understood. The present analysis focuses on the gas-particle mass transfer that occurs within a charged aerosol in an ESP. As a necessary step in gas-phase mercury adsorption or transformation, gas-particle mass transfer - particularly in configurations other than fixed beds - has received far less attention than studies of adsorption kinetics. Our previous analysis showed that only a small fraction of gas-phase mercury entering an ESP is likely to be adsorbed by collected particulate matter on the plate electrodes. The present simplified analysis provides insight into gas-particle mass transfer within an ESP under two limiting conditions: laminar and turbulent fluid flows. The analysis reveals that during the process of particulate collection, gas-particle mass transfer can be quite high, easily exceeding the mass transfer to ESP plate electrodes in most cases. Decreasing particle size, increasing particle mass loading, and increasing temperature all result in increased gas-particle mass transfer. The analysis predicts significantly greater gas-particle mass transfer in the laminar limit than in the turbulent limit; however, the differences become negligible under conditions where other factors, such as total mass of suspended particulates, are the controlling mass transfer parameters. Results are compared to selected pilot- and full-scale sorbent injection data. 41 refs., 5 figs.

  1. Laboratory experiments on the effect of trace chemicals on charge transfer during ice-hail collision

    NASA Astrophysics Data System (ADS)

    Prakash, P. Jish; Kumar, P. Pradeep

    Laboratory experiments were carried out inside the cylindrical steel chamber kept inside the walk-in cold room, which can reach a temperature of - 30 °C, to investigate the effect of ionic compounds on charge transfer during the collision between ice crystals and graupel in the presence of supercooled water droplets. Experiments were carried out at a constant impact velocity of 2.2 m/s using pure water (Milli-Q, 18.2 M?-cm) and trace amount of ionic compounds at low rime accretion rate (RAR) and crystal sizes below 50 µm diameter in the temperature regions of - 6 to - 10 °C, - 16 to - 19 °C and - 21 to - 25 °C. It was observed that ice crystals interacting with graupel made of pure water obeys the charge sign regimes [Saunders, C.P.R., Keith, W.D., and Mitzeva, R.P., 1991. The effect of liquid water on thunderstorm charging. J. Geophys. Res. 96, D6, 11007-11017.] as a function of temperature and RAR for all temperatures ranging from - 6 to - 25 °C. The validity of the positive and negative charging zones of Saunders et al. [Saunders, C.P.R., Keith, W.D., and Mitzeva, R.P., 1991. The effect of liquid water on thunderstorm charging. J. Geophys. Res. 96, D6, 11007-11017.] for low effective liquid water content (EW) was verified.

  2. Electronic and vibronic properties of a discotic liquid-crystal and its charge transfer complex.

    PubMed

    Haverkate, Lucas A; Zbiri, Mohamed; Johnson, Mark R; Carter, Elizabeth; Kotlewski, Arek; Picken, S; Mulder, Fokko M; Kearley, Gordon J

    2014-01-01

    Discotic liquid crystalline (DLC) charge transfer (CT) complexes combine visible light absorption and rapid charge transfer characteristics, being favorable properties for photovoltaic (PV) applications. We present a detailed study of the electronic and vibrational properties of the prototypic 1:1 mixture of discotic 2,3,6,7,10,11-hexakishexyloxytriphenylene (HAT6) and 2,4,7-trinitro-9-fluorenone (TNF). It is shown that intermolecular charge transfer occurs in the ground state of the complex: a charge delocalization of about 10(-2) electron from the HAT6 core to TNF is deduced from both Raman and our previous NMR measurements [L. A. Haverkate, M. Zbiri, M. R. Johnson, B. Deme, H. J. M. de Groot, F. Lefeber, A. Kotlewski, S. J. Picken, F. M. Mulder, and G. J. Kearley, J. Phys. Chem. B 116, 13098 (2012)], implying the presence of permanent dipoles at the donor-acceptor interface. A combined analysis of density functional theory calculations, resonant Raman and UV-VIS absorption measurements indicate that fast relaxation occurs in the UV region due to intramolecular vibronic coupling of HAT6 quinoidal modes with lower lying electronic states. Relatively slower relaxation in the visible region the excited CT-band of the complex is also indicated, which likely involves motions of the TNF nitro groups. The fast quinoidal relaxation process in the hot UV band of HAT6 relates to pseudo-Jahn-Teller interactions in a single benzene unit, suggesting that the underlying vibronic coupling mechanism can be generic for polyaromatic hydrocarbons. Both the presence of ground state CT dipoles and relatively slow relaxation processes in the excited CT band can be relevant concerning the design of DLC based organic PV systems. PMID:24410238

  3. Chandra Observations of the "Dark" Moon and Geocoronal Solar-Wind Charge Transfer

    E-print Network

    B. J. Wargelin; M. Markevitch; M. Juda; V. Kharchenko; R. Edgar; A. Dalgarno

    2004-02-11

    We have analyzed data from two sets of calibration observations of the Moon made by the Chandra X-ray Observatory. In addition to obtaining a spectrum of the bright side that shows several distinct fluorescence lines, we also clearly detect time-variable soft X-ray emission, primarily O VII Ka and O VIII Lya, when viewing the optically dark side. The apparent dark-side brightness varied by at least an order of magnitude, up to 2x10^-6 phot/s/arcmin^2/cm^2 between 500 and 900 eV, which is comparable to the typical 3/4-keV-band background emission measured in the ROSAT All-Sky Survey. The spectrum is also very similar to background spectra recorded by Chandra in low or moderate-brightness regions of the sky. Over a decade ago, ROSAT also detected soft X-rays from the dark side of the Moon, which were tentatively ascribed to continuum emission from energetic solar wind electrons impacting the lunar surface. The Chandra observations, however, with their better spectral resolution, combined with contemporaneous measurements of solar-wind parameters, strongly favor charge transfer between highly charged solar-wind ions and neutral hydrogen in the Earth's geocorona as the mechanism for this emission. We present a theoretical model of geocoronal emission and show that predicted spectra and intensities match the Chandra observations very well. We also model the closely related process of heliospheric charge transfer and estimate that the total charge transfer flux observed from Earth amounts to a significant fraction of the soft X-ray background, particularly in the ROSAT 3/4-keV band.

  4. 41 CFR 102-36.290 - How much do we charge for excess personal property on a transfer with reimbursement?

    Code of Federal Regulations, 2010 CFR

    2010-07-01

    ... false How much do we charge for excess personal property on a transfer with reimbursement...Continued) FEDERAL MANAGEMENT REGULATION PERSONAL PROPERTY 36-DISPOSITION OF EXCESS PERSONAL PROPERTY Disposition of Excess...

  5. 41 CFR 102-36.285 - May we charge for personal property transferred to another federal agency?

    Code of Federal Regulations, 2011 CFR

    2011-01-01

    ...2011-01-01 false May we charge for personal property transferred to another federal agency...Continued) FEDERAL MANAGEMENT REGULATION PERSONAL PROPERTY 36-DISPOSITION OF EXCESS PERSONAL PROPERTY Disposition of Excess...

  6. 41 CFR 102-36.290 - How much do we charge for excess personal property on a transfer with reimbursement?

    Code of Federal Regulations, 2011 CFR

    2011-01-01

    ... false How much do we charge for excess personal property on a transfer with reimbursement...Continued) FEDERAL MANAGEMENT REGULATION PERSONAL PROPERTY 36-DISPOSITION OF EXCESS PERSONAL PROPERTY Disposition of Excess...

  7. An accurate and linear-scaling method for calculating charge-transfer excitation energies and diabatic couplings

    E-print Network

    Pavanello, Michele

    Quantum–mechanical methods that are both computationally fast and accurate are not yet available for electronic excitations having charge transfer character. In this work, we present a significant step forward towards this ...

  8. Class IV charge models: A new semiempirical approach in quantum chemistry

    Microsoft Academic Search

    Joey W. Storer; David J. Giesen; Christopher J. Cramer; Donald G. Truhlar

    1995-01-01

    We propose a new criterion for defining partial charges on atoms in molecules, namely that physical observables calculated from those partial charges should be as accurate as possible. We also propose a method to obtain such charges based on a mapping from approximate electronic wave functions. The method is illustrated by parameterizing two new charge models called AM1-CM1A and PM3-CM1P,

  9. Charge-Transfer States and Upper Limit of the Open-Circuit Voltage in Polymer:Fullerene Organic Solar Cells

    Microsoft Academic Search

    Koen Vandewal; Kristofer Tvingstedt; Jean V. Manca; Olle Inganas

    2010-01-01

    The power conversion efficiency of polymer:fullerene bulk heterojunction solar cells depends on the generated photocurrent and photovoltage. Here we show, using the thermodynamic theory of detailed balance, that the photovoltage in particular is limited by the presence of polymer:fullerene material interaction, resulting in the formation of a weak donor-acceptor charge transfer complex (CTC). Excited CTCs, or charge transfer (CT) states,

  10. First Year Chemistry Laboratory Courses for Distance Learners: Development and Transfer Credit Acceptance

    ERIC Educational Resources Information Center

    Brewer, Sharon E.; Cinel, Bruno; Harrison, Michelle; Mohr, Christina L.

    2013-01-01

    In delivering chemistry courses by distance, a key challenge is to offer the learner an authentic and meaningful laboratory experience that still provides the rigour required to continue on in science. To satisfy this need, two distance general chemistry laboratory courses appropriate for Bachelor of Science (B.Sc.) students, including chemistry

  11. Trifluoromethylmetallate anions as components of molecular charge transfer salts and superconductors.

    SciTech Connect

    Schlueter, J. A.

    1998-10-14

    Whereas polymeric and common inorganic anions frequently deprive the synthetic chemist of a chance to modify a charge transfer salt's structure through anion alterations, discrete organometallic anions provide a vast opportunity to probe the structure/property correlations of a material through rational synthetic methods. We have recently undertaken a research effort aimed at the crystallization of conducting charge transfer salts which possess modifiable, organometallic anions as the charge compensating entities. This research has been richly rewarded with the discovery of a new family of bis(ethylenedithio) tetrathiafulvalene (BEDT-TTF or ET) based molecular superconductors. Herein is presented a summary of over twenty {kappa}(ET){sub 2}M(CF{sub 3}){sub 4}(1,1,2-trihaloethane) (M = Cu, Ag, Au) superconducting salts. Three new related salts are also reported: (ET){sub 2} [trans-Ag(CF{sub 3}),(CN){sub 2}], {kappa}{sub L}(BEDT-TSF){sub 2}Ag(CF{sub 3}){sub 4}(TCE), and {kappa}{sub L}(ET){sub 2}Ag(CF{sub 3}){sub 3}Cl(TCE).

  12. Charge-transfer-based Gas Sensing Using Atomic-layer MoS2

    PubMed Central

    Cho, Byungjin; Hahm, Myung Gwan; Choi, Minseok; Yoon, Jongwon; Kim, Ah Ra; Lee, Young-Joo; Park, Sung-Gyu; Kwon, Jung-Dae; Kim, Chang Su; Song, Myungkwan; Jeong, Yongsoo; Nam, Kee-Seok; Lee, Sangchul; Yoo, Tae Jin; Kang, Chang Goo; Lee, Byoung Hun; Ko, Heung Cho; Ajayan, Pulickel M.; Kim, Dong-Ho

    2015-01-01

    Two-dimensional (2D) molybdenum disulphide (MoS2) atomic layers have a strong potential to be used as 2D electronic sensor components. However, intrinsic synthesis challenges have made this task difficult. In addition, the detection mechanisms for gas molecules are not fully understood. Here, we report a high-performance gas sensor constructed using atomic-layered MoS2 synthesised by chemical vapour deposition (CVD). A highly sensitive and selective gas sensor based on the CVD-synthesised MoS2 was developed. In situ photoluminescence characterisation revealed the charge transfer mechanism between the gas molecules and MoS2, which was validated by theoretical calculations. First-principles density functional theory calculations indicated that NO2 and NH3 molecules have negative adsorption energies (i.e., the adsorption processes are exothermic). Thus, NO2 and NH3 molecules are likely to adsorb onto the surface of the MoS2. The in situ PL characterisation of the changes in the peaks corresponding to charged trions and neutral excitons via gas adsorption processes was used to elucidate the mechanisms of charge transfer between the MoS2 and the gas molecules. PMID:25623472

  13. Charge-transfer-based Gas Sensing Using Atomic-layer MoS2

    NASA Astrophysics Data System (ADS)

    Cho, Byungjin; Hahm, Myung Gwan; Choi, Minseok; Yoon, Jongwon; Kim, Ah Ra; Lee, Young-Joo; Park, Sung-Gyu; Kwon, Jung-Dae; Kim, Chang Su; Song, Myungkwan; Jeong, Yongsoo; Nam, Kee-Seok; Lee, Sangchul; Yoo, Tae Jin; Kang, Chang Goo; Lee, Byoung Hun; Ko, Heung Cho; Ajayan, Pulickel M.; Kim, Dong-Ho

    2015-01-01

    Two-dimensional (2D) molybdenum disulphide (MoS2) atomic layers have a strong potential to be used as 2D electronic sensor components. However, intrinsic synthesis challenges have made this task difficult. In addition, the detection mechanisms for gas molecules are not fully understood. Here, we report a high-performance gas sensor constructed using atomic-layered MoS2 synthesised by chemical vapour deposition (CVD). A highly sensitive and selective gas sensor based on the CVD-synthesised MoS2 was developed. In situ photoluminescence characterisation revealed the charge transfer mechanism between the gas molecules and MoS2, which was validated by theoretical calculations. First-principles density functional theory calculations indicated that NO2 and NH3 molecules have negative adsorption energies (i.e., the adsorption processes are exothermic). Thus, NO2 and NH3 molecules are likely to adsorb onto the surface of the MoS2. The in situ PL characterisation of the changes in the peaks corresponding to charged trions and neutral excitons via gas adsorption processes was used to elucidate the mechanisms of charge transfer between the MoS2 and the gas molecules.

  14. Beyond vibrationally mediated electron transfer: interfacial charge injection on a sub-10-fs time scale

    NASA Astrophysics Data System (ADS)

    Huber, Robert; Moser, Jacques E.; Gratzel, Michael; Wachtveitl, Josef L.

    2003-12-01

    The electron transfer (ET) from organic dye molecules to semiconductor-colloidal systems is characterized by a special energetic situation with a charge transfer reaction from a system of discrete donor levels to a continuum of acceptor states. If these systems show a strong electronic coupling they are amongst the fastest known ET systems with transfer times of less than 10 fs. In the first part a detailed discussion of the direct observation of an ET reaction with a time constant of about 6 fs will be given, with an accompanying argumentation concerning possible artifacts or other interfering signal contributions. In a second part we will try to give a simple picture for the scenario of such superfast ET reactions and one main focus will be the discussion of electronic dephasing and its consequences for the ET reaction. The actual ET process can be understood as a kind of dispersion process of the initially located electron into the colloid representing a real motion of charge density from the alizarin to the colloid.

  15. Ultrafast charge transfer in atomically thin MoS?/WS? heterostructures.

    PubMed

    Hong, Xiaoping; Kim, Jonghwan; Shi, Su-Fei; Zhang, Yu; Jin, Chenhao; Sun, Yinghui; Tongay, Sefaattin; Wu, Junqiao; Zhang, Yanfeng; Wang, Feng

    2014-09-01

    Van der Waals heterostructures have recently emerged as a new class of materials, where quantum coupling between stacked atomically thin two-dimensional layers, including graphene, hexagonal-boron nitride and transition-metal dichalcogenides (MX2), give rise to fascinating new phenomena. MX2 heterostructures are particularly exciting for novel optoelectronic and photovoltaic applications, because two-dimensional MX2 monolayers can have an optical bandgap in the near-infrared to visible spectral range and exhibit extremely strong light-matter interactions. Theory predicts that many stacked MX2 heterostructures form type II semiconductor heterojunctions that facilitate efficient electron-hole separation for light detection and harvesting. Here, we report the first experimental observation of ultrafast charge transfer in photoexcited MoS2/WS2 heterostructures using both photoluminescence mapping and femtosecond pump-probe spectroscopy. We show that hole transfer from the MoS2 layer to the WS2 layer takes place within 50?fs after optical excitation, a remarkable rate for van der Waals coupled two-dimensional layers. Such ultrafast charge transfer in van der Waals heterostructures can enable novel two-dimensional devices for optoelectronics and light harvesting. PMID:25150718

  16. Ultrafast charge transfer in atomically thin MoS2/WS2 heterostructures

    NASA Astrophysics Data System (ADS)

    Hong, Xiaoping; Kim, Jonghwan; Shi, Su-Fei; Zhang, Yu; Jin, Chenhao; Sun, Yinghui; Tongay, Sefaattin; Wu, Junqiao; Zhang, Yanfeng; Wang, Feng

    2014-09-01

    Van der Waals heterostructures have recently emerged as a new class of materials, where quantum coupling between stacked atomically thin two-dimensional layers, including graphene, hexagonal-boron nitride and transition-metal dichalcogenides (MX2), give rise to fascinating new phenomena. MX2 heterostructures are particularly exciting for novel optoelectronic and photovoltaic applications, because two-dimensional MX2 monolayers can have an optical bandgap in the near-infrared to visible spectral range and exhibit extremely strong light-matter interactions. Theory predicts that many stacked MX2 heterostructures form type II semiconductor heterojunctions that facilitate efficient electron-hole separation for light detection and harvesting. Here, we report the first experimental observation of ultrafast charge transfer in photoexcited MoS2/WS2 heterostructures using both photoluminescence mapping and femtosecond pump-probe spectroscopy. We show that hole transfer from the MoS2 layer to the WS2 layer takes place within 50?fs after optical excitation, a remarkable rate for van der Waals coupled two-dimensional layers. Such ultrafast charge transfer in van der Waals heterostructures can enable novel two-dimensional devices for optoelectronics and light harvesting.

  17. Creation of ternary multicomponent crystals by exploitation of charge-transfer interactions.

    PubMed

    Seaton, Colin C; Blagden, Nicholas; Munshi, Tasnim; Scowen, Ian J

    2013-08-01

    Four new ternary crystalline molecular complexes have been synthesised from a common 3,5-dinitrobenzoic acid (3,5-dnda) and 4,4'-bipyridine (bipy) pairing with a series of amino-substituted aromatic compounds (4-aminobenzoic acid (4-aba), 4-(N,N-dimethylamino)benzoic acid (4-dmaba), 4-aminosalicylic acid (4-asa) and sulfanilamide (saa)). The ternary crystals were created through the application of complementary charge transfer and hydrogen-bonding interactions. For these systems a dimer was created through a charge-transfer interaction between two of the components, while hydrogen bonding between the third molecule and this dimer completed the construction of the ternary co-crystal. All resulting structures display the same acid???pyridine interaction between 3,5-dnba and bipy. However, changing the third component causes the proton of this bond to shift from neutral OH???N to a salt form, O(-) ???HN(+) , as the nature of the group hydrogen bonding to the carboxylic acid was changed. This highlights the role of the crystal environment on the level of proton transfer and the utility of ternary systems for the study of this process. PMID:23794534

  18. Quantum dynamics of ultrafast charge transfer at an oligothiophene-fullerene heterojunction

    NASA Astrophysics Data System (ADS)

    Tamura, Hiroyuki; Martinazzo, Rocco; Ruckenbauer, Matthias; Burghardt, Irene

    2012-12-01

    Following up on our recent study of ultrafast charge separation at oligothiophene-fullerene interfaces [H. Tamura, I. Burghardt, and M. Tsukada, J. Phys. Chem. C 115, 10205 (2011), 10.1021/jp203174e], we present here a detailed quantum dynamical perspective on the charge transfer process. To this end, electron-phonon coupling is included non-perturbatively, by an explicit quantum dynamical treatment using the multi-configuration time-dependent Hartree (MCTDH) method. Based upon a distribution of electron-phonon couplings determined from electronic structure studies, a spectral density is constructed and employed to parametrize a linear vibronic coupling Hamiltonian. The diabatic coupling is found to depend noticeably on the inter-fragment distance, whose effect on the dynamics is here investigated. MCTDH calculations of the nonadiabatic transfer dynamics are carried out for the two most relevant electronic states and 60 phonon modes. The electron transfer process is found to be ultrafast and mediated by electronic coherence, resulting in characteristic oscillatory features during a period of about 100 fs.

  19. Engineering Interfacial Photo-Induced Charge Transfer Based on Nanobamboo Array Architecture for Efficient Solar-to-Chemical Energy Conversion.

    PubMed

    Wang, Xiaotian; Liow, Chihao; Bisht, Ankit; Liu, Xinfeng; Sum, Tze Chien; Chen, Xiaodong; Li, Shuzhou

    2015-04-01

    Engineering interfacial photo-induced charge transfer for highly synergistic photocatalysis is successfully realized based on nanobamboo array architecture. Programmable assemblies of various components and heterogeneous interfaces, and, in turn, engineering of the energy band structure along the charge transport pathways, play a critical role in generating excellent synergistic effects of multiple components for promoting photocatalytic efficiency. PMID:25704499

  20. Toward a quantitative understanding of dipole-moment changes in charge-transfer transitions. Electroabsorption spectroscopy of transition-metal complexes

    Microsoft Academic Search

    Yeung-gyo K. Shin; B. S. Brumschwig; Carol Creutz; Norman Sutin

    1995-01-01

    This paper reports results for metal-to-ligand charge transfer (MLCT) and ligand-to-metal charge transfer (LMCT) absorption bands of Ru(II) and Ru(III) complexes and shows that the dipole-moment changes can be understood in terms of a two-state model which considers polarization, induced-dipole, and delocalization effects. In summary, the change in the charge of the metal center produced by charge-transfer excitation results in

  1. Charge transfer during low energy metal/semiconductor ion-surface interactions

    NASA Astrophysics Data System (ADS)

    Chen, Xiaojian

    Ion-surface charge exchange is a central process in many surface analysis techniques and technical processes. Previous ion scattering studies have extensively investigated the interactions between alkali/noble gas ions and surfaces. Investigations of the interactions between metal/semiconductor ions and metal surfaces have seldom been reported, although they are of central importance in understanding processes involving the removal material from metal/semiconductor surfaces. This dissertation uses low energy ion scattering and direct recoil to reveal charge transfer mechanisms between metal/semiconductor atomic particles and clean and adsorb ate-covered Al and Si surfaces. All involved experiments were performed in ultra-high vacuum. Charge transfer between an Al atom and an Al surface is studied by producing energetic recoiled Al from a Al(100) surface via Xe+ bombardment. The measured neutral fractions of the recoils show that resonant charge transfer (RCT) is a key mechanism. The ion formation of recoiled and sputtered atoms can be both described by RCT. The characteristic difference between recoiled and sputtered atoms is interpreted as due to different surface conditions at the time of ion emission. 1˜5 keV Si+ ions were incident on atomically clean Al(100) surface. All scattered Si was neutralized, while Al ions were found in multi-charged states. In contrast to the traditional sputtering studies, there is an abnormally high yield of Al2+ and Al3+. The multiply charged ions are attributed to the charge promotion of Al 2p level during the electronically nearly-symmetric Si-Al collision, and subsequent shake-off processes. This mechanism is supported by the energy dependence of Al ions as well as ion induced Auger electrons. Si+ ions were scattered from submonolayers of Cs deposited onto Al(100). Because of the high ionization energy of Si, resonant charge transfer would be expected to completely neutralize the scattered projectiles. In contrast, a considerable fraction of the Si scatters from the adatoms as positive and negative ions. Negative ions are produced by normal RCT when the work function is lowered. It is proposed that the positive ions are produced by the promotion of Si ionization level, which interacts with the I 5p level during the collision. The final ion fraction is then determined by RCT as the Si level crosses the Fermi energy along the exit trajectory. Similar ionization formation were observed for Si scattered from I adatoms on Al(100) and Si(111) surfaces. The promotion of the ionization level of Si is still invoked to explain the ion formation. The ion fractions, however, are lower than expected if only the surface potential and promotion are considered. This can be explained as a new neutralization channel resulting from the chemisorption states of the I adatom.

  2. Compton scattering and charge transfer in Er substituted DyAl2

    NASA Astrophysics Data System (ADS)

    Ahuja, B. L.; Mohammad, F. M.; Mohammed, S. F.; Sahariya, Jagrati; Mund, H. S.; Heda, N. L.

    2015-02-01

    A unique applicability of Compton spectroscopy in probing the electronic states of rare earth aluminides using high energy (662 keV) ?-rays is reported. We have measured first-ever Compton profiles of Dy1-xErxAl2 (x=0, 0.2) using 20Ci 137Cs Compton spectrometer. The charge reorganization in Dy1-xErxAl2 (x=0, 0.2), on the formation of compound, has been discussed using the valence band Compton profile data. The experimental Compton profile data unambiguously establish charge transfer from Al to Dy (Dy and Er) on formation of x=0.0 (0.2) compound, which is in tune with spin polarized relativistic Korringa-Kohn-Rostoker (SPR-KKR) calculations. A reasonable agreement between SPR-KKR based Compton profiles and the experimental data show applicability of the Green function method in predicting the electronic properties of rare earth compounds.

  3. Visualizing interfacial charge transfer in dye sensitized nanoparticles using x-ray transient absorption spectroscopy.

    SciTech Connect

    Zhang, X. Y.; Smolentsev, G.; Guo, J.; Attenkofer, K.; Kurtz, C.; Jennings, G.; Lockard, J. V.; Stickrath, A. B.; Chen, L. X. (X-Ray Science Division); (Southern Federal Univ.); (Lund Univ.); (Northwestern Univ.)

    2011-01-01

    A molecular level understanding of the structural reorganization accompanying interfacial electron transfer is important for rational design of solar cells. Here we have applied XTA (X-ray transient absorption) spectroscopy to study transient structures in a heterogeneous interfacial system mimicking the charge separation process in dye-sensitized solar cell (DSSC) with Ru(dcbpy){sub 2}(NCS){sub 2} (RuN3) dye adsorbed to TiO{sub 2} nanoparticle surfaces. The results show that the average Ru-NCS bond length reduces by 0.06 {angstrom}, whereas the average Ru-N(dcbpy) bond length remains nearly unchanged after the electron injection. The differences in bond-order change and steric hindrance between two types of ligands are attributed to their structural response in the charge separation. This study extends the application of XTA into optically opaque hybrid interfacial systems relevant to the solar energy conversion.

  4. Theoretical Investigation of OCN(-) Charge Transfer Complexes in Condensed Phase Media: Spectroscopic Properties in Amorphous Ice

    NASA Technical Reports Server (NTRS)

    Park, Jin-Young; Woon, David E.

    2004-01-01

    Density functional theory (DFT) calculations of cyanate (OCN(-)) charge-transfer complexes were performed to model the "XCN" feature observed in interstellar icy grain mantles. OCN(-) charge-transfer complexes were formed from precursor combinations of HNCO or HOCN with either NH3 or H2O. Three different solvation strategies for realistically modeling the ice matrix environment were explored, including (1) continuum solvation, (2) pure DFT cluster calculations, and (3) an ONIOM DFT/PM3 cluster calculation. The model complexes were evaluated by their ability to reproduce seven spectroscopic measurements associated with XCN: the band origin of the OCN(-) asymmetric stretching mode, shifts in that frequency due to isotopic substitutions of C, N, O, and H, plus two weak features. The continuum solvent field method produced results consistent with some of the experimental data but failed to account for other behavior due to its limited capacity to describe molecular interactions with solvent. DFT cluster calculations successfully reproduced the available spectroscopic measurements very well. In particular, the deuterium shift showed excellent agreement in complexes where OCN(-) was fully solvated. Detailed studies of representative complexes including from two to twelve water molecules allowed the exploration of various possible solvation structures and provided insights into solvation trends. Moreover, complexes arising from cyanic or isocyanic acid in pure water suggested an alternative mechanism for the formation of OCN(-) charge-transfer complexes without the need for a strong base such as NH3 to be present. An extended ONIOM (B3LYP/PM3) cluster calculation was also performed to assess the impact of a more realistic environment on HNCO dissociation in pure water.

  5. Charge Transfer Fluorescence and 34 nm Exciton Diffusion Length in Polymers with Electron Acceptor End Traps.

    PubMed

    Zaikowski, Lori; Mauro, Gina; Bird, Matthew; Karten, Brianne; Asaoka, Sadayuki; Wu, Qin; Cook, Andrew R; Miller, John R

    2015-06-18

    Photoexcitation of conjugated poly-2,7-(9,9-dihexylfluorene) polyfluorenes with naphthylimide (NI) and anthraquinone (AQ) electron-acceptor end traps produces excitons that form charge transfer states at the end traps. Intramolecular singlet exciton transport to end traps was examined by steady state fluorescence for polyfluorenes of 17-127 repeat units in chloroform, dimethylformamide (DMF), tetrahydrofuran (THF), and p-xylene. End traps capture excitons and form charge transfer (CT) states at all polymer lengths and in all solvents. The CT nature of the end-trapped states is confirmed by their fluorescence spectra, solvent and trap group dependence, and DFT descriptions. Quantum yields of CT fluorescence are as large as 46%. This strong CT emission is understood in terms of intensity borrowing. Energies of the CT states from onsets of the fluorescence spectra give the depths of the traps which vary with solvent polarity. For NI end traps, the trap depths are 0.06 (p-xylene), 0.13 (THF), and 0.19 eV (CHCl3). For AQ, CT fluorescence could be observed only in p-xylene where the trap depth is 0.27 eV. Quantum yields, emission energies, charge transfer energies, solvent reorganization, and vibrational energies were calculated. Fluorescence measurements on chains >100 repeat units indicate that end traps capture ?50% of the excitons, and that the exciton diffusion length is LD = 34 nm, which is much larger than diffusion lengths reported in polymer films or than previously known for diffusion along isolated chains. The efficiency of exciton capture depends on chain length but not on trap depth, solvent polarity, or which trap group is present. PMID:25531034

  6. Photodriven electron transfer in triad molecules: a two-step charge recombination reaction

    SciTech Connect

    Gust, D.; Moore, T.A.; Makings, L.R.; Liddell, P.A.; Nemeth, G.A.; Moore, A.L.

    1986-12-10

    Excitation of carotenoid-porphyrin-quinone (C-P-Q) triad molecules initiates a two-step electron transfer to yield a final charge separated state of the form C/sup .+/-P-Q/sup .-/. This state has a very long lifetime in solution (10/sup -7/-10/sup -6/ s), and the nature of the ultimate charge recombination reaction has not previously been investigated. Nanosecond transient absorption spectroscopic studies have been performed on a series of such triad molecules wherein the nature of the linkages joining the porphyrin to the quinone and/or carotenoid moieties is varied systematically. The results reveal that charge recombination in C/sup .+/-P-Q/sup .-/ does not occur in a single step but rather via an unusual two-step electron transfer involving an intermediate C-P/sup .+/-Q/sup .-/ species. The temperature dependence is consistent with the formation of C-P/sup .+/-Q/sup .-/ via a thermally activated process, and measurements over the range 221-296 K yield ..delta..H double dagger = 2.7 kcal/mol and ..delta..S double dagger = -20 cal/(deg x mol). The transient absorption measurements also reveal that the quantum yield of the C/sup .+/-P-Q/sup .-/ state is a function of three electron transfer rate constants and that it can therefore be maximized by controlling the ratios of these rate constants to one another and to the rates of other pathways which depopulate the relevant excited states.

  7. Role of charge transfer in the structure and dynamics of the hydrated proton.

    PubMed

    Swanson, Jessica M J; Simons, Jack

    2009-04-16

    Although it has long been recognized that multiple water molecules strongly associate with an extra proton in bulk water, some models and conceptual frameworks continue to utilize the classical hydronium ion (H(3)O(+)) as a fundamental building block. In this work, the nature of the hydronium ion in aqueous systems is examined using an ab initio energy decomposition analysis (EDA) that evaluates both the magnitude of and energetic stabilization due to charge transfer among H(3)O(+) and the surrounding water molecules. The EDA is performed on structures extracted from dynamical bulk-phase simulations and used to determine how frequently the pure hydronium ion, where the excess charge is primarily localized on H(3)O(+), occurs under dynamic conditions. The answer is essentially never. The energetic stabilization of H(3)O(+) due to charge delocalization to neighboring water molecules is found to be much larger (16-49 kcal/mol) than for other ions (even Li(+)) and to constitute a substantial portion (20-52%) of the complex's binding energy. The charge defect is also shown to have intrinsic dynamical asymmetry and to display dynamical signatures that can be related to features appearing in IR spectra. PMID:19309128

  8. The role of charge transfer in the structure and dynamics of the hydrated proton

    PubMed Central

    Swanson, Jessica M.J.; Simons, Jack

    2009-01-01

    Although it has long been recognized that multiple water molecules strongly associate with an extra proton in bulk water, some models and conceptual frameworks continue to utilize the classical hydronium ion (H3O+) as a fundamental building block. In this work, the nature of the hydronium ion in aqueous systems is examined using an ab initio energy decomposition analysis (EDA) that evaluates both the magnitude of and energetic stabilization due to charge transfer among H3O+ and the surrounding water molecules. The EDA is performed on structures extracted from dynamical bulk-phase simulations, and used to determine how frequently the pure hydronium ion, where the excess charge is primarily localized on H3O+, occurs under dynamic conditions. The answer is essentially never. The energetic stabilization of H3O+ due to charge delocalization to neighboring water molecules is found to be much larger (16 to 49 kcal/mol) than for other ions (even Li+) and to constitute a substantial portion (20% to 52%) of the complex's binding energy. The charge defect is also shown to have intrinsic dynamical asymmetry and to display dynamical signatures that can be related to features appearing in IR spectra. PMID:19309128

  9. Photophysics and charge transfer in donor-acceptor triblock copolymer photovoltaic materials

    NASA Astrophysics Data System (ADS)

    Schwarz, Kyra N.; Jones, David J.; Smith, Trevor A.; Ghiggino, Kenneth P.

