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Sample records for charge transfer characteristics

  1. 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 π-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 μg mL -1, 0.017-2.63 μg mL -1 and 0.019-2.14 μg 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.

  2. Simulation of solid oxide iron-air battery: Effects of heat and mass transfer on charge/discharge characteristics

    NASA Astrophysics Data System (ADS)

    Ohmori, Hiroko; Iwai, Hiroshi

    2015-07-01

    A time-dependent 2-D numerical simulation was performed on a solid oxide iron-air battery (SOIAB) to reveal the fundamental characteristics of this new system. The SOIAB is a rechargeable battery consisting of a solid oxide electrochemical cell (SOEC) and iron as a redox metal. A simple battery configuration was employed assuming a system with a small capacity. A simulation model for a unit element was developed considering heat and mass transfer in the system, taking both electrochemical and redox reactions into account. The numerical results showed the spatial and temporal changes in the temperature field in the charge and discharge operations, which were due to the combined effects of heat generation/absorption by the electrochemical and redox reactions and heat exchange with the air supplied through convective heat transfer. As the reaction rates are functions of the local temperature, the predicted results show the importance of considering the heat transfer phenomena in this system. It was also found that the active reaction region in the redox metal evolves with time. The nonuniform distribution of iron utilization is affected by the effective gas diffusion coefficients in the porous redox metal, and consequently the change in the current density distribution in the SOEC.

  3. Charge transferred in brush discharges

    NASA Astrophysics Data System (ADS)

    Talarek, M.; Kacprzyk, R.

    2015-10-01

    Electrostatic discharges from surfaces of plastic materials can be a source of ignition, when appear in explosive atmospheres. Incendivity of electrostatic discharges can be estimated using the transferred charge test. In the case of brush discharges not all the energy stored at the tested sample is released and the effective surface charge density (or surface potential) crater is observed after the discharge. Simplified model, enabling calculation of a charge transferred during electrostatic brush discharge, was presented. Comparison of the results obtained from the simplified model and from direct measurements of transferred charge are presented in the paper.

  4. Catalysis: Quantifying charge transfer

    NASA Astrophysics Data System (ADS)

    James, Trevor E.; Campbell, Charles T.

    2016-02-01

    Improving the design of catalytic materials for clean energy production requires a better understanding of their electronic properties, which remains experimentally challenging. Researchers now quantify the number of electrons transferred from metal nanoparticles to an oxide support as a function of particle size.

  5. 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.

  6. Charge-Transfer Versus Charge-Transfer-Like Excitations Revisited

    SciTech Connect

    Moore, Barry; Sun, Haitao; Govind, Niranjan; Kowalski, Karol; Autschbach, Jochen

    2015-07-14

    Criteria to assess charge-transfer (CT) and `CT-like' character of electronic excitations are examined. Time-dependent density functional theory (TDDFT) with non-hybrid, hybrid, and tuned long-range corrected (LC) functionals is compared with with coupled-cluster (CC) benchmarks. The test set includes an organic CT complex, two `push-pull' donor-acceptor chromophores, a cyanine dye, and several polycyclic aromatic hydrocarbons. Proper CT is easily identified. Excitations with significant density changes upon excitation within regions of close spatial proximity can also be diagnosed. For such excitations, the use of LC functionals in TDDFT sometimes leads to dramatic improvements of the singlet energies, similar to proper CT, which has led to the concept of `CT-like' excitations. However, `CT-like' excitations are not like charge transfer, and the improvements are not obtained for the right reasons. The triplet excitation energies are underestimated for all systems, often severely. For the `CT-like' candidates, when going from a non-hybrid to an LC functional the error in the singlet-triplet (S/T) separation changes from negative to positive, providing error compensation. For the cyanine, the S/T separation is too large with all functionals, leading to the best error compensation for non-hybrid functionals.

  7. Photoinduced intramolecular charge transfer and photophysical characteristics of (2Z)-3-[4-(dimethylamino) phenyl]-2-(2-methylphenyl) prop-2-ene-nitrile (DPM) in different media

    NASA Astrophysics Data System (ADS)

    Asiri, Abdullah M.; El-Daly, Samy A.; Alamry, Khalid A.; Arshad, Muhammad Nadeem; Pannipara, Mehboobali

    2015-10-01

    A new fluorophore, (2Z)-3-[4-(dimethylamino) phenyl]-2-(2-methylphenyl) prop-2-ene-nitrile (DPM), was synthesized by knoevenagel condensation of 4-(dimethylamino) benzaldehyde and 2-methylbenzyl cyanide in ethanol using NaOH as base. The electronic absorption and emission characteristic of DPM was studied in different solvents. The X-ray crystallographic structure of DPM was also investigated. A crystalline solid of DPM gives a strong green emission at about 533 nm; these phenomena are important for the application of DPM dye in organic photo emitting diode. DPM exhibits a red shift in its emission spectrum as solvent polarity increases, indicating a large change in the dipole moment of dye molecule upon excitation due to intramolecular charge transfer in excited DPM*. The fluorescence quantum yield depends strongly on the properties of the solvents, which was attributed to positive and negative solvatokinetic effects. The DPM dye displays solubilization in cationic (CTAB) micelle and could be used as a probe to determine the critical micelle concentration (CMC) of CTAB.