    2014-10-01

    Efficient conversion of solar energy to electricity in low-cost organic photovoltaic (OPV) devices requires the complex interplay between multiple processes and components over various length and time scales. Optimizing device morphology to ensure efficient exciton diffusion and charge transport as well as ensuring efficient charge photogeneration is necessary to achieve optimum performance in new materials. The conjugated polymer electron donor PFM (poly(9,9-diocetyluorene-co-bis-N,N-(4-methylphenyl)-bis-N,N-phenyl-1,4-phenylenediamine)) and electron acceptor F8BT (poly[(9,9-di-n-octyluorenyl-2,7-diyl)-alt-(benzo[2,1,3]thiadiazol-4,8-diyl)), comprise the novel triblock copolymer PFM-F8BT-PFM. This copolymer is designed to phase separate on the 20-30 nm scale, a domain size ideal for maximizing exciton collection at the donor-acceptor interface. Using steady-state and ultrafast spectroscopic characterization including high repetition rate transient absorption spectroscopy, the dynamics of charge and energy transfer of the component polymers and the triblock co-polymer have been investigated. The results demonstrate that for the homopolymers solvent dependent exciton transport processes dominate, while in the triblock copolymer solutions transient spectroscopy provides evidence for interfacial charge separation.

  10. Results of experimental and theoretical investigations in charge transfer transitions, scintillators and Eu 2+ based phosphors

    NASA Astrophysics Data System (ADS)

    Srivastava, Alok M.

    2009-11-01

    A brief overview of recent results obtained in scintillator and phosphors are presented. Four topics, that are at the center of considerable research, and which are important from both fundamental and practical point of view, are chosen. The identification and behavior of ligand-to-RE 3+ (RE 3+ = rare earth) charge transfer transition when the ligand ions are halides and N 3- is reviewed. The reasons for the high light yield of the LuI 3:Ce 3+ scintillator is investigated theoretically and a new channel of energy transfer to excitons and directly to the Ce 3+ ion identified. The prospect of increasing the light yield of Ce 3+ based scintillators by the Pr 3+ ion is discussed. Finally, the remarkable luminescence of octahedrally coordinated Eu 2+ ion in Cs 2M 2+P 2O 7 (M 2+ = Ca, Sr) is discussed.

  11. Projectile charge state effects on electron emission in transfer ionization processes

    NASA Astrophysics Data System (ADS)

    Zhang, R. T.; Zhu, X. L.; Feng, W. T.; Guo, D. L.; Gao, Y.; Qian, D. B.; Li, B.; Yan, S. C.; Xu, S.; Zhang, P.; Ma, X.

    2015-07-01

    Electron emissions in transfer ionization processes were studied for 75 keV u?1 He2+, and 80 keV u?1 Ne8+on He collisions, using the well-developed reaction microscope techniques. Momentum distributions in the scattering plane, doubly differential distributions as a function of longitudinal momentum and emission angles of the ejected electrons were obtained. An apparent enhancement of electrons distributed around the projectile in the scattering plane was found for the Ne8+ incident case. Furthermore, we report the ratio of doubly differential distributions at the emission angle of 0° between these two transfer ionization processes, in which an abrupt rise is found at and above the electron capture to the continuum peak. This rise qualitatively agrees with the prediction within the framework of Dettmann’s theory. We conclude that this kind of enhancement was caused by the charge state effect of the projectile.

  12. Electric-field control of solitons in a ferroelectric organic charge-transfer salt.

    PubMed

    Kagawa, F; Horiuchi, S; Matsui, H; Kumai, R; Onose, Y; Hasegawa, T; Tokura, Y

    2010-06-01

    The role of solitons in transport, dielectric, and magnetic properties has been revealed for the quasi-one-dimensional organic charge-transfer salt, TTF-QBrCl3 [tetrathiafulvalene (TTF)-2-bromo-3,5,6-trichloro-p-benzoquinone (QBrCl3)]. The material was found to be ferroelectric and hence the solitons should be located at the boundary of the segments with opposite electric polarization. This feature enabled the electric-field control of soliton density and hence the clear-cut detection of soliton contributions. The gigantic dielectric response in the ferroelectric phase is ascribed to the dynamical bound and creeping motions of spinless solitons. PMID:20867204

  13. Electric-Field Control of Solitons in a Ferroelectric Organic Charge-Transfer Salt

    Microsoft Academic Search

    F. Kagawa; S. Horiuchi; H. Matsui; R. Kumai; Y. Onose; T. Hasegawa; Y. Tokura

    2010-01-01

    The role of solitons in transport, dielectric, and magnetic properties has been revealed for the quasi-one-dimensional organic charge-transfer salt, TTF-QBrCl3 [tetrathiafulvalene (TTF)-2-bromo-3,5,6-trichloro-p-benzoquinone (QBrCl3)]. The material was found to be ferroelectric and hence the solitons should be located at the boundary of the segments with opposite electric polarization. This feature enabled the electric-field control of soliton density and hence the clear-cut

  14. Luminescent charge-transfer complexes: tuning emission in binary fluorophore mixtures.

    PubMed

    Gujrati, Maneesh D; Kumar, N S Saleesh; Brown, Adrienne S; Captain, Burjor; Wilson, James N

    2011-06-01

    Charge-transfer (CT) complexes composed of a ?-electron-poor naphthalene diimide (NDI) derivative combined with a series of ?-electron-rich donors were investigated. Solutions of the CT complexes are nonemissive; however, solid-state complexes and aqueous suspensions display emission that is dependent on the energy of the HOMO of the electron donor. Crystallographic analysis of a pyrene-NDI complex reveals columnar packing and a high degree of frontier molecular orbital (FMO) overlap that likely contributes to the observed optical properties. The fluorescent CT particles are utilized as imaging agents; additional luminescent CT complexes may be realized by considering FMO energies and topologies. PMID:21548624

  15. Nanohydration of uracil: emergence of three-dimensional structures and proton-induced charge transfer.

    PubMed

    Bacchus-Montabonel, Marie-Christine; Calvo, Florent

    2015-04-21

    Stepwise hydration of uracil has been theoretically revisited using different methods ranging from classical force fields to quantum chemical approaches. Hydration initially begins within the uracil plane but proceeds at four molecules into three-dimensional configurations or even water clusters next to the nucleobase. The relative stability between the various structures is significantly affected by zero-point energy and finite temperature (entropy) effects and also gives rise to markedly different responses to an excitation by an impinging high-energy proton. In particular, charge transfer to the molecular complex is dramatically altered in collisions toward the coating cluster but barely modified for peripheral hydration patterns. PMID:25793649

  16. Scale-model charge-transfer technique for measuring enhancement factors

    NASA Technical Reports Server (NTRS)

    Kositsky, J.; Nanevicz, J. E.

    1991-01-01

    Determination of aircraft electric field enhancement factors is crucial when using airborne field mill (ABFM) systems to accurately measure electric fields aloft. SRI used the scale model charge transfer technique to determine enhancement factors of several canonical shapes and a scale model Learjet 36A. The measured values for the canonical shapes agreed with known analytic solutions within about 6 percent. The laboratory determined enhancement factors for the aircraft were compared with those derived from in-flight data gathered by a Learjet 36A outfitted with eight field mills. The values agreed to within experimental error (approx. 15 percent).

  17. Doubly interpenetrated chiral (10,3)-a network with charge-transfer-type guest inclusion.

    PubMed

    Han, Lei; Qin, Lan; Xu, Lan-Ping; Zhao, Wen-Na

    2013-02-18

    A doubly interpenetrated metal-organic framework, [Zn(3)(TATB)(2)(H(2)O)(2)](n) (2), with chiral (10,3)-a topology, has been synthesized from an achiral, trigonal-planar ligand, 4,4',4?-s-triazine-2,4,6-triyltribenzoate (TATB). The large chiral channels in 2 act as scaffolds for the inclusion of N,N-dimethylaniline (DMA) molecules by donor-acceptor interactions. The resulting host-guest composite, DMA@2, shows desirably intense luminescence, which originated from photoinduced charge-transfer interactions in excited states. PMID:23374148

  18. A theoretical study of charge transfer and ionization processes in He+-H2O collisions

    NASA Astrophysics Data System (ADS)

    Murakami, Mitsuko; Kirchner, Tom; Horbatsch, Marko; Lüdde, Hans Jürgen

    2011-05-01

    A recently introduced method for the description of ion-molecule collisions is extended to deal with a situation, in which not only target but also projectile electrons undergo transitions. All initially populated orbitals are propagated simultaneously in the same effective mean-field potential to ensure their orthogonality at all times. The asymptotic solutions are combined to many-electron transition probabilities by using the inclusive probabilities formalism which respects the Pauli principle. It will be shown that this analysis has interesting consequences for the charge transfer channels in intermediate energy He+-H2O collisions. This work has been supported by NSERC Canada and SHARCNET.

  19. Examination of charge transfer in Au/YSZ for high-temperature optical gas sensing

    SciTech Connect

    Baltrus, John P. [U.S. DOE; Ohodnicki, Paul R. [U.S. DOE

    2014-01-01

    Au-nanoparticle incorporated oxide thin film materials demonstrate significant promise as functionalsensor materials for high temperature optical gas sensing in severe environments relevant for fossil andnuclear based power generation. The Au/yttria-stabilized zirconia (YSZ) system has been extensivelystudied in the literature and serves as a model system for fundamental investigations that seek to betterunderstand the mechanistic origin of the plasmonic gas sensing response. In this work, X-ray photoelec-tron spectroscopy techniques are applied to Au/YSZ films in an attempt to provide further experimentalevidence for a proposed sensing mechanism involving a change in free carrier density of Au nanoparticles due to charge transfer.

  20. Estimation of instantaneous heat transfer coefficients for a direct-injection stratified-charge rotary engine

    NASA Technical Reports Server (NTRS)

    Lee, C. M.; Addy, H. E.; Bond, T. H.; Chun, K. S.; Lu, C. Y.

    1987-01-01

    The main objective of this report was to derive equations to estimate heat transfer coefficients in both the combustion chamber and coolant pasage of a rotary engine. This was accomplished by making detailed temperature and pressure measurements in a direct-injection stratified-charge rotary engine under a range of conditions. For each sppecific measurement point, the local physical properties of the fluids were calculated. Then an empirical correlation of the coefficients was derived by using a multiple regression program. This correlation expresses the Nusselt number as a function of the Prandtl number and Reynolds number.

  1. Molecular distortion and charge transfer effects in ZnPc/Cu(111)

    PubMed Central

    Amin, B.; Nazir, S.; Schwingenschlögl, U.

    2013-01-01

    The adsorption geometry and electronic properties of a zinc-phthalocyanine molecule on a Cu(111) substrate are studied by density functional theory. In agreement with experiment, we find remarkable distortions of the molecule, mainly as the central Zn atom tends towards the substrate to minimize the Zn-Cu distance. As a consequence, the Zn-N chemical bonding and energy levels of the molecule are significantly modified. However, charge transfer induces metallic states on the molecule and therefore is more important for the ZnPc/Cu(111) system than the structural distortions.

  2. Electric-Field Control of Solitons in a Ferroelectric Organic Charge-Transfer Salt

    NASA Astrophysics Data System (ADS)

    Kagawa, F.; Horiuchi, S.; Matsui, H.; Kumai, R.; Onose, Y.; Hasegawa, T.; Tokura, Y.

    2010-06-01

    The role of solitons in transport, dielectric, and magnetic properties has been revealed for the quasi-one-dimensional organic charge-transfer salt, TTF-QBrCl3 [tetrathiafulvalene (TTF)-2-bromo-3,5,6-trichloro-p-benzoquinone (QBrCl3)]. The material was found to be ferroelectric and hence the solitons should be located at the boundary of the segments with opposite electric polarization. This feature enabled the electric-field control of soliton density and hence the clear-cut detection of soliton contributions. The gigantic dielectric response in the ferroelectric phase is ascribed to the dynamical bound and creeping motions of spinless solitons.

  3. Direct observation of charge transfer region at interfaces in graphene devices

    SciTech Connect

    Nagamura, Naoka [Department of Applied Chemistry, Graduate School of Engineering, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656 (Japan) [Department of Applied Chemistry, Graduate School of Engineering, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656 (Japan); Synchrotron Radiation Research Organization, The University of Tokyo, 1-1-1 Kouto, Sayo-cho, Sayo-gun, Hyogo 679-5198 (Japan); Horiba, Koji; Oshima, Masaharu [Department of Applied Chemistry, Graduate School of Engineering, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656 (Japan) [Department of Applied Chemistry, Graduate School of Engineering, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656 (Japan); Synchrotron Radiation Research Organization, The University of Tokyo, 1-1-1 Kouto, Sayo-cho, Sayo-gun, Hyogo 679-5198 (Japan); Core Research for Evolutional Science and Technology, Japan Science and Technology Agency, 5-7, Goban-cho, Chiyoda-ku, Tokyo, 102-0076 (Japan); Toyoda, Satoshi [Synchrotron Radiation Research Organization, The University of Tokyo, 1-1-1 Kouto, Sayo-cho, Sayo-gun, Hyogo 679-5198 (Japan) [Synchrotron Radiation Research Organization, The University of Tokyo, 1-1-1 Kouto, Sayo-cho, Sayo-gun, Hyogo 679-5198 (Japan); Core Research for Evolutional Science and Technology, Japan Science and Technology Agency, 5-7, Goban-cho, Chiyoda-ku, Tokyo, 102-0076 (Japan); Kurosumi, Shodai; Shinohara, Toshihiro [Department of Applied Chemistry, Graduate School of Engineering, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656 (Japan)] [Department of Applied Chemistry, Graduate School of Engineering, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656 (Japan); Fukidome, Hirokazu; Suemitsu, Maki [Research Institute of Electrical Communication, Tohoku University, 2-1-1 Katahira, Aoba-ku, Sendai 980-8577 (Japan)] [Research Institute of Electrical Communication, Tohoku University, 2-1-1 Katahira, Aoba-ku, Sendai 980-8577 (Japan); Nagashio, Kosuke; Toriumi, Akira [Department of Materials Engineering, Graduate School of Engineering, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656 (Japan)] [Department of Materials Engineering, Graduate School of Engineering, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656 (Japan)

    2013-06-17

    Nanoscale spectromicroscopic characterizing technique is indispensable for realization of future high-speed graphene transistors. Highly spatially resolved soft X-ray photoelectron microscopy measurements have been performed using our '3D nano-ESCA' (three-dimensional nanoscale electron spectroscopy for chemical analysis) equipment in order to investigate the local electronic states at interfaces in a graphene device structure. We have succeeded in detecting a charge transfer region at the graphene/metal-electrode interface, which extends over {approx}500 nm with the energy difference of 60 meV. Moreover, a nondestructive depth profiling reveals the chemical properties of the graphene/SiO{sub 2}-substrate interface.

  4. Optically enhanced charge transfer between C60 and single-wall carbon nanotubes in hybrid electronic devices.

    PubMed

    Allen, Christopher S; Liu, Guoquan; Chen, Yabin; Robertson, Alex W; He, Kuang; Porfyrakis, Kyriakos; Zhang, Jin; Briggs, G Andrew D; Warner, Jamie H

    2014-01-01

    In this article we probe the nature of electronic interactions between the components of hybrid C60-carbon nanotube structures. Utilizing an aromatic mediator we selectively attach C60 molecules to carbon nanotube field-effect transistor devices. Structural characterization via atomic force and transmission electron microscopy confirm the selectivity of this attachment. Charge transfer from the carbon nanotube to the C60 molecules is evidenced by a blue shift of the Raman G(+) peak position and increased threshold voltage of the transistor transfer characteristics. We estimate this charge transfer to increase the device density of holes per unit length by up to 0.85 nm(-1) and demonstrate further optically enhanced charge transfer which increases the hole density by an additional 0.16 nm(-1). PMID:24241690

  5. Dipole-Bound Anions Supported by ChargeTransfer Interaction: Anionic

    E-print Network

    Simons, Jack

    2 1 Department of Chemistry, University of Gdan´sk, Sobieskiego 18, 80-952 Gdan´sk, Poland 2 Henry Eyring Center for Theoretical Chemistry, Department of Chemistry, University of Utah, Salt Lake City, UT

  6. Charge Density Quantification of Polyelectrolyte Polysaccharides by Conductometric Titration: An Analytical Chemistry Experiment

    ERIC Educational Resources Information Center

    Farris, Stefano; Mora, Luigi; Capretti, Giorgio; Piergiovanni, Luciano

    2012-01-01

    An easy analytical method for determination of the charge density of polyelectrolytes, including polysaccharides and other biopolymers, is presented. The basic principles of conductometric titration, which is used in the pulp and paper industry as well as in colloid and interface science, were adapted to quantify the charge densities of a…

  7. Investigating photoinduced charge transfer in double- and single-emission PbS@CdS core@shell quantum dots.

    PubMed

    Zhao, Haiguang; Liang, Hongyan; Gonfa, Belete Atomsa; Chaker, Mohamed; Ozaki, Tsuneyuki; Tijssen, Peter; Vidal, François; Ma, Dongling

    2014-01-01

    We present for the first time detailed investigation of the charge transfer behavior of PbS@CdS core@shell quantum dots (QDs) showing either a single emission peak from the core or intriguing double emission peaks from the core and shell, respectively. A highly non-concentric core@shell structure model was proposed to explain the origin of double emissions from monodisperse QDs. Their charge transfer behavior was investigated by monitoring photoluminescence (PL) intensity variation with the introduction of electron or hole scavengers. It was found that the PL quenching of the PbS core is more efficient than that of the CdS shell, suggesting more efficient charge transfer from the core to scavengers, although the opposite was expected. Further measurements of the PL lifetime followed by wave function calculations disclosed that the time scale is the critical factor explaining the more efficient charge transfer from the core than from the shell. The charge transfer behavior was also examined on a series of single-emission core@shell QDs with either different core sizes or different shell thicknesses and dominant factors were identified. Towards photovoltaic applications, these PbS@CdS QDs were attached onto multi-walled carbon nanotubes (MWCNTs) and their charge transfer behavior was compared with that in the PbS-QD/MWCNT system. Results demonstrate that although the CdS shell serves as an electron transfer barrier, the electrons excited in the PbS cores can still be transferred into the MWCNTs efficiently when the shell thickness is ?0.7 nm. Considering their higher stability, these core@shell QDs are very promising for the development of highly efficient QD-based photovoltaic devices. PMID:24132400

  8. Charge Transfer in Single Chains of a Donor-Acceptor Conjugated Tri-Block Copolymer.

    PubMed

    Hooley, Emma N; Jones, David J; Greenham, Neil C; Ghiggino, Kenneth P; Bell, Toby D M

    2015-06-18

    The photophysics of a conjugated triblock copolymer comprising poly(9,9-dioctylfluorene-co-bis-N,N'-(4-methylphenyl)-bis-N,N'-phenyl-1,4-phenylenediamine) (PFM) electron donor and poly(4-(9,9-dioctyl-9H-fluoren-2-yl)benzo[c][1,2,5]-thiadiazole) (F8BT) electron acceptor blocks has been studied in solution, in films, and as single chains. While an additional long-wavelength emission apparent in neat films of the copolymer is attributed to interchain exciplex formation, no such long-wavelength emission is apparent in solution or from single molecules. However, in these cases, time-resolved fluorescence measurements indicate the presence of a delayed fluorescence. The kinetics of the delayed emission can be interpreted in terms of an equilibrium between a locally excited and a charge-transfer state at the interface of the copolymer block components. Rate constants and thermodynamic quantities associated with these processes have been evaluated. The single-molecule results allow the assignment of an intramolecular charge-transfer state in an isolated conjugated block copolymer chain. PMID:25417793

  9. Lead-iodide nanowire perovskite with methylviologen showing interfacial charge-transfer absorption: a DFT analysis.

    PubMed

    Fujisawa, Jun-ichi; Giorgi, Giacomo

    2014-09-01

    Methylviologen lead-iodide perovskite (MVPb2I6) is a self-assembled one-dimensional (1-D) material consisting of lead-iodide nanowires and intervening organic electron-accepting molecules, methylviologen (MV(2+)). MVPb2I6 characteristically shows optical interfacial charge-transfer (ICT) transitions from the lead-iodide nanowire to MV(2+) in the visible region and unique ambipolar photoconductivity, in which electrons are transported through the three-dimensional (3-D) organic network and holes along the 1-D lead-iodide nanowire. In this work, we theoretically study the electronic band-structure and photocarrier properties of MVPb2I6 by density functional theory (DFT) calculations. Our results clearly confirm the experimentally reported type-II band alignment, whose valence band mainly consists of 5p (I) orbitals of the lead-iodide nanowires and the conduction band of the lowest unoccupied molecular orbital of MV(2+). The DFT calculation also reveals weak charge-transfer interactions between the lead-iodide nanowires and MV(2+). In addition, the electronic distributions of the valence and conduction bands indicate the 3-D transport of electrons and 1-D transport of holes, supporting the reported experimental result. PMID:25050419

  10. Inelastic vibrational processes in charge transfers between H/D and molecular ions

    NASA Astrophysics Data System (ADS)

    Heczko, Sarah L.; Bacani, Kieffer G.; Strom, Richard A.; Andrianarijaona, Vola M.; Seely, David G.; Havener, Charles C.

    2014-03-01

    Charge transfer on molecule proceeds through dynamically coupled electronic, vibrational, and rotational degrees of freedom. The inelastic vibrational processes, which go along with the reaction, can be experimentally investigated by using H/D systems, which do not allow multi-electron capture. Using the upgraded ion-atom merged-beams apparatus at Oak Ridge National Laboratory, absolute direct charge transfer cross sections for H2+, D2+, CO+, O2+, and H3+ are measured from keV/u collision energies where the collision is considered ``ro-vibrationally frozen'' to few eV/u energies where collision times are long enough to sample vibrational modes. The measurements presented here benchmark high energy theory and vibrationally specific adiabatic theory (V. M. Andrianarijaona et al., Phys. Rev. A 84, 062716, 2011). Research supported by the NASA Solar & Heliospheric Physics Program NNH07ZDA001N, the Office of Fusion Energy Sciences and Division of Chemical Sciences, Geosciences, and Biosciences, the Office of Basic Energy Sciences of the US Department of Energy. VA et al. is supported by the National Science Foundation through Grant No. PHY-106887.

  11. Colossal negative thermal expansion in BiNiO3 induced by intermetallic charge transfer.

    PubMed

    Azuma, Masaki; Chen, Wei-tin; Seki, Hayato; Czapski, Michal; Olga, Smirnova; Oka, Kengo; Mizumaki, Masaichiro; Watanuki, Tetsu; Ishimatsu, Naoki; Kawamura, Naomi; Ishiwata, Shintaro; Tucker, Matthew G; Shimakawa, Yuichi; Attfield, J Paul

    2011-01-01

    The unusual property of negative thermal expansion is of fundamental interest and may be used to fabricate composites with zero or other controlled thermal expansion values. Here we report that colossal negative thermal expansion (defined as linear expansion <-10(-4) K(-1) over a temperature range ~100 K) is accessible in perovskite oxides showing charge-transfer transitions. BiNiO(3) shows a 2.6% volume reduction under pressure due to a Bi/Ni charge transfer that is shifted to ambient pressure through lanthanum substitution for Bi. Changing proportions of coexisting low- and high-temperature phases leads to smooth volume shrinkage on heating. The crystallographic linear expansion coefficient for Bi(0.95)La(0.05)NiO(3) is -137×10(-6) K(-1) and a value of -82×10(-6) K(-1) is observed between 320 and 380 K from a dilatometric measurement on a ceramic pellet. Colossal negative thermal expansion materials operating at ambient conditions may also be accessible through metal-insulator transitions driven by other phenomena such as ferroelectric orders. PMID:21673668

  12. Observation of excited state charge transfer with fs/ps-CARS

    SciTech Connect

    Blom, Alex Jason

    2009-08-01

    Excited state charge transfer processes are studied using the fs/ps-CARS probe technique. This probe allows for multiplexed detection of Raman active vibrational modes. Systems studied include Michler's Ketone, Coumarin 120, 4-dimethylamino-4{prime}-nitrostilbene, and several others. The vibrational spectrum of the para di-substituted benzophenone Michler's Ketone in the first excited singlet state is studied for the first time. It is found that there are several vibrational modes indicative of structural changes of the excited molecule. A combined experimental and theoretical approach is used to study the simplest 7-amino-4-methylcoumarin, Coumarin 120. Vibrations observed in FTIR and spontaneous Raman spectra are assigned using density functional calculations and a continuum solvation model is used to predict how observed modes are affected upon inclusion of a solvent. The low frequency modes of the excited state charge transfer species 4-dimethylamino-4{prime}-nitrostilbene are studied in acetonitrile. Results are compared to previous work on this molecule in the fingerprint region. Finally, several partially completed projects and their implications are discussed. These include the two photon absorption of Coumarin 120, nanoconfinement in cyclodextrin cavities and sensitization of titania nanoparticles.

  13. Empirical Corrections for Charge Transfer Inefficiency and Associated Centroid Shifts for STIS CCD Observations

    E-print Network

    Paul Goudfrooij; Ralph C. Bohlin; Jesus Maiz-Apellaniz; Randy A. Kimble

    2007-03-02

    A variety of on-orbit imaging and spectroscopic observations are used to characterize the Charge Transfer Efficiency (CTE) of the Charge-Coupled Device (CCD) of the Space Telescope Imaging Spectrograph (STIS) aboard the Hubble Space Telescope. A set of formulae is presented to correct observations of point sources for CTE-related loss of signal. For data taken in imaging mode, the CTE loss is parametrized in terms of the location of the source on the CCD, the source signal level within the measurement aperture, the background level, and the time of observation. For spectroscopic data, it is found that one additional parameter is needed to provide an adequate calibration of the CTE loss, namely the signal in the point spread function located between the signal extraction box and the read-out amplifier. The effect of the latter parameter is significant for spectra taken using the G750L or G750M gratings of STIS. The algorithms presented here correct flux calibration inaccuracies due to CTE losses as large as 30% to within ~ 1.5% RMS throughout the wavelength range covered by the STIS CCD modes. This uncertainty is similar to the Poisson noise associated with a source detected at a signal level of about 2500 electrons per resolution element. Using bi-directional CCD readouts, centroid shifts incurred due to CTE loss are also derived. A tight correlation is found between the CTE loss and the centroid shift (both for imaging and spectroscopic modes), thus enabling one to correct for both effects of imperfect charge transfer to STIS CCD observations.

  14. Simulation of charge transfer and orbital rehybridization in molecular and condensed matter systems

    NASA Astrophysics Data System (ADS)

    Nistor, Razvan A.

    The mixing and shifting of electronic orbitals in molecules, or between atoms in bulk systems, is crucially important to the overall structure and physical properties of materials. Understanding and accurately modeling these orbital interactions is of both scientific and industrial relevance. Electronic orbitals can be perturbed in several ways. Doping, adding or removing electrons from systems, can change the bond-order and the physical properties of certain materials. Orbital rehybridization, driven by either thermal or pressure excitation, alters the short-range structure of materials and changes their long-range transport properties. Macroscopically, during bond formation, the shifting of electronic orbitals can be interpreted as a charge transfer phenomenon, as electron density may pile up around, and hence, alter the effective charge of, a given atom in the changing chemical environment. Several levels of theory exist to elucidate the mechanisms behind these orbital interactions. Electronic structure calculations solve the time-independent Schrodinger equation to high chemical accuracy, but are computationally expensive and limited to small system sizes and simulation times. Less fundamental atomistic calculations use simpler parameterized functional expressions called force-fields to model atomic interactions. Atomistic simulations can describe systems and time-scales larger and longer than electronic-structure methods, but at the cost of chemical accuracy. In this thesis, both first-principles and phenomenological methods are addressed in the study of several encompassing problems dealing with charge transfer and orbital rehybridization. Firstly, a new charge-equilibration method is developed that improves upon existing models to allow next-generation force-fields to describe the electrostatics of changing chemical environments. Secondly, electronic structure calculations are used to investigate the doping dependent energy landscapes of several high-temperature superconducting materials in order to parameterize the apparently large nonlinear electron-phonon coupling. Thirdly, ab initio simulations are used to investigate the role of pressure-driven structural re-organization in the crystalline-to-amorphous (or, metallic-to-insulating) transition of a common binary phase-change material composed of Ge and Sb. Practical applications of each topic will be discussed. Keywords. Charge-equilibration methods, molecular dynamics, electronic structure calculations, ab initio simulations, high-temperature superconductors, phase-change materials.

  15. Competition between covalent bonding and charge transfer tendencies at complex-oxides interfaces

    NASA Astrophysics Data System (ADS)

    Salafranca, J.; Tornos, J.; García-Barriocanal, J.; León, C.; Santamaria, J.; Rincón, J.; Álvarez, G.; Pennycook, S. J.; Dagotto, E.; Varela, M.

    2013-03-01

    Interfaces alter the subtle balance among different degrees of freedom responsible for exotic phenomena in complex oxides, such as cuprate-manganite interfaces. We study these interfaces by means of scanning transmission electron microscopy and theoretical calculations. Microscopy and EEL spectroscopy indicate that the interfaces are sharp, and the chemical profile is symmetric with two equivalent interfaces. Spectroscopy also allows us to establish an oxidation state profile with sub-nanometer resolution. We find an anomalous charge redistribution: a non-monotonic behavior of the occupancy of d orbitals in the manganite layers as a function of distance to the interface. Relying on model calculations, we establish that this profile is a result of the competition between standard charge transfer tendencies involving materials with different chemical potentials and strong bonding effects across the interface. The competition can be tuned by different factors (temperature, doping, magnetic fields...). As examples, we report different charge distributions as a function of doping of the manganite layers. ACKNOWLEDGEMENTS ORNL:U.S. DOE-BES, Material Sciences and Engineering Division & ORNL's ShaRE. UCM:Juan de la Cierva, Ramon y Cajal, & ERC Starting Investigator Award programs.

  16. Modeling the electrical conduction in DNA nanowires: Charge transfer and lattice fluctuation theories

    NASA Astrophysics Data System (ADS)

    Behnia, S.; Fathizadeh, S.

    2015-02-01

    An analytical approach is proposed for the investigation of the conductivity properties of DNA. The charge mobility of DNA is studied based on an extended Peyrard-Bishop-Holstein model when the charge carrier is also subjected to an external electrical field. We have obtained the values of some of the system parameters, such as the electron-lattice coupling constant, by using the mean Lyapunov exponent method. On the other hand, the electrical current operator is calculated directly from the lattice operators. Also, we have studied Landauer resistance behavior with respect to the external field, which could serve as the interface between chaos theory tools and electronic concepts. We have examined the effect of two types of electrical fields (dc and ac) and variation of the field frequency on the current flowing through DNA. A study of the current-voltage (I -V ) characteristic diagram reveals regions with a (quasi-)Ohmic property and other regions with negative differential resistance (NDR). NDR is a phenomenon that has been observed experimentally in DNA at room temperature. We have tried to study the affected agents in charge transfer phenomena in DNA to better design nanostructures.

  17. Microgravity and Charge Transfer in the Neuronal Membrane: Implications for Computational Neurobiology

    NASA Technical Reports Server (NTRS)

    Wallace, Ron

    1995-01-01

    Evidence from natural and artificial membranes indicates that the neural membrane is a liquid crystal. A liquid-to-gel phase transition caused by the application of superposed electromagnetic fields to the outer membrane surface releases spin-correlated electron pairs which propagate through a charge transfer complex. The propagation generates Rydberg atoms in the lipid bilayer lattice. In the present model, charge density configurations in promoted orbitals interact as cellular automata and perform computations in Hilbert space. Due to the small binding energies of promoted orbitals, their automata are highly sensitive to microgravitational perturbations. It is proposed that spacetime is classical on the Rydberg scale, but formed of contiguous moving segments, each of which displays topological equivalence. This stochasticity is reflected in randomized Riemannian tensor values. Spacetime segments interact with charge automata as components of a computational process. At the termination of the algorithm, an orbital of high probability density is embedded in a more stabilized microscopic spacetime. This state permits the opening of an ion channel and the conversion of a quantum algorithm into a macroscopic frequency code.

  18. Polarization effects and charge transfer in the KcsA potassium channel.

    PubMed

    Bucher, Denis; Raugei, Simone; Guidoni, Leonardo; Dal Peraro, Matteo; Rothlisberger, Ursula; Carloni, Paolo; Klein, Michael L

    2006-12-01

    The electronic structure of the selectivity filter of KcsA K(+) channel is investigated by density functional theory (DFT/BLYP) and QM/MM methods. The quantum part includes the selectivity filter, which is polarized by the electrostatic field of the environment treated with the Amber force field. The details of the electronic structure were investigated using the maximally localized Wannier function centers of charge and Bader's atoms in molecules charge analysis. Our results show that the channel backbone carbonyl groups are largely polarized and that there is a sizeable charge transfer from the backbone to the cations. These effects are expected to be important for an accurate description of the carbonyl groups and the ion-ion electrostatic repulsion, which have been proposed to play a central role for the selectivity mechanism of the channel [S.Y. Noskov, S. Berneche, B. Roux, Control of ion selectivity in potassium channels by electrostatic and dynamic properties of carbonyl ligands. Nature 431 (2004) 830-834]. PMID:16737771

  19. Quantum effects in energy and charge transfer in an artificial photosynthetic complex

    SciTech Connect

    Ghosh, Pulak Kumar [Advanced Science Institute, RIKEN, Wako, Saitama 351-0198 (Japan); Smirnov, Anatoly Yu.; Nori, Franco [Advanced Science Institute, RIKEN, Wako, Saitama 351-0198 (Japan); Physics Department, University of Michigan, Ann Arbor, Michigan 41109-1040 (United States)

    2011-06-28

    We investigate the quantum dynamics of energy and charge transfer in a wheel-shaped artificial photosynthetic antenna-reaction center complex. This complex consists of six light-harvesting chromophores and an electron-acceptor fullerene. To describe quantum effects on a femtosecond time scale, we derive the set of exact non-Markovian equations for the Heisenberg operators of this photosynthetic complex in contact with a Gaussian heat bath. With these equations we can analyze the regime of strong system-bath interactions, where reorganization energies are of the order of the intersite exciton couplings. We show that the energy of the initially excited antenna chromophores is efficiently funneled to the porphyrin-fullerene reaction center, where a charge-separated state is set up in a few picoseconds, with a quantum yield of the order of 95%. In the single-exciton regime, with one antenna chromophore being initially excited, we observe quantum beatings of energy between two resonant antenna chromophores with a decoherence time of {approx}100 fs. We also analyze the double-exciton regime, when two porphyrin molecules involved in the reaction center are initially excited. In this regime we obtain pronounced quantum oscillations of the charge on the fullerene molecule with a decoherence time of about 20 fs (at liquid nitrogen temperatures). These results show a way to directly detect quantum effects in artificial photosynthetic systems.

  20. How well can Charge Transfer Inefficiency be corrected? A parameter sensitivity study for iterative correction

    E-print Network

    Israel, Holger; Prod'homme, Thibaut; Cropper, Mark; Cordes, Oliver; Gow, Jason; Kohley, Ralf; Marggraf, Ole; Niemi, Sami; Rhodes, Jason; Short, Alex; Verhoeve, Peter

    2015-01-01

    Radiation damage to space-based Charge-Coupled Device (CCD) detectors creates defects which result in an increasing Charge Transfer Inefficiency (CTI) that causes spurious image trailing. Most of the trailing can be corrected during post-processing, by modelling the charge trapping and moving electrons back to where they belong. However, such correction is not perfect -- and damage is continuing to accumulate in orbit. To aid future development, we quantify the limitations of current approaches, and determine where imperfect knowledge of model parameters most degrade measurements of photometry and morphology. As a concrete application, we simulate $1.5\\times10^{9}$ "worst case" galaxy and $1.5\\times10^{8}$ star images to test the performance of the Euclid visual instrument detectors. There are two separable challenges: If the model used to correct CTI is perfectly the same as that used to add CTI, $99.68$ % of spurious ellipticity is corrected in our setup. This is because readout noise is not subject to CTI,...

  1. A charge transfer inefficiency correction model for the Chandra Advanced CCD Imaging Spectrometer

    E-print Network

    C. E. Grant; M. W. Bautz; S. M. Kissel; B. LaMarr

    2004-07-09

    Soon after launch, the Advanced CCD Imaging Spectrometer (ACIS), one of the focal plane instruments on the Chandra X-ray Observatory, suffered radiation damage from exposure to soft protons during passages through the Earth's radiation belts. The primary effect of the damage was to increase the charge transfer inefficiency (CTI) of the eight front illuminated CCDs by more than two orders of magnitude. The ACIS instrument team is continuing to study the properties of the damage with an emphasis on developing techniques to mitigate CTI and spectral resolution degradation. We will discuss the characteristics of the damage, the detector and the particle background and how they conspire to degrade the instrument performance. We have developed a model for ACIS CTI which can be used to correct each event and regain some of the lost performance. The correction uses a map of the electron trap distribution, a parameterization of the energy dependent charge loss and the fraction of the lost charge re-emitted into the trailing pixel to correct the pixels in the event island. This model has been implemented in the standard Chandra data processing pipeline. Some of the correction algorithm was inspired by the earlier work on ACIS CTI correction by Townsley et al. (2000; 2002). The details of the CTI model and how each parameter improves performance will be discussed, as well as the limitations and the possibilities for future improvement.

  2. Photophysical investigations on supramolecular fullerene/phthalocyanine charge transfer interactions in solution

    NASA Astrophysics Data System (ADS)

    Ray, Anamika; Pal, Haridas; Bhattacharya, Sumanta

    2014-01-01

    The photophysical features of non-covalently linked fullerenes C60 and C70 with a designed free-base phthalocyanine, namely, 2,3,9,10,16,17,23,24-octakis-(octyloxy)-29H,31H-phthalocyanine (1) have been investigated employing various spectroscopic tools like UV-vis absorption spectrophotometry, steady state and time resolved fluorescence along with proton NMR measurements in toluene. The ground state interaction between fullerenes and 1 is nicely demonstrated with the appearance of well defined charge transfer absorption bands in the visible region of the electronic spectra. Steady state fluorescence experiment reveals efficient quenching of the excited singlet state of 1 in presence of both C60 and C70. The average values of binding constants for the non-covalent complexes of C60 and C70 with 1 are determined to be ?18,150 and ?32,000 dm3 mol-1, respectively. The magnitude of K suggests that 1 preferentially binds C70 in comparison to C60 although average value of selectivity in binding is measured to be low (?1.75). Time resolved emission measurements establish photoinduced energy transfer from the excited singlet state of 1 to fullerene in toluene. Measurements of free energy of electron transfer and free energy of radical ion-pair formation elicit that C70/1 complex is stabilized more in comparison to C60/1 complex regarding generation of charge-separated state. Proton NMR studies provide very good support in favor of effective ground state complexation between fullerenes and 1. Semi empirical theoretical calculations on fullerene/1 systems in vacuo substantiate the stronger binding between C70 and 1 in comparison to C60/1 system in terms of heat of formation value of the respective complexes, and determine the orientation of bound guest (here C70) towards the plane of 1 during complexation.

  3. Magneto-Dielectric Effects Induced by Optically-Generated Intermolecular Charge-Transfer States in Organic Semiconducting Materials

    PubMed Central

    Zang, Huidong; Yan, Liang; Li, Mingxing; He, Lei; Gai, Zheng; Ivanov, Ilia; Wang, Min; Chiang, Long; Urbas, Augustine; Hu, Bin

    2013-01-01

    Traditionally, magneto-dielectric effects have been developed by combining ferroelectric and magnetic materials. Here, we show a magneto-dielectric effect from optically-generated intermolecular charge-transfer states in an organic semiconducting donor:acceptor (PVK:TCNB) system. We observe in magnetic field effects of photoluminescence that a magnetic field can change singlet/triplet population ratio in intermolecular charge-transfer states. Furthermore, our theoretical analysis and experimental evidence indicate that the singlets and triplets in charge-transfer states have stronger and weaker electrical polarizations, respectively. Therefore, the observed magneto-dielectric effect can be attributed to magnetically-dependent singlet/triplet ratio in intermolecular charge-transfer states. In principle, a magneto-dielectric effect can be generated through two different channels based on magneto-polarization and magneto-current effects when the singlet/triplet ratio in intermolecular charge-transfer states is changed by a magnetic field. We find, from the simulation of dielectric effects, that magneto-polarization and magneto-current effects play primary and secondary roles in the generation of magneto-dielectric effect. PMID:24084983

  4. Mechanism of charge transfer and its impacts on Fermi-level pinning for gas molecules adsorbed on monolayer WS2.

    PubMed

    Zhou, Changjie; Yang, Weihuang; Zhu, Huili

    2015-06-01

    Density functional theory calculations were performed to assess changes in the geometric and electronic structures of monolayer WS2 upon adsorption of various gas molecules (H2, O2, H2O, NH3, NO, NO2, and CO). The most stable configuration of the adsorbed molecules, the adsorption energy, and the degree of charge transfer between adsorbate and substrate were determined. All evaluated molecules were physisorbed on monolayer WS2 with a low degree of charge transfer and accept charge from the monolayer, except for NH3, which is a charge donor. Band structure calculations showed that the valence and conduction bands of monolayer WS2 are not significantly altered upon adsorption of H2, H2O, NH3, and CO, whereas the lowest unoccupied molecular orbitals of O2, NO, and NO2 are pinned around the Fermi-level when these molecules are adsorbed on monolayer WS2. The phenomenon of Fermi-level pinning was discussed in light of the traditional and orbital mixing charge transfer theories. The impacts of the charge transfer mechanism on Fermi-level pinning were confirmed for the gas molecules adsorbed on monolayer WS2. The proposed mechanism governing Fermi-level pinning is applicable to the systems of adsorbates on recently developed two-dimensional materials, such as graphene and transition metal dichalcogenides. PMID:26049513

  5. Mechanism of charge transfer and its impacts on Fermi-level pinning for gas molecules adsorbed on monolayer WS2

    NASA Astrophysics Data System (ADS)

    Zhou, Changjie; Yang, Weihuang; Zhu, Huili

    2015-06-01

    Density functional theory calculations were performed to assess changes in the geometric and electronic structures of monolayer WS2 upon adsorption of various gas molecules (H2, O2, H2O, NH3, NO, NO2, and CO). The most stable configuration of the adsorbed molecules, the adsorption energy, and the degree of charge transfer between adsorbate and substrate were determined. All evaluated molecules were physisorbed on monolayer WS2 with a low degree of charge transfer and accept charge from the monolayer, except for NH3, which is a charge donor. Band structure calculations showed that the valence and conduction bands of monolayer WS2 are not significantly altered upon adsorption of H2, H2O, NH3, and CO, whereas the lowest unoccupied molecular orbitals of O2, NO, and NO2 are pinned around the Fermi-level when these molecules are adsorbed on monolayer WS2. The phenomenon of Fermi-level pinning was discussed in light of the traditional and orbital mixing charge transfer theories. The impacts of the charge transfer mechanism on Fermi-level pinning were confirmed for the gas molecules adsorbed on monolayer WS2. The proposed mechanism governing Fermi-level pinning is applicable to the systems of adsorbates on recently developed two-dimensional materials, such as graphene and transition metal dichalcogenides.

  6. Radiation-induced charge transfer inefficiency in charge-coupled devices: Sentinel-4 CCD pre-development as a case study

    NASA Astrophysics Data System (ADS)

    Prod'homme, T.; Belloir, J.-M.; Weber, H.; Bazalgette Courrèges-Lacoste, G.; Meynart, R.; Nowicki-Bringuier, Y.-R.; Caron, J.; Levillain, Y.; Woffinden, C.; Lord, B.; Mackie, R.

    2014-10-01

    Energetic particles in space damage electronic components, and in particular affect the capability of Charge-Coupled Devices (CCD) to transfer photo-generated charge packets to the output node. If not properly accounted for either during the instrument design process or in the mission data processing pipeline, radiation-induced Charge Transfer Inefficiency (CTI) causes image distortion, decreases the signal-to-noise ratio, and ultimately leads to bias in the measurement carried out. CTI is a well-identified error budget contributor for mission operating in the photon-starving regime like space telescopes dedicated to Astronomy, but is less studied in the context of Earth Observation missions. We present a study conducted during the Sentinel-4/UVN CCD pre-development to provide a first assessment of the CTI effects on the Sentinel-4 measurements.

  7. New Developments in Charge Transfer Multiplet Calculations: Projection Operations, Mixed-Spin States and pi-Bonding

    SciTech Connect

    de Groot, F.M.F.; /Utrecht U.; Hocking, R.K.; /Stanford U., Chem. Dept.; Piamonteze, C.; /LBL, Berkeley; Hedman, B.; Hodgson, K.O.; Solomon, E.I.; /Stanford U., Chem. Dept.

    2007-01-02

    This paper presents a number of new additions to the charge transfer multiplet calculations as used in the calculation of L edge X-ray absorption spectra of 3d and 4d transition metal systems, both oxides and coordination compounds. The focus of the paper is on the consequences of the optimized spectral simulations for the ground state, where we make use of a recently developed projection technique. This method is also used to develop the concept of a mixed-spin ground state, i.e. a state that is a mixture of a high-spin and low-spin state due to spin-orbit coupling combined with strong covalency. The charge transfer mechanism to describe {pi}-bonding uses the mixing of the metal-to-ligand charge transfer (MLCT) channel in addition to the normal CT channel and allows for the accurate simulation of {pi}-bonding systems, for example cyanides.

  8. Direct Observation and Control of Ultrafast Photoinduced Twisted Intramolecular Charge Transfer (TICT) in Triphenyl-Methane Dyes

    PubMed Central

    Li, Guifeng; Magana, Donny; Dyer, R. Brian

    2012-01-01

    Femtosecond time-resolved infrared spectroscopy was employed to study intramolecular charge transfer in triphenylmethane dyes, including malachite green (MG), malachite green carbinol base (MGCB), and leucomalachite green (LMG). A local excited state (LE) and a twisted intramolecular charge-transfer (TICT) state have been observed directly in MG. Furthermore, solvent-controlled TICT measurements in a series of linear alcohols indicate that the transition time (4–11 ps) from LE to TICT is strongly dependent on alcohol viscosity, which is due to rotational hindrance of dimethylaniline in high-viscosity solvents. For LMG, no TICT is observed due to steric hindrance caused by the sp3-hybridized central carbon atom. However, for MGCB, TICT is rescued by the addition of the electron-donating hydroxyl group to the bridge. These results for MG and its analogues provide new insight regarding the dynamics and mechanism of twisted intramolecular charge transfer (TICT) in triphenylmethane dyes. PMID:23009668

  9. Effect of covalency, zero-point energy and charge transfer on the phase-transition, elastic and thermophysical properties of Ca-chalcogenides under compression

    Microsoft Academic Search

    D. C. Gupta; K. C. Singh

    2010-01-01

    The pressure induced phase-transition, elastic and thermophysical properties of Ca-chalcogenides have been investigated by means of many body potential. The modified charge transfer potential consists of long-range Coulomb and charge-transfer interactions modified by covalency and short-range overlap repulsion extended up to second neighbours and zero-point energy effects. Another charge-transfer model excludes covalency and zero-point energy effects. These chalcogenides undergo first-order

  10. Modelling and Ni/Yttria-Stabilized-Zirconia pattern anode experimental validation of a new charge transfer reactions mechanism for hydrogen electrochemical oxidation on solid oxide fuel cell anodes

    NASA Astrophysics Data System (ADS)

    Yao, Weifang; Croiset, Eric

    2014-02-01

    Good understanding of the H2 electrochemical reaction mechanism helps optimize SOFC anode design and improve its performance. Controversies still exist regarding H2 oxidation mechanism despite extensive studies performed. In this work, a new charge transfer reactions mechanism proposed by Shishkin and Ziegler (2010) based on Density Functional Theory (DFT) study was investigated through kinetic modelling and pattern anode experimental validation. The new charge transfer reactions mechanism considers hydrogen oxidation at the interface of Ni and YSZ. It involves a hydrogen atom reacting with the oxygen ions bound to both Ni and YSZ to produce hydroxyl (Charge transfer reaction 1), the latter reacting with the other hydrogen atom to form water (Charge transfer reaction 2). The predictive capability of this reaction mechanism to represent our experimental results was evaluated. The simulated Tafel plots were compared with our experimental data for a wide range of H2 and H2O partial pressures and at different temperatures. Good agreements between simulation and experimental results were obtained. Charge transfer reaction 1 was found to dominate the overall charge transfer reaction under cathodic polarization. Under anodic polarization, a change in the dominating charge transfer reaction from charge transfer reaction 1 to charge transfer reaction 2 was found when increasing the H2O partial pressure.

  11. On the theory of the coulostatic pulse technique as applied to redox electrodes with two consecutive charge transfer steps

    Microsoft Academic Search

    O. A. Kopistko; M. K. Nauryzbaev

    1998-01-01

    Analysis of the coulostatic pulse technique, as applied to a redox electrode with two consecutive charge-transfer steps, Red-e?=X and X-e?=Ox, under conditions of non-stationary linear semi-infinite diffusion of the reagents Red, Ox and the intermediate X has been carried out. Relaxation equations for the linear current density–overpotential region and for different excitations (coulostatic pulse of a charge, trapezoidal and triangular

  12. Exciton delocalization, charge transfer, and electronic coupling for singlet excitation energy transfer between stacked nucleobases in DNA: An MS-CASPT2 study

    SciTech Connect

    Blancafort, Lluís, E-mail: lluis.blancafort@udg.edu [Institut de Química Computacional i Catàlisi (IQCC) and Departament de Química, Universitat de Girona, Campus de Montilivi, 17071 Girona (Spain)] [Institut de Química Computacional i Catàlisi (IQCC) and Departament de Química, Universitat de Girona, Campus de Montilivi, 17071 Girona (Spain); Voityuk, Alexander A., E-mail: alexander.voityuk@icrea.cat [Institut de Química Computacional i Catàlisi (IQCC) and Departament de Química, Universitat de Girona, Campus de Montilivi, 17071 Girona (Spain); Institució Catalana de Recerca i Estudis Avançats (ICREA), Barcelona 08010 (Spain)

    2014-03-07

    Exciton delocalization and singlet excitation energy transfer have been systematically studied for the complete set of 16 DNA nucleobase dimers in their ideal, single-strand stacked B-DNA conformation, at the MS-CASPT2 level of theory. The extent of exciton delocalization in the two lowest (?,?{sup *}) states of the dimers is determined using the symmetrized one-electron transition density matrices between the ground and excited states, and the electronic coupling is calculated using the delocalization measure and the energy splitting between the states [see F. Plasser, A. J. A. Aquino, W. L. Hase, and H. Lischka, J. Phys. Chem. A 116, 11151–11160 (2012)]. The calculated couplings lie between 0.05 eV and 0.14 eV. In the B-DNA conformation, where the interchromophoric distance is 3.38 Å, our couplings deviate significantly from those calculated with the transition charges, showing the importance of orbital overlap components for the couplings in this conformation. The calculation of the couplings is based on a two-state model for exciton delocalization. However, in three stacks with a purine in the 5{sup ?} position and a pyrimidine in the 3{sup ?} one (AT, GC, and GT), there is an energetically favored charge transfer state that mixes with the two lowest excited states. In these dimers we have applied a three-state model that considers the two locally excited diabatic states and the charge transfer state. Using the delocalization and charge transfer descriptors, we obtain all couplings between these three states. Our results are important in the context of DNA photophysics, since the calculated couplings can be used to parametrize effective Hamiltonians to model extended DNA stacks. Our calculations also suggest that the 5{sup ?}-purine-pyrimidine-3{sup ?} sequence favors the formation of charge transfer excited states.

  13. Photoinitiated charge separation in a carotenoid-porphyrin-diquinone tetra: enhanced quantum yields via multistep electron transfers

    SciTech Connect

    Gust, D.; Moore, T.A.; Moore, A.L.; Barrett, D.; Harding, L.O.; Makings, L.R.; Liddell, P.A.; De Schryver, F.C.; Van der Auweraer, M.; Bensasson, R.; Rougee, M.

    1988-01-06

    Photosynthesis converts light to chemical potential energy in the form of long-lived charge separation across a bilayer membrane. Recombination of the charge-separated state is prevented by the large distance between the final electron donor and acceptor. Because the quantum yield of a single long-range electron transfer across the bilayer would be vanishingly small, reaction centers employ a series of electron-transfer steps, each of which occurs over a short distance with high yield. Synthetic carotenoid-porphyrin-quinone triad molecules and other molecular systems which begin to model this approach have recently been reported. In photosynthetic bacteria, the charge separation sequence includes electron donation from a bacteriopheophytin to a quinone which then transfers an electron to a second quinone. An elegant molecule that models such electron transfer has been prepared, although it did not reproduce the long-lived charge separation characteristic of the natural system. The authors now report the synthesis of a tetrachromophoric molecule 1 consisting of a porphyrin (P) covalently linked to both a carotenoid polyene (C) and a rigid diquinone moiety (Q/sub A/-Q/sub B/), excitation of which produces a long-lived (460 ns in dichloromethane, 4 ..mu..s in acetonitrile charge-separated state C/sup .+/-P-Q/sub A/-Q/sub B//sup 0 -/ with a quantum yield of 0.23 at ambient temperatures and 0.50 at 240 K.

  14. Ab initio molecular treatment for charge transfer by P{sup 3+} ions on hydrogen and helium

    SciTech Connect

    Moussa, A.; Zaidi, A.; Lahmar, S. [Laboratoire de Spectrosopie Atomique, Moleculaire et Applications (LSAMA), Faculte des Sciences de Tunis, Universite Tunis El Manar, Campus Universitaire, TN-1060 Tunis (Tunisia); Bacchus-Montabonel, M.-C. [Laboratoire de Spectrometrie Ionique et Moleculaire, UMR 5579, CNRS et Universite Lyon I, 43 Boulevard du 11 Novembre 1918, F-69622 Villeurbanne Cedex (France)

    2010-02-15

    A theoretical treatment of charge-transfer processes induced by collision of phosphorus P{sup 3+}(3s{sup 2}){sup 1}S ions on atomic hydrogen and helium has been carried out using ab initio potential-energy curves and couplings at the multireference configuration interaction level of theory. The cross sections calculated by means of semiclassical collision methods show the existence of a significant charge transfer in the 0.1-700-keV laboratory energy range. Radial and rotational coupling interactions were analyzed for both collision systems.

  15. Optical spectroscopy of neutral-ionic phase transition in charge-transfer complexes: TTF and Tetrahalo-p-benzoquinones

    Microsoft Academic Search

    Yoichi Okimoto; Sachio Horiuchi; Reiji Kumai; Eiji Saitoh; Yoshinori Tokura

    2001-01-01

    Physical properties of 1:1 mixed stack charge-transfer (CT) crystals have been extensively investigated in recent years. We measured temperature dependencies of infrared reflectivity spectra in typical charge-transfer complexes, tetrathiafulvalene(TTF)-p-chloranil (TTF-CA) and the isostructural analog, TTF-2-bromo-3,5,6-trichloro-p-benzoquinone (TTF-QBrCl_3). With decreasing temperature, the C=O stretching phonon spectrum in TTF-QBrCl3 which is closely related to the degree of CT shows anomalous broadening just above

  16. Photoinduced charge transfer and acetone sensitivity of single-walled carbon nanotube-titanium dioxide hybrids.

    PubMed

    Ding, Mengning; Sorescu, Dan C; Star, Alexander

    2013-06-19

    The unique physical and chemical properties of single-walled carbon nanotubes (SWNTs) make them ideal building blocks for the construction of hybrid nanostructures. In addition to increasing the material complexity and functionality, SWNTs can probe the interfacial processes in the hybrid system. In this work, SWNT-TiO2 core/shell hybrid nanostructures were found to exhibit unique electrical behavior in response to UV illumination and acetone vapors. By experimental and theoretical studies of UV and acetone sensitivities of different SWNT-TiO2 hybrid systems, we established a fundamental understanding on the interfacial charge transfer between photoexcited TiO2 and SWNTs as well as the mechanism of acetone sensing. We further demonstrated a practical application of photoinduced acetone sensitivity by fabricating a microsized room temperature acetone sensor that showed fast, linear, and reversible detection of acetone vapors with concentrations in few parts per million range. PMID:23734594

  17. Charge transfer behavior of graphene-titania photoanode in CO2 photoelectrocatalysis process

    NASA Astrophysics Data System (ADS)

    Hasan, Md. Rakibul; Hamid, Sharifah Bee Abd; Basirun, Wan Jeffrey

    2015-06-01

    In the present study, a graphene-titania composite photoelectrode was synthesized, characterized and examined for the photoelectrocatalytic (PEC) response. The charge transfer process on the semiconductor/electrolyte interface was investigated via electrochemical impedance spectroscopy (EIS) and voltammetry. In addition, the influence of pH toward the photoanode performance was also investigated and it was noticed that a high pH condition was favorable higher photocurrent response from the EIS measurements. The main reason could be attributed to the decrease of recombination process at the photoanode with fast quenching of the photogenerated holes with OH- ions at high pH. The experiment was also run for CO2 photoreduction and increased photocurrent was observed.

  18. Field and chirality effects on electrochemical charge transfer rates: spin dependent electrochemistry.

    PubMed

    Mondal, Prakash Chandra; Fontanesi, Claudio; Waldeck, David H; Naaman, Ron

    2015-03-24

    This work examines whether electrochemical redox reactions are sensitive to the electron spin orientation by examining the effects of magnetic field and molecular chirality on the charge transfer process. The working electrode is either a ferromagnetic nickel film or a nickel film that is coated with an ultrathin (5-30 nm) gold overlayer. The electrode is coated with a self-assembled monolayer that immobilizes a redox couple containing chiral molecular units, either the redox active dye toluidine blue O with a chiral cysteine linking unit or cytochrome c. By varying the direction of magnetization of the nickel, toward or away from the adsorbed layer, we demonstrate that the electrochemical current depends on the orientation of the electrons' spin. In the case of cytochrome c, the spin selectivity of the reduction is extremely high, namely, the reduction occurs mainly with electrons having their spin-aligned antiparallel to their velocity. PMID:25752750

  19. Symmetric charge-transfer cross sections of IIIa rare-earth-metal elements

    SciTech Connect

    Hashida, Masaki; Sakabe, Shuji; Izawa, Yasukazu [ARCBS, Institute for Chemical Research, Kyoto University, Gokasho, Uji, Kyoto 611-0011 (Japan) and Department of Physics, Graduate School of Science, Kyoto University, Kitashirakawa, Sakyo, Kyoto 606-8502 (Japan); Institute of Laser Engineering, Osaka University, Suita, Osaka 565-0871 (Japan) and Institute for Laser Technology, 2-6 Yamadaoka, Suita, Osaka 565-0871 (Japan)

    2011-03-15

    Symmetric charge-transfer cross sections of IIIa rare-earth-metal elements (Sc, Y, and Gd) in the impact energy range of 30 to 1000 eV were measured for the first time. The experiments were performed with a crossed-beam apparatus that featured primary ion production by photoionization with a tunable dye laser. Comparing the cross sections of IIIa rare-earth-metal elements ({sigma}{sub Sc}, {sigma}{sub Y}, and {sigma}{sub Gd}) with those of alkali metals or helium {sigma}{sub 0}, we found that {sigma}{sub 0{approx_equal}{sigma}Sc}<{sigma}{sub Y}<{sigma}{sub Gd{approx_equal}}2{sigma}{sub 0}at an impact energy of 1000 eV.

  20. Interface modification of cathode electrode using dimmethyldicyanoquinonediimine as a charge transfer layer in organic photovoltaic cell.

    PubMed

    So, Byoung Min; Yang, Eui Yeol; Park, Jong Wook; Cho, Jeong Ho; Oh, Se Young

    2012-04-01

    Various metals for the cathode electrode of organic electronic devices have been used in order to improve carrier injection and contact resistance etc. However, metal electrodes have some disadvantages such as rough surfaces, inadequate interfacial durability and unsuitable work functions. In the present work, we have fabricated an organic photovoltaic cell consisting of ITO/PEDOT:PSS/P3HT:PCBM/DMDCNQI/Al. The dimmethyldicyanoquinonediimine (DMDCNQI) compound was used as an organic n-type charge transfer complex between the cathode electrode and an organic active layer to improve contact resistance and electron transport ability. The prepared device shows a high short-circuit current density of 10.39 mA/cm2 and a maximum power conversion efficiency of 3.10%. PMID:22849164

  1. Charge-Transfer induced EUV and Soft X-ray emissions in the Heliosphere

    E-print Network

    D. Koutroumpa; R. Lallement; V. Kharchenko; A. Dalgarno; R. Pepino; V. Izmodenov; E. Quémerais

    2006-09-08

    We study the EUV/soft X-ray emission generated by charge transfer between solar wind heavy ions and interstellar H and He neutral atoms in the inner Heliosphere. We present heliospheric maps and spectra for stationary solar wind, depending on solar cycle phase, solar wind anisotropies and composition, line of sight direction and observer position. A time-dependant simulation of the X-ray intensity variations due to temporary solar wind enhancement is compared to XMM Newton recorded data of the Hubble Deep Field North observation (Snowden et al. 2004). Results show that the heliospheric component can explain a large fraction of the line intensity below 1.3 keV, strongly attenuating the need for soft X-ray emission from the Local Interstellar Bubble.

  2. Vibronic induced one- and two-photon absorption in a charge-transfer stilbene derivate

    NASA Astrophysics Data System (ADS)

    Lin, Na; Zhao, Xian; Rizzo, Antonio; Luo, Yi

    2007-06-01

    Both the electronic and the vibronic contributions to one- and two-photon absorption of a D-?-D charge-transfer molecule (4-dimethylamino-4'-methyl-trans stilbene) are studied by means of density functional response theory combined with a linear coupling model. Vibronic profiles of the first four excited states are fully explored. The dominating vibrational modes for both Franck-Condon and Herzberg-Teller contributions are identified. The Franck-Condon contribution dominates the spectra of first, second, and fourth excited states. The Herzberg-Teller contribution is on the other hand of comparable size for the third excited state, where its inclusion leads to a blueshift with respect to the vertical transition. A similar vibronic coupling behavior is found for both one- and two-photon absorptions.

  3. Determination of magnetic form factors for organic charge-transfer salts: A first-principles investigation

    NASA Astrophysics Data System (ADS)

    Salvat-Pujol, Francesc; Jeschke, Harald O.; Valentí, Roser

    2014-07-01

    Organic charge-transfer salts show a variety of complex phases ranging from antiferromagnetic long-range order, spin liquid, bad metal, or even superconductivity. A powerful method to investigate magnetism is spin-polarized inelastic neutron scattering. However, such measurements have often been hindered in the past by the small size of available crystals as well as by the fact that the spin in these materials is distributed over molecular rather than atomic orbitals, and good estimates for the magnetic form factors are missing. By considering Wannier functions obtained from density-functional theory calculations, we derive magnetic form factors for a number of representative organic molecules. Compared to Cu2+, the form factors |F(q)|2 fall off more rapidly as function of q, reflecting the fact that the spin density is very extended in real space. Form factors |F(q)|2 for TMTTF, BEDT-TTF, and (BEDT-TTF)2 have anisotropic and nonmonotonic structures.

  4. Identifying the magnetoconductance responses by the induced charge transfer complex states in pentacene-based diodes

    NASA Astrophysics Data System (ADS)

    Huang, Wei-Shun; Lee, Tsung-Hsun; Guo, Tzung-Fang; Huang, J. C. A.; Wen, Ten-Chin

    2012-07-01

    We investigate the magnetoconductance (MC) responses in photocurrent, unipolar injection, and bipolar injection regimes in pentacene-based diodes. Both photocurrent and bipolar injection contributed MC responses show large difference in MC line shape, which are attributed to triplet-polaron interaction modulated by the magnetic field dependent singlet fission and the intersystem crossing of the polaron pair, respectively. By blending 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane into pentacene, all the MC responses are suppressed but the MC response at unipolar injection regime is enhanced, which is attributed to the induced charge transfer complex states (CT complex states). This work identify the MC responses between single carrier contributed MC and exciton related MC by the induced CT complex states.

  5. Ultrafast intramolecular charge transfer and dual fluorescence of dimethylamino-substituted triphenylphosphines in polar solvents

    SciTech Connect

    Changenet, P.; Plaza, P.; Martin, M. M.; Meyer, Y. H.; Rettig, W. [Laboratoire de Photophysique Moleculaire du CNRS (UPR 3361), Bat 213, universite Paris-Sud, 91405 Orsay (France); Institute fuer Physikalische und Theoretische Chemie der Humboldt-Universitaet Berlin, Bunsenstr. 1, D-10117 Berlin (Germany)

    1996-04-01

    Dimethylamino-substituted triphenylphosphines show a dual fluorescence in polar solvents. The strong red-shift of the new fluorescence band in solvents of increasing polarity indicates emission from a species of charge transfer character, by analogy with dimethylaminobenzonitrile. In this study, we give evidence for the fast formation of a polar transient species in the first excited state of substituted triphenylphosphines, by picosecond time-resolved fluorescence and transient absorption spectroscopy. The risetime of the long wavelength fluorescence band is slowed down in solvents of decreasing polarity, and when the number of dimethylamino substituents increases. Furthermore, time-resolved transient absorption spectra show the rise of a new transient absorption band in polar solvents which has a profile similar to that of the dimethylaniline cation radical.

  6. Charge-induced distortion and stabilization of surface transfer doped porphyrin films

    SciTech Connect

    Smets, Y.; Stark, C. B.; Wright, C. A.; Pakes, C. I. [Department of Physics, La Trobe University, Bundoora, Victoria 3086 (Australia)] [Department of Physics, La Trobe University, Bundoora, Victoria 3086 (Australia); Lach, S.; Schmitt, F.; Ziegler, C. [Department of Physics and Research Center OPTIMAS, University of Kaiserslautern, 67663 Kaiserslautern (Germany)] [Department of Physics and Research Center OPTIMAS, University of Kaiserslautern, 67663 Kaiserslautern (Germany); Wanke, M. [Institut für Physik, Technische Universität Chemnitz, 09126 Chemnitz (Germany)] [Institut für Physik, Technische Universität Chemnitz, 09126 Chemnitz (Germany); Ley, L. [Department of Physics, La Trobe University, Bundoora, Victoria 3086 (Australia) [Department of Physics, La Trobe University, Bundoora, Victoria 3086 (Australia); Institut für Technische Physik, Universität Erlangen-Nürnberg, 91058 Erlangen (Germany)

    2013-07-28

    The interaction between zinc-tetraphenylporphyrin (ZnTPP) and fullerenes (C{sub 60} and C{sub 60}F{sub 48}) are studied using ultraviolet photoelectron spectroscopy (UPS) and scanning tunneling microscopy (STM). Low temperature STM reveals highly ordered ZnTPP monolayers on Au(111). In contrast to C{sub 60}, a submonolayer coverage of C{sub 60}F{sub 48} results in long-range disorder of the underlying single ZnTPP layer and distortion of individual ZnTPP molecules. This is induced by substantial charge transfer at the organic-organic interface, revealed by the interface energetics from UPS. However, a second layer of ZnTPP prevents C{sub 60}F{sub 48} guests from breaking the self-assembled porphyrin template. This finding is important for understanding the growth behaviour of “bottom-up” functional nanostructures involving strong donor-acceptor heterojunctions in molecular electronics.

  7. Spectroscopic studies of charge transfer complexes between colchicine and some ? acceptors

    NASA Astrophysics Data System (ADS)

    Arslan, Mustafa; Duymus, Hulya

    2007-07-01

    Charge transfer complexes between colchicine as donor and ? acceptors such as tetracyanoethylene (TCNE), 2,3-dichloro-5,6-dicyano- p-benzoquinone (DDQ), p-chloranil ( p-CHL) have been studied spectrophotometrically in dichloromethane at 21 °C. The stoichiometry of the complexes was found to be 1:1 ratio by the Job method between donor and acceptors with the maximum absorption band at a wavelength of 535, 585 and 515 nm. The equilibrium constant and thermodynamic parameters of the complexes were determined by Benesi-Hildebrand and van't Hoff equations. Colchicine in pure form and in dosage form was applied in this study. The formation constants for the complexes were shown to be dependent on the structure of the electron acceptors used.

  8. Enhancement of thermal expansion of organic charge-transfer salts by strong electronic correlations

    NASA Astrophysics Data System (ADS)

    Kokalj, J.; McKenzie, Ross H.

    2015-05-01

    Organic charge-transfer salts exhibit thermal expansion anomalies similar to those found in other strongly correlated electron systems. The thermal expansion can be anisotropic and have a nonmonotonic temperature dependence. We show how these anomalies can arise from electronic effects and be significantly enhanced, particularly at temperatures below 100 K, by strong electronic correlations. For the relevant Hubbard model the thermal expansion is related to the dependence of the entropy on the parameters (t , t', and U ) in the Hamiltonian or the temperature dependence of bond orders and double occupancy. The latter are calculated on finite lattices with the finite-temperature Lanczos method. Although many features seen in experimental data, in both the metallic and Mott insulating phase, are described qualitatively, the calculated magnitude of the thermal expansion is smaller than that observed experimentally.