  8. Charge Characteristics of Rechargeable Batteries

    NASA Astrophysics Data System (ADS)

    Maheswaranathan, Ponn; Kelly, Cormac

    2014-03-01

    Rechargeable batteries play important role in technologies today and they are critical for the future. They are used in many electronic devices and their capabilities need to keep up with the accelerated pace of technology. Efficient energy capture and storage is necessary for the future rechargeable batteries. Charging and discharging characteristics of three popular commercially available re-chargeable batteries (NiCd, NiMH, and Li Ion) are investigated and compared with regular alkaline batteries. Pasco's 850 interface and their voltage & current sensors are used to monitor the current through and the potential difference across the battery. The discharge current and voltage stayed fairly constant until the end, with a slightly larger drop in voltage than current, which is more pronounced in the alkaline batteries. After 25 charge/discharge cycling there is no appreciable loss of charge capacities in the Li Ion battery. Energy densities, cycle characteristics, and memory effects will also be presented. Sponsored by the South Carolina Governor's school for Science and Mathematics under the Summer Program for Research Interns program.

  9. Opposites Attract: Organic Charge Transfer Salts

    ERIC Educational Resources Information Center

    van de Wouw, Heidi L.; Chamorro, Juan; Quintero, Michael; Klausen, Rebekka S.

    2015-01-01

    A laboratory experiment is described that introduces second-year undergraduate organic chemistry students to organic electronic materials. The discovery of metallic conductivity in the charge transfer salt tetrathiafulvalene tetracyanoquinodimethane (TTF-TCNQ) is a landmark result in the history of organic electronics. The charge transfer…

  10. Charge transfer in algebraic quantum field theory

    NASA Astrophysics Data System (ADS)

    Wright, Jill Dianne

    We discuss aspects of the algebraic structure of quantum field theory. We take the view that the superselection structure of a theory should be determinable from the vacuum representation of the observable algebra, and physical properties of the charge. Hence one determines the nature of the charge transfer operations: the automorphisms of the observable algebra corresponding to the movement of charge along space-time paths. New superselection sectors are obtained from the vacuum sector by an automorphism which is a limit of charge transfer operations along paths with an endpoint tending to spacelike infinity. Roberts has shown that for a gauge theory of the first kind, the charge transfer operations for a given charge form a certain kind of 1-cocycle over Minkowski space. The local 1-cohomology group of their equivalence classes corresponds to the superselection structure. The exact definition of the cohomology group depends on the properties of the charge. Using displaced Fock representations of free fields, we develop model field theories which illustrate this structure. The cohomological classification of displaced Fock representations has been elucidated by Araki. For more general representations, explicit determination of the cohomology group is a hard problem. Using our models, we can illustrate ways in which fields with reasonable physical properties depart fromthe abovementioned structure. In 1+1 dimensions, we use the Streater-Wilde model to illustrate explicitly the representation-dependence of the cohomology structure, and the direction-dependence of the limiting charge transfer operation. The cohomology structure may also be representation-dependent in higher-dimensional theories without strict localization of charge, for example the electromagnetic field. The algebraic structure of the electromagnetic field has many other special features, which we discuss in relation to the concept of charge transfer. We also give some indication of the modifications

  11. Charge transfer between fullerenes and highly charged noble gas ions

    NASA Astrophysics Data System (ADS)

    Narits, A. A.

    2008-07-01

    A semiclassical model for the description of charge-exchange processes in collisions between fullerenes and multiply charged ions is developed. It is based on the decay model combined with the impact-parameter representation for the heavy particles' relative motion. The charge-transfer process in our model is treated as a transition of the active electron over and under the quasistatic potential barrier formed by the electric fields of the target and projectile. Due to the high electron delocalization on the surface of fullerene we represent it as a perfectly conducting hard sphere, whose radius is determined by the dipole polarizability of C60. The energies of the active electrons are assumed to be equal to the corresponding ionization potentials including the Stark-shift effect. We have developed an efficient technique for the evaluation of the electron transmission coefficient through the asymmetric potential barrier. It is shown that our model provides a good agreement with the available experimental data on single-electron charge-exchange processes. Moreover, it allows us to get an adequate description of multi-electron transfer processes. The first theoretical results on charge exchange between the fullerene ions and highly charged ions have been obtained.

  12. Utilizing Electrical Characteristics of Individual Nanotube Devices to Study the Charge Transfer between CdSe Quantum Dots and Double-Walled Nanotubes

    DOE PAGES

    Zhu, Yuqi; Zhou, Ruiping; Wang, Lei; ...

    2017-03-02

    To study the charge transfer between cadmium selenide (CdSe) quantum dots (QDs) and double-walled nanotubes (DWNTs), various sizes of CdSe-ligand-DWNT structures are synthesized, and field-effect transistors (FETs) from individual functionalized DWNTs rather than networks of the same are fabricated. From the electrical measurements, two distinct electron transfer mechanisms from the QD system to the nanotube are identified. By the formation of the CdSe-ligand-DWNT heterostructure, an effectively n-doped nanotube is created due to the smaller work function of CdSe as compared with the nanotube. In addition, once the QD-DWNT system is exposed to laser light, further electron transfer from the QDmore » through the ligand, i.e. 4-mercaptophenol (MTH), to the nanotube occurs and a clear QD-size dependent tunneling process is observed. Furthermore, the detailed analysis of a large set of devices and the particular methodology employed here for the first time allowed for extracting a wavelength and quantum dot size dependent charge transfer efficiency – a quantity that is evaluated for the first time through electrical measurement.« less

  13. Ultrafast charge transfer and atomic orbital polarization

    SciTech Connect

    Deppe, M.; Foehlisch, A.; Hennies, F.; Nagasono, M.; Beye, M.; Sanchez-Portal, D.; Echenique, P. M.; Wurth, W.