  9. Optical charge transfer for the dope in GaAs

    SciTech Connect

    Vakulenko, O.V.; Skirda, A.S.; Skryshevskii, V.A.

    1984-05-01

    It is concluded that the chromium dope is amphoteric in behavior on the basis of the spectra, kinetics, and lux-ampere characteristics of the absorption and photoconductivity induced by 1.15-um IR laser radiation in high-resistance specimens of GaAs. It is assumed that the additional IR illumination produces optical charge transfer in the chromium in accordance with Cr/sup 3 +/3d/sup 3/ + h..nu.. ..-->.. Cr/sup 2 +/3d/sup 4/ + Cr/sup 4 +/3d/sup 2/. The photoneutralization of the Cr/sup 4 +/3d/sup 2/ centers is responsible for additional optical-absorption and photoconductivity bands appearing in the long-wave region. The kinetic equations for these centers are solved, which describes the experimental results satisfactorily. It is suggested that chromium may compensate not only shallow donors in GaAs but also shallow acceptors.

  10. The interface between phthalocyanines and PEDOT:PSS: evidence for charge transfer and doping

    NASA Astrophysics Data System (ADS)

    Peisert, H.; Knupfer, M.; Zhang, F.; Petr, A.; Dunsch, L.; Fink, J.

    2004-09-01

    As model systems, differently fluorinated representatives from the family of phthalocyanines (CuPC, CuPCF 4, and CuPCF 16) with different ionization potentials were evaporated onto PEDOT:PSS (mixture of poly-3,4-ethylenedioxy-thiophene (PEDOT) and polystyrenesulfonate (PSS)) thin films, which are often applied as electrode material in (all-)organic semiconductor devices. The electronic interface properties were studied using both core and valence level photoemission spectroscopy. The alignment of the electronic levels of the phthalocyanines on PEDOT:PSS is compared to inert and reactive inorganic substrates. For reactive systems, the direction of the charge transfer depends clearly on both the ionization potential of the organic semiconductor and the work function of the substrate.

  11. Intramolecular charge transfer in pyrromethene laser dyes: photophysical behaviour of PM650.

    PubMed

    López Arbeloa, F; Bañuelos Prieto, J; Martínez Martínez, V; Arbeloa López, T; López Arbeloa, I

    2004-11-12

    Absorption and fluorescence (steady-state and time-correlated) techniques are used to study the photophysical characteristics of the pyrromethene 650 (PM650) dye. The presence of the cyano group at the 8 position considerably shifts the absorption and fluorescence bands to lower energies with respect to other related pyrromethene dyes; this is attributed to the strong electron-acceptor character of the cyano group, as is theoretically confirmed by quantum mechanical methods. The fluorescence properties of PM650 are intensively solvent-dependent. The fluorescence band is shifted to lower energies in polar/protic solutions, and the evolution of the corresponding wavelength with the solvent is analysed by a multicomponent linear regression. The fluorescence quantum yield and the lifetime strongly decrease in polar/protic solvents, which can be ascribed to an extra nonradiative deactivation, via an intramolecular charge-transfer state (ICT state), favoured in polar media. PMID:15580938

  12. Phosphonic Acid Functionalized Asymmetric Phthalocyanines: Synthesis, Modification of Indium Tin Oxide (ITO), and Charge Transfer

    SciTech Connect

    Polaske, Nathan W. [Univ. of Arizona, Tucson, AZ (United States); Lin, Hsiao-Chu [Univ. of Arizona, Tucson, AZ (United States); Tang, Anna [Univ. of Arizona, Tucson, AZ (United States); Mayukh, Mayank [Univ. of Arizona, Tucson, AZ (United States); Oquendo, Luis E. [Univ. of Arizona, Tucson, AZ (United States); Green, John [Univ. of Arizona, Tucson, AZ (United States); Ratcliff, Erin L. [Univ. of Arizona, Tucson, AZ (United States); Armstrong, Neal R. [Univ. of Arizona, Tucson, AZ (United States); Saavedra, S. Scott [Univ. of Arizona, Tucson, AZ (United States); McGrath, Dominic V. [Univ. of Arizona, Tucson, AZ (United States)

    2011-12-20

    Metalated and free-base A?B-type asymmetric phthalocyanines (Pcs) bearing, in the asymmetric quadrant, a flexible alkyl linker of varying chain lengths terminating in a phosphonic acid (PA) group have been synthesized. Two parallel series of asymmetric Pc derivatives bearing aryloxy and arylthio substituents are reported, and their synthesis and characterization through NMR, combustion analysis, and MALDI-MS are described. We also demonstrate the modification of indium tin oxide (ITO) substrates using the PA functionalized asymmetric Pc derivatives and monitoring their electrochemistry. The PA functionalized asymmetric Pcs were anchored to the ITO surface through chemisorption and their electrochemical properties characterized using cyclic voltammetry to investigate the effects of PA structure on the thermodynamics and kinetics of charge transfer. Ionization energies of the modified ITO surfaces were measured using ultraviolet photoemission spectroscopy.

  13. Charge transfer in Fe-doped GaN: The role of the donor

    NASA Astrophysics Data System (ADS)

    Sunay, Ustun; Dashdorj, J.; Zvanut, M. E.; Harrison, J. G.; Leach, J. H.; Udwary, K.

    2014-02-01

    Several nitride-based device structures would benefit from the availability of high quality, large-area, freestanding semi-insulating GaN substrates. Due to the intrinsic n-type nature of GaN, however, the incorporation of compensating centers such as Fe is necessary to achieve the high resistivity required. We are using electron paramagnetic resonance (EPR) to explore charge transfer in 450 um thick GaN:Fe plates to understand the basic mechanisms related to compensation so that the material may be optimized for device applications. The results suggest that the simple model based on one shallow donor and a single Fe level is insufficient to describe compensation. Rather, the observation of the neutral donor and Fe3+ indicates that either the two species are spatially segregated or additional compensating and donor defects must be present.

  14. Synthesis, characterization and biological studies of a charge transfer complex: 2-Aminopyridinium-4-methylbenzenesulfonate

    NASA Astrophysics Data System (ADS)

    Vadivelan, Ganesan; Saravanabhavan, Munusamy; Murugesan, Venkatesan; Sekar, Marimuthu

    2015-06-01

    A single crystal charge transfer (CT) complex, 2-aminopyridinium-4-methylbenzenesulfonate (APTS) was synthesized and recrystallized by slow solvent evaporation solution growth method at room temperature. The complex has been characterized with the elemental analysis, UV-visible, infrared (IR), 1H and 13C nuclear magnetic resonance (NMR) spectra. Thermogravimetric (TG) and differential thermal analysis (DTA) were reported the thermal behaviour of the complex. Single crystal XRD studies showed that the orthorhombic nature of the crystal with space group Pbca. The biological activities of CT complex, such as DNA binding and antioxidant activity has been carried out. The results indicated that the compound could interact with DNA through intercalation and show significant capacity of scavenging with 2,2-diphenyl-2-picryl-hydrazyl (DPPH).

  15. Charge-transfer model for the electronic structure of layered ruthenates

    NASA Astrophysics Data System (ADS)

    Ro?ciszewski, Krzysztof; Ole?, Andrzej M.

    2015-04-01

    Motivated by the earlier experimental results and ab initio studies on the electronic structure of layered ruthenates (Sr2RuO4 and Ca2RuO4 ) we introduce and investigate the multiband d -p charge transfer model describing a single RuO4 layer, similar to the charge transfer model for a single CuO2 plane including apical oxygen orbitals in high Tc cuprates. The present model takes into account nearest-neighbor anisotropic ruthenium-oxygen d -p and oxygen-oxygen p -p hopping elements, crystal-field splittings, and spin-orbit coupling. The intraorbital Coulomb repulsion and Hund's exchange are defined not only at ruthenium but also at oxygen ions. Our results demonstrate that the RuO4 layer cannot be regarded to be a pure ruthenium t2 g system. We examine a different scenario in which ruthenium eg orbitals are partly occupied and highlight the significance of oxygen orbitals. We point out that the predictions of an idealized model based on ionic configuration (with n0=4 +4 ×6 =28 electrons per RuO4 unit) do not agree with the experimental facts for Sr2RuO4 which support our finding that the electron number in the d -p states is significantly smaller. In fact, we find the electron occupation of d and p orbitals for a single RuO4 unit n =28 -x , being smaller by at least 1-1.5 electrons from that in the ionic model and corresponding to self-doping with x ?1.5 .

  16. The role of electronic symmetry in charge-transfer-to-solvent reactions: Quantum nonadiabatic computer simulation of photoexcited sodium anions

    Microsoft Academic Search

    C. Jay Smallwood; Wayne B. Bosma; Ross E. Larsen; Benjamin J. Schwartz

    2003-01-01

    Since charge-transfer-to-solvent (CTTS) reactions represent the simplest class of solvent-driven electron transfer reactions, there has been considerable interest in understanding the solvent motions responsible for electron ejection. The major question that we explore in this paper is what role the symmetry of the electronic states plays in determining the solvent motions that account for CTTS. To this end, we have

  17. A charge transfer complex nematic liquid crystalline gel with high electrical conductivity

    NASA Astrophysics Data System (ADS)

    Bhargavi, R.; Nair, Geetha G.; Krishna Prasad, S.; Majumdar, R.; Bag, Braja G.

    2014-10-01

    We describe the rheological, dielectric and elastic properties of a nematic liquid crystal gel created using an anthrylidene derivative of arjunolic acid, a chiral triterpenoid, obtained from the extracts of the wood of Terminalia arjuna. In this novel gel, having the electron-donor and acceptor components as minority constituents, the gelation and strengthening of charge-transfer complex (CTC) formation are seen to be occurring concomitantly. In addition to being mechanically strong with a large storage modulus, the gel with the maximized CTC exhibits Frank bend elastic constant values that approach nanonewton levels. The highlight of the study is the observation of 4-5 orders of magnitude increase in electrical conductivity for this gel, a value that is higher than even in the CT complexes of 2-d ordered columnar structures. A further important advantage of the present system over the columnar complex is that the high conductivity is seen for ac probing also, and owing to the nematic nature can be switched between its anisotropic limits. Some of these features are ascribed to a specific molecular packing architecture, which reduces the trapping of the charge carriers.

  18. Charge-Transfer Induced Magnetic Field Effects of Nano-Carbon Heterojunctions

    E-print Network

    Qin, Wei; Gong, Maogang; Shastry, Tejas; Hersam, Mark C.; Ren, Shenqiang

    2014-08-22

    SNCT{SzcTNCT{T{kD(E)NCT{S {aS1NCT{SzaS2NEX{S dNCT{T dt ~bL 3 4 n{nz{cTNCT{TzcSNCT{S{kD(E)NCT{T {aT1NCT{TzaT2NEX{T dNEX{S dt ~aS1NCT{S{aS2NEX{S dNEX{T dt ~aT1NCT{T{aT2NEX{T{kTNEX{T ð1Þ Electron (hole) density n2(n1) is determined by three parts: recom- bination (b...L), dissociation of charge-transfers (kD) and triplet exciton-free charge interaction induced triplet exciton dissociation (kT)9,24,25. The recombination coefficient is bL5 e(m21 m1)/e0er and dissociation rate is kD Eð Þ~ 3vmwe 4pe0erd2 exp ({RC d ) J1...

  19. An analytical model of radiation-induced Charge Transfer Inefficiency for CCD detectors

    NASA Astrophysics Data System (ADS)

    Short, A.; Crowley, C.; de Bruijne, J. H. J.; Prod'homme, T.

    2013-04-01

    The European Space Agency's Gaia mission is scheduled for launch in 2013. It will operate at L2 for 5 years, rotating slowly to scan the sky so that its two optical telescopes will repeatedly observe more than one billion stars. The resulting data set will be iteratively reduced to solve for the position, parallax and proper motion of every observed star. The focal plane contains 106 large area silicon CCDs continuously operating in a mode where the line transfer rate and the satellite rotation are in synchronization. One of the greatest challenges facing the mission is radiation damage to the CCDs which will cause charge deferral and image shape distortion. This is particularly important because of the extreme accuracy requirements of the mission. Despite steps taken at hardware level to minimize the effects of radiation, the residual distortion will need to be calibrated during the pipeline data processing. Due to the volume and inhomogeneity of data involved, this requires a model which describes the effects of the radiation damage which is physically realistic, yet fast enough to implement in the pipeline. The resulting charge distortion model was developed specifically for the Gaia CCD operating mode. However, a generalized version is presented in this paper and this has already been applied in a broader context, for example to investigate the impact of radiation damage on the Euclid dark-energy mission data.

  20. Charge transfer and quantum coherence in solar cells and artificial light harvesting system

    NASA Astrophysics Data System (ADS)

    Lienau, Christoph

    2014-03-01

    In artificial light harvesting systems the conversion of light into electrical or chemical energy happens on the femtosecond time scale, and is thought to involve the incoherent jump of an electron from the optical absorber to an electron acceptor. Here we investigate the primary dynamics of the photoinduced electronic charge transfer process in two prototypical structures: (i) a carotene-porphyrin-fullerene triad, a prototypical elementary component for an artificial light harvesting system and (ii) a polymer:fullerene blend as a model system for an organic solar cell. Our approach combines coherent femtosecond spectroscopy and first-principles quantum dynamics simulations. Our experimental and theoretical results provide strong evidence that the driving mechanism of the primary step within the current generation cycle is a quantum-correlated wavelike motion of electrons and nuclei on a timescale of few tens of femtoseconds. We furthermore highlight the fundamental role played by the flexible interface between the light-absorbing chromophore and the charge acceptor in triggering the coherent wavelike electron-hole splitting.

  1. Charge transfer effects of ions at the liquid water/vapor interface

    SciTech Connect

    Soniat, Marielle; Rick, Steven W., E-mail: srick@uno.edu [Department of Chemistry, University of New Orleans, New Orleans, Louisiana 70148 (United States)

    2014-05-14

    Charge transfer (CT), the movement of small amounts of electron density between non-bonded pairs, has been suggested as a driving force for a variety of physical processes. Herein, we examine the effect of CT on ion adsorption to the water liquid-vapor interface. Using a CT force field for molecular dynamics, we construct a potential of mean force (PMF) for Na{sup +}, K{sup +}, Cl{sup ?}, and I{sup ?}. The PMFs were produced with respect to an average interface and an instantaneous interface. An analysis of the PMF relative to the instantaneous surface reveals that the area in which the anions experience a free energy minimum is quite narrow, and the cations feel a steeply repulsive free energy near the interface. CT is seen to have only minor effects on the overall free energy profiles. However, the long-ranged effects of ions are highlighted by the CT model. Due to CT, the water molecules at the surface become charged, even when the ion is over 15 Å away from the surface.

  2. Cellular and molecular analysis of mutagenesis induced by charged particles of defined linear energy transfer

    NASA Technical Reports Server (NTRS)

    Zhu, L. X.; Waldren, C. A.; Vannias, D.; Hei, T. K.; Chatterjee, A. (Principal Investigator)

    1996-01-01

    Mutation induction by charged particles of defined linear energy transfer (LET) and gamma rays was scored using human-hamster hybrid AL cells. The LET values for charged particles accelerated at the Radiological Research Accelerator Facility ranged from 10 keV/microm protons to 150 keV/microm 4He ions. The induced mutant fractions at both the S1 and HGPRT loci were dependent on the dose and LET. In addition, for each dose examined, the mutant yield at the S1 locus was 30-60 fold higher than at the corresponding HGPRT locus. To determine whether the mutation spectrum was comparably dependent on dose and LET, independent S1- and HGPRT- mutants induced by 150 keV/microm 4He ions and gamma rays were isolated, and their DNA was analyzed by both Southern blotting and multiplex PCR methods. While the majority of radiation-induced mutants showed deletions of varying sizes, the relative percentage of large deletions was found to be related to both the dose and LET of the radiation examined. Using a mutation system that can detect multilocus changes, results of the present study show that radiation-induced chromosomal loss can be in the millions of base pairs.

  3. Enhancement of Charge Transfer and Quenching of Photoluminescence of Capped CdS Quantum Dots

    PubMed Central

    Mehata, Mohan Singh

    2015-01-01

    Quantum dots (Q-dots) of cadmium sulfide (CdS) with three different capping ligands, 1-butanethiol (BT), 2-mercaptoethanol (ME) and benzyl mercaptan (BM) have been investigated. An external electric field of variable strength of 0.2–1.0?MV?cm?1 was applied to the sample of capped CdS Q-dots doped in a poly(methyl methacrylate) (PMMA) films. Field-induced changes in optical absorption of capped CdS Q-dots were observed in terms of purely the second-derivative of the absorption spectrum (the Stark shift), indicating an enhancement in electric dipole moment following transition to the first exciton state. The enhancement depends on the shape and size of the Q-dots prepared using different capping ligands. Field induced-change in photoluminescence (PL) reveals similar changes, an enhancement in charge-transfer (CT) character in exciton state. PL of capped CdS Q-dots is significantly quenched in presence of external electric field. The strong field-induced quenching occurs as a result of the increased charge separation resulting exciton dissociation. Thus, understanding the CT character and field-induced PL quenching of CdS Q-dots is important for photovoltaic, LEDs and biological applications. PMID:26166553

  4. A charge transfer complex nematic liquid crystalline gel with high electrical conductivity

    SciTech Connect

    Bhargavi, R.; Nair, Geetha G., E-mail: geeraj88@gmail.com, E-mail: skpras@gmail.com; Krishna Prasad, S., E-mail: geeraj88@gmail.com, E-mail: skpras@gmail.com [Centre for Nano and Soft Matter Sciences, Jalahalli, Bangalore 560013 (India); Majumdar, R.; Bag, Braja G. [Department of Chemistry and Chemical Technology, Vidyasagar University, Midnapore (W) 721 102 (India)

    2014-10-21

    We describe the rheological, dielectric and elastic properties of a nematic liquid crystal gel created using an anthrylidene derivative of arjunolic acid, a chiral triterpenoid, obtained from the extracts of the wood of Terminalia arjuna. In this novel gel, having the electron-donor and acceptor components as minority constituents, the gelation and strengthening of charge-transfer complex (CTC) formation are seen to be occurring concomitantly. In addition to being mechanically strong with a large storage modulus, the gel with the maximized CTC exhibits Frank bend elastic constant values that approach nanonewton levels. The highlight of the study is the observation of 4–5 orders of magnitude increase in electrical conductivity for this gel, a value that is higher than even in the CT complexes of 2-d ordered columnar structures. A further important advantage of the present system over the columnar complex is that the high conductivity is seen for ac probing also, and owing to the nematic nature can be switched between its anisotropic limits. Some of these features are ascribed to a specific molecular packing architecture, which reduces the trapping of the charge carriers.

  5. Pseudocapacitive hausmannite nanoparticles with (101) facets: synthesis, characterization, and charge-transfer mechanism.

    PubMed

    Yeager, Matthew P; Du, Wenxin; Wang, Qi; Deskins, N Aaron; Sullivan, Matthew; Bishop, Brendan; Su, Dong; Xu, Wenqian; Senanayake, Sanjaya D; Si, Rui; Hanson, Jonathan; Teng, Xiaowei

    2013-10-01

    Hausmannite Mn3 O4 octahedral nanoparticles of 18.3 ± 7.0 nm with (101) facets have been prepared by an oxygen-mediated growth. The electrochemical properties of the Mn3 O4 particles as pseudocapacitive cathode materials were characterized both in half-cells and in button-cells. The Mn3 O4 nanoparticles exhibited a high mass-specific capacitance of 261 F g(-1), which was calculated from cyclic voltammetry analyses, and a capacitive retention of 78% after 10,000 galvanostatic charge-discharge cycles. The charge-transfer mechanisms of the Mn3 O4 nanoparticles were further studied by using synchrotron-based in situ X-ray absorption near edge spectroscopy and XRD. Both measurements showed concurrently that throughout the potential window of 0-1.2?V (vs. Ag/AgCl), a stable spinel structure of Mn3 O4 remained, and a reversible electrochemical conversion between tetrahedral [Mn(II) O4 ] and octahedral [Mn(III) O6 ] units accounted for the redox activity. Density functional theory calculations further corroborated this mechanism by confirming the enhanced redox stability afforded by the abundant and exposed (101) facets of Mn3 O4 octahedra. PMID:23650213

  6. Surface Restricted Grating Studies of Interfacial Charge Transfer Dynamics at N-Gallium ARSENIDE(100) Liquid Junction.

    NASA Astrophysics Data System (ADS)

    Wang, Xiangdong

    1995-01-01

    Heterogeneous electron transfer involves the coupling of a dense manifold of highly delocalized electronic levels of the solid state to a discrete molecular state as well as an abrupt change in phase in the reaction coordinate. These features make this problem unique relative to homogeneous solution phase or gas phase reaction mechanisms which involve coupling between discrete states within a uniform medium. In this work, the advances in Surface Restricted Transient Grating Spectroscopy (Surface Restricted Transient Grating) are discussed in the context of studying interfacial charge transfer processes at single crystal semiconductor surfaces as a means to probe the primary processes governing heterogeneous electron transfer. In situ grating studies of n-GaAs/(Se ^{-2/-1}) aqueous liquid junction have observed 1 ~ 2 picosecond decay components in the presence of the selenium redox couple. Bias voltage and injection intensity dependencies have shown that field focusing of the hole carrier distribution to the surface reaction plane was achieved. Based on the bias voltage and injection intensity dependence, and known hole scavenging properties of Se^{ -2}, the fast initial decay is assigned to interfacial hole transfer. This time scale is coincident with the highly damped diffusive relaxation components of water under the high ionic concentrations present in the Helmholtz double layer of the GaAs electrode surface. The similarity in time scales between charge transfer and the rate limiting nuclear motion in the barrier crossing dynamics indicates that the electronic coupling at the interface is in the strong coupling regime. This study was the first direct time-resolved measurement of interfacial electron transfer from a single crystal surface. The observation that the dynamics are essentially in the strong coupling limit is contrary to conventional treatments of interfacial transfer processes, which assume weak coupling conditions. This result is important as it demonstrates that there is no intrinsic barrier to electron transfer processes at the electrode surface and the interfacial charge transfer can approach the theoretical upper limit to the charge transfer processes. This work should be important in fully optimizing charge transfer at surfaces. The observed dynamics also illustrates the feasibility of hot electron channels for solar energy conversion.

  7. Ultrafast Charge Transfer in Nickel Phthalocyanine Probed by Femtosecond Raman-Induced Kerr Effect Spectroscopy

    PubMed Central

    2015-01-01

    The recently developed technique of femtosecond stimulated Raman spectroscopy, and its variant, femtosecond Raman-induced Kerr effect spectroscopy (FRIKES), offer access to ultrafast excited-state dynamics via structurally specific vibrational spectra. We have used FRIKES to study the photoexcitation dynamics of nickel(II) phthalocyanine with eight butoxy substituents, NiPc(OBu)8. NiPc(OBu)8 is reported to have a relatively long-lived ligand-to-metal charge-transfer (LMCT) state, an essential characteristic for efficient electron transfer in photocatalysis. Following photoexcitation, vibrational transitions in the FRIKES spectra, assignable to phthalocyanine ring modes, evolve on the femtosecond to picosecond time scales. Correlation of ring core size with the frequency of the ?10 (asymmetric C–N stretching) mode confirms the identity of the LMCT state, which has a ?500 ps lifetime, as well as that of a precursor d-d excited state. An even earlier (?0.2 ps) transient is observed and tentatively assigned to a higher-lying Jahn–Teller-active LMCT state. This study illustrates the power of FRIKES spectroscopy in elucidating ultrafast molecular dynamics. PMID:24841906

  8. The dynamics of energy and charge transfer in lead sulfide quantum dot solids

    SciTech Connect

    Lingley, Zachary [Mork Family Department of Chemical Engineering and Materials Science, University of Southern California, Los Angeles, California 90089 (United States); Lu, Siyuan [Department of Physics and Astronomy, University of Southern California, Los Angeles, California 90089 (United States); Madhukar, Anupam, E-mail: madhukar@usc.edu [Mork Family Department of Chemical Engineering and Materials Science, University of Southern California, Los Angeles, California 90089 (United States); Department of Physics and Astronomy, University of Southern California, Los Angeles, California 90089 (United States)

    2014-02-28

    We report on a systematic time-resolved photoluminescence study of the competing energy and charge transfer rates in PbS QDs of differing sizes in the same QD solid as a function of both temperature and ligand-controlled different inter-QD average separations. This complements previous studies that typically varied only one parameter and reveals new aspects while also confirming some known features. For the smallest PbS QDs, the dominant decay process is nonradiative resonant energy transfer (NRET) to adjacent larger dots for all separations but at a rate that increases with decreasing temperature. For the largest QDs, NRET being forbidden, the decay is found to be exponential in the inter-QD separation consistent with carrier tunneling but, for each fixed tunneling distance, exhibiting a thermally activated tunneling carrier population with the activation energy dependent upon the ligand length controlling the inter-QD separation. A consistent understanding of this expanded and rich decay rate behavior of both large and small QDs, we show, can be obtained by accounting for the ligand length dependent (a) dielectric environment of the QD solid modeled using an effective medium description, (b) the energy cost of dissociating the exciton into electron and hole in neighboring QDs, and (c) the potential participation of midgap states. Implications of the findings for NRET based photovoltaics are discussed.

  9. Nanostructure and charge transfer in Bi2S3-TiO2 heterostructures

    NASA Astrophysics Data System (ADS)

    Yu, Haijing; Huang, Jing; Zhang, Hua; Zhao, Qingfei; Zhong, Xinhua

    2014-05-01

    Interfacial nanostructures in Bi2S3-TiO2 nanorod-nanoparticle heterostructures with a change of coupling mode have been engineered. The samples were characterized by x-ray diffraction, scanning electron microscopy, transmission electron microscopy, and ultraviolet-visual light absorption spectroscopy. By means of in situ growth of TiO2 nanoparticles on the surfaces of Bi2S3 nanorods in one pot, heterostructures with high-quality interfaces were obtained in which the {105} facet of anatase TiO2 selectively coupled with the {010} facet of orthorhombic Bi2S3 nanorods without any crystal defects, showing the epitaxial relationship of Bi2S3 {011} // TiO2 {101}. By means of a two-step method, TiO2 nanoparticles also could be grown on the {310} facet of the pre-prepared Bi2S3 nanorods to form heterostructures but with interfacial defects. Charge transfer in the interface-different heterostructures was evaluated by photodegradation of methyl orange under visible-light irradiation. The defect-free interfaces favored electron-hole separation and transfer, resulting in improved photocatalytic activity. The current structural characterization and interface engineering should be expanded to other heterostructures when studying the relationship between synthesis, interfacial structure, and photocatalytic or photovoltaic applications.

  10. The nature of the rapid relaxation of excited charge-transfer complexes.

    PubMed

    Levy, D; Arnold, B R

    2004-09-01

    Examples of contact radical-ion-pair (CRIP) formation from excited charge-transfer (CT) complexes are described. The reduced absorption and emission spectra of the CT complexes formed between hexamethylbenzene, pentamethylbenzene, and durene donors and 1,2,4,5-tetracyanobenzene (TCNB) in 1,2-dichloroethane (DCLE) exhibit a mirror image relationship, suggesting that each set of spectra describes transitions between the same two states. It was concluded that a CRIP is produced immediately upon excitation of the CT complex and that relaxation of the CRIP includes only minor geometry changes and changes in solvent polarization. In contrast to these results, the reduced absorption and emission spectra of the mesitylene (MES)/TCNB CT complex in DCLE are distinctly different and do not display a mirror image relationship. Time-resolved emission decay traces reveal the presence of an initial intermediate species that contributes approximately 10% of the total steady-state emission. The emission spectrum of this initial species mirrors the absorption spectrum of the MES/TCNB complex. In the MES/TCNB complex, excitation does not lead directly to the CRIP, and the relaxation of the excited complex must include an electronic component in addition to changes in geometry and solvation. The implications of these results on the applicability of golden-rule expressions of electron transfer are discussed. PMID:15327332

  11. Charge-Transfer Mobility Parameters in Photoelectronic Devices: The Advanced Miller-Abrahams Computation.

    PubMed

    Basilevsky, M V; Odinokov, A V; Komarova, K G

    2015-06-18

    The local hopping step of the electron transfer (ET) reaction is investigated for a real organic material composed of molecules M (N,N'-di(1-naphthyl)-N,N'-diphenyl-(1,1'-biphenyl)-4,4'-diamine). This material is implemented in light-emitting photoelectronic devices. The conductivity effect is simulated and calculated at a molecular level. We have studied the ET mechanism alternative to that suggested by the usually employed Marcus-like polaron model. The ion-molecular binary complex M(+)M (for hole transfer) is considered as a reaction center. The reaction dynamics is carried through the low-frequency intermolecular vibration coordinate connecting its fragments (the promotion mode). Its coupling to the acoustic phonon bath serves for a dissipation of the reaction energy misfit. The high-frequency intramolecular vibrations (the reorganization modes) modulate the reaction kinetics via Franck-Condon factors induced by their polarization. The ET rate constants are evaluated in terms of the computational algorithm described earlier (Basilevsky, M. V.; et al. J. Chem. Phys. 2013 139, 234102). Standard quantum-chemical and molecular dynamical techniques are used for a calculation of all necessary parameters of this model. The macroscopic charge-carrier mobility of the material is estimated by properly averaging the rate constants over the total simulation cell. PMID:25636079

  12. Self-assembly of intramolecular charge-transfer compounds into functional molecular systems.

    PubMed

    Li, Yongjun; Liu, Taifeng; Liu, Huibiao; Tian, Mao-Zhong; Li, Yuliang

    2014-04-15

    Highly polarized compounds exhibiting intramolecular charge transfer (ICT) are used widely as nonlinear optical (NLO) materials and red emitters and in organic light emitting diodes. Low-molecular-weight donor/acceptor (D/A)-substituted ICT compounds are ideal candidates for use as the building blocks of hierarchically structured, multifunctional self-assembled supramolecular systems. This Account describes our recent studies into the development of functional molecular systems with well-defined self-assembled structures based on charge-transfer (CT) interactions. From solution (sensors) to the solid state (assembled structures), we have fully utilized intrinsic and stimulus-induced CT interactions to construct these functional molecular systems. We have designed some organic molecules capable of ICT, with diversity and tailorability, that can be used to develop novel self-assembled materials. These ICT organic molecules are based on a variety of simple structures such as perylene bisimide, benzothiadiazole, tetracyanobutadiene, fluorenone, isoxazolone, BODIPY, and their derivatives. The degree of ICT is influenced by the nature of both the bridge and the substituents. We have developed new methods to synthesize ICT compounds through the introduction of heterocycles or heteroatoms to the ?-conjugated systems or through extending the conjugation of diverse aromatic systems via another aromatic ring. Combining these ICT compounds featuring different D/A units and different degrees of conjugation with phase transfer methodologies and solvent-vapor techniques, we have self-assembled various organic nanostructures, including hollow nanospheres, wires, tubes, and ribbonlike architectures, with controllable morphologies and sizes. For example, we obtained a noncentrosymmetric microfiber structure that possessed a permanent dipole along its fibers' long axis and a transition dipole perpendicular to it; the independent NLO responses of this material can be separated and tuned spectroscopically and spatially. The ready processability and intrinsically high NLO efficiency of these microfibers offer great opportunities for applications in photonic devices. We have also designed molecular sensors based on changes in the efficiency of the ICT process upon complexation of an analyte with the D or A moieties in the ICT compounds. Such sensors, which display evident Stokes shifts or changes in quantum yields or fluorescence lifetimes, have promise for applications in chemical and biological recognition and sensing. In this Account, we shed light on the structure-function relationships of these functional molecular systems with well-defined self-assembled structures based on ICT interactions. The encouraging results that we have obtained suggest that such self-assembled ICT molecular materials can guide the design of new nanostructures and materials from organic systems, and that these materials, across a range of compositions, sizes, shapes, and functionalities, can potentially be applied in the fields of electronics, optics, and optoelectronics. PMID:24666347

  13. Challenges to computational quantum chemistry from contemporary advances in polyatomic molecular electronic spectroscopy

    Microsoft Academic Search

    Michael Kasha; Dimitri Parthenopoulos; Barry Dellinger

    1993-01-01

    Molecular electronic spectroscopy featuring intramolecular proton transfer and twisted intramolecular charge transfer poses a whole new range of problems for computational quantum chemistry. The development of the four-level laser based on the intramolecular proton-transfer focuses on the subtleties of the interaction of the singlet and triplet electronic state manifolds of the two different tautomeric species. Examples are given of the

  14. Photogeneration of ions via delocalized charge transfer states. I. XezH+ and XePD+ in solid Xe

    E-print Network

    Apkarian, V. Ara

    demonstrated that optically accessed charge-transfer states of solid xenon doped with atomic halogens (I by the host dielectric. The excitation resonances were successfully treated as a Rydberg series of a valence hole with an effective mass reflecting the full valence band- width.4 More recently, Kunz et al. showed

  15. Intramolecular Charge Transfer Reaction, Polarity, and Dielectric Relaxation in AOT/ Water/Heptane Reverse Micelles: Pool Size Dependence

    E-print Network

    Biswas, Ranjit

    )-sulfosuccinate (AOT) forms reverse micelles in the presence of water and a nonpolar solvent (usually isooctaneIntramolecular Charge Transfer Reaction, Polarity, and Dielectric Relaxation in AOT/ Water and Technology, S. N. Bose National Centre for Basic Sciences, JD Block, Sector III, Salt Lake, Kolkata 700 098

  16. Measuring Intramolecular Charge Transfer via Coherent Generation of THz Radiation Matthew C. Beard, Gordon M. Turner, and Charles A. Schmuttenmaer*

    E-print Network

    ARTICLES Measuring Intramolecular Charge Transfer via Coherent Generation of THz Radiation Matthew of 10 ns.9,8 Two techniques closely related to this method are THz generation from biased semiconductors and the transient dc photocurrent (TDP) technique. THz generation from biased semiconductors utilizes the

  17. Charge-transfer interactions of metoclopramide nausea drug against six kind of ?-acceptors: spectral and thermal discussions.

    PubMed

    El-Habeeb, Abeer A; Al-Saif, Foziah A; Refat, Moamen S

    2014-04-01

    The target of this paper is aimed to discuss the fast and newly techniques in order to assessment the metoclopramide (Mcp) nausea drug in pure form in solid and solution shape with different kind of ?-acceptors upon charge transfer interactions. Charge-transfer complexes (CTC) of metoclopramide with picric acid (PA), 2,3-dichloro-5,6-dicyano-p-benzoquinon (DDQ), tetracyanoquinodimethane (TCNQ), m-dinitrobenzene (DNB), p-nitrobenzoic acid (p-NBA) and tetrachloro-p-quinon (p-CL) have been studied spectrophotometrically in absolute methanol at room temperature. The stoichiometries of the complexes were found to be 1:1 ratio by the spectrophotometric titration between metoclopramide and represented ?-acceptors. The equilibrium constants, molar extinction coefficient (?CT) and spectroscopic-physical parameters (standard free energy (?G°), oscillator strength (ƒ), transition dipole moment (?), resonance energy (RN) and ionization potential (ID)) of the complexes were determined upon the modified Benesi-Hildebrand equation. The results indicate that the formation constants for the complexes depend on the nature of electron acceptors and configuration of drug donor, and also the spectral studies of the complexes were determined by (infrared, Raman, and (1)H NMR) spectra and X-ray powder diffraction (XRD). The charge-transfer complexes are formed during the interaction of electron-acceptors and electron-donors as result of partial or complete transfer of a negative charge from (D(+)-A(-)). PMID:24434200

  18. Large Stokes shift induced by intramolcular charge transfer in N,O-chelated naphthyridine-BF2 complexes.

    PubMed

    Wu, Yun-Ying; Chen, Yong; Gou, Gao-Zhang; Mu, Wei-Hua; Lv, Xiao-Jun; Du, Mei-Ling; Fu, Wen-Fu

    2012-10-19

    Novel N,O-chelated naphthyridine-BF(2) complexes with push-pull structures have been synthesized and characterized. Spectral investigations on these complexes reveal that photoinduced intramolecular charge transfer occurs and results in a large Stokes shift, which is further supported by density functional theory based theoretical calculations. PMID:23050580

  19. Calculation of rate constants for asymmetric charge transfer, and their effect on relative sensitivity factors in glow discharge mass spectrometry

    Microsoft Academic Search

    Annemie Bogaerts; Krassimir A. Temelkov; Nikolay K. Vuchkov; Renaat Gijbels

    2007-01-01

    For this paper, we have calculated the rate coefficients for asymmetric charge transfer between Ar+ ions and all elements of interest in analytical glow discharges, based on a semi-classical approach. These values were then used to make predictions on the relative sensitivity factors (RSFs) in glow discharge mass spectrometry (GDMS) (VG9000 discharge cell) for various elements. The RSFs were calculated

  20. Study of low energy Ytterbium atom-ion charge transfer collisions using a surface-electrode trap

    E-print Network

    Pruttivarasin, Thaned

    2008-01-01

    We demonstrate a new isotope-selective system to measure low energy charge transfer collisions between ytterbium ions and atoms in the range of collisional energy from 2.2x 10-5 eV to 4.3x 10-3 eV, corresponding to effective ...

  1. Electrically Active Magnetic Nanoparticles for Concentrating and Detecting Bacillus anthracis Spores in a Direct-Charge Transfer Biosensor

    Microsoft Academic Search

    Sudeshna Pal; Emma B. Setterington; Evangelyn C. Alocilja

    2008-01-01

    Bacillus anthracis, the causative agent of anthrax, is considered as one of the most important pathogens in the list of bioterrorism threats. This paper describes the synthesis of electrically active magnetic (EAM) nanoparticles and their application in a direct-charge transfer biosensor for detecting B. anthracis Sterne endospores. These EAM nanoparticles were synthesized from aniline monomer made electrically active by acid

  2. 46 CFR 251.31 - Charges for processing applications for authorization to transfer ownership of ships built with...

    Code of Federal Regulations, 2011 CFR

    2011-10-01

    46 ? Shipping ? 8 ? 2011-10-01 ? 2011-10-01 ? false ? Charges for processing applications for authorization to transfer ownership of ships built with construction-differential subsidy. ? 251.31 ? Section 251.31 ? Shipping ? MARITIME ADMINISTRATION, DEPARTMENT OF TRANSPORTATION ?...

  3. 46 CFR 251.31 - Charges for processing applications for authorization to transfer ownership of ships built with...

    Code of Federal Regulations, 2010 CFR

    2010-10-01

    46 ? Shipping ? 8 ? 2010-10-01 ? 2010-10-01 ? false ? Charges for processing applications for authorization to transfer ownership of ships built with construction-differential subsidy. ? 251.31 ? Section 251.31 ? Shipping ? MARITIME ADMINISTRATION, DEPARTMENT OF TRANSPORTATION ?...

  4. The role of charge-transfer interactions and delocalization in annelated nitronyl nitroxides

    NASA Astrophysics Data System (ADS)

    Dooley, Brynn Mary

    The design and synthesis of stable organic radicals with delocalized spin density distribution and low energy optical and redox processes is central to the development of magneto-conducting materials. Towards this end, a generalized synthetic methodology has been developed allowing for the synthesis of a series of annelated benzonitronyl nitroxide (BNN) radicals. The BNN radicals exhibited remarkably low reduction potentials (~0.0 V vs SCE) and a near-infrared absorption attributed to a HOMO--SOMO charge-transfer excitation. The annelated BNN radicals were found to be less stable than the closely related tetramethyl nitronyl nitroxide radicals, particularly in solution. A series of pi-delocalized and heteroaromatic radicals were synthesized to determine if the instability was due to the delocalization of electron density onto the carbon skeleton or the low reduction potential. DFT calculations with the EPR-II basis gave rise to calculated electronic structures that were consistent with EPR spectroscopy and suggested changes in spin density distribution are occurring with perturbation of the annelated ring. Cyclic voltammetry revealed the heteroaromatic and pi-delocalized radicals had reduction potentials lower than BNN, with some systems reducing at potentials of 0.2 V vs SCE, comparable to that of 7,7,8,8-tetracyanoquinodimethane. The distribution of spin throughout the molecular framework and the low reduction potential of the annelated nitronyl nitroxide radicals were both found to contribute to the lowered stability of the annelated nitronyl nitroxides relative to the far less redox active tetramethyl nitronyl nitroxides. The low reduction potential of the BNN radicals suggested that incorporation into acceptor--donor (A--D) systems would allow for investigation of the role of charge transfer interactions on the electronic structure and properties of neutral open-shell A--D radicals. Two D--A--D radicals were prepared using metal catalyzed coupling and furoxan condensation methodologies which resulted in incorporation of a second donor in the C5 position of the BNN moiety. The radical D1--A--D2 triads, where D1 = thiophene and D2 = thiophene or phenyl, exhibited three intramolecular charge-transfer excitations (lambdamax = 550, 580 and 1000 nm) that were investigated by variable temperature absorption spectroscopy. Structural characterization of the triads in the solid state by single crystal and powder X-ray diffraction revealed slipped pi stacks that arise from intermolecular pi-- pi and D--A interactions, providing pathways for antiferromagnetic (AFM) and ferromagnetic (FM) exchange. While the phenyl substituted triad (Th--BNN--Ph) exhibited antiferromagnetic interactions and a room temperature conductivity of sigmaRT = 10-7 S cm-1, the thienyl substituted derivative (Th--BNN--Th) exhibited short-range FM interactions and increased conductivity (sigmaRT = 10-5 S cm-1), giving rise to an organic semiconductor exhibiting FM exchange. The differences in conductivity and magnetic behavior were rationalized by the degree of slippage dictated by an interplay between pi-- pi and intermolecular D--A interactions. Finally, a series of BNN--D radicals were investigated where the donor ability of D was systematically varied from Eox = 2.30 V vs SCE (benzene) to 0.32 V vs SCE (tetrathiafulvalene). Calculations of the near-infrared charge transfer excitation suggested that the HOMO--SOMO gap could be significantly decreased with increasing donor ability, consistent with charge transfer theory. A subset of the series of BNN--D radicals with D = anisole, benzo[b]thiophene, N-methylindole, N-ethylcarbazole, and N,N-diphenylaniline were synthesized. Solution state spectroscopic studies of the series by EPR and electronic absorption spectroscopy revealed spin-delocalized structures with extremely low reduction potentials (~0 V vs SCE). The solid state properties of the BNN--D radicals were investigated by magnetometry and room temperature conductivity measurements. Due to primarily steric interactions, weak D--A coupling was observ

  5. Full-electron calculation of effective electronic couplings and excitation energies of charge transfer states: Application to hole transfer in DNA ?-stacks

    PubMed Central

    Migliore, Agostino

    2009-01-01

    In this work I develop and apply a theoretical method for calculating effective electronic couplings (or transfer integrals) between redox sites involved in hole or electron transfer reactions. The resulting methodology is a refinement and a generalization of a recently developed approach for transfer integral evaluation. In fact, it holds for any overlap between the charge-localized states used to represent charge transfer (CT) processes in the two-state model. The presented theoretical and computational analyses show that the prototype approach is recovered for sufficiently small overlaps. The method does not involve any empirical parameter. It allows a complete multielectron description, therefore including electronic relaxation effects. Furthermore, its theoretical formulation holds at any value of the given reaction coordinate and yields a formula for the evaluation of the vertical excitation energy (i.e., the energy difference between the adiabatic ground and first-excited electronic states) that rests on the same physical quantities used in transfer integral calculation. In this paper the theoretical approach is applied to CT in B-DNA base dimers within the framework of Density Functional Theory (DFT), although it can be implemented in other computational schemes. The results of this work, as compared with previous Hartree–Fock (HF) and post-HF evaluations, support the applicability of the current implementation of the method to larger ?-stacked arrays, where post-HF approaches are computationally unfeasible. PMID:19778106

  6. CoPc and CoPcF16 on gold: Site-specific charge-transfer processes

    PubMed Central

    Petraki, Fotini; Uihlein, Johannes; Aygül, Umut; Chassé, Thomas

    2014-01-01

    Summary Interface properties of cobalt(II) phthalocyanine (CoPc) and cobalt(II) hexadecafluoro-phthalocyanine (CoPcF16) to gold are investigated by photo-excited electron spectroscopies (X-ray photoemission spectroscopy (XPS), ultraviolet photoemission spectroscopy (UPS) and X-ray excited Auger electron spectroscopy (XAES)). It is shown that a bidirectional charge transfer determines the interface energetics for CoPc and CoPcF16 on Au. Combined XPS and XAES measurements allow for the separation of chemical shifts based on different local charges at the considered atom caused by polarization effects. This facilitates a detailed discussion of energetic shifts of core level spectra. The data allow the discussion of site-specific charge-transfer processes. PMID:24991487

  7. Proton Irradiation Experiment for X-ray Charge-Coupled Devices of the Monitor of All-Sky X-ray Image Mission Onboard the International Space Station: I. Experimental Setup and Measurement of the Charge Transfer Inefficiency

    Microsoft Academic Search

    Emi Miyata; Tomoyuki Kamazuka; Hirohiko Kouno; Mitsunori Fukuda; Mototsugu Mihara; Kensaku Matsuta; Hiroshi Tsunemi; Kanenobu Tanaka; Tadanori Minamisono; Hiroshi Tomida; Kazuhisa Miyaguchi

    2002-01-01

    We have investigated the radiation damage effects on a charge-cloupled device (CCD) to be employed in the Japanese X-ray astronomy mission including the monitor of all-sky X-ray image (MAXI) onboard the international space station (ISS). Since low-energy protons release their energy mainly at the charge transfer channel, resulting in a decrease of the charge transfer efficiency, we focused on low-energy

  8. Coupled quantum-classical method for long range charge transfer: relevance of the nuclear motion to the quantum electron dynamics.

    PubMed

    da Silva, Robson; Hoff, Diego A; Rego, Luis G C

    2015-04-10

    Charge and excitonic-energy transfer phenomena are fundamental for energy conversion in solar cells as well as artificial photosynthesis. Currently, much interest is being paid to light-harvesting and energy transduction processes in supramolecular structures, where nuclear dynamics has a major influence on electronic quantum dynamics. For this reason, the simulation of long range electron transfer in supramolecular structures, under environmental conditions described within an atomistic framework, has been a difficult problem to study. This work describes a coupled quantum mechanics/molecular mechanics method that aims at describing long range charge transfer processes in supramolecular systems, taking into account the atomistic details of large molecular structures, the underlying nuclear motion, and environmental effects. The method is applied to investigate the relevance of electron-nuclei interaction on the mechanisms for photo-induced electron-hole pair separation in dye-sensitized interfaces as well as electronic dynamics in molecular structures. PMID:25767107

  9. Coupled quantum-classical method for long range charge transfer: relevance of the nuclear motion to the quantum electron dynamics

    NASA Astrophysics Data System (ADS)

    da Silva, Robson; Hoff, Diego A.; Rego, Luis G. C.

    2015-04-01

    Charge and excitonic-energy transfer phenomena are fundamental for energy conversion in solar cells as well as artificial photosynthesis. Currently, much interest is being paid to light-harvesting and energy transduction processes in supramolecular structures, where nuclear dynamics has a major influence on electronic quantum dynamics. For this reason, the simulation of long range electron transfer in supramolecular structures, under environmental conditions described within an atomistic framework, has been a difficult problem to study. This work describes a coupled quantum mechanics/molecular mechanics method that aims at describing long range charge transfer processes in supramolecular systems, taking into account the atomistic details of large molecular structures, the underlying nuclear motion, and environmental effects. The method is applied to investigate the relevance of electron–nuclei interaction on the mechanisms for photo-induced electron–hole pair separation in dye-sensitized interfaces as well as electronic dynamics in molecular structures.

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

    PubMed

    Bazant, Martin Z

    2013-05-21

    Advances in the fields of catalysis and electrochemical energy conversion often involve nanoparticles, which can have kinetics surprisingly different from the bulk material. Classical theories of chemical kinetics assume independent reactions in dilute solutions, whose rates are determined by mean concentrations. In condensed matter, strong interactions alter chemical activities and create variations that can dramatically affect the reaction rate. The extreme case is that of a reaction coupled to a phase transformation, whose kinetics must depend not only on the order parameter but also on its gradients at phase boundaries. Reaction-driven phase transformations are common in electrochemistry, when charge transfer is accompanied by ion intercalation or deposition in a solid phase. Examples abound in Li-ion, metal-air, and lead-acid batteries, as well as metal electrodeposition-dissolution. Despite complex thermodynamics, however, the standard kinetic model is the Butler-Volmer equation, based on a dilute solution approximation. The Marcus theory of charge transfer likewise considers isolated reactants and neglects elastic stress, configurational entropy, and other nonidealities in condensed phases. The limitations of existing theories recently became apparent for the Li-ion battery material LixFePO4 (LFP). It has a strong tendency to separate into Li-rich and Li-poor solid phases, which scientists believe limits its performance. Chemists first modeled phase separation in LFP as an isotropic "shrinking core" within each particle, but experiments later revealed striped phase boundaries on the active crystal facet. This raised the question: What is the reaction rate at a surface undergoing a phase transformation? Meanwhile, dramatic rate enhancement was attained with LFP nanoparticles, and classical battery models could not predict the roles of phase separation and surface modification. In this Account, I present a general theory of chemical kinetics, developed over the past 7 years, which is capable of answering these questions. The reaction rate is a nonlinear function of the thermodynamic driving force, the free energy of reaction, expressed in terms of variational chemical potentials. The theory unifies and extends the Cahn-Hilliard and Allen-Cahn equations through a master equation for nonequilibrium chemical thermodynamics. For electrochemistry, I have also generalized both Marcus and Butler-Volmer kinetics for concentrated solutions and ionic solids. This new theory provides a quantitative description of LFP phase behavior. Concentration gradients and elastic coherency strain enhance the intercalation rate. At low currents, the charge-transfer rate is focused on exposed phase boundaries, which propagate as "intercalation waves", nucleated by surface wetting. Unexpectedly, homogeneous reactions are favored above a critical current and below a critical size, which helps to explain the rate capability of LFP nanoparticles. Contrary to other mechanisms, elevated temperatures and currents may enhance battery performance and lifetime by suppressing phase separation. The theory has also been extended to porous electrodes and could be used for battery engineering with multiphase active materials. More broadly, the theory describes nonequilibrium chemical systems at mesoscopic length and time scales, beyond the reach of molecular simulations and bulk continuum models. The reaction rate is consistently defined for inhomogeneous, nonequilibrium states, for example, with phase separation, large electric fields, or mechanical stresses. This research is also potentially applicable to fluid extraction from nanoporous solids, pattern formation in electrophoretic deposition, and electrochemical dynamics in biological cells. PMID:23520980

  11. Carrier control via charge transfer at the topological-insulator/organic-molecule interface

    NASA Astrophysics Data System (ADS)

    Tanigaki, Katsumi; Tanabe, Yoichi; Kuynh, Khuong; Urata, Takahiro; Nouchi, Ryo; Heguri, Satoshi; Shimotani, Hidekazu; AIMR, Tohoku University Collaboration; Department of Pysics, Graduate School of Science, Tohoku University Collaboration; Osaka Prefecture University Collaboration

    2013-03-01

    A topological insulator is a material that behaves as an insulator as a bulk state, while permitting metallicity on its Dirac cone surface state. One of the most serious issues of recent researches in this field, however, has been the fact that the Fermi levels in many TIs actually fall in either the conduction or valence band due to the naturally occurring defects and must be controlled by further doping. We report here that the major electron carriers on the SS of a Bi2-xSbxTe3-ySey(BSTS) single crystal can be converted to the hole carriers via interface control using 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane(F4-TCNQ), with strong electron affinity. The evidence can be elucidated using a detailed three-carrier model. The results apparently demonstrate that the charge transfer at the TI/organic-molecule interface is very efficient in order to control the carrier density of TIs, particularly on the SS. Our present results will be very important for studying the fundamental aspects of TIs as well as their future device applications. A topological insulator is a material that behaves as an insulator as a bulk state, while permitting metallicity on its Dirac cone surface state. One of the most serious issues of recent researches in this field, however, has been the fact that the Fermi levels in many TIs actually fall in either the conduction or valence band due to the naturally occurring defects and must be controlled by further doping. We report here that the major electron carriers on the SS of a Bi2-xSbxTe3-ySey(BSTS) single crystal can be converted to the hole carriers via interface control using 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane(F4-TCNQ), with strong electron affinity. The evidence can be elucidated using a detailed three-carrier model. The results apparently demonstrate that the charge transfer at the TI/organic-molecule interface is very efficient in order to control the carrier density of TIs, particularly on the SS. Our present results will be very important for studying the fundamental aspects of TIs as well as their future device applications. Osaka Prefecture University

  12. Investigating photoinduced charge transfer in double- and single-emission PbS@CdS core@shell quantum dots

    NASA Astrophysics Data System (ADS)

    Zhao, Haiguang; Liang, Hongyan; Gonfa, Belete Atomsa; Chaker, Mohamed; Ozaki, Tsuneyuki; Tijssen, Peter; Vidal, François; Ma, Dongling

    2013-12-01

    We present for the first time detailed investigation of the charge transfer behavior of PbS@CdS core@shell quantum dots (QDs) showing either a single emission peak from the core or intriguing double emission peaks from the core and shell, respectively. A highly non-concentric core@shell structure model was proposed to explain the origin of double emissions from monodisperse QDs. Their charge transfer behavior was investigated by monitoring photoluminescence (PL) intensity variation with the introduction of electron or hole scavengers. It was found that the PL quenching of the PbS core is more efficient than that of the CdS shell, suggesting more efficient charge transfer from the core to scavengers, although the opposite was expected. Further measurements of the PL lifetime followed by wave function calculations disclosed that the time scale is the critical factor explaining the more efficient charge transfer from the core than from the shell. The charge transfer behavior was also examined on a series of single-emission core@shell QDs with either different core sizes or different shell thicknesses and dominant factors were identified. Towards photovoltaic applications, these PbS@CdS QDs were attached onto multi-walled carbon nanotubes (MWCNTs) and their charge transfer behavior was compared with that in the PbS-QD/MWCNT system. Results demonstrate that although the CdS shell serves as an electron transfer barrier, the electrons excited in the PbS cores can still be transferred into the MWCNTs efficiently when the shell thickness is ~0.7 nm. Considering their higher stability, these core@shell QDs are very promising for the development of highly efficient QD-based photovoltaic devices.We present for the first time detailed investigation of the charge transfer behavior of PbS@CdS core@shell quantum dots (QDs) showing either a single emission peak from the core or intriguing double emission peaks from the core and shell, respectively. A highly non-concentric core@shell structure model was proposed to explain the origin of double emissions from monodisperse QDs. Their charge transfer behavior was investigated by monitoring photoluminescence (PL) intensity variation with the introduction of electron or hole scavengers. It was found that the PL quenching of the PbS core is more efficient than that of the CdS shell, suggesting more efficient charge transfer from the core to scavengers, although the opposite was expected. Further measurements of the PL lifetime followed by wave function calculations disclosed that the time scale is the critical factor explaining the more efficient charge transfer from the core than from the shell. The charge transfer behavior was also examined on a series of single-emission core@shell QDs with either different core sizes or different shell thicknesses and dominant factors were identified. Towards photovoltaic applications, these PbS@CdS QDs were attached onto multi-walled carbon nanotubes (MWCNTs) and their charge transfer behavior was compared with that in the PbS-QD/MWCNT system. Results demonstrate that although the CdS shell serves as an electron transfer barrier, the electrons excited in the PbS cores can still be transferred into the MWCNTs efficiently when the shell thickness is ~0.7 nm. Considering their higher stability, these core@shell QDs are very promising for the development of highly efficient QD-based photovoltaic devices. Electronic supplementary information (ESI) available: The PL and absorption spectra of PbS@CdS QDs in solution and in films with and without the combination of MWCNTs, Gaussian curve fit to the PL spectra of representative QD film samples, PL lifetime and charge transfer rate from QDs to electron or hole scavengers, radial distribution functions for 1s electron levels of the PbS@CdS core@shell QD with a different core size and constant shell thickness. See DOI: 10.1039/c3nr03691j

  13. Impedance analysis of inherently redox-active ionic-liquid-based photoelectrochemical cells: charge-transfer mechanism in the presence of an additional redox couple.

    PubMed

    Patel, Dipal B; Chauhan, Khushbu R; Mukhopadhyay, Indrajit

    2015-06-01

    An intensive electrochemical impedance study was carried out to understand the charge-transfer processes in photoelectrochemical (PEC) cells based on ionic liquid (IL) electrolytes. Three different electrolytes were utilized to understand the role of redox species as well as the medium on the charge-transfer mechanism. The negligible diffusion resistance, despite the presence of two different redox species in the case of Fe(CN)6 (-4/-3) in IL, was explained on the basis of charge transfer between species of two different redox couples. Accordingly, the redox species are not required to travel through the bulk of the electrolyte for the removal of accumulated charges, as short-range charge transfer between the IL and the Fe(CN)6 (-4/-3) species facilitates the removal of accumulated charges. It is also shown that PEC cells utilizing dual redox couples are highly stable with larger photoelectrochmeical windows, >3 V. PMID:25820185

  14. Catalytic and charge transfer properties of transition metal dichalcogenides arising from electrochemical pretreatment.

    PubMed

    Chia, Xinyi; Ambrosi, Adriano; Sofer, Zdenek; Luxa, Jan; Pumera, Martin

    2015-05-26

    Layered transition metal dichalcogenides (TMDs) have been the center of attention in the scientific community due to their properties that can be tapped on for applications in electrochemistry and hydrogen evolution reaction (HER) catalysis. We report on the effect of electrochemical treatment of exfoliated MoS2, WS2, MoSe2 and WSe2 nanosheets toward the goal of activating the electrochemical and HER catalytic properties of the TMDs. In particular, electrochemical activation of the heterogeneous electron transfer (HET) abilities of MoS2, MoSe2 and WSe2 is achieved via reductive treatments at identified reductive potentials based on their respective inherent electrochemistry. Comparing all TMDs, the charge transfer activation is most accentuated in MoSe2 and can be concluded that Mo metal and Se chalcogen type are more susceptible to electrochemical activation than W metal and S chalcogen type. With regards to the HER, we show that while MoS2 displayed enhanced performance when subjected to electrochemical reduction, WS2 fared worse upon oxidation. On the other hand, the HER performance of MoSe2 and WSe2 is independent of electrochemical redox treatment. We can conclude therefore that for the HER, S-containing TMDs are more responsive to redox treatment than compounds with the Se chalcogen. Our findings are beneficial toward understanding the electrochemistry of TMDs and the extent to which activation by electrochemical means is effective. In turn, when such knowledge is administered aptly, it will be promising for electrochemical uses. PMID:25894369

  15. Partial charge transfer in the shortest possible metallofullerene peapod, La@C82 ?[11]cycloparaphenylene.

    PubMed

    Iwamoto, Takahiro; Slanina, Zdenek; Mizorogi, Naomi; Guo, Jingdong; Akasaka, Takeshi; Nagase, Shigeru; Takaya, Hikaru; Yasuda, Nobuhiro; Kato, Tatsuhisa; Yamago, Shigeru

    2014-10-27

    [11]Cycloparaphenylene ([11]CPP) selectively encapsulates La@C82 to form the shortest possible metallofullerene-carbon nanotube (CNT) peapod, La@C82 ?[11]CPP, in solution and in the solid state. Complexation in solution was affected by the polarity of the solvent and was 16?times stronger in the polar solvent nitrobenzene than in the nonpolar solvent 1,2-dichlorobenzene. Electrochemical analysis revealed that the redox potentials of La@C82 were negatively shifted upon complexation from free La@C82 . Furthermore, the shifts in the redox potentials increased with polarity of the solvent. These results are consistent with formation of a polar complex, (La@C82 )(?-) ?[11]CPP(?+) , by partial electron transfer from [11]CPP to La@C82 . This is the first observation of such an electronic interaction between a fullerene pea and CPP pod. Theoretical calculations also supported partial charge transfer (0.07) from [11]CPP to La@C82 . The structure of the complex was unambiguously determined by X-ray crystallographic analysis, which showed the La atom inside the C82 near the periphery of the [11]CPP. The dipole moment of La@C82 was projected toward the CPP pea, nearly perpendicular to the CPP axis. The position of the La atom and the direction of the dipole moment in La@C82 ?[11]CPP were significantly different from those observed in La@C82 ?CNT, thus indicating a difference in orientation of the fullerene peas between fullerene-CPP and fullerene-CNT peapods. These results highlight the importance of pea-pea interactions in determining the orientation of the metallofullerene in metallofullerene-CNT peapods. PMID:25224281

  16. Transfer and computation of optical topological charges via light pulse buffer memory in an electromagnetically-induced-transparency solid

    NASA Astrophysics Data System (ADS)

    Zhai, Zhaohui; Li, Zhixiang; Xu, Jingjun; Zhang, Guoquan

    2013-09-01

    We verified that optical topological charges are conserved in a two-step light-pulse storage and retrieval process based on the electromagnetically-induced-transparency (EIT) effect in a Pr3+:Y2SiO5 crystal. Based on this conservation law, one could transfer topological charges from the interacting beams, which may not be overlapped in space and time domains, to the targeted output signal beam, and algebraic operations such as summation and subtraction of topological charges carried by the interacting beams were demonstrated via the EIT-assisted two-step light-pulse storage-retrieval process. The results may be useful for classical and quantum information processing based on optical topological charge buffer memory in EIT media.

  17. Southern Blotting -Alkaline Transfer to Positively Charged Nylon 1. Prepare and run a 0.75 -1.25 % agarose gel 1 cm thick. Include DNA standards. Stain with

    E-print Network

    Aris, John P.

    Southern Blotting - Alkaline Transfer to Positively Charged Nylon 1. Prepare and run a 0.75 - 1 evaporation. 6. Alkaline capillary transfer is faster than high salt (SSC) transfer. Transfer is usually at 4°C. DNA is covalently linked to positively charged nylon membrane during alkaline transfer. Baking

  18. Lithium adsorption on MgO(100) and its defects: Charge transfer, structure, and energetics

    NASA Astrophysics Data System (ADS)

    Farmer, J. A.; Ruzycki, N.; Zhu, J. F.; Campbell, Charles T.

    2009-07-01

    The adsorption energetics and growth of lithium vapor on MgO(100) at 300 K was studied using microcalorimetry, in combination with low-energy electron diffraction (LEED), low-energy ion scattering (ISS), Auger electron spectroscopy (AES), and work-function measurements. The MgO(100) samples were films of ˜4nm thickness grown on a Mo(100) single crystal. The initial sticking probability of lithium was ˜0.97 , reaching unity by 0.5 monolayer (ML). The AES and ISS signals vary with Li coverage up to 3 ML as expected if the Li atoms stay within the layer where they initially hit (i.e., with no interlayer transport). Initially, lithium adsorbs strongly at the intrinsic surface defects and as two-dimensional (2D) lithium clusters, with a heat of adsorption of 260 kJ/mol. The heat approaches the heat of sublimation of bulk Li (159 kJ/mol) by 0.4 ML, due to the growth of 2D and then three-dimensional (3D) Li islands. Argon-ion sputtering of the surface increases the defect density and the probability for adsorbing Li to find a defect, and thus the heat of adsorption at low coverages. When defects only are being populated, Li exhibits a heat of adsorption of 410 kJ/mol. Comparing heats with recent density functional theory (DFT) calculations suggests that the defect sites are under-coordinated O atoms at steps or kinks, or related structures at dislocations. The work function decreases by ˜1.8eV within the first 0.5 ML and then increases to near the value of bulk Li(solid), ˜2.6eV , by 3 ML. These results support recent DFT calculations predicting stronger electron transfer from Li to the MgO when at steps and kinks than at terraces, and decreasing charge transfer as 2D Li clusters grow. The work function starts to increase when the growth mode becomes dominated by growth of 3D Li(solid). In spite of a large amount of electron transfer from Li to MgO, Li adatoms have attractive interactions that lead to 2D clustering. For 1-nm-thick MgO films, the heat of adsorption was higher by 60-20 kJ/mol than for 4 nm films in the entire range from 0 to 0.7 ML, where adsorption in the first layer dominates.

  19. The simplest equivalent circuit of a pulsed dielectric barrier discharge and the determination of the gas gap charge transfer

    SciTech Connect

    Pipa, A. V.; Brandenburg, R.; Hoder, T. [Leibniz Institute for Plasma Science and Technology (INP Greifswald), Felix-Hausdorff-Str. 2, Greifswald 17489 (Germany); Koskulics, J. [Light and Life Laboratory, Department of Physics and Engineering Physics, Stevens Institute of Technology, Hoboken, New Jersey 07030 (United States)

    2012-11-15

    The concept of the simplest equivalent circuit for a dielectric barrier discharge (DBD) is critically reviewed. It is shown that the approach is consistent with experimental data measured either in large-scale sinusoidal-voltage driven or miniature pulse-voltage driven DBDs. An expression for the charge transferred through the gas gap q(t) is obtained with an accurate account for the displacement current and the values of DBD reactor capacitance. This enables (i) the significant reduction of experimental error in the determination of q(t) in pulsed DBDs, (ii) the verification of the classical electrical theory of ozonizers about maximal transferred charge q{sub max}, and (iii) the development of a graphical method for the determination of q{sub max} from charge-voltage characteristics (Q-V plots, often referred as Lissajous figures) measured under pulsed excitation. The method of graphical presentation of q{sub max} is demonstrated with an example of a Q-V plot measured under pulsed excitation. The relations between the discharge current j{sub R}(t), the transferred charge q(t), and the measurable parameters are presented in new forms, which enable the qualitative interpretation of the measured current and voltage waveforms without the knowledge about the value of the dielectric barrier capacitance C{sub d}. Whereas for quantitative evaluation of electrical measurements, the accurate estimation of the C{sub d} is important.

  20. An insight into the mechanism of charge-transfer of hybrid polymer:ternary/quaternary chalcopyrite colloidal nanocrystals.

    PubMed

    Chawla, Parul; Singh, Son; Sharma, Shailesh Narain

    2014-01-01

    In this work, we have demonstrated the structural and optoelectronic properties of the surface of ternary/quaternary (CISe/CIGSe/CZTSe) chalcopyrite nanocrystallites passivated by tri-n-octylphosphine-oxide (TOPO) and tri-n-octylphosphine (TOP) and compared their charge transfer characteristics in the respective polymer: chalcopyrite nanocomposites by dispersing them in poly(3-hexylthiophene) polymer. It has been found that CZTSe nanocrystallites due to their high crystallinity and well-ordered 3-dimensional network in its pristine form exhibit a higher steric- and photo-stability, resistance against coagulation and homogeneity compared to the CISe and CIGSe counterparts. Moreover, CZTSe nanocrystallites display efficient photoluminescence quenching as evident from the high value of the Stern-Volmer quenching constant (K SV) and eventually higher charge transfer efficiency in their respective polymer P3HT:CZTSe composites. We modelled the dependency of the charge transfer from the donor and the charge separation mechanism across the donor-acceptor interface from the extent of crystallinity of the chalcopyrite semiconductors (CISe/CIGSe/CZTSe). Quaternary CZTSe chalcopyrites with their high crystallinity and controlled morphology in conjunction with regioregular P3HT polymer is an attractive candidate for hybrid solar cells applications. PMID:25161859

  1. An insight into the mechanism of charge-transfer of hybrid polymer:ternary/quaternary chalcopyrite colloidal nanocrystals

    PubMed Central

    Chawla, Parul; Singh, Son

    2014-01-01

    Summary In this work, we have demonstrated the structural and optoelectronic properties of the surface of ternary/quaternary (CISe/CIGSe/CZTSe) chalcopyrite nanocrystallites passivated by tri-n-octylphosphine-oxide (TOPO) and tri-n-octylphosphine (TOP) and compared their charge transfer characteristics in the respective polymer: chalcopyrite nanocomposites by dispersing them in poly(3-hexylthiophene) polymer. It has been found that CZTSe nanocrystallites due to their high crystallinity and well-ordered 3-dimensional network in its pristine form exhibit a higher steric- and photo-stability, resistance against coagulation and homogeneity compared to the CISe and CIGSe counterparts. Moreover, CZTSe nanocrystallites display efficient photoluminescence quenching as evident from the high value of the Stern–Volmer quenching constant (K SV) and eventually higher charge transfer efficiency in their respective polymer P3HT:CZTSe composites. We modelled the dependency of the charge transfer from the donor and the charge separation mechanism across the donor–acceptor interface from the extent of crystallinity of the chalcopyrite semiconductors (CISe/CIGSe/CZTSe). Quaternary CZTSe chalcopyrites with their high crystallinity and controlled morphology in conjunction with regioregular P3HT polymer is an attractive candidate for hybrid solar cells applications. PMID:25161859

  2. Influence of atomic layer deposition chemistry on high- k dielectrics for charge trapping memories

    NASA Astrophysics Data System (ADS)

    Nikolaou, Nikolaos; Dimitrakis, Panagiotis; Normand, Pascal; Ioannou-Sougleridis, Vassilios; Giannakopoulos, Konstantinos; Mergia, Konstantina; Kukli, Kaupo; Niinistö, Jaakko; Ritala, Mikko; Leskelä, Markku

    2012-02-01

    In this work we report the performance of the SiO 2/Si 3N 4/HfO 2 and SiO 2/Si 3N 4/ZrO 2 stacks with emphasis on the influence of atomic layer deposition chemistry used for forming the HfO 2 and ZrO 2 blocking layers. Two Hf precursors were employed - tetrakis(ethylmethylamino)hafnium (TEMAH) and bis(methylcyclopentadienyl)methoxymethyl hafnium (HfD-04). For ZrO 2, tetrakis(ethylmethylamino)zirconium (TEMAZ) and bis(methylcyclopentadienyl)methoxymethyl zirconium (ZrD-04) were used as metal precursors. Ozone was used as the oxygen source. The structural characteristics of the stacks were examined by transmission electron microscopy and grazing incidence X-ray diffraction. The electrical properties of the stacks were studied using platinum-gated capacitor structures. The memory performance of the stacks was evaluated by write/erase (W/E) measurements, endurance and retention testing. Endurance measurements revealed the most important difference between the stacks. The films grown from TEMAH and TEMAZ could withstand a significantly higher number of W/E pulses (>3 × 10 5 in the 10 V/-11 V, 10 ms regime), in comparison to the stacks made from HfD-04 and ZrD-04 precursors (<5 × 10 3 W/E cycles). This difference in endurance characteristics is attributed mainly to the different deposition temperatures suited for these two precursors and the nature of the layer formed at the Si 3N 4/HfO 2 and the Si 3N 4/ZrO 2 interfaces.