    2007-11-07

    The role of orbital polarization for ultrafast charge transfer between an atomic adsorbate and a substrate is explored. Core hole clock spectroscopy with linearly polarized x-ray radiation allows to selectively excite adsorbate resonance states with defined spatial orientation relative to the substrate surface. For c(4x2)S/Ru(0001) the charge transfer times between the sulfur 2s{sup -1}3p*{sup +1} antibonding resonance and the ruthenium substrate have been studied, with the 2s electron excited into the 3p{sub perpendicular}* state along the surface normal and the 3p{sub parallel}* state in the surface plane. The charge transfer times are determined as 0.18{+-}0.07 and 0.84{+-}0.23 fs, respectively. This variation is the direct consequence of the different adsorbate-substrate orbital overlap.

  14. Charge Transfer in Iridate-Manganite Superlattices.

    PubMed

    Okamoto, Satoshi; Nichols, John; Sohn, Changhee; Kim, So Yeun; Noh, Tae Won; Lee, Ho Nyung

    2017-03-07

    Charge transfer in superlattices consisting of SrIrO3 and SrMnO3 is investigated using density functional theory. Despite the nearly identical work function and nonpolar interfaces between SrIrO3 and SrMnO3, rather large charge transfer was experimentally reported at the interface between them. Here, we report a microscopic model that captures the mechanism behind this phenomenon, providing a qualitative understanding of the experimental observation. This leads to unique strain dependence of such charge transfer in iridate-manganite superlattices. The predicted behavior is consistently verified by experiment with soft X-ray and optical spectroscopy. Our work thus demonstrates a new route to control electronic states in nonpolar oxide heterostructures.

  15. 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.

  16. Charge dynamic characteristics in corona-charged polytetrafluoroethylene film electrets.

    PubMed

    Chen, Gang-Jin; Xiao, Hui-Ming; Zhu, Chun-Feng

    2004-08-01

    In this work, the charge dynamics characteristics of injection, transport and decay in porous and non-porous polytetrafluoroethylene (PTFE) film electrets were investigated by means of corona charging, isothermal and thermal stimulating surface-potential decay measurements. The results showed that the initial surface potential, whether positively or negatively charging, is much higher in non-porous PTFE than in porous PTFE. For porous film the value of initial surface potentials increases with increase of film thickness. Higher charging temperature can remarkably improve charge stability. The charge dynamics are correlated to materials microstructure according to their scanning electron micrographs. For non-porous PTFE films, polarizability change of C-F bonds is the main origin of electret charges; but for porous PTFE film a large number of bulk and interface type traps are expected because of the greater area of interface and higher crystallinity.

  17. 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

  18. Charge transfer states of the reaction center

    NASA Astrophysics Data System (ADS)

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

    1998-08-01

    The energies of the low lying charge transfer states relevant for the photoinduced charge separation are analysed for Rps. viridis. The main prosthetic groups consisting of the special pair dimer P, the two adjacent monomers BL, and BM and the two pheophytines HL and HM are treated together with the surrounding residues quantum mechanically within a supermolecule approach on the basis of an INDO approximation. High order configuration interactions are incorporated to account for polarization effects and long range electrostatic effects of the protein are considered. The results are analyzed with regard to symmetry breaking effects between the L- and the M-branch. Internal reorganization effects within the dimer are also discussed.

  19. Multiple-charge transfer and trapping in DNA dimers

    NASA Astrophysics Data System (ADS)

    Tornow, Sabine; Bulla, Ralf; Anders, Frithjof B.; Zwicknagl, Gertrud

    2010-11-01

    We investigate the charge transfer characteristics of one and two excess charges in a DNA base-pair dimer using a model Hamiltonian approach. The electron part comprises diagonal and off-diagonal Coulomb matrix elements such a correlated hopping and the bond-bond interaction, which were recently calculated by Starikov [E. B. Starikov, Philos. Mag. Lett. 83, 699 (2003)10.1080/0950083031000151374] for different DNA dimers. The electronic degrees of freedom are coupled to an ohmic or a superohmic bath serving as dissipative environment. We employ the numerical renormalization group method in the nuclear tunneling regime and compare the results to Marcus theory for the thermal activation regime. For realistic parameters, the rate that at least one charge is transferred from the donor to the acceptor in the subspace of two excess electrons significantly exceeds the rate in the single charge sector. Moreover, the dynamics is strongly influenced by the Coulomb matrix elements. We find sequential and pair transfer as well as a regime where both charges remain self-trapped. The transfer rate reaches its maximum when the difference of the on-site and intersite Coulomb matrix element is equal to the reorganization energy which is the case in a guanine/cytosine (GC)-dimer. Charge transfer is completely suppressed for two excess electrons in adenine/thymine (AT)-dimer in an ohmic bath and replaced by damped coherent electron-pair oscillations in a superohmic bath. A finite bond-bond interaction W alters the transfer rate: it increases as function of W when the effective Coulomb repulsion exceeds the reorganization energy (inverted regime) and decreases for smaller Coulomb repulsion.

  20. Charge transfer reactions in Xe plasma expansion

    SciTech Connect

    Jiao, C. Q.; Garscadden, A.; Ganguly, B. N.