  3. Geometry and quadratic nonlinearity of charge transfer complexes in solution: A theoretical study

    SciTech Connect

    Mukhopadhyay, S.; Ramasesha, S. [Solid State and Structural Chemistry Unit, Indian Institute of Science, Bangalore 560012 (India); Pandey, Ravindra; Das, Puspendu K. [Department of Inorganic and Physical Chemistry, Indian Institute of Science, Bangalore 560012 (India)

    2011-01-28

    In this paper, we have computed the quadratic nonlinear optical (NLO) properties of a class of weak charge transfer (CT) complexes. These weak complexes are formed when the methyl substituted benzenes (donors) are added to strong acceptors like chloranil (CHL) or di-chloro-di-cyano benzoquinone (DDQ) in chloroform or in dichloromethane. The formation of such complexes is manifested by the presence of a broad absorption maximum in the visible range of the spectrum where neither the donor nor the acceptor absorbs. The appearance of this visible band is due to CT interactions, which result in strong NLO responses. We have employed the semiempirical intermediate neglect of differential overlap (INDO/S) Hamiltonian to calculate the energy levels of these CT complexes using single and double configuration interaction (SDCI). The solvent effects are taken into account by using the self-consistent reaction field (SCRF) scheme. The geometry of the complex is obtained by exploring different relative molecular geometries by rotating the acceptor with respect to the fixed donor about three different axes. The theoretical geometry that best fits the experimental energy gaps, {beta}{sub HRS} and macroscopic depolarization ratios is taken to be the most probable geometry of the complex. Our studies show that the most probable geometry of these complexes in solution is the parallel displaced structure with a significant twist in some cases.

  4. Formation of an intermolecular charge-transfer compound in UHV codeposited tetramethoxypyrene and tetracyanoquinodimethane

    NASA Astrophysics Data System (ADS)

    Medjanik, K.; Perkert, S.; Naghavi, S.; Rudloff, M.; Solovyeva, V.; Chercka, D.; Huth, M.; Nepijko, S. A.; Methfessel, T.; Felser, C.; Baumgarten, M.; Müllen, K.; Elmers, H. J.; Schönhense, G.

    2010-12-01

    Ultrahigh vacuum (UHV)-deposited films of the mixed phase of tetramethoxypyrene and tetracyanoquinodimethane (TMP1-TCNQ1) on gold have been studied using ultraviolet photoelectron spectroscopy (UPS), x-ray diffraction (XRD), infrared (IR) spectroscopy, and scanning tunneling spectroscopy (STS). The formation of an intermolecular charge-transfer (CT) compound is evident from the appearance of new reflexes in XRD ( d1=0.894nm and d2=0.677nm ). A softening of the CN stretching vibration (redshift by 7cm-1 ) of TCNQ is visible in the IR spectra, being indicative of a CT on the order of 0.3e from TMP to TCNQ in the complex. Characteristic shifts in the electronic level positions occur in UPS and STS that are in reasonable agreement with the prediction of density-functional theory (DFT) calculations (GAUSSIAN03 with hybrid functional B3LYP). STS reveals a highest occupied molecular orbital (HOMO)-lowest unoccupied molecular orbital (LUMO) gap of the CT complex of about 1.25 eV being much smaller than the gaps (>3.0eV) of the pure moieties. The electron-injection and hole-injection barriers are 0.3 eV and 0.5 eV, respectively. Systematic differences in the positions of the HOMOs determined by UPS and STS are discussed in terms of the different information content of the two methods.

  5. Kinetics of charge transfer at the lipid bilayer-water interface on the nanosecond time scale.

    PubMed Central

    Woodle, M; Zhang, J W; Mauzerall, D

    1987-01-01

    Advances in instrumentation allow electrical measurements across the planar lipid bilayer to be made with nanosecond time resolution. The electron transfer reaction between photoexcited magnesium octaethylporphyrin in the lipid to a variety of ionically charged acceptors in the water is found to be purely dynamic over a wide range of concentrations of acceptors and up to the time constant of the apparatus, 4 ns. The saturation of the amplitude of the photovoltage with increasing concentration of acceptor is caused by the finite lifetime of the excited state, not by formation of a static pigment-acceptor complex. The reactions are an excellent probe of the lipid-water interface over an extended time scale. No appreciable barrier to reaction exists at this interface beyond the 5-ns time. That is, any water or choline group structure may be evanescent on this time scale. Electrostatic interactions indicate that the acceptor molecules penetrate to the level of the phosphocholine groups with differing orientations. It will be possible to extend the time scale into the picosecond range by decreasing the response time and by deconvolutions. PMID:3676439

  6. Study of fluorescence characteristics of the charge-transfer reaction of quinolone agents with bromanil

    NASA Astrophysics Data System (ADS)

    Li, Wen-Ying; Chen, Xiao-Fang; Xuan, Chun-Sheng

    2009-01-01

    A spectrofluorimetric method was discussed for the determination of three antibacterial quinolone derivatives, ofloxacin (OFL), norfloxacin (NOR) and ciprofloxacin (CIP) through charge-transfer complexation (CTC) with 2,3,5,6-tetrabromo-1,4-benzoquinone (bromanil, TBBQ). The method was based on the reaction of these drugs as n-electron donors with the ?-acceptor TBBQ. TBBQ was found to react with these drugs to produce a kind of yellow complexes and the fluorescence intensities of the complexes were enhanced by 29-36 times more than those of the corresponding monomers. UV-vis, 1H NMR and XPS techniques were used to study the complexes formed. The various experimental parameters affecting the fluorescence intensity were studied and optimized. Under optimal reaction conditions, the rectilinear calibration graphs were obtained in the concentration range of 0.021-2.42 ?g mL -1, 0.017-2.63 ?g mL -1 and 0.019-2.14 ?g mL -1 for OFL, NOR and CIP, respectively. The methods developed were applied successfully to the determination of the subject drugs in their pharmaceutical dosage forms with good precision and accuracy compared to official and reported methods as revealed by t- and F-tests.

  7. Tuning the charge transfer plasmon in a metallic nanoparticle dimer bridged by a quantum dot

    NASA Astrophysics Data System (ADS)

    Kulkarni, Vikram; Manjavacas, Alejandro; Nordlander, Peter

    2015-03-01

    Localized surface plasmon resonances (LSPR) are a subject of intense experimental and theoretical research interest. LSPR have found applications in catalysis, solar energy, cancer therapy, and surface enhanced Raman spectroscopy (SERS). This is due to the exceptional light capturing and focusing capabilities of plasmonic nanostructures. An LSPR of particular interest is the charge transfer plasmon (CTP). This mode may be excited when two plasmonic nanoparticles are bridged by a conductive junction. The CTP is extraordinarily sensitive to the conductive properties of the junction. Here we perform a theoretical investigation of the CTP when two plasmonic nanoparticles are bridged by a quantum dot. All simulations are done using the time dependent density functional theory (TDDFT). By modulating the electronic structure of the quantum dot we are able to effectively turn the CTP on and off. Specifically, the CTP emerges only when a quantum dot energy level is resonant with the fermi energy of the plasmonic nanoparticles. We verify that the conductance through the junction is on the order of the quantum unit of conductance. This work is of great interest to the future design of plasmonic and molecular electronic systems. This work was supported in part by the Data Analysis and Visualization Cyberinfrastructure funded by NSF under Grant OCI-0959097.

  8. Non-adiabatic couplings in resonant charge transfer during atom surface collisions

    NASA Astrophysics Data System (ADS)

    Bahrim, B.; Teillet-Billy, D.; Gauyacq, J. P.

    1999-07-01

    The formation of the metastable ( 1D and 1S) negative ion levels associated with the 2p 4 electronic configuration of nitrogen is theoretically investigated in the course of collisions on an aluminium surface with alkali adsorbates. The multi-electron and multi-state aspects due to the presence of a few quasi-equivalent electrons in nitrogen are shown to lead to a complex structure of the resonant charge transfer (RCT) process. The RCT between the metal target and the nitrogen is deeply influenced by the presence of alkali adsorbates on the surface. The interaction between the N - ion levels and the adsorbate level leads to the possibility of non-adiabatic transitions induced by the collision movement. A diabatic modelling is presented, allowing an easy treatment of these non-adiabatic transitions and an evaluation of their importance. These theoretical results are then used for a discussion of the experimental results by Müller et al. [H. Müller, R. Hausmann, H. Brenten, V. Kempter, Surf. Sci. 303 (1994) 56]. They can account for the unexpected experimental observation of a sizeable electron emission due to the decay of free N -( 1D) ions formed by collisions on alkali-covered metal surfaces.

  9. Spectroscopy and dynamics of charge transfer excitons in type-II band aligned quantum confined heterostructures

    NASA Astrophysics Data System (ADS)

    Kushavah, Dushyant; Mohapatra, P. K.; Rustagi, K. C.; Bahadur, D.; Vasa, P.; Singh, B. P.

    2015-05-01

    We illustrate effect of charge transfer (CT) in type-II quantum confined heterostructure by comparing CdSe quantum dots (QDs), CdSe/CdTe heterostructure quantum dots (HQDs) and CdSe/CdTe/CdSe quantum well-quantum dots (QWQDs) heterostructures. CdSe core QDs were synthesized using a kinetic growth method where QD size depends on reaction time. For shell coating we used modified version of successive ionic layer adsorption and reaction (SILAR). Size of different QDs ˜5 to 7 nm were measured by transmission electron microscopy (TEM). Strong red shift from ˜597 to ˜746 nm in photoluminescence (PL) spectra from QDs to QWQDs shows high tunability which is not possible with single constituent semiconductor QDs. PL spectra have been recorded at different temperatures (10K-300K). Room temperature time correlated single photon counting (TCSPC) measurements for QDs to QWQDs show three exponential radiative decay. The slowest component decay constant in QWQDs comes around eight fold to ˜51 ns as compared to ˜6.5 ns in HQD suggesting new opportunities to tailor the radiative carrier recombination rate of CT excitons.

  10. Vibrational coherences in charge-transfer dyes: A non-adiabatic picture

    NASA Astrophysics Data System (ADS)

    Sissa, Cristina; Delchiaro, Francesca; Di Maiolo, Francesco; Terenziani, Francesca; Painelli, Anna

    2014-10-01

    Essential-state models efficiently describe linear and nonlinear spectral properties of different families of charge-transfer chromophores. Here, the essential-state machinery is applied to the calculation of the early-stage dynamics after ultrafast (coherent) excitation of polar and quadrupolar chromophores. The fully non-adiabatic treatment of coupled electronic and vibrational motion allows for a reliable description of the dynamics of these intriguing systems. In particular, the proposed approach is reliable even when the adiabatic and harmonic approximations do not apply, such as for quadrupolar dyes that show a multistable, broken-symmetry excited state. Our approach quite naturally leads to a clear picture for a dynamical Jahn-Teller effect in these systems. The recovery of symmetry due to dynamical effects is however disrupted in polar solvents where a static symmetry lowering is observed. More generally, thermal disorder in polar solvents is responsible for dephasing phenomena, damping the coherent oscillations with particularly important effects in the case of polar dyes.

  11. S-, N- and C-doped titanium dioxide nanoparticles: Synthesis, characterization and redox charge transfer study

    SciTech Connect

    Madhusudan Reddy, K. [Inorganic and Physical Chemistry Division, Indian Institute of Chemical Technology, Hyderabad 500 007 (India); Baruwati, Babita [Inorganic and Physical Chemistry Division, Indian Institute of Chemical Technology, Hyderabad 500 007 (India); Jayalakshmi, M. [Inorganic and Physical Chemistry Division, Indian Institute of Chemical Technology, Hyderabad 500 007 (India); Mohan Rao, M. [Inorganic and Physical Chemistry Division, Indian Institute of Chemical Technology, Hyderabad 500 007 (India); Manorama, Sunkara V [Inorganic and Physical Chemistry Division, Indian Institute of Chemical Technology, Hyderabad 500 007 (India)]. E-mail: manorama@iict.res.in

    2005-11-15

    Herein we report on the synthesis and characterization of TiO{sub 2} nanomaterials doped with anions like sulfur, carbon and nitrogen. Upon doping, the absorption extends well into the visible region. This shift in the absorption edge is accompanied by a concomitant narrowing of band gap. The resulting anion-doped TiO{sub 2} nanomaterials were characterized by XRD, XPS, elemental analysis, EDAX, TEM, UV-DRS, DC conductivity, AC impedance and cyclic voltammetric studies. XPS confirms the presence of the dopants and the elemental analysis determined the amount of dopants in TiO{sub 2}. Electrochemical characterization was carried out by cyclic voltammetry at pHs 2, 6.5 and 10. As against the response of undoped TiO{sub 2}, the doped samples show an active electrochemical response indicating an induced charge transfer across the titania/solution interface, thus forming two anodic peaks and a cathodic peak. This interesting and significant observation was understood in terms of band bending due to anion doping as well as to the pH changes in the experimental solutions.

  12. Antibacterial activity of large-area monolayer graphene film manipulated by charge transfer

    PubMed Central

    Li, Jinhua; Wang, Gang; Zhu, Hongqin; Zhang, Miao; Zheng, Xiaohu; Di, Zengfeng; Liu, Xuanyong; Wang, Xi

    2014-01-01

    Graphene has attracted increasing attention for potential applications in biotechnology due to its excellent electronic property and biocompatibility. Here we use both Gram-positive Staphylococcus aureus (S. aureus) and Gram-negative Escherichia coli (E. coli) to investigate the antibacterial actions of large-area monolayer graphene film on conductor Cu, semiconductor Ge and insulator SiO2. The results show that the graphene films on Cu and Ge can surprisingly inhibit the growth of both bacteria, especially the former. However, the proliferation of both bacteria cannot be significantly restricted by the graphene film on SiO2. The morphology of S. aureus and E. coli on graphene films further confirms that the direct contact of both bacteria with graphene on Cu and Ge can cause membrane damage and destroy membrane integrity, while no evident membrane destruction is induced by graphene on SiO2. From the viewpoint of charge transfer, a plausible mechanism is proposed here to explain this phenomenon. This study may provide new insights for the better understanding of antibacterial actions of graphene film and for the better designing of graphene-based antibiotics or other biomedical applications. PMID:24619247

  13. Oscillatory Non-collinear Magnetism Induced by Interfacial Charge Transfer in Metallic Oxide Superlattices

    NASA Astrophysics Data System (ADS)

    Hoffman, Jason

    2015-03-01

    Non-collinear magnetic textures give rise to interesting charge and spin transport properties, and allow for control of magnetism using small electric currents. While these textures have been observed in a number of bulk materials and in thin films, realizing non-collinear magnetism in heterostructures presents new avenues to control their properties using tailored interfaces and gate electric fields. We have discovered a non-collinear magnetic coupling in superlattices comprised of two metallic perovskites, La2/3Sr1/3MnO3 (LSMO) and LaNiO3 (LNO). The superlattices are synthesized using oxide molecular beam epitaxy, and characterized with a variety of means, including x-ray and neutron scattering. We find that the angle between the magnetization of the LSMO layers varies in an oscillatory manner with the thickness of the intervening LNO. The magnetic field and temperature dependence of this coupling angle cannot be explained using models that incorporate bilinear and biquadratic coupling, which are commonly used to describe non-collinear magnetism in conventional metallic heterostructures. Furthermore, we observe substantial electron transfer from the LSMO into the LNO layer, causing the Ni sites in the vicinity of interfaces to be in approximately a 2+ oxidation state. We propose a model where these localized Ni2+ spins in the LNO couple to a momentum dependent spin susceptibility, giving rise to a spiral magnetic structure within the LNO.

  14. Antibacterial activity of large-area monolayer graphene film manipulated by charge transfer.

    PubMed

    Li, Jinhua; Wang, Gang; Zhu, Hongqin; Zhang, Miao; Zheng, Xiaohu; Di, Zengfeng; Liu, Xuanyong; Wang, Xi

    2014-01-01

    Graphene has attracted increasing attention for potential applications in biotechnology due to its excellent electronic property and biocompatibility. Here we use both Gram-positive Staphylococcus aureus (S. aureus) and Gram-negative Escherichia coli (E. coli) to investigate the antibacterial actions of large-area monolayer graphene film on conductor Cu, semiconductor Ge and insulator SiO2. The results show that the graphene films on Cu and Ge can surprisingly inhibit the growth of both bacteria, especially the former. However, the proliferation of both bacteria cannot be significantly restricted by the graphene film on SiO2. The morphology of S. aureus and E. coli on graphene films further confirms that the direct contact of both bacteria with graphene on Cu and Ge can cause membrane damage and destroy membrane integrity, while no evident membrane destruction is induced by graphene on SiO2. From the viewpoint of charge transfer, a plausible mechanism is proposed here to explain this phenomenon. This study may provide new insights for the better understanding of antibacterial actions of graphene film and for the better designing of graphene-based antibiotics or other biomedical applications. PMID:24619247

  15. Origin and impact of recombination via charge transfer excitons in polymer/fullerene solar cells

    NASA Astrophysics Data System (ADS)

    Hallermann, Markus; da Como, Enrico; Feldmann, Jochen

    2010-03-01

    To further advance the performances of organic photovoltaic cells a thorough understanding of loss mechanisms in polymer/fullerene blends is mandatory. Recombination via charge transfer excitons (CTEs) appears to be a fundamental loss, potentially impacting the open circuit voltage (VOC) and the short circuit current (ISC) of cells. We unravel the origin of CTEs forming in polymer/fullerene blends and discuss their importance in recombination processes considering binding energy [1], polymer conformation [2], and energetic position. CTE photoluminescence (PL) is observed in material combinations such as P3HT and PPV blended with fullerene acceptors. By combining electron microscopy and PL spectroscopy, we show that CTE recombination is only slightly influenced by the mesoscopic morphology, whereas strongly by the polymer chain conformation [2]. By shifting the orbital energies of the fullerene, we tune the CTE PL characteristics. High energy CTE emission results in cells with a beneficial increase in VOC. On the other hand, high energy CTE emission leads to a more efficient recombination impacting directly the ISC. The results highlight a fundamental limit in the efficiency of organic solar cells with CTE recombination. [1] Hallermann et al. APL 2008 [2] Hallermann et al. AFM 2009

  16. Photosynthesis Revisited: Optimization of Charge and Energy Transfer in Quantum Materials

    NASA Astrophysics Data System (ADS)

    Gabor, Nathaniel

    2014-03-01

    The integration of new nano- and molecular-scale quantum materials into ultra-efficient energy harvesting devices presents significant scientific challenges. Of the many challenges, the most difficult is achieving high photon-to-electron conversion efficiency while maintaining broadband absorption. Due to exciton effects, devices composed of quantum materials may allow near-unity optical absorption efficiency yet require the choice of precisely one fundamental energy (HOMO-LUMO gap). To maximize absorption, the simplest device would absorb at the peak of the solar spectrum, which spans the visible wavelengths. If the peak of the solar spectrum spans the visible wavelengths, then why are terrestrial plants green? Here, I discuss a physical model of photosynthetic absorption and photoprotection in which the cell utilizes active feedback to optimize charge and energy transfer, thus maximizing stored energy rather than absorption. This model, which addresses the question of terrestrial greenness, is supported by several recent results that have begun to unravel the details of photoprotection in higher plants. More importantly, this model indicates a novel route for the design of next-generation energy harvesting systems based on nano- and molecular-scale quantum materials.

  17. Spectrophotometric Determination of Mycophenolate Mofetil as Its Charge-Transfer Complexes with Two ?-Acceptors

    PubMed Central

    Vinay, K. B.; Revanasiddappa, H. D.; Raghu, M. S.; Abdulrahman, Sameer. A. M.; Rajendraprasad, N.

    2012-01-01

    Two simple, selective, and rapid spectrophotometric methods are described for the determination of mycophenolate mofetil (MPM) in pure form and in tablets. Both methods are based on charge-transfer complexation reaction of MPM with p-chloranilic acid (p-CA) or 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) in dioxane-acetonitrile medium resulting in coloured product measurable at 520 nm (p-CA) or 580?nm (DDQ). Beer's law is obeyed over the concentration ranges of 40–400 and 12–120??g?mL?1 MPM for p-CA and DDQ, respectively, with correlation coefficients (r) of 0.9995 and 0.9947. The apparent molar absorptivity values are calculated to be 1.06 × 103 and 3.87 × 103?L?mol?1?cm?1, respectively, and the corresponding Sandell's sensitivities are 0.4106 and 0.1119??g?cm?1. The limits of detection (LOD) and quantification (LOQ) are also reported for both methods. The described methods were successfully applied to the determination of MPM in tablets. Statistical comparison of the results with those of the reference method showed excellent agreement. No interference was observed from the common excipients present in tablets. Both methods were validated statistically for accuracy and precision. The accuracy and reliability of the methods were further ascertained by recovery studies via standard addition procedure. PMID:22567572

  18. [Ultraviolet spectral characteristics of charge-transfer reaction complex in micellar system and its application].

    PubMed

    Du, Li-ming; Chen, Cai-ping; Li, Jian-hua

    2005-02-01

    Charge-transfer (CT) reaction of chloranil (TCBQ) as a pi-electron acceptor with fleroxacin (FLX) as an electron donor has been studied by ultraviolet spectrophotometry method. Experiment showed that FLX reacted with TCBQ in sodium dodecyl sulfate (SDS) micellar systems, and a stable complex was formed and the absorbency was remarkably enhanced. Therefore, a simple, rapid, accurate and sensitive method for the determination of FLX has been developed. Beer's law is obeyed in the range of 0.6-24 mg x L(-1) of FLX and r = 0.9993. The apparent molar absorptivity of CT complexes at 326 nm is 3.3 x 10(4) L x mol(-1) x cm(-1). The composition of CT complex was found to be 1:1 by Bent-French and curved intersection methods. The proposed method has been applied to the determination of ESL in tablets. The recoveries are 99.2%-99.7%. The relative standard deviation is 0.7%-2.1%. The proposed methods are suitable for the routine quality control of drug alone and in tablets or capsules without fear of interference caused by the excipients expected to be present in tablets or capsules. PMID:15852876

  19. High-surface-area architectures for improved charge transfer kinetics at the dark electrode in dye-sensitized solar cells.

    PubMed

    Hoffeditz, William L; Katz, Michael J; Deria, Pravas; Martinson, Alex B F; Pellin, Michael J; Farha, Omar K; Hupp, Joseph T

    2014-06-11

    Dye-sensitized solar cell (DSC) redox shuttles other than triiodide/iodide have exhibited significantly higher charge transfer resistances at the dark electrode. This often results in poor fill factor, a severe detriment to device performance. Rather than moving to dark electrodes of untested materials that may have higher catalytic activity for specific shuttles, the surface area of platinum dark electrodes could be increased, improving the catalytic activity by simply presenting more catalyst to the shuttle solution. A new copper-based redox shuttle that experiences extremely high charge-transfer resistance at conventional Pt dark electrodes yields cells having fill-factors of less than 0.3. By replacing the standard Pt dark electrode with an inverse opal Pt electrode fabricated via atomic layer deposition, the dark electrode surface area is boosted by ca. 50-fold. The resulting increase in interfacial electron transfer rate (decrease in charge-transfer resistance) nearly doubles the fill factor and therefore the overall energy conversion efficiency, illustrating the utility of this high-area electrode for DSCs. PMID:24828106

  20. Effects of Electron-Transfer Coupled with Collision-Induced Dissociation (ET/CID) on Doubly Charged Peptides and Phosphopeptides

    NASA Astrophysics Data System (ADS)

    Liu, Chih-Wei; Lai, Chien-Chen

    2011-01-01

    Electron-transfer dissociation (ETD) is a useful peptide fragmentation technique that can be applied to investigate post-translational modifications (PTMs), the sequencing of highly hydrophilic peptides, and the identification of large peptides and even intact proteins. In contrast to traditional fragmentation methods, such as collision-induced dissociation (CID), ETD produces c- and z·-type product ions by randomly cleaving the N-C? bonds. The disappointing fragmentation efficiency of ETD for doubly charged peptides and phosphopeptide ions has been improved by ETcaD (supplemental activation). However, the ETD data derived from most database search algorithms yield low confidence scores due to the presence of unreacted precursors and charge-reduced ions within MS/MS spectra. In this work, we demonstrate that eight out of ten standard doubly charged peptides and phosphopeptides can be effortlessly identified by electron-transfer coupled with collision-induced dissociation (ET/CID) using the SEQUEST algorithm without further spectral processing. ET/CID was performed with the further dissociation of the charge-reduced ions isolated from ETD ion/ion reactions. ET/CID had high fragmentation efficiency, which elevated the confidence scores of doubly charged peptide and phosphospeptide sequencing. ET/CID was found to be an effective fragmentation strategy in "bottom-up" proteomic analysis.

  1. Molecular layers of ZnPc and FePc on Au(111) surface: Charge transfer and chemical interaction

    NASA Astrophysics Data System (ADS)

    Ahmadi, Sareh; Shariati, M. Nina; Yu, Shun; Göthelid, Mats

    2012-08-01

    We have studied zinc phthalocyanine (ZnPc) and iron phthalocyanine (FePc) thick films and monolayers on Au(111) using photoelectron spectroscopy and x-ray absorption spectroscopy. Both molecules are adsorbed flat on the surface at monolayer. ZnPc keeps this orientation in all investigated coverages, whereas FePc molecules stand up in the thick film. The stronger inter-molecular interaction of FePc molecules leads to change of orientation, as well as higher conductivity in FePc layer in comparison with ZnPc, which is reflected in thickness-dependent differences in core-level shifts. Work function changes indicate that both molecules donate charge to Au; through the ?-system. However, the Fe3d derived lowest unoccupied molecular orbital receives charge from the substrate when forming an interface state at the Fermi level. Thus, the central atom plays an important role in mediating the charge, but the charge transfer as a whole is a balance between the two different charge transfer channels; ?-system and the central atom.

  2. Unimolecular reaction chemistry of a charge-tagged beta-hydroxyperoxyl radical.

    PubMed

    So, Sui; Kirk, Benjamin B; Trevitt, Adam J; Wille, Uta; Blanksby, Stephen J; da Silva, Gabriel

    2014-12-01

    ?-Hydroxyperoxyl radicals are formed during atmospheric oxidation of unsaturated volatile organic compounds such as isoprene. They are intermediates in the combustion of alcohols. In these environments the unimolecular isomerization and decomposition of ?-hydroxyperoxyl radicals may be of importance, either through chemical or thermal activation. We have used ion-trap mass spectrometry to generate the distonic charge-tagged ?-hydroxyalkyl radical anion, ?CH2C(OH)(CH3)CH2C(O)O(-), and investigated its subsequent reaction with O2 in the gas phase under conditions that are devoid of complicating radical-radical reactions. Quantum chemical calculations and master equation/RRKM theory modeling are used to rationalize the results and discern a reaction mechanism. Reaction is found to proceed via initial hydrogen abstraction from the ?-methylene group and from the ?-hydroxyl group, with both reaction channels eventually forming isobaric product ions due to loss of either ?OH + HCHO or ?OH + CO2. Isotope labeling studies confirm that a 1,5-hydrogen shift from the ?-hydroxyl functionality results in a hydroperoxyalkoxyl radical intermediate that can undergo further unimolecular dissociations. Furthermore, this study confirms that the facile decomposition of ?-hydroxyperoxyl radicals can yield ?OH in the gas phase. PMID:25325244

  3. Using computational chemistry to understand proton transfer in Green Fluorescent Protein

    NASA Astrophysics Data System (ADS)

    Hoskin, Christa; Champion, Paul; Sage, Timothy; Benabbas, Abdelkrim; Demidov, Alexander; Salna, Bridget

    2012-02-01

    Green Fluorescent Protein has been studied experimentally by the scientific community for years yet frustratingly little is known about the underlying proton transfer process that produces the green fluorescence. We are trying to elucidate more about this process using Density Functional Theory to prepare and run various calculations on GFP that we compare with kinetics data, Raman and vibrational coherence spectra. I am building a model of wild type GFP that is realistically sized for our computational power, yet still contains key residues that might affect the proton transport process. I will compare my results to those of the E222D GFP mutant. This comparison will allow us to see any differences in energy and normal modes that give insights regarding the proton transfer process. For example, how does it depend on a variety of factors such as temperature, buffer, pH, mutations, etc.? We also plan to examine if the proton transfer propagates through the three donor-acceptor pairs of the ``proton wire'' consecutively versus the three protons on the wire transferring simultaneously. Finally, we will consider how quantum tunneling may be involved in the proton transfer.

  4. Charge transfer and in-cloud structure of large-charge-moment positive lightning strokes in a mesoscale convective system

    E-print Network

    Cummer, Steven A.

    in a mesoscale convective system Gaopeng Lu,1 Steven A. Cummer,1 Jingbo Li,1 Feng Han,1 Richard J. Blakeslee,2 positive cloud-to-ground (+CG) strokes in a mesoscale convective system. Although no high altitude images of large-charge-moment positive lightning strokes in a mesoscale convective system, Geophys. Res. Lett., 36

  5. The Complex Core Level Spectra of CeO2: An Analysis in Terms of Atomic and Charge Transfer Effects

    SciTech Connect

    Bagus, Paul S.; Nelin, Constance J.; Ilton, Eugene S.; Baron, Martin; Abbott, Heather; Primorac, Elena; Kuhlenbeck, Helmut; Shaikhutdinov, Shamil; Freund, Hans-Joachim

    2010-03-05

    We present a rigorous parameter-free theoretical treatment of the Ce 4s and 5s photoelectron spectra of CeO2. In the currently accepted model the satellite structure in the photoelectron spectra is explained in terms of a mixed valence (Ce 4f0 O 2p6, Ce 4f1 O 2p5, and Ce 4f2 O 2p4) con?guration. We show that charge transfer (CT) into Ce 5d as well as con?gurations involving intra-atomic movement of charge must be considered in addition and compute their contributions to the spectra.

  6. Localization of a charge transfer excited state in molecular crystals: a direct confirmation by femtosecond diffuse reflectance spectroscopy

    NASA Astrophysics Data System (ADS)

    Asahi, Tsuyoshi; Matsuo, Yasutaka; Masuhara, Hiroshi

    1996-07-01

    Transient absorption spectra of the durene-pyromellitic dianhydride (PMDA) charge transfer (CT) crystal, PMDA-doped durene crystal and its molten state were measured by femtosecond diffuse reflectance spectroscopy, and electronic structure and dynamics of the excited state in the CT crystal are discussed. It is directly confirmed that the excited CT singlet state is almost localized (self-trapped) in one donor(D)-acceptor(A) unit within a few picoseconds after excitation. The electronic structure of the excited state is quite polar but it is not an electron transfer state from D to A.

  7. A 27-mW 10-bit 125-MSPS charge domain pipelined ADC with a PVT insensitive boosted charge transfer circuit

    NASA Astrophysics Data System (ADS)

    Zhenhai, Chen; Songren, Huang; Hong, Zhang; Zongguang, Yu; Huicai, Ji

    2013-03-01

    A low power 10-bit 125-MSPS charge-domain (CD) pipelined analog-to-digital converter (ADC) based on MOS bucket-brigade devices (BBDs) is presented. A PVT insensitive boosted charge transfer (BCT) that is able to reject the charge error induced by PVT variations is proposed. With the proposed BCT, the common mode charge control circuit can be eliminated in the CD pipelined ADC and the system complexity is reduced remarkably. The prototype ADC based on the proposed BCT is realized in a 0.18 ?m CMOS process, with power consumption of only 27 mW at 1.8-V supply and active die area of 1.04 mm2. The prototype ADC achieves a spurious free dynamic range (SFDR) of 67.7 dB, a signal-to-noise ratio (SNDR) of 57.3 dB, and an effective number of bits (ENOB) of 9.0 for a 3.79 MHz input at full sampling rate. The measured differential nonlinearity (DNL) and integral nonlinearity (INL) are +0.5/-0.3 LSB and +0.7/-0.55 LSB, respectively.

  8. Charge transfer in dynamical biosystems, or the treachery of (static) images.

    PubMed

    Beratan, David N; Liu, Chaoren; Migliore, Agostino; Polizzi, Nicholas F; Skourtis, Spiros S; Zhang, Peng; Zhang, Yuqi

    2015-02-17

    CONSPECTUS: The image is not the thing. Just as a pipe rendered in an oil painting cannot be smoked, quantum mechanical coupling pathways rendered on LCDs do not convey electrons. The aim of this Account is to examine some of our recent discoveries regarding biological electron transfer (ET) and transport mechanisms that emerge when one moves beyond treacherous static views to dynamical frameworks. Studies over the last two decades introduced both atomistic detail and macromolecule dynamics to the description of biological ET. The first model to move beyond the structureless square-barrier tunneling description is the Pathway model, which predicts how protein secondary motifs and folding-induced through-bond and through-space tunneling gaps influence kinetics. Explicit electronic structure theory is applied routinely now to elucidate ET mechanisms, to capture pathway interferences, and to treat redox cofactor electronic structure effects. Importantly, structural sampling of proteins provides an understanding of how dynamics may change the mechanisms of biological ET, as ET rates are exponentially sensitive to structure. Does protein motion average out tunneling pathways? Do conformational fluctuations gate biological ET? Are transient multistate resonances produced by energy gap fluctuations? These questions are becoming accessible as the static view of biological ET recedes and dynamical viewpoints take center stage. This Account introduces ET reactions at the core of bioenergetics, summarizes our team's progress toward arriving at an atomistic-level description, examines how thermal fluctuations influence ET, presents metrics that characterize dynamical effects on ET, and discusses applications in very long (micrometer scale) bacterial nanowires. The persistence of structural effects on the ET rates in the face of thermal fluctuations is considered. Finally, the flickering resonance (FR) view of charge transfer is presented to examine how fluctuations control low-barrier transport among multiple groups in van der Waals contact. FR produces exponential distance dependence in the absence of tunneling; the exponential character emerges from the probability of matching multiple vibronically broadened electronic energies within a tolerance defined by the rms coupling among interacting groups. FR thus produces band like coherent transport on the nanometer length scale, enabled by conformational fluctuations. Taken as a whole, the emerging context for ET in dynamical biomolecules provides a robust framework to design and interpret the inner workings of bioenergetics from the molecular to the cellular scale and beyond, with applications in biomedicine, biocatalysis, and energy science. PMID:25307316

  9. Coupling of electrons to intermolecular phonons in molecular charge transfer dimers: A resonance Raman study

    NASA Astrophysics Data System (ADS)

    Pedron, D.; Speghini, A.; Mulloni, V.; Bozio, R.

    1995-08-01

    We report resonance Raman scattering (RRS) spectra and Raman excitation profiles (REP) of a system containing ? dimers of identical molecular radical ions measured with laser excitation in resonance with the charge transfer (CT) transition. A Peierls-Hubbard (PH) Hamiltonian has been used to model the investigated system and to calculate its optical and RRS properties. Results are reported for two polyoxometallate salts of tetrathiafulvalene (TTF), namely (TTF)2(W6O19) and (TTF)2(Mo6O19) whose structures contain almost isolated (TTF+)2 dimers. The RRS spectra of (TTF)2(W6O19), measured in resonance with the CT absorption band centered at 832 nm, show three phonon modes located at 55, 90, and 116 cm-1 which are strongly resonance enhanced. These modes have been associated to the out-of-phase combinations of the translational motions of the two molecules composing the dimer. Such modes are effective in modulating the intradimer transfer integral, thus providing an efficient mechanism for coupling with the electronic system and for enhancement of the scattering intensity at resonance with the CT transition. The REP for the three strongly coupled modes of (TTF)2(W6O19) have been measured with laser excitation wavelengths ranging from 740 to 930 nm. Quantitative analysis of the REP data has been performed based on a perturbative solution of the PH model to second order in the electron-molecular-vibration (EMV) and electron-intermolecular-phonon (EIP) interactions. The CT absorption profile and the REP's have been calculated using a time correlator technique and the model parameters have been optimized in order to fit the experimental REP data. Infrared vibronic absorptions of (TTF)2(W6O19), originated by the EMV coupling, have been measured and independent information on the electronic parameters of the PH model have been derived. This has made the choice of the fitting parameters used for the REP calculations rather unambiguous and has allowed us to obtain, for the first time, reliable experimental estimates of the EIP coupling constants.

  10. High performance organic integrated device with ultraviolet photodetective and electroluminescent properties consisting of a charge-transfer-featured naphthalimide derivative

    NASA Astrophysics Data System (ADS)

    Wang, Hanyu; Zhou, Jie; Wang, Xu; Lu, Zhiyun; Yu, Junsheng

    2014-08-01

    A high performance organic integrated device (OID) with ultraviolet photodetective and electroluminescent (EL) properties was fabricated by using a charge-transfer-featured naphthalimide derivative of 6-{3,5-bis-[9-(4-t-butylphenyl)-9H-carbazol-3-yl]-phenoxy}-2-(4-t-butylphenyl)-benzo[de]isoquinoline-1,3-dione (CzPhONI) as the active layer. The results showed that the OID had a high detectivity of 1.5 × 1011 Jones at -3 V under the UV-350 nm illumination with an intensity of 0.6 mW/cm2, and yielded an exciplex EL light emission with a maximum brightness of 1437 cd/m2. Based on the energy band diagram, both the charge transfer feature of CzPhONI and matched energy level alignment were responsible for the dual ultraviolet photodetective and EL functions of OID.

  11. Core-shell hematite nanorods: a simple method to improve the charge transfer in the photoanode for photoelectrochemical water splitting.

    PubMed

    Gurudayal; Chee, Png Mei; Boix, Pablo P; Ge, Hu; Yanan, Fang; Barber, James; Wong, Lydia Helena

    2015-04-01

    We report a simple method to produce a stable and repeatable photoanode for water splitting with a core-shell hematite (?-Fe2O3) nanorods system by combining spray pyrolysis and hydrothermal synthesis. Impedance spectroscopy revealed passivation of the surface states by the shell layer, which results in an increase of the charge injection through the hematite conduction band. In pristine hematite more holes are accumulated on the surface and the charge transfer to the electrolyte occurs through surface states, whereas in the core-shell hematite photoanode the majority of hole transfer process occurs through the valence band. As a result the photoactivity of the core-shell nanorods, 1.2 mA cm(-2), at 1.23 V vs RHE, is twice that of pristine hematite nanorods. The alteration of the interface energetics is supported by TEM, showing that the crystallinity of the surface has been improved by the deposition of the shell. PMID:25790720

  12. High performance organic integrated device with ultraviolet photodetective and electroluminescent properties consisting of a charge-transfer-featured naphthalimide derivative

    SciTech Connect

    Wang, Hanyu; Wang, Xu; Yu, Junsheng, E-mail: luzhiyun@scu.edu.cn, E-mail: jsyu@uestc.edu.cn [State Key Laboratory of Electronic Thin Films and Integrated Devices, School of Optoelectronic Information, University of Electronic Science and Technology of China, Chengdu 610054 (China); Zhou, Jie; Lu, Zhiyun, E-mail: luzhiyun@scu.edu.cn, E-mail: jsyu@uestc.edu.cn [College of Chemistry, Sichuan University, Chengdu 610064 (China)

    2014-08-11

    A high performance organic integrated device (OID) with ultraviolet photodetective and electroluminescent (EL) properties was fabricated by using a charge-transfer-featured naphthalimide derivative of 6-(3,5-bis-[9-(4-t-butylphenyl)-9H-carbazol-3-yl]-phenoxy)-2- (4-t-butylphenyl)-benzo[de]isoquinoline-1,3-dione (CzPhONI) as the active layer. The results showed that the OID had a high detectivity of 1.5?×?10{sup 11} Jones at ?3?V under the UV-350?nm illumination with an intensity of 0.6 mW/cm{sup 2}, and yielded an exciplex EL light emission with a maximum brightness of 1437?cd/m{sup 2}. Based on the energy band diagram, both the charge transfer feature of CzPhONI and matched energy level alignment were responsible for the dual ultraviolet photodetective and EL functions of OID.

  13. Electronic structure disorder, vibronic coupling, and charge transfer excitons in poly(fluorene-alt-bithiophene):fullerene films

    SciTech Connect

    Riisness, I.; Gordon, M. J. [Department of Chemical Engineering, University of California-Santa Barbara, Santa Barbara, California 93106-5080 (United States)] [Department of Chemical Engineering, University of California-Santa Barbara, Santa Barbara, California 93106-5080 (United States)

    2013-03-18

    Charge transfer processes in conjugated polymer:fullerene blends play an important role in the operation of organic solar cells and organic light emitting diodes. Herein, near-infrared emission from poly-(9,9-dioctylfluorene-alt-bithiophene) (F8T2) and [6,6]-phenyl-C{sub 61}-butyric acid methyl ester blends was studied and attributed to charge transfer exciton (CTX) recombination. Polymer and CTX emission were monitored via low-temperature/transient photoluminescence and absorbance to elucidate the effects of annealing and composition on donor-acceptor morphology. CTX emission decreased and F8T2 vibronic structure was partially restored due to lower fullerene dispersion and polymer realignment upon annealing. Differences in the temperature-dependent emissions of the polymer singlet vs. CTX were attributed to exciton diffusion in the polymer phase vs. enhanced quenching at the donor-acceptor interface, respectively.

  14. A non-adiabatic wavepacket dynamical study of the low energy charge transfer process in the S3+ + H collision

    NASA Astrophysics Data System (ADS)

    ?abuda, Marta; González-Vázquez, Jesús; Martín, Fernando; González, Leticia

    2012-05-01

    The collisional system S3+ + H ? S2+ + H+ has been studied using a time-dependent wavepacket methodology in two-dimensions. Using available potential energy surfaces and coupling matrix elements obtained from multireference ab initio calculations, five non-adiabatically coupled electronic states of 1? symmetry have been included in the dynamical simulations. The collision has been studied in the low energy regime of 1-10 eV. The wavepacket treatment accounts for the description of the collision including all possible impact parameters simultaneously in all spatial directions of the considered plane. The molecular movie of the scattered products arising from charge transfer yields the angular distribution and the total charge transfer probability vs. initial kinetic energy of the projectile. A detailed analysis of the forward, sideways, and backward scattering mechanisms showing different patterns is presented.

  15. Time-resolved x-ray photoelectron spectroscopy techniques for real-time studies of interfacial charge transfer dynamics

    SciTech Connect

    Shavorskiy, Andrey; Hertlein, Marcus; Guo Jinghua; Tyliszczak, Tolek [Advanced Light Source, Lawrence Berkeley National Laboratory (United States); Cordones, Amy; Vura-Weis, Josh [Department of Chemistry, University of California Berkeley (United States); Siefermann, Katrin; Slaughter, Daniel; Sturm, Felix; Weise, Fabian; Khurmi, Champak; Belkacem, Ali; Weber, Thorsten; Gessner, Oliver [Ultrafast X-ray Science Laboratory, Chemical Sciences Division, Lawrence Berkeley National Laboratory (United States); Bluhm, Hendrik [Chemical Sciences Division, Lawrence Berkeley National Laboratory (United States); Strader, Matthew; Cho, Hana; Coslovich, Giacomo; Kaindl, Robert A. [Materials Sciences Division, Lawrence Berkeley National Laboratory (United States); Lin, Ming-Fu [Department of Chemistry, University of California Berkeley (United States); Ultrafast X-ray Science Laboratory, Chemical Sciences Division, Lawrence Berkeley National Laboratory (United States); and others

    2013-04-19

    X-ray based spectroscopy techniques are particularly well suited to gain access to local oxidation states and electronic dynamics in complex systems with atomic pinpoint accuracy. Traditionally, these techniques are applied in a quasi-static fashion that usually highlights the steady-state properties of a system rather than the fast dynamics that often define the system function on a molecular level. Novel x-ray spectroscopy techniques enabled by free electron lasers (FELs) and synchrotron based pump-probe schemes provide the opportunity to monitor intramolecular and interfacial charge transfer processes in real-time and with element and chemical specificity. Two complementary time-domain xray photoelectron spectroscopy techniques are presented that are applied at the Linac Coherent Light Source (LCLS) and the Advanced Light Source (ALS) to study charge transfer processes in N3 dye-sensitized ZnO semiconductor nanocrystals, which are at the heart of emerging light-harvesting technologies.

  16. Charge transfer and hybrid ferroelectricity in (YFeO3)n/(YTiO3)n magnetic superlattices

    NASA Astrophysics Data System (ADS)

    Zhang, Huimin; Weng, Yakui; Yao, Xiaoyan; Dong, Shuai

    2015-05-01

    Interfaces in oxide heterostructures always provide a fertile ground for emergent properties. Charge transfer from a high energy band to a low energy opponent is naturally expected, as occurring in semiconductor p -n junctions. In this study, several exceptional physical phenomena have been predicted in (YFeO3)n/(YTiO3)n superlattices. First, the charge transfer between these Mott insulators is in opposition to the intuitive band alignment scenario. Second, hybrid ferroelectricity with a moderate polarization is generated in the n =2 magnetic superlattice. Furthermore, the ferroelectric-type distortion can persist even if the (A B O3 )2/(A B'O3 )2 system turns out to be metallic, rending possible metallic ferroelectricity.

  17. Charge transfer in the electron donor-acceptor complexes of a meso-phenol BODIPY dye with chloranils and fullerenes

    NASA Astrophysics Data System (ADS)

    Karmakar, Animesh; Chaudhuri, Tandrima; Mula, Soumyaditya; Chattopadhyay, Subrata

    2015-02-01

    UV-Vis spectral investigations of electron donor-acceptor complexes of laser dye 2,6-Diethyl-4,4-difluoro-1,3,5,7-tetramethyl-8-(4?-hydroxyphenyl)-4-bora-3a,4a-diaza-s-indecene (1c) with chloranils and fullerenes are reported in toluene medium. Well defined charge transfer (CT) absorption bands have been located in the visible region. Oscillator strengths, transition dipole and resonance energies of the CT complexes have been estimated. Vertical ionization potential of 1c has been determined utilizing Mulliken's equation. A possible mechanism for the interaction between electronic subsystems of chloranils, [60]- and [70]fullerenes with three different BODIPY dyes (1a, 1b and 1c shown in Fig. 1) have been discussed in comparing the parameters like degree of charge transfer and binding constant in nonpolar toluene. Comparison of 1c complexes is done with DFT/B3LYP/6-31G optimized gas phase geometries.

  18. Ionic Electrets: Electrostatic Charging of Surfaces by Transferring Mobile Ions upon Contact

    E-print Network

    Prentiss, Mara

    . These observations suggest that the charge density of these ionic electret microspheres is limited by the dielectric between the number of cationic and anionic charges in the material. Crosslinked polystyrene microspheres elementary charge per 2000 nm2 ) and close to the theoretical limit imposed by the dielectric breakdown

  19. Determining the Transference Number of H[superscript +](aq) by a Modified Moving Boundary Method: A Directed Study for the Undergraduate Physical Chemistry Laboratory

    ERIC Educational Resources Information Center

    Dabke, Rajeev B.; Gebeyehu, Zewdu; Padelford, Jonathan

    2012-01-01

    A directed study for the undergraduate physical chemistry laboratory for determining the transference number of H[superscript +](aq) using a modified moving boundary method is presented. The laboratory study combines Faraday's laws of electrolysis with mole ratios and the perfect gas equation. The volume of hydrogen gas produced at the cathode is…

  20. Ultrafast Photoinduced Electron Transfer and Charge Stabilization in Donor-Acceptor Dyads Capable of Harvesting Near-Infrared Light.

    PubMed

    Bandi, Venugopal; Gobeze, Habtom B; D'Souza, Francis

    2015-08-01

    To harvest energy from the near-infrared (near-IR) and infrared (IR) regions of the electromagnetic spectrum, which constitutes nearly 70?% of the solar radiation, there is a great demand for near-IR and IR light-absorbing sensitizers that are capable of undergoing ultrafast photoinduced electron transfer when connected to a suitable electron acceptor. Towards achieving this goal, in the present study, we report multistep syntheses of dyads derived from structurally modified BF2 -chelated azadipyrromethene (ADP; to extend absorption and emission into the near-IR region) and fullerene as electron-donor and electron-acceptor entities, respectively. The newly synthesized dyads were fully characterized based on optical absorbance, fluorescence, geometry optimization, and electrochemical studies. The established energy level diagram revealed the possibility of electron transfer either from the singlet excited near-IR sensitizer or singlet excited fullerene. Femtosecond and nanosecond transient absorption studies were performed to gather evidence of excited state electron transfer and to evaluate the kinetics of charge separation and charge recombination processes. These studies revealed the occurrence of ultrafast photoinduced electron transfer leading to charge stabilization in the dyads, and populating the triplet states of ADP, benzanulated-ADP and benzanulated thiophene-ADP in the respective dyads, and triplet state of C60 in the case of BF2 -chelated dipyrromethene derived dyad during charge recombination. The present findings reveal that these sensitizers are suitable for harvesting light energy from the near-IR region of the solar spectrum and for building fast-responding optoelectronic devices operating under near-IR radiation input. PMID:26130432

  1. Semiconducting mixed Langmuir–Blodgett films of new charge-transfer complex II: N-octadecylbenzidine-TCNQ

    Microsoft Academic Search

    A. Jaiswal; R. A Singh

    2001-01-01

    The charge-transfer complex of N-octadecylbenzidine–TCNQ has been synthesized and characterized by various spectroscopic techniques. Mixed Langmuir–Blodgett films were constructed onto hydrophobic glass substrates using a 1:1 molar mixture of this complex with 1-docosanol. These films were characterized by small angle X-ray diffraction, microstructures, d.c. and a.c. electrical analyses. Analyses have also been done after exposing these LB films to iodine

  2. Understanding the charge-transfer state and singlet exciton emission from solution-processed small-molecule organic solar cells.

    PubMed

    Ran, Niva A; Kuik, Martijn; Love, John A; Proctor, Christopher M; Nagao, Ikuhiro; Bazan, Guillermo C; Nguyen, Thuc-Quyen

    2014-11-19

    Electroluminescence (EL) from the charge-transfer state and singlet excitons is observed at low applied voltages from high-performing small-molecule bulk-heterojunction solar cells. Singlet emission from the blends emerges upon altering the processing conditions, such as thermal annealing and processing with a solvent additive, and correlates with improved photovoltaic performance. Low-temperature EL measurements are utilized to access the physics behind the singlet emission. PMID:25212949

  3. Effect of surface ion charge transfer on electric conductivity of gas-polymer heterogeneous structure in pulsed. gamma. radiation

    SciTech Connect

    Elokhin, A.P.; Makeev, S.N.; Filatov, N.F.

    1988-11-01

    The radiation electric conductivity of gas-polymer heterogeneous structures with plane-parallel geometry of the electrodes in pulsed ..gamma.. radiation in the 5 x 10/sup 3/-10/sup 5/ Gy x sec/sup -1/ dose rate range was analyzed in consideration of surface ion charge transfer. An analytical expression was obtained for the radiation leakage current and it can be used in solving practical problems.

  4. Energy gap of a molecularly doped polymer measured by a new method of electron spectroscopy: Measurement of charge transfer force

    Microsoft Academic Search

    Chikara Manabe; Taishi Shigematsu; Hiroyuki Watanabe; Masaaki Shimizu

    2001-01-01

    We have proposed a new method of electron spectroscopy which is measuring charge transfer (CT) force by atomic force microscopy. We have applied this new method to a typical molecularly doped polymer system [N,N'-diphenyl-N,N'-bis(3-methylphenyl)-[1,1'-biphenyl]-4,4' diamine (TPD) and polycarbonate] to elucidate the electronic structure of the system. CT force spectra obtained show that the energy gap (Eg) continuously decreases with increasing

  5. Dissociation of Charge Transfer States and Carrier Separation in Bilayer Organic Solar Cells: A Time-Resolved Electroabsorption Spectroscopy Study.

    PubMed

    Devižis, Andrius; De Jonghe-Risse, Jelissa; Hany, Roland; Nüesch, Frank; Jenatsch, Sandra; Gulbinas, Vidmantas; Moser, Jacques-E

    2015-07-01

    Ultrafast optical probing of the electric field by means of Stark effect in planar heterojunction cyanine dye/fullerene organic solar cells enables one to directly monitor the dynamics of free electron formation during the dissociation of interfacial charge transfer (CT) states. Motions of electrons and holes is scrutinized separately by selectively probing the Stark shift dynamics at selected wavelengths. It is shown that only charge pairs with an effective electron-hole separation distance of less than 4 nm are created during the dissociation of Frenkel excitons. Dissociation of the coulombically bound charge pairs is identified as the major rate-limiting step for charge carriers' generation. Interfacial CT states split into free charges on the time-scale of tens to hundreds of picoseconds, mainly by electron escape from the Coulomb potential over a barrier that is lowered by the electric field. The motion of holes in the small molecule donor material during the charge separation time is found to be insignificant. PMID:26037526

  6. High-resolution electronic spectroscopy of the doorway states to intramolecular charge transfer.

    PubMed

    Fleisher, Adam J; Bird, Ryan G; Zaleski, Daniel P; Pate, Brooks H; Pratt, David W

    2013-04-25

    Reported here are several of the ground, first, and second excited state structures and dipole moments of three benchmark intramolecular charge transfer (ICT) systems; 4-(1H-pyrrol-1-yl)benzonitrile (PBN), 4,4'-dimethylaminobenzonitrile (DMABN), and 4-(1-pyrrolidinyl)benzonitrile (PYRBN), isolated in the gas phase and probed by rotationally resolved spectroscopy in a molecular beam. The related molecules 1-phenylpyrrole (PP) and 4-aminobenzonitrile (ABN) also are discussed. We find that the S1 electronic state is of B symmetry in all five molecules. In PBN, a second excited state (S2) of A symmetry is found only ~400 cm(-1) above the presumed origin of the S1 state. The change in dipole moment upon excitation to the A state is measured to be ?? ? 3.0 D, significantly smaller than the value predicted by theory and also smaller than that observed for the "anomalous" ICT band of PBN in solution. The B state dipole moments of DMABN and PYRBN are large, ~10.6 D, slightly larger than those attributed to "normal" LE fluorescence in solution. In addition, we find the unsaturated donor molecules (PP, PBN) to be twisted in their ground states and to become more planar upon excitation, even in the A state, whereas the saturated donor molecules (ABN, DMABN, PYRBN), initially planar, either remain planar or become more twisted in their excited states. It thus appears that the model that is appropriate for describing ICT in these systems depends on the geometry of the ground state. PMID:22913563

  7. Micelle-induced versatile performance of amphiphilic intramolecular charge-transfer fluorescent molecular sensors.

    PubMed

    Wang, Jiaobing; Qian, Xuhong; Qian, Junhong; Xu, Yufang

    2007-01-01

    A series of amphiphilic intramolecular charge-transfer fluorescent molecular sensors AS1-3, equipped with a rod-shaped hydrophobic 2-phenylbenzoxazole fluorophore and a hydrophilic tetraamide Hg(2+)-ion receptor, have been prepared. These sensor molecules could be incorporated into the hydrophobic sodium dodecyl sulfate (SDS) micelle, which is confirmed by the clear spectral blue shift and emission enhancement observed at the critical micelle concentration of SDS. Systematic examination of the sensor-Hg(2+) complexation, by using both UV/visible and fluorescence spectroscopy, indicates that SDS significantly modulates both the binding event and signal transformation of these sensor molecules. The potential advantages are fourfold: 1) SDS substantially increases the Hg(2+)-ion association constant and results in an amplified sensitivity. 2) SDS initiates spectral features which facilitate Hg(2+)-ion analysis, for example, in addition to the strengthened fluorescence of the free sensors AS1-3, the original "on-off" response of AS2 toward the Hg(2+) ion is transformed into a self-calibrated two-wavelength ratiometric signal, while for AS3, Hg(2+)-ion complexation in the presence of SDS results in a 180 nm blue shift, which is preferred to the 51 nm spectral shift obtained without SDS. 3) Thermoreversible tuning of the dynamic detection range is realized. 4) Highly specific Hg(2+)-ion identification could be achieved by using the SDS-induced fingerprint emission (358 nm) of the AS2-Hg(2+) complex. Altogether, this work demonstrates a convenient and powerful strategy that remarkably elevates the performance of a given fluorescent molecular sensor. It also implies that for a specific utilization, much attention should be paid to the microenvironment in which the sensor resides, as the behavior of the sensor might be different from that in the bulk solution. PMID:17582820

  8. Dynamics of charge-transfer excited states relevant to photochemical energy conversion

    NASA Astrophysics Data System (ADS)

    Lim, E. C.

    1991-03-01

    Photoinduced Charge Transfer (CT) processes in a series of N-R-N systems, where N stands for naphthalene and R is -CH-, -O-, etc., were studied in solvents of different polarity. In N-CH2-N and N-O-N, time resolved emission spectra show that initial naphthalene-like monomer band undergoes gradual shift and broadening to yield a structured emission at longer wavelength, as the delay after the laser excitation is increased. Further delay leads to mostly structureless band at still longer wavelength, which resembles the bicimer emission in polar solvents. Formation of the precursor state, and hence the CT state, is shown to involve rotation of one electronically excited moiety with respect to the other to form a twisted structure. Studies of the kinetics of these systems under varying experimental conditions show that the twisted intramolecular CT state can be formed on nanosecond time scales by one-photon excitation of one of the chromophores into a singlet state or on microsecond time scales by two-photon excitations of both chromophores into the lowest triplet state. The fluorescence excitation and dispersed fluorescence spectra of the van der Waals complexes of fluorene with durene, 1,2,4,5-tetrafluorobenzene, and 1,2,4,5-tetrachlorobenzene were studied in supersonic jets. The fluorene tetrachlorobenzene system, unlike the others, exhibits exciplex formation upon excitation of fluorene to its lowest excited singlet state (S sub 1). The stability of the fluorene tetrachlorobenzene exciplex state is attributed to the small electronic gap between S sub 1 fluorene and S sub 1 tetrachlorobenzene, which increases exciton resonance between the component molecules.

  9. Dynamics of charge-transfer excited states relevant to photochemical energy conversion

    SciTech Connect

    Lim, E.C.

    1991-01-01

    Photoinduced Charge Transfer (CT) processes in a series of N-R-N systems, where N stands for naphthalene and R is {minus}CH{sub 2}{minus}, {minus}O{minus}, etc., have been studied in solvents of different polarity. In N-CH{sub 2}{minus}N and N-O-N, time-resolved emission spectra show that initial naphthalene-like monomer band undergoes gradual shift and broadening to yield a structured emission at longer wavelength, as the delay after the laser excitation is increased. Further delay leads to mostly structureless band at still longer wavelength, which resembles the bicimer emission in polar solvents. Formation of the precursor state, and hence the CT state, is shown to involve rotation of one electronically excited moiety with respect to the other to form a twisted structure. Studies of the kinetics of these systems under varying experimental conditions show that the twisted intramolecular CT state can be formed on nanosecond time scales by one-photon excitation of one of the chromophores into a singlet state or on microsecond time scales by two-photon excitations of both chromophores into the lowest triplet state. The fluorescence excitation and dispersed fluorescence spectra of the van der Waals complexes of fluorene with durene, 1,2,4,5-tetrafluorobenzene, and 1,2,4,5-tetrachlorobenzene have been studied in supersonic jets. The fluorene/tetrachlorobenzene system, unlike the others, exhibits exciplex formation upon excitation of fluorene to its lowest excited singlet state (S{sub 1}). The stability of the fluorene/tetrachlorobenzene exciplex state is attributed to the small electronic gap between S{sub 1} fluorene and S{sub 1} tetrachlorobenzene, which increases exciton resonance between the component molecules. 6 refs., 1 fig.

  10. Single-molecule conductance of a chemically modified, ?-extended tetrathiafulvalene and its charge-transfer complex with F4TCNQ

    PubMed Central

    García, Raúl; Herranz, M Ángeles; González, M Teresa; Bollinger, Gabino Rubio; Bürkle, Marius; Zotti, Linda A; Asai, Yoshihiro; Pauly, Fabian; Cuevas, Juan Carlos; Agraït, Nicolás

    2015-01-01

    Summary We describe the synthesis and single-molecule electrical transport properties of a molecular wire containing a ?-extended tetrathiafulvalene (exTTF) group and its charge-transfer complex with F4TCNQ. We form single-molecule junctions using the in situ break junction technique using a homebuilt scanning tunneling microscope with a range of conductance between 10 G0 down to 10?7 G0. Within this range we do not observe a clear conductance signature of the neutral parent molecule, suggesting either that its conductance is too low or that it does not form a stable junction. Conversely, we do find a clear conductance signature in the experiments carried out on the charge-transfer complex. Due to the fact we expected this species to have a higher conductance than the neutral molecule, we believe this supports the idea that the conductance of the neutral molecule is very low, below our measurement sensitivity. This idea is further supported by theoretical calculations. To the best of our knowledge, these are the first reported single-molecule conductance measurements on a molecular charge-transfer species. PMID:26199662

  11. Organic chemistry. Rh-catalyzed C-C bond cleavage by transfer hydroformylation.

    PubMed

    Murphy, Stephen K; Park, Jung-Woo; Cruz, Faben A; Dong, Vy M

    2015-01-01

    The dehydroformylation of aldehydes to generate olefins occurs during the biosynthesis of various sterols, including cholesterol in humans. Here, we implement a synthetic version that features the transfer of a formyl group and hydride from an aldehyde substrate to a strained olefin acceptor. A Rhodium (Xantphos)(benzoate) catalyst activates aldehyde carbon-hydrogen (C-H) bonds with high chemoselectivity to trigger carbon-carbon (C-C) bond cleavage and generate olefins at low loadings (0.3 to 2 mole percent) and temperatures (22° to 80°C). This mild protocol can be applied to various natural products and was used to achieve a three-step synthesis of (+)-yohimbenone. A study of the mechanism reveals that the benzoate counterion acts as a proton shuttle to enable transfer hydroformylation. PMID:25554782

  12. Site-dependent charge transfer at the Pt(111)-ZnPc interface and the effect of iodine

    SciTech Connect

    Ahmadi, Sareh, E-mail: sareha@kth.se, E-mail: gothelid@kth.se; Wojek, Bastian M.; Noël, Quentin; Göthelid, Mats, E-mail: sareha@kth.se, E-mail: gothelid@kth.se [KTH Royal Institute of Technology, ICT MNF Materials Physics, Electrum 229, 16440 Kista (Sweden)] [KTH Royal Institute of Technology, ICT MNF Materials Physics, Electrum 229, 16440 Kista (Sweden); Agnarsson, Björn [Department of Applied Physics, Biological Physics, Chalmers University of Technology, Fysikgränd 3, 412 96 Göteborg (Sweden)] [Department of Applied Physics, Biological Physics, Chalmers University of Technology, Fysikgränd 3, 412 96 Göteborg (Sweden); Bidermane, Ieva [Department of Physics and Astronomy, Uppsala University, Box 516, 75120 Uppsala (Sweden)] [Department of Physics and Astronomy, Uppsala University, Box 516, 75120 Uppsala (Sweden); Sun, Chenghua [Australian Institute for Bioengineering and Nanotechnology, The University of Queensland, Brisbane, St Lucia QLD 4072 (Australia)] [Australian Institute for Bioengineering and Nanotechnology, The University of Queensland, Brisbane, St Lucia QLD 4072 (Australia)

    2014-05-07

    The electronic structure of ZnPc, from sub-monolayers to thick films, on bare and iodated Pt(111) is studied by means of X-ray photoelectron spectroscopy, X-ray absorption spectroscopy, and scanning tunneling microscopy. Our results suggest that at low coverage ZnPc lies almost parallel to the Pt(111) substrate, in a non-planar configuration induced by Zn-Pt attraction, leading to an inhomogeneous charge distribution within the molecule and an inhomogeneous charge transfer to the molecule. ZnPc does not form a complete monolayer on the Pt surface, due to a surface-mediated intermolecular repulsion. At higher coverage ZnPc adopts a tilted geometry, due to a reduced molecule-substrate interaction. Our photoemission results illustrate that ZnPc is practically decoupled from Pt, already from the second layer. Pre-deposition of iodine on Pt hinders the Zn-Pt attraction, leading to a non-distorted first layer ZnPc in contact with Pt(111)-I(?3×?3) or Pt(111)-I(?7×?7), and a more homogeneous charge distribution and charge transfer at the interface. On increased ZnPc thickness iodine is dissolved in the organic film where it acts as an electron acceptor dopant.

  13. Time-dependent transition density matrix for visualizing charge-transfer excitations in photoexcited organic donor-acceptor systems

    NASA Astrophysics Data System (ADS)

    Li, Yonghui; Ullrich, Carsten

    2013-03-01

    The time-dependent transition density matrix (TDM) is a useful tool to visualize and interpret the induced charges and electron-hole coherences of excitonic processes in large molecules. Combined with time-dependent density functional theory on a real-space grid (as implemented in the octopus code), the TDM is a computationally viable visualization tool for optical excitation processes in molecules. It provides real-time maps of particles and holes which gives information on excitations, in particular those that have charge-transfer character, that cannot be obtained from the density alone. Some illustration of the TDM and comparison with standard density difference plots will be shown for photoexcited organic donor-acceptor molecules. The time-dependent transition density matrix (TDM) is a useful tool to visualize and interpret the induced charges and electron-hole coherences of excitonic processes in large molecules. Combined with time-dependent density functional theory on a real-space grid (as implemented in the octopus code), the TDM is a computationally viable visualization tool for optical excitation processes in molecules. It provides real-time maps of particles and holes which gives information on excitations, in particular those that have charge-transfer character, that cannot be obtained from the density alone. Some illustration of the TDM and comparison with standard density difference plots will be shown for photoexcited organic donor-acceptor molecules. This work is supported by NSF Grant DMR-1005651

  14. Site-dependent charge transfer at the Pt(111)-ZnPc interface and the effect of iodine

    NASA Astrophysics Data System (ADS)

    Ahmadi, Sareh; Agnarsson, Björn; Bidermane, Ieva; Wojek, Bastian M.; Noël, Quentin; Sun, Chenghua; Göthelid, Mats

    2014-05-01

    The electronic structure of ZnPc, from sub-monolayers to thick films, on bare and iodated Pt(111) is studied by means of X-ray photoelectron spectroscopy, X-ray absorption spectroscopy, and scanning tunneling microscopy. Our results suggest that at low coverage ZnPc lies almost parallel to the Pt(111) substrate, in a non-planar configuration induced by Zn-Pt attraction, leading to an inhomogeneous charge distribution within the molecule and an inhomogeneous charge transfer to the molecule. ZnPc does not form a complete monolayer on the Pt surface, due to a surface-mediated intermolecular repulsion. At higher coverage ZnPc adopts a tilted geometry, due to a reduced molecule-substrate interaction. Our photoemission results illustrate that ZnPc is practically decoupled from Pt, already from the second layer. Pre-deposition of iodine on Pt hinders the Zn-Pt attraction, leading to a non-distorted first layer ZnPc in contact with Pt(111)-I(?3×?3) or Pt(111)-I(?7×?7), and a more homogeneous charge distribution and charge transfer at the interface. On increased ZnPc thickness iodine is dissolved in the organic film where it acts as an electron acceptor dopant.