    2007-04-15

    Charge transfer reactions of fast Xe ions with hydrocarbons including methane (CH{sub 4}), ethene (C{sub 2}H{sub 4}), and propane (C{sub 3}H{sub 8}) are studied by adding these hydrocarbon gases into a cross flowing Xe plasma expansion. Branching ratios and relative reaction rates for the charge transfers of fast Xe{sup +} with each of the three hydrocarbon gases are measured under different rf powers of the inductively coupled Xe discharge. For CH{sub 4}/Xe system, we find that fast Xe{sup +} reacts readily with CH{sub 4} generating CH{sub 4}{sup +} and CH{sub 3}{sup +} in a ratio of 1:0.56, with an estimated rate coefficient of (2.3{+-}0.3)x10{sup -10} cm{sup 3}/s at 75 W rf power which slowly increases to (2.9{+-}0.3)x10{sup -10} cm{sup 3}/s at 250 W (error bars reflect only the uncertainties due to the unknown extent of the ion recombination that follows the charge transfer reaction). These observed charge transfer reactions are made possible by the kinetically excited Xe ions produced by free expansion of the plasma. For the C{sub 2}H{sub 4}/Xe system product ions C{sub 2}H{sub 4}{sup +} and C{sub 2}H{sub 2}{sup +} are observed, and for C{sub 3}H{sub 8}/Xe, C{sub 2}H{sub 4}{sup +} and C{sub 2}H{sub 5}{sup +} and minor product ions including C{sub 2}H{sub 2}{sup +} and C{sub 3}H{sub 7}{sup +} are observed.

  1. Coronene-based charge-transfer complexes

    NASA Astrophysics Data System (ADS)

    Yoshida, Yukihiro; Isomura, Kazuhide; Kumagai, Yoshihide; Maesato, Mitsuhiko; Kishida, Hideo; Mizuno, Motohiro; Saito, Gunzi

    2016-08-01

    Recent developments in the arena of charge-transfer complexes composed of the D 6h-symmetric polycyclic aromatic hydrocarbon, coronene, are highlighted with emphasis on the structural and physical properties of these complexes. Because of the dual electron-donating and -accepting abilities of coronene, this group involves structurally-defined four cation salts and three anion salts. The Jahn-Teller distortions and in-plane motion of coronene molecules in the solids, both of which are closely associated with the high symmetry of coronene molecules, and syntheses of clathrate-type complexes are also presented.

  2. Pattern classification using charge transfer devices

    NASA Technical Reports Server (NTRS)

    1980-01-01

    The feasibility of using charge transfer devices in the classification of multispectral imagery was investigated by evaluating particular devices to determine their suitability in matrix multiplication subsystem of a pattern classifier and by designing a protype of such a system. Particular attention was given to analog-analog correlator devices which consist of two tapped delay lines, chip multipliers, and a summed output. The design for the classifier and a printed circuit layout for the analog boards were completed and the boards were fabricated. A test j:g for the board was built and checkout was begun.

  3. Improved Charge-Transfer Fluorescent Dyes

    NASA Technical Reports Server (NTRS)

    Meador, Michael

    2005-01-01

    Improved charge-transfer fluorescent dyes have been developed for use as molecular probes. These dyes are based on benzofuran nuclei with attached phenyl groups substituted with, variously, electron donors, electron acceptors, or combinations of donors and acceptors. Optionally, these dyes could be incorporated as parts of polymer backbones or as pendant groups or attached to certain surfaces via self-assembly-based methods. These dyes exhibit high fluorescence quantum yields -- ranging from 0.2 to 0.98, depending upon solvents and chemical structures. The wavelengths, quantum yields, intensities, and lifetimes of the fluorescence emitted by these dyes vary with (and, hence, can be used as indicators of) the polarities of solvents in which they are dissolved: In solvents of increasing polarity, fluorescence spectra shift to longer wavelengths, fluorescence quantum yields decrease, and fluorescence lifetimes increase. The wavelengths, quantum yields, intensities, and lifetimes are also expected to be sensitive to viscosities and/or glass-transition temperatures. Some chemical species -- especially amines, amino acids, and metal ions -- quench the fluorescence of these dyes, with consequent reductions in intensities, quantum yields, and lifetimes. As a result, the dyes can be used to detect these species. Another useful characteristic of these dyes is a capability for both two-photon and one-photon absorption. Typically, these dyes absorb single photons in the ultraviolet region of the spectrum (wavelengths < 400 nm) and emit photons in the long-wavelength ultraviolet, visible, and, when dissolved in some solvents, near-infrared regions. In addition, these dyes can be excited by two-photon absorption at near-infrared wavelengths (600 to 800 nm) to produce fluorescence spectra identical to those obtained in response to excitation by single photons at half the corresponding wavelengths (300 to 400 nm). While many prior fluorescent dyes exhibit high quantum yields

  4. Theoretical Evidence for Multiple Charge Transfer Pathways in Bacteriorhodopsin.

    PubMed

    Lee, Choongkeun; Mertz, Blake

    2016-04-12

    The development of molecular-scale junctions utilizing biomolecules is a challenging field that requires intimate knowledge of the relationship between molecular structure and conductance characteristics. One of the key parameters to understanding conductance efficiency is the charge mobility, which strongly influences the response time of electronic devices. The charge mobility of bacteriorhodopsin (bR), a membrane protein that has been studied experimentally in detail, was theoretically investigated using extended Marcus-Hush theory. Charge mobilities of 1.3 × 10(-2) and 9.7 × 10(-4) cm(2)/(V s) for hole and electron transfer, respectively, were determined. The computed electron mobility is comparable to experimentally measured values (9 × 10(-4) cm(2)/(V s)). Interestingly, the pathways for hole and electron hopping were very distinct from each other, utilizing different transmembrane helices to traverse the protein. In particular, only the electron transfer pathway involved the retinal chromophore, indicating that the efficiency of charge transfer is directly affected by the tertiary arrangement of proteins. Our results provide a template for obtaining the molecular and electronic-level details that can reveal fundamental insights into experimental studies on protein electron transport and inform efficient design of biomolecular-based junctions on the nanoscale.

  5. 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.

  6. 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

  7. Flavin Charge Transfer Transitions Assist DNA Photolyase Electron Transfer

    NASA Astrophysics Data System (ADS)

    Skourtis, Spiros S.; Prytkova, Tatiana; Beratan, David N.

    2007-12-01

    This contribution describes molecular dynamics, semi-empirical and ab-initio studies of the primary photo-induced electron transfer reaction in DNA photolyase. DNA photolyases are FADH--containing proteins that repair UV-damaged DNA by photo-induced electron transfer. A DNA photolyase recognizes and binds to cyclobutatne pyrimidine dimer lesions of DNA. The protein repairs a bound lesion by transferring an electron to the lesion from FADH-, upon photo-excitation of FADH- with 350-450 nm light. We compute the lowest singlet excited states of FADH- in DNA photolyase using INDO/S configuration interaction, time-dependent density-functional, and time-dependent Hartree-Fock methods. The calculations identify the lowest singlet excited state of FADH- that is populated after photo-excitation and that acts as the electron donor. For this donor state we compute conformationally-averaged tunneling matrix elements to empty electron-acceptor states of a thymine dimer bound to photolyase. The conformational averaging involves different FADH--thymine dimer confromations obtained from molecular dynamics simulations of the solvated protein with a thymine dimer docked in its active site. The tunneling matrix element computations use INDO/S-level Green's function, energy splitting, and Generalized Mulliken-Hush methods. These calculations indicate that photo-excitation of FADH- causes a π→π* charge-transfer transition that shifts electron density to the side of the flavin isoalloxazine ring that is adjacent to the docked thymine dimer. This shift in electron density enhances the FADH--to-dimer electronic coupling, thus inducing rapid electron transfer.

  8. Charge Transfer Calculations and Database for Astrophysics

    NASA Technical Reports Server (NTRS)

    Wang, J. G.; Stancil, P. C.; Rakovic, M.; Schultz, D. R.; Zygelman, B.

    2002-01-01

    A variety of theoretical approaches, having different but overlapping energy ranges of applicability, are applied to investigate charge transfer processes for collisions of atomic ions with atoms and molecules. The methods include quantal molecular-orbital close-coupling, classical trajectory Monte Carlo, and continuum distorted wave methods. Recent collision systems studied include S(+4) + H, S(+4) + He, N(+7) + He, H2O, CO, and CO2, O(+q)(q = 1 - 8) + H, H2, and S(+q)(q = 1 - 16) + H2. The database effort is concentrating on astrophysically important reactions of atomic ions X(+q)(X=H-Zn, q=1-4, and selected higher charges) with H, He, various metal atoms, H2, and other selected molecular targets. Existing data, much of it produced by us, has been compiled and critically evaluated. Data for many reactions missing in the literature are estimated using the multichannel Landau-Zener approximation. Fits to cross sections and rate coefficients using standard functions are provided as well as tabulations of the raw data. The database is available on the World Wide Web at cfadc.phy.ornl.gov/astro/ps/data.

  9. Switching of the fluorescence emission of single molecules between the locally excited and charge transfer states

    NASA Astrophysics Data System (ADS)

    Angeles Izquierdo, M.; Bell, Toby D. M.; Habuchi, Satoshi; Fron, Eduard; Pilot, Roberto; Vosch, Tom; De Feyter, Steven; Verhoeven, Jan; Jacob, Josemon; Müllen, Klaus; Hofkens, Johan; De Schryver, Frans C.

    2005-01-01

    A novel perylene imide and oligo-pentaphenyl bisfluorene containing molecule is shown to undergo electron transfer to form an emissive charge transfer state in di-benzyl ether and THF. At the single molecule level in a PMMA film, fluorescence spectra characteristic of both emissive states (locally excited and charge transfer) are observed with 44% of the molecules studied showing switching between the two states. These results demonstrate that charge transfer fluorescence from single molecules can be used to report on the properties and dynamics of a molecule's immediate surroundings or nano-environment.

  10. 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.

  11. 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).

  12. Ion momentum and energy transfer rates for charge exchange collisions

    NASA Technical Reports Server (NTRS)

    Horwitz, J.; Banks, P. M.

    1973-01-01

    The rates of momentum and energy transfer have been obtained for charge exchange collisions between ion and neutral gases having arbitrary Maxwellian temperatures and bulk transport velocities. The results are directly applicable to the F-region of the ionosphere where 0+ - 0 charge is the dominant mechanism affecting ion momentum and energy transfer.

  13. DNA charge transfer: Hot holes break the speed limit

    NASA Astrophysics Data System (ADS)

    Beratan, D. N.; Waldeck, D. H.

    2016-11-01

    Charge transfer through DNA has been well studied over recent decades from both a biological and electronics perspective. It has now been shown that charge transfer can be accelerated one hundredfold by using highly energetic 'hot holes', revealing a new mechanism that could help to create useful electronic biomaterials.

  14. Proton Transfer Reactivity of Large Multiply Charged Ions

    PubMed Central

    Williams, Evan R.