  15. Aluminum coordination chemistry and the inhibition of phosphoryl-transferring enzymes

    Microsoft Academic Search

    N. C. Furumo; R. E. Viola

    1986-01-01

    Aluminium ion is a potent inhibitor of the enzymes hexokinase (K\\/sub i\\/ = 0.16 ..mu..M) and glycerokinase (K\\/sub i\\/ = 4.0 ..mu..M). It has been shown that aluminum forms a complex with ATP that is 80 times more stable than the magnesium complex with ATP which is the normal substrate for phosphoryl-transferring enzymes. Kinetic studies performed on several kinases at

  16. Charge transport in micas: The kinetics of FeII/III electron transfer in the octahedral sheet

    SciTech Connect

    Rosso, Kevin M.; Ilton, Eugene S.

    2003-11-01

    The two principal FeII/III electron exchange reactions underlying charge transport in the octahedral sheet of ideal end-member annite were modeled using a combination of ab initio calculations and Marcus electron transfer theory. A small polaron model was applied which yielded electron hopping activation energies that agree well with the limited available experimental data. A small ab initio cluster model successfully reproduced several important structural, energetic, and magnetic characteristics of the M1 and M2 Fe sites in the annite octahedral sheet. The cluster enabled calculation of the internal reorganization energy and electronic coupling matrix elements for the M2-M2 and M1-M2 electron transfer reactions. The M2-M2 electron transfer is symmetric with a predicted forward/reverse electron hopping rate of 106 s-1. The M1-M2 electron transfers are asymmetric due to the higher ionization potential by 0.46 eV of FeII in the M1 site. The electronic coupling matrix elements for these reactions are predicted to be small and of similar magnitude, suggesting the possibility that the coupling is essentially direction independent amongst hopping directions in the octahedral sheet. M1 Fe sites are predicted to be efficient electron traps and charge transport should occur by nearest-neighbor electron hops along the M2 Fe sublattice.

  17. Endohedral fullerene as acceptor: A DFT study on charge transfer states of Sc3N@C80-porphyrin complex

    NASA Astrophysics Data System (ADS)

    Amerikheirabadi, Fatameh; Basurto, Luis; Zope, Rajendra; Baruah, Tunna

    2013-03-01

    C60 fullerene and its derivatives are the most popular acceptors which are used in molecular/polymeric complexes used in organic photovoltaics. Endohedral fullerenes are shown to produce long lived charge separated states. The Sc3N@C80, the third most abundant fullerene after C60 and C70, has a larger cage with a radius of 4.1 Ang. We have carried out a DFT study on the electronic structure of ground and charge transfer states of a model Sc3N@C80-Zn tetraphenyl porphyrin cofacial complex. The C80 cage used in our calculations has icosahedral symmetry. We find that the lowest charge transfer state with a hole on the porphyrin and an electron on the Sc3N@C80 is at 2.1 eV above the ground state. The calculations show that different orientations of the Sc3N unit to the porphyrin plane do not significantly alter the electronic structure. The electronic structure of the complex and its components along with the exciton binding energies will be presented. C60 fullerene and its derivatives are the most popular acceptors which are used in molecular/polymeric complexes used in organic photovoltaics. Endohedral fullerenes are shown to produce long lived charge separated states. The Sc3N@C80, the third most abundant fullerene after C60 and C70, has a larger cage with a radius of 4.1 Ang. We have carried out a DFT study on the electronic structure of ground and charge transfer states of a model Sc3N@C80-Zn tetraphenyl porphyrin cofacial complex. The C80 cage used in our calculations has icosahedral symmetry. We find that the lowest charge transfer state with a hole on the porphyrin and an electron on the Sc3N@C80 is at 2.1 eV above the ground state. The calculations show that different orientations of the Sc3N unit to the porphyrin plane do not significantly alter the electronic structure. The electronic structure of the complex and its components along with the exciton binding energies will be presented. Supported by NSF through grant no. DMR 1205302.

  18. Momentum transfer theory of ion transport under the influence of resonant charge transfer collisions: the case of argon and neon ions in parent gases

    NASA Astrophysics Data System (ADS)

    Jovanovi?, J. V.; Vrhovac, S. B.; Petrovi?, Z. Lj.

    2002-12-01

    Transport properties of ion swarms in presence of Resonant Charge Transfer (RCT) collisions are studied using Momentum Transfer Theory (MTT). It was shown that, not surprisingly, RCT collisions may be represented as a special case of elastic scattering. Using the developed MTT we tested a previously available anisotropic set of cross-sections for Ar+Ar^+ collisions by making the comparisons with the available data for the transverse diffusion coefficient. We also developed an anisotropic set of Ne+Ne^+ integral cross-sections based on the available data for mobility, longitudinal and transverse diffusion. Anisotropic sets of cross-sections are needed for Monte Carlo simulations of ion transport and plasma models.

  19. Synthesis, spectroscopic studies and thermal analysis of charge-transfer complex of 2,2?-bipyridine with 4-hydroxybenzoic acid in different polar solvents

    NASA Astrophysics Data System (ADS)

    Rzokee, Abdulsatar Abduljabbar; Ahmad, Afaq

    2014-11-01

    The charge-transfer (CT) complex formed between 2,2?-bipyridine with 4-hydroxybenzoic acid has been studied in methanol and acetone at room temperature. The charge-transfer complex was characterized on the basis of FT-IR, 1H NMR, XRD studies of the solid CT complex, UV-Visible spectroscopy, thermogravimetric analysis (TGA-DTA) and conductivity and the results were discussed. The particle size and the energy of the charge-transfer complex were also determined. The data obtained from the spectroscopic studies indicate the formation of 1:1 charge-transfer complex, associated with a proton migration from the acceptor to the donor followed by intermolecular hydrogen bonding. The conductivity was found to increase with increase in the concentration of the donor.

  20. Web-Based Computational Chemistry Education with CHARMMing III: Reduction Potentials of Electron Transfer Proteins

    PubMed Central

    Perrin, B. Scott; Miller, Benjamin T.; Schalk, Vinushka; Woodcock, H. Lee; Brooks, Bernard R.; Ichiye, Toshiko

    2014-01-01

    A module for fast determination of reduction potentials, E°, of redox-active proteins has been implemented in the CHARMM INterface and Graphics (CHARMMing) web portal (www.charmming.org). The free energy of reduction, which is proportional to E°, is composed of an intrinsic contribution due to the redox site and an environmental contribution due to the protein and solvent. Here, the intrinsic contribution is selected from a library of pre-calculated density functional theory values for each type of redox site and redox couple, while the environmental contribution is calculated from a crystal structure of the protein using Poisson-Boltzmann continuum electrostatics. An accompanying lesson demonstrates a calculation of E°. In this lesson, an ionizable residue in a [4Fe-4S]-protein that causes a pH-dependent E° is identified, and the E° of a mutant that would test the identification is predicted. This demonstration is valuable to both computational chemistry students and researchers interested in predicting sequence determinants of E° for mutagenesis. PMID:25058418

  1. Theoretical study of interstellar hydroxylamine chemistry: protonation and proton transfer mediated by H3+.

    NASA Astrophysics Data System (ADS)

    Boulet, P.; Gilardoni, F.; Weber, J.; Chermette, H.; Ellinger, Y.

    1999-06-01

    Protonated species are known to play a key role for ion-molecule reactions in gas phase interstellar chemistry. As hydroxylamine (H2NOH) has never been observed as an interstellar molecule, a detailed theoretical investigation of the protonation of H2NOH is carried out at high level of quantum chemical theories (CCSD(T) and DFT-B3LYP). As protonation may occur directly by reaction with H+ or mediated by H3+, both processes are investigated on the nitrogen and the oxygen sites of hydroxylamine. The present results show that the N-protonated form is more stable than the O-protonated one and that the protonation initiated by H3+ is by far less exothermic than the other one. A particular attention is paid to the intramolecular rearrangement leading from H3NOH+ to H2NOH2+ which involves a highly energetic transition state exhibiting proton bridged between N and O sites. As this barrier is too high to be easily overcome in the interstellar medium, an alternative process mediated by H2 and involving a bridged H3+ as a transition state is considered. The calculations show that the corresponding activation energy is significantly lowered.

  2. Web-based computational chemistry education with CHARMMing III: Reduction potentials of electron transfer proteins.

    PubMed

    Perrin, B Scott; Miller, Benjamin T; Schalk, Vinushka; Woodcock, H Lee; Brooks, Bernard R; Ichiye, Toshiko

    2014-07-01

    A module for fast determination of reduction potentials, E°, of redox-active proteins has been implemented in the CHARMM INterface and Graphics (CHARMMing) web portal (www.charmming.org). The free energy of reduction, which is proportional to E°, is composed of an intrinsic contribution due to the redox site and an environmental contribution due to the protein and solvent. Here, the intrinsic contribution is selected from a library of pre-calculated density functional theory values for each type of redox site and redox couple, while the environmental contribution is calculated from a crystal structure of the protein using Poisson-Boltzmann continuum electrostatics. An accompanying lesson demonstrates a calculation of E°. In this lesson, an ionizable residue in a [4Fe-4S]-protein that causes a pH-dependent E° is identified, and the E° of a mutant that would test the identification is predicted. This demonstration is valuable to both computational chemistry students and researchers interested in predicting sequence determinants of E° for mutagenesis. PMID:25058418

  3. Localized States and Charge Transfer at ZnO Surfaces and Interfaces

    NASA Astrophysics Data System (ADS)

    Brillson, Leonard

    2006-03-01

    With the advent of techniques to probe semiconductor electronic properties in the near-interface region on a nanometer scale, it is now possible to understand and control the mechanisms playing a role in localized state formation and charge transfer at ZnO interfaces. While world-wide research activity into this major new semiconductor has increased dramatically, the ability to control ZnO interfaces has been a major challenge to their opto- and microelectronic applications. Nanoscale depth-resolved cathodoluminescence and x-ray photoemission spectroscopies reveal the segregation of point defects and the donor character of hydrogen in the near-surface region. A conversion from ohmic to rectifying behavior is observed for gold contacts on atomically ordered polar ZnO surfaces following remote oxygen plasma treatment. This transition is accompanied by reduction of the well-known ``green'' deep level emission, suppression of the hydrogen donor-bound exciton photoluminescence and a large increase in n-type band bending. These results demonstrate that the contact type conversion involves more than one mechanism, specifically, removal of the adsorbate-induced accumulation layer plus lowered tunneling due to reduction of near-surface donor density and defect-assisted hopping transport. Schottky barriers for a wide array of metals on ZnO reveal that the strength of interface reaction plays a dominant role in forming near-interface defects and the resultant Schottky barriers. Similar correlations for other compound semiconductors indicate that the impact of near-interface native defects on Schottky barriers is more general in nature. [1] H.L. Mosbacker, Y.M. Strzhemechny, B.D. White, P.E. Smith, D.C. Look, D.C. Reynolds, C.W. Litton, and L.J. Brillson, ``Role of Near-Surface States in Ohmic-Schottky Conversion of Au Contacts to ZnO,'' Appl. Phys. Lett. 87, 012102 (2005). [2] Y.M. Strzhemechny, H.L. Mosbacker, D.C. Look, D.C. Reynolds, C.W. Litton, N.Y.Garces, NC. Giles, L.E. Halliburton, S. Niki, and L.J. Brillson, ``Remote Hydrogen Plasma Doping of Single Crystal ZnO,'' Appl. Phys. Lett. 84, 2545 (2004).

  4. Effect of charge transfer on the local order in liquid group IV isoelectronic compounds: neutron diffraction data versus numerical tight-binding simulations

    Microsoft Academic Search

    G. Prigent; J.-P. Gaspard; R. Bellissent; C. Bichara

    1999-01-01

    In a simple tight-binding approach, we consider the role of charge transfer and entropy in the semiconductor-to-metal transition which may occur upon melting group IV elements and their isoelectronic III-V and II-VI compounds. In the liquid state, entropy is shown to destabilise the diamond structure in favor of a metallic simple cubic-like local order, while charge transfer tends to keep

  5. Relaxation dynamics in the B(1/2) and C(3/2) charge transfer states of XeF in solid Ar

    E-print Network

    Apkarian, V. Ara

    Relaxation dynamics in the B(1/2) and C(3/2) charge transfer states of XeF in solid Ar G. J to study the relaxation dynamics of Xe+F- (B 281,2 and C211Z12) charge transfer states in solid Ar. Very-l are observed for B(v=O). 1. INTRODUCTION As the first solid state excimer laser, XeF in solid Ar has generated

  6. Electron Doping by Charge Transfer at LaFeO 3 /Sm 2 CuO 4 Epitaxial Interfaces

    SciTech Connect

    Bruno, Flavio Y. [Universidad Complutense, Spain; Schmidt, R [Universidad Complutense de Madrid, Spain; Varela, Maria [UCM, Dept Fis Aplicada 3, Madrid, Spain; Garcia-Barriocanal, Javier [Universidad Complutense, Spain; Rivera-Calzada, Alberto [Universidad Complutense, Spain; Cuellar, F. [Universidad Complutense de Madrid, Spain; Leon, Carlos [Universidad Complutense de Madrid, Spain; Thakur, P. [European Synchrotron Radiation Facility (ESRF); Cezar, J. C. [European Synchrotron Radiation Facility (ESRF); Brookes, N. B. [European Synchrotron Radiation Facility (ESRF); Garcia-Hernandez, M [Instituto de Ciencia de Materiales de Madrid (ICMM); Dagotto, Elbio R [ORNL; Pennycook, Stephen J [ORNL; Santamaria, J. [Universidad Complutense, Spain

    2013-01-01

    The breakdown of the lattice translational invariance symmetry that occurs at complex oxide interfaces may profoundly modify their electronic structure, leading to interfacial states with properties drastically different from those of the superlattice individual components. The appearance of a conducting two dimensional (2D) electron gas at the interface between two insulating oxides and induced magnetism in a non-magnetic material are just two among many fascinating examples. [ 1 8 ] One of the key factors underlying novel properties is the modifi cation of the doping and orbital occupancy near those interfaces, which may result from charge transfer processes. [ 3 , 9 11 ] If materials used in heterostructures have different work functions, a non-equilibrium situation will be created at the interface and charge will be transferred until the chemical potential levels off. [ 12 ] The use of such phenomena to modify doping in heterostructures has been proposed theoretically as a new route to avoid the quenched disorder that inevitably accompanies the chemical doping. At the interface between a Mott insulating parent compound of the high critical temperature superconductor (HTSC) family and a suitable material that would act as the charge donor, electron doped phases could be stabilized which would eventually turn metallic and perhaps superconducting. [ 12 , 13 ] Such charge transfer processes have been observed at interfaces involving copper oxides such as La 0.7 Ca 0.3 MnO 3 / YBa 2 Cu 3 O 7 , [ 14 ] La 2 x Sr x CuO 4 /La 2 CuO 4 [ 15 ] and SrTi 1 x Nb x O 3 / Sm 2 CuO 4 . [ 16 ] While a novel 2D superconducting state was found at the La 2-x Sr x CuO 4 /La 2 CuO 4 interface, [ 17 ] the effect of doping by charge transfer could not be examined in the other two cases due to the detrimental effect on the YBa 2 Cu 3 O 7 superconductivity of the spin polarized electrons from La 0.7 Ca 0.3 MnO 3 in one case and due to the conducting nature of the SrTi 1 x Nb x O 3 in the other case, which obscures changes in the conducting properties of the interface layer. In this paper, the structural and

  7. Comparison of Static and Microfluidic Protease Assays Using Modified Bioluminescence Resonance Energy Transfer Chemistry

    PubMed Central

    Wu, Nan; Dacres, Helen; Anderson, Alisha; Trowell, Stephen C.; Zhu, Yonggang

    2014-01-01

    Background Fluorescence and bioluminescence resonance energy transfer (F/BRET) are two forms of Förster resonance energy transfer, which can be used for optical transduction of biosensors. BRET has several advantages over fluorescence-based technologies because it does not require an external light source. There would be benefits in combining BRET transduction with microfluidics but the low luminance of BRET has made this challenging until now. Methodology We used a thrombin bioprobe based on a form of BRET (BRETH), which uses the BRET1 substrate, native coelenterazine, with the typical BRET2 donor and acceptor proteins linked by a thrombin target peptide. The microfluidic assay was carried out in a Y-shaped microfluidic network. The dependence of the BRETH ratio on the measurement location, flow rate and bioprobe concentration was quantified. Results were compared with the same bioprobe in a static microwell plate assay. Principal Findings The BRETH thrombin bioprobe has a lower limit of detection (LOD) than previously reported for the equivalent BRET1–based version but it is substantially brighter than the BRET2 version. The normalised BRETH ratio of the bioprobe changed 32% following complete cleavage by thrombin and 31% in the microfluidic format. The LOD for thrombin in the microfluidic format was 27 pM, compared with an LOD of 310 pM, using the same bioprobe in a static microwell assay, and two orders of magnitude lower than reported for other microfluidic chip-based protease assays. Conclusions These data demonstrate that BRET based microfluidic assays are feasible and that BRETH provides a useful test bed for optimising BRET-based microfluidics. This approach may be convenient for a wide range of applications requiring sensitive detection and/or quantification of chemical or biological analytes. PMID:24551097

  8. Electron-molecular vibration coupling effect on the Raman spectrum of organic charge transfer salts

    NASA Astrophysics Data System (ADS)

    Yamamoto, Kaoru; Yakushi, Kyuya

    2004-04-01

    Vibrational spectra of dimerized and tetramerized radical clusters have been calculated to understand the features of electron-molecular vibration (EMV) coupling effects for the charge ordered system (CO). The calculated spectra show that the totally in-phase Raman band, which is usually used as a measure of the molecular ionicity, approaches to the frequency corresponding to the average molecular ionicity in the cluster, with increasing the EMV coupling constant. On the other hand, when large charge disproportionation (CD) presents, vibronic bands show steep shift for small variation of the CD ratio. These results suggest that concerning to the normal modes with a large EMV coupling constant, we should focus on the frequency of the vibronic bands instead of the totally in-phase mode to discuss the charge distribution. Key words. Charge ordering charge disproportionation Raman spectroscopy vibrational spectroscopy

  9. Solution Phase Exciton Diffusion Dynamics of a Charge-Transfer Copolymer PTB7 and a Homopolymer P3HT.

    PubMed

    Cho, Sung; Rolczynski, Brian S; Xu, Tao; Yu, Luping; Chen, Lin X

    2015-06-18

    Using ultrafast polarization-controlled transient absorption (TA) measurements, dynamics of the initial exciton states were investigated on the time scale of tens of femtoseconds to about 80 ps in two different types of conjugated polymers extensively used in active layers of organic photovoltaic devices. These polymers are poly(3-fluorothienothiophenebenzodithiophene) (PTB7) and poly-3-hexylthiophene (P3HT), which are charge-transfer polymers and homopolymers, respectively. In PTB7, the initial excitons with excess vibrational energy display two observable ultrafast time constants, corresponding to coherent exciton diffusion before the vibrational relaxation, and followed by incoherent exciton diffusion processes to a neighboring local state after the vibrational relaxation. In contrast, P3HT shows only one exciton diffusion or conformational motion time constant of 34 ps, even though its exciton decay kinetics are multiexponential. Based on the experimental results, an exciton dynamics mechanism is conceived taking into account the excitation energy and structural dependence in coherent and incoherent exciton diffusion processes, as well as other possible deactivation processes including the formation of the pseudo-charge-transfer and charge separate states, as well as interchain exciton hopping or coherent diffusion. PMID:25620363

  10. Enhanced Performance of nano-Bi2WO6-Graphene as Pseudocapacitor Electrodes by Charge Transfer Channel

    NASA Astrophysics Data System (ADS)

    Zhang, Jun; Liu, Pengliang; Zhang, Yupeng; Xu, Guolong; Lu, Zhengda; Wang, Xiyu; Wang, Yan; Yang, Lingxia; Tao, Xi; Wang, Hongbo; Zhang, Erpan; Xi, Junhua; Ji, Zhenguo

    2015-02-01

    The nano-Bi2WO6/reduced graphene oxide composite obtained by a simple hydrothermal reaction demonstrates a larger specific capacitance of 922 F/g at a charge and discharge currents of 3 A/g with longer cycle life. The As comparison, pristine Bi2WO6 nanoparticles have poor specific capacitance of 574 F/g at a charge and discharge currents of 2 A/g with weak cycle life. Though analyzing the Cyclic voltammetry curves, it is found that there are two oxidation reaction occurring in the materials: oxidation of Bi (III) to Bi (IV) and Bi (III) to Bi (V). The oxidation of Bi (III) to Bi (IV) is reversible while Bi (III) to Bi (V) will cause nonreversible destroy on structure. In this nano-Bi2WO6/reduced graphene oxide composite, graphene with well conductivity will enhance the electrically conducting as charge transfer channel, so that electrons will be transfer much faster in oxidation and most Bi (III) is oxidized to be Bi (IV) which ensure larger specific capacitance and long cycle life. This nano-Bi2WO6/reduced graphene oxide composite has application prospect in high-performance pseudo-capacitors.

  11. Spectroscopic studies and molecular orbital calculations of charge transfer complexation between 3,5-dimethylpyrazole with DDQ in acetonitrile

    NASA Astrophysics Data System (ADS)

    Habeeb, Moustafa M.; Al-Attas, Amirah S.; Al-Raimi, Doaa S.

    2015-05-01

    Charge transfer (CT) interaction between 3,5-dimethylpyrazole (DMP) with the ?-acceptor 2,3-dichloro-5,6-dicyano-p-benzoquinon (DDQ) has been investigated spectrophotometrically in acetonitrile (AN). Simultaneous reddish brown color has been observed upon mixing donor with acceptor solutions attributing to CT complex formation. The electronic spectra of the formed complex exhibited multi-charge transfer bands at 429, 447, 506, 542 and 589 nm, respectively. Job's method of continuous variations and spectrophotometric titration methods confirmed the formation of the studied complex in 1:2 ratio between DMP and DDQ. Benesi-Hildebrand equation has been applied to calculate the stability constant of the formed complex where it recorded high value supporting formation of stable complex. Molecular orbital calculations using MM2 method and GAMESS (General Atomic and Molecular Electronic Structure System) interface computations as a package of ChemBio3D Ultra12 software were carried out for more analysis of the formed complex in the gas phase. The computational analysis included energy minimisation, stabilisation energy, molecular geometry, Mullikan charges, molecular electrostatic potential (MEP) surfaces of reactants and complex as well as characterization of the higher occupied molecular orbitals (HOMO) and lower unoccupied molecular orbitals (LUMO) surfaces of the complex. A good consistency between experimental and theoretical results has been recorded.

  12. Graphene field effect transistor as a probe of electronic structure and charge transfer at organic molecule-graphene interfaces.

    PubMed

    Cervenka, Jiri; Budi, Akin; Dontschuk, Nikolai; Stacey, Alastair; Tadich, Anton; Rietwyk, Kevin J; Schenk, Alex; Edmonds, Mark T; Yin, Yuefeng; Medhekar, Nikhil; Kalbac, Martin; Pakes, Chris I

    2015-01-28

    The electronic structure of physisorbed molecules containing aromatic nitrogen heterocycles (triazine and melamine) on graphene is studied using a combination of electronic transport, X-ray photoemission spectroscopy and density functional theory calculations. The interfacial electronic structure and charge transfer of weakly coupled molecules on graphene is found to be governed by work function differences, molecular dipole moments and polarization effects. We demonstrate that molecular depolarization plays a significant role in these charge transfer mechanisms even at submonolayer coverage, particularly for molecules which possess strong dipoles. Electronic transport measurements show a reduction of graphene conductivity and charge carrier mobility upon the adsorption of the physisorbed molecules. This effect is attributed to the formation of additional electron scattering sites in graphene by the molecules and local molecular electric fields. Our results show that adsorbed molecules containing polar functional groups on graphene exhibit different coverage behaviour to nonpolar molecules. These effects open up a range of new opportunities for recognition of different molecules on graphene-based sensor devices. PMID:25502349

  13. A comparison of approximate techniques for the determination of potential energy surfaces of ion-molecule charge transfer systems

    NASA Astrophysics Data System (ADS)

    Diaz, B. Ramiro; Wahnon, P.; Sidis, V.

    1992-11-01

    The (HO2)+ molecular ion is used to experiment two approximate procedures which aim at reducing the computation effort that is needed for the determination of potential energy surfaces of ion-molecule charge transfer systems. The two procedures involve configuration interaction (CI) calculations of moderate sizes and are based on diagonal corrections of the electronic Hamiltonian matrix in a basis of projected-valence bond (PVB) configuration-state functions (CSF). The PVB-CSF's used in practice correspond to a full valence CI for each ionic or neutral partner as well as single excitations accounting for polarization and electron transfer. The diagonal corrections are of two sorts: (i) if insufficiently large orbital expansion bases are used they remove the relative ion-molecule basis set superposition error; (ii) if asymptotic energy levels of the involved neutrals or ions in their ground or valence excited states are misplaced they properly adjust these levels. When applied to (HO2)+ using a minimal or an extended orbital basis set expansion the proposed approaches yield concording results. The results also agree with the effective model potential (EMP) data of Grimbert et al. [Chem. Phys. 124, 187 (1988)] which have proved successful in the description of the H++O2 charge transfer dynamics. Comparison with fragmentary results from MRD-CI calculations by Vazquez et al. [Mol. Phys. 59, 291 (1986)] and Schneider et al. [Chem. Phys. 128, 311 (1988)] is somewhat mitigated. The method should be particularly useful for bulky ion-molecule systems.

  14. Linear and third- and fifth-order nonlinear spectroscopies of a charge transfer system coupled to an underdamped vibration

    NASA Astrophysics Data System (ADS)

    Dijkstra, Arend G.; Tanimura, Yoshitaka

    2015-06-01

    We study hole, electron, and exciton transports in a charge transfer system in the presence of underdamped vibrational motion. We analyze the signature of these processes in the linear and third-, and fifth-order nonlinear electronic spectra. Calculations are performed with a numerically exact hierarchical equations of motion method for an underdamped Brownian oscillator spectral density. We find that combining electron, hole, and exciton transfers can lead to non-trivial spectra with more structure than with excitonic coupling alone. Traces taken during the waiting time of a two-dimensional (2D) spectrum are dominated by vibrational motion and do not reflect the electron, hole, and exciton dynamics directly. We find that the fifth-order nonlinear response is particularly sensitive to the charge transfer process. While third-order 2D spectroscopy detects the correlation between two coherences, fifth-order 2D spectroscopy (2D population spectroscopy) is here designed to detect correlations between the excited states during two different time periods.

  15. Linear and third- and fifth-order nonlinear spectroscopies of a charge transfer system coupled to an underdamped vibration.

    PubMed

    Dijkstra, Arend G; Tanimura, Yoshitaka

    2015-06-01

    We study hole, electron, and exciton transports in a charge transfer system in the presence of underdamped vibrational motion. We analyze the signature of these processes in the linear and third-, and fifth-order nonlinear electronic spectra. Calculations are performed with a numerically exact hierarchical equations of motion method for an underdamped Brownian oscillator spectral density. We find that combining electron, hole, and exciton transfers can lead to non-trivial spectra with more structure than with excitonic coupling alone. Traces taken during the waiting time of a two-dimensional (2D) spectrum are dominated by vibrational motion and do not reflect the electron, hole, and exciton dynamics directly. We find that the fifth-order nonlinear response is particularly sensitive to the charge transfer process. While third-order 2D spectroscopy detects the correlation between two coherences, fifth-order 2D spectroscopy (2D population spectroscopy) is here designed to detect correlations between the excited states during two different time periods. PMID:26049443

  16. Light-induced EPR study of charge transfer in poly(3-hexylthiophene)/fullerene bulk heterojunction

    NASA Astrophysics Data System (ADS)

    Krinichnyi, V. I.; Yudanova, E. I.; Denisov, N. N.

    2009-07-01

    The first results of the light-induced EPR study of magnetic, relaxation, and dynamic parameters of charge carriers background photoinduced by optical photons (1.7-3.4 eV) in poly(3-hexylthiophene)/fullerene bulk heterojunctions are described. All magnetic resonance parameters for positively charged polaron and negatively charged fullerene ion-radical in radical pairs photoinduced in the composite were determined separately by the steady-state microwave saturation method. Paramagnetic susceptibility of charge carriers reflects their activation dynamics and exchange interaction. A decay of long-living radical pairs depends on the spatial distance between photoinduced charge carriers. The one-dimensional polaron diffusion along the polymer chain and fullerene rotation near the main molecular axis was shown to follow activation Elliot hopping model and to be governed by photon energy. The difference in activation energies of the charge carriers' dynamics and in their dependence on the exciting photon energy proves their noninteracting character in the polymer/fullerene composite. Main magnetic, relaxation and dynamics parameters of charge carriers are governed by the photon energy band due to inhomogeneity of distribution of polymer and fullerene domains in the composite.

  17. Light-induced EPR study of charge transfer in poly(3-hexylthiophene)/fullerene bulk heterojunction.

    PubMed

    Krinichnyi, V I; Yudanova, E I; Denisov, N N

    2009-07-28

    The first results of the light-induced EPR study of magnetic, relaxation, and dynamic parameters of charge carriers background photoinduced by optical photons (1.7-3.4 eV) in poly(3-hexylthiophene)/fullerene bulk heterojunctions are described. All magnetic resonance parameters for positively charged polaron and negatively charged fullerene ion-radical in radical pairs photoinduced in the composite were determined separately by the steady-state microwave saturation method. Paramagnetic susceptibility of charge carriers reflects their activation dynamics and exchange interaction. A decay of long-living radical pairs depends on the spatial distance between photoinduced charge carriers. The one-dimensional polaron diffusion along the polymer chain and fullerene rotation near the main molecular axis was shown to follow activation Elliot hopping model and to be governed by photon energy. The difference in activation energies of the charge carriers' dynamics and in their dependence on the exciting photon energy proves their noninteracting character in the polymer/fullerene composite. Main magnetic, relaxation and dynamics parameters of charge carriers are governed by the photon energy band due to inhomogeneity of distribution of polymer and fullerene domains in the composite. PMID:19655902

  18. Light-induced EPR study of charge transfer in poly(3-hexylthiophene)/fullerene bulk heterojunction

    SciTech Connect

    Krinichnyi, V. I.; Yudanova, E. I.; Denisov, N. N. [Institute of Problems of Chemical Physics, RAS, Semenov Avenue 1, Chernogolovka 142432 (Russian Federation)

    2009-07-28

    The first results of the light-induced EPR study of magnetic, relaxation, and dynamic parameters of charge carriers background photoinduced by optical photons (1.7-3.4 eV) in poly(3-hexylthiophene)/fullerene bulk heterojunctions are described. All magnetic resonance parameters for positively charged polaron and negatively charged fullerene ion-radical in radical pairs photoinduced in the composite were determined separately by the steady-state microwave saturation method. Paramagnetic susceptibility of charge carriers reflects their activation dynamics and exchange interaction. A decay of long-living radical pairs depends on the spatial distance between photoinduced charge carriers. The one-dimensional polaron diffusion along the polymer chain and fullerene rotation near the main molecular axis was shown to follow activation Elliot hopping model and to be governed by photon energy. The difference in activation energies of the charge carriers' dynamics and in their dependence on the exciting photon energy proves their noninteracting character in the polymer/fullerene composite. Main magnetic, relaxation and dynamics parameters of charge carriers are governed by the photon energy band due to inhomogeneity of distribution of polymer and fullerene domains in the composite.

  19. Photoinduced electron transfer in a charge-transfer complex formed between corannulene and Li+@C60 by concave-convex ?-? interactions.

    PubMed

    Yamada, Mihoko; Ohkubo, Kei; Shionoya, Mitsuhiko; Fukuzumi, Shunichi

    2014-09-24

    A charge-transfer (CT) complex was formed between corannulene (C20H10) and lithium ion-encapsulated [60]fullerene (Li(+)@C60) with the binding constant KG = 1.9 × 10 M(-1) by concave-convex ?-? CT interactions in benzonitrile at 298 K, exhibiting a broad CT absorption extended to the NIR region. Femotosecond laser excitation of the C20H10/Li(+)@C60 CT complex resulted in the singlet charge-separated (CS) state, (1)(C20H10(•+)/Li(+)@C60(•-)), which decayed with the lifetime of 1.4 ns. Nanosecond laser excitation of Li(+)@C60 resulted in intermolecular electron transfer (ET) from C20H10 to the triplet excited state of Li(+)@C60 [(3)(Li(+)@C60)*] to produce the triplet CS state (3)(C20H10(•+)/Li(+)@C60(•-)). The distance between two electron spins in the triplet CS state was estimated to be 10 Å from the zero-field splitting pattern observed by EPR measurements at 4 K. The triplet CS state decayed to the ground state via intramolecular back electron transfer (BET). The CS lifetime was determined to be 240 ?s in benzonitrile at 298 K. The temperature dependence of the rate constant of BET afforded the reorganization energy (? = 1.04 eV) and the electronic coupling term (V = 0.0080 cm(-1)). The long lifetime of triplet CS state results from the spin-forbidden BET process and a small V value. PMID:25166343

  20. PAPER www.rsc.org/pps | Photochemical & Photobiological Sciences Charge separation and energy transfer in a carotenoC60 dyad: photoinduced

    E-print Network

    van Stokkum, Ivo

    transfer in a caroteno­C60 dyad: photoinduced electron transfer from the carotenoid excited states Rudi a carotenoid pigment linked to a fullerene derivative (C­C60) in which the carotenoid acts both as an antenna·+ ­C60 ·- . The charge-separated state is also formed from the excited fullerene following energy