    2005-01-01

    Charge-charge interactions dramatically influence the dissociation and proton transfer reactivity of large multiply protonated ions. In combination with tandem mass spectrometry, proton transfer reactions have been used to determine the charge state of an ion and to increase the effective mass resolution of electrospray ionization mass spectra. A model for the proton transfer reactivity of multiply protonated ions, in which protons are assigned to specific sites in an ion based on the intrinsic reactivity of the site and the sum of point-charge Coulomb interactions between charges, is discussed. In combination with experimentally measured rates of proton transfer to bases of known gas-phase basicity, information about the intramolecular electrostatic interactions, gas-phase ion conformation and maximum charge state of an ion produced by electrospray ionization can be obtained. PMID:8799309

  15. Tunable charge transfer properties in metal-phthalocyanine heterojunctions

    NASA Astrophysics Data System (ADS)

    Siles, P. F.; Hahn, T.; Salvan, G.; Knupfer, M.; Zhu, F.; Zahn, D. R. T.; Schmidt, O. G.

    2016-04-01

    Organic materials such as phthalocyanine-based systems present a great potential for organic device applications due to the possibility of integrating films of different organic materials to create organic heterostructures which combine the electrical capabilities of each material. This opens the possibility to precisely engineer and tune new electrical properties. In particular, similar transition metal phthalocyanines demonstrate hybridization and charge transfer properties which could lead to interesting physical phenomena. Although, when considering device dimensions, a better understanding and control of the tuning of the transport properties still remain in the focus of research. Here, by employing conductive atomic force microscopy techniques, we provide an insight about the nanoscale electrical properties and transport mechanisms of MnPc and fluorinated phthalocyanines such as F16CuPc and F16CoPc. We report a transition from typical diode-like transport mechanisms for pure MnPc thin films to space-charge-limited current transport regime (SCLC) for Pc-based heterostructures. The controlled addition of fluorinated phthalocyanine also provides highly uniform and symmetric-polarized transport characteristics with conductance enhancements up to two orders of magnitude depending on the polarization. We present a method to spatially map the mobility of the MnPc/F16CuPc structures with a nanoscale resolution and provide theoretical calculations to support our experimental findings. This well-controlled nanoscale tuning of the electrical properties for metal transition phthalocyanine junctions stands as key step for future phthalocyanine-based electronic devices, where the low dimension charge transfer, mediated by transition metal atoms could be intrinsically linked to a transfer of magnetic moment or spin.Organic materials such as phthalocyanine-based systems present a great potential for organic device applications due to the possibility of integrating films of

  16. Tunable charge transfer properties in metal-phthalocyanine heterojunctions.

    PubMed

    Siles, P F; Hahn, T; Salvan, G; Knupfer, M; Zhu, F; Zahn, D R T; Schmidt, O G

    2016-04-28

    Organic materials such as phthalocyanine-based systems present a great potential for organic device applications due to the possibility of integrating films of different organic materials to create organic heterostructures which combine the electrical capabilities of each material. This opens the possibility to precisely engineer and tune new electrical properties. In particular, similar transition metal phthalocyanines demonstrate hybridization and charge transfer properties which could lead to interesting physical phenomena. Although, when considering device dimensions, a better understanding and control of the tuning of the transport properties still remain in the focus of research. Here, by employing conductive atomic force microscopy techniques, we provide an insight about the nanoscale electrical properties and transport mechanisms of MnPc and fluorinated phthalocyanines such as F16CuPc and F16CoPc. We report a transition from typical diode-like transport mechanisms for pure MnPc thin films to space-charge-limited current transport regime (SCLC) for Pc-based heterostructures. The controlled addition of fluorinated phthalocyanine also provides highly uniform and symmetric-polarized transport characteristics with conductance enhancements up to two orders of magnitude depending on the polarization. We present a method to spatially map the mobility of the MnPc/F16CuPc structures with a nanoscale resolution and provide theoretical calculations to support our experimental findings. This well-controlled nanoscale tuning of the electrical properties for metal transition phthalocyanine junctions stands as key step for future phthalocyanine-based electronic devices, where the low dimension charge transfer, mediated by transition metal atoms could be intrinsically linked to a transfer of magnetic moment or spin.

  17. Quantifying the intrinsic surface charge density and charge-transfer resistance of the graphene-solution interface through bias-free low-level charge measurement

    NASA Astrophysics Data System (ADS)

    Ping, Jinglei; Johnson, A. T. Charlie

    2016-07-01

    Liquid-based bio-applications of graphene require a quantitative understanding of the graphene-liquid interface, with the surface charge density of adsorbed ions, the interfacial charge transfer resistance, and the interfacial charge noise being of particular importance. We quantified these properties through measurements of the zero-bias Faradaic charge-transfer between graphene electrodes and aqueous solutions of varying ionic strength using a reproducible, low-noise, minimally perturbative charge measurement technique. The measurements indicated that the adsorbed ions had a negative surface charge density of approximately -32.8 mC m-2 and that the specific charge transfer resistance was 6.5 ± 0.3 MΩ cm2. The normalized current noise power spectral density for all ionic concentrations tested collapsed onto a 1/fα characteristic with α = 1.1 ± 0.2. All the results are in excellent agreement with predictions of the theory for the graphene-solution interface. This minimally perturbative method for monitoring charge-transfer at the sub-pC scale exhibits low noise and ultra-low power consumption (˜fW), making it suitable for use in low-level bioelectronics in liquid environments.

  18. Charge Transfer and Catalysis at the Metal Support Interface

    SciTech Connect

    Baker, Lawrence Robert

    2012-07-31

    Kinetic, electronic, and spectroscopic characterization of model Pt–support systems are used to demonstrate the relationship between charge transfer and catalytic activity and selectivity. The results show that charge flow controls the activity and selectivity of supported metal catalysts. This dissertation builds on extensive existing knowledge of metal–support interactions in heterogeneous catalysis. The results show the prominent role of charge transfer at catalytic interfaces to determine catalytic activity and selectivity. Further, this research demonstrates the possibility of selectively driving catalytic chemistry by controlling charge flow and presents solid-state devices and doped supports as novel methods for obtaining electronic control over catalytic reaction kinetics.

  19. Ytterbocene charge-transfer molecular wire complexes.

    PubMed

    Carlson, Christin N; Kuehl, Christopher J; Da Re, Ryan E; Veauthier, Jacqueline M; Schelter, Eric J; Milligan, Ashley E; Scott, Brian L; Bauer, Eric D; Thompson, J D; Morris, David E; John, Kevin D

    2006-06-07

    A systematic study of the novel charge-transfer [(f)14-(pi)0-(f)14 --> (f)13-(pi)2-(f)13] electronic state found in 2:1 metal-to-ligand adducts of the type [(Cp)2Yb](BL)[Yb(Cp)2] [BL = tetra(2-pyridyl)pyrazine (tppz) (1), 6',6' '-bis(2-pyridyl)-2,2':4',4'':2'',2'''-quaterpyridine (qtp) (2), 1,4-di(terpyridyl)-benzene (dtb) (3), Cp = (C5Me5)] has been conducted with the aim of determining the effects of increased Yb-Yb separation on the magnetic and electronic properties of these materials. The neutral [(f)13-(pi)2-(f)13], cationic [(f)13-(pi)1-(f)13] and dicationic [(f)13-(pi)0-(f)13] states of these complexes were studied by cyclic voltammetry, UV-vis-NIR electronic absorption spectroscopy, NMR, X-ray crystallography, and magnetic susceptibility measurements. The spectroscopic and magnetic data for the neutral bimetallic complexes is consistent with an [(f)13(pi)2(f)13] ground-state electronic configuration in which each ytterbocene fragment donates one electron to give a singlet dianionic bridging ligand with two paramagnetic Yb(III) centers. The voltammetric data demonstrate that the electronic interaction in the neutral molecular wires 1-3, as manifested in the separation between successive metal reduction waves, is large compared to analogous transition metal systems. Electronic spectra for the neutral and monocationic bimetallic species are dominated by pi-pi and pi-pi transitions, masking the f-f bands that are expected to best reflect the electronic metal-metal interactions. However, these metal-localized transitions are observed when the electrons are removed from the bridging ligand via chemical oxidation to yield the dicationic species, and they suggest very little electronic interaction between metal centers in the absence of pi electrons on the bridging ligands. Analysis of the magnetic data reveals that the qtp complex displays antiferromagnetic coupling of the type Yb(alpha)(alphabeta)Yb(beta) at approximately 13 K.

  20. Energy Transfer of a Shaped Charge.

    SciTech Connect

    Milinazzo, Jared Joseph

    2016-11-01

    A cylinder of explosive with a hollow cavity on one and a detonator at the other is considered a hollow charge. When the explosive is detonated the detonation products form a localized intense force. If the hollow charge is placed near or in contact with a steel plate then the damage to the plate is greater than a solid cylinder of explosive even though there is a greater amount of explosive in the latter charge. The hollow cavity can take almost any geometrical shape with differing amounts of damage associated with each shape. This phenomenon is known in the United States as the Munroe effect.

  1. Charge transfer reactions in nematic liquid crystals

    SciTech Connect

    Wiederrecht, G.P.; Wasielewski, M.R. |; Galili, T.; Levanon, H.

    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.

  2. Interfacial charge transfer absorption: Application to metal molecule assemblies

    NASA Astrophysics Data System (ADS)

    Creutz, Carol; Brunschwig, Bruce S.; Sutin, Norman

    2006-05-01

    Optically induced charge transfer between adsorbed molecules and a metal electrode was predicted by Hush to lead to new electronic absorption features, but has been only rarely observed experimentally. Interfacial charge transfer absorption (IFCTA) provides information concerning the barriers to charge transfer between molecules and the metal/semiconductor and the magnitude of the electronic coupling and could thus provide a powerful tool for understanding interfacial charge-transfer kinetics. Here, we utilize a previously published model [C. Creutz, B.S. Brunschwig, N. Sutin, J. Phys. Chem. B 109 (2005) 10251] to predict IFCTA spectra of metal-molecule assemblies and compare the literature observations to these predictions. We conclude that, in general, the electronic coupling between molecular adsorbates and the metal levels is so small that IFCTA is not detectable. However, few experiments designed to detect IFCTA have been done. We suggest approaches to optimizing the conditions for observing the process.

  3. Charge transfer processes: the role of optimized molecular orbitals.

    PubMed

    Meyer, Benjamin; Domingo, Alex; Krah, Tim; Robert, Vincent

    2014-08-07

    The influence of the molecular orbitals on charge transfer (CT) reactions is analyzed through wave function-based calculations. Characteristic CT processes in the organic radical 2,5-di-tert-butyl-6-oxophenalenoxyl linked with tetrathiafulvalene and the inorganic crystalline material LaMnO3 show that changes in the inner shells must be explicitly taken into account. Such electronic reorganization can lead to a reduction of the CT vertical transition energy up to 66%. A state-specific approach accessible through an adapted CASSCF (complete active space self-consistent field) methodology is capable of reaching good agreement with the experimental spectroscopy of CT processes. A partitioning of the relaxation energy in terms of valence- and inner-shells is offered and sheds light on their relative importance. This work paves the way to the intimate description of redox reactions using quantum chemistry methods.

  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

    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. Screen charge transfer by grounded tip on ferroelectric surfaces.

    SciTech Connect

    Kim, Y.; Kim, J.; Buhlmann, S.; Hong, S.; Kim, Y. K.; Kim, S.-H.; No, K.; Materials Science Division; Korea Advanced Inst. of Science and Technology; Samsung Advanced Inst. of Technology; Inostek Inc.

    2008-03-01

    We have investigated polarization reversal and charge transfer effects by a grounded tip on 50 nm thick ferroelectric thin films using piezoelectric force microscopy and Kelvin force microscopy. We observed the polarization reversal in the center of written domains, and also identified another mechanism, which is the transfer of screen charges toward the grounded tip. In order to overcome these phenomena, we successfully applied a modified read/write scheme featuring a bias voltage.

  6. 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.

  7. Discrete electrostatic charge transfer by the electrophoresis of a charged droplet in a dielectric liquid.

    PubMed

    Im, Do Jin; Ahn, Myung Mo; Yoo, Byeong Sun; Moon, Dustin; Lee, Dong Woog; Kang, In Seok

    2012-08-14

    We have experimentally investigated the electrostatic charging of a water droplet on an electrified electrode surface to explain the detailed inductive charging processes and use them for the detection of droplet position in a lab-on-a-chip system. The periodic bouncing motion of a droplet between two planar electrodes has been examined by using a high-resolution electrometer and an image analysis method. We have found that this charging process consists of three steps. The first step is inductive charge accumulation on the opposite electrode by the charge of a droplet. This induction process occurs while the droplet approaches the electrode, and it produces an induction current signal at the electrometer. The second step is the discharging of the droplet by the accumulated induced charge at the moment of contact. For this second step, there is no charge-transfer detection at the electrometer. The third step is the charging of the neutralized droplet to a certain charged state while the droplet is in contact with the electrode. The charge transfer of the third step is detected as the pulse-type signal of an electrometer. The second and third steps occur simultaneously and rapidly. We have found that the induction current by the movement of a charged droplet can be accurately used to measure the charge of the droplet and can also be used to monitor the position of a droplet under actuation. The implications of the current findings for understanding and measuring the charging process are discussed.

  8. Charge transfer reactions in multiply charged ion-atom collisions. [in interstellar clouds

    NASA Technical Reports Server (NTRS)

    Steigman, G.

    1975-01-01

    Charge-transfer reactions in collisions between highly charged ions and neutral atoms of hydrogen and/or helium may be rapid at thermal energies. If these reactions are rapid, they will suppress highly charged ions in H I regions and guarantee that the observed absorption features from such ions cannot originate in the interstellar gas. A discussion of such charge-transfer reactions is presented and compared with the available experimental data. The possible implications of these reactions for observations of the interstellar medium, H II regions, and planetary nebulae are outlined.

  9. INTRAMOLECULAR CHARGE AND ENERGY TRANSFER IN MULTICHROMOPHORIC AROMATIC SYSTEMS

    SciTech Connect

    Edward C. Lim

    2008-09-09

    A concerted experimental and computational study of energy transfer in nucleic acid bases and charge transfer in dialkylaminobenzonitriles, and related electron donor-acceptor molecules, indicate that the ultrafast photoprocesses occur through three-state conical interactions involving an intermediate state of biradical character.

  10. 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.

  11. What Controls the Rate of Ultrafast Charge Transfer and Charge Separation Efficiency in Organic Photovoltaic Blends.

    PubMed

    Jakowetz, Andreas C; Böhm, Marcus L; Zhang, Jiangbin; Sadhanala, Aditya; Huettner, Sven; Bakulin, Artem A; Rao, Akshay; Friend, Richard H

    2016-09-14

    In solar energy harvesting devices based on molecular semiconductors, such as organic photovoltaics (OPVs) and artificial photosynthetic systems, Frenkel excitons must be dissociated via charge transfer at heterojunctions to yield free charges. What controls the rate and efficiency of charge transfer and charge separation is an important question, as it determines the overall power conversion efficiency (PCE) of these systems. In bulk heterojunctions between polymer donor and fullerene acceptors, which provide a model system to understand the fundamental dynamics of electron transfer in molecular systems, it has been established that the first step of photoinduced electron transfer can be fast, of order 100 fs. But here we report the first study which correlates differences in the electron transfer rate with electronic structure and morphology, achieved with sub-20 fs time resolution pump-probe spectroscopy. We vary both the fullerene substitution and donor/fullerene ratio which allow us to control both aggregate size and the energetic driving force for charge transfer. We observe a range of electron transfer times from polymer to fullerene, from 240 fs to as short as 37 fs. Using ultrafast electro-optical pump-push-photocurrent spectroscopy, we find the yield of free versus bound charges to be weakly dependent on the energetic driving force, but to be very strongly dependent on fullerene aggregate size and packing. Our results point toward the importance of state accessibility and charge delocalization and suggest that energetic offsets between donor and acceptor levels are not an important criterion for efficient charge generation. This provides design rules for next-generation materials to minimize losses related to driving energy and boost PCE.

  12. Transfer function characteristics of super resolving systems

    NASA Technical Reports Server (NTRS)

    Milster, Tom D.; Curtis, Craig H.

    1992-01-01

    Signal quality in an optical storage device greatly depends on the optical system transfer function used to write and read data patterns. The problem is similar to analysis of scanning optical microscopes. Hopkins and Braat have analyzed write-once-read-many (WORM) optical data storage devices. Herein, transfer function analysis of magnetooptic (MO) data storage devices is discussed with respect to improving transfer-function characteristics. Several authors have described improving the transfer function as super resolution. However, none have thoroughly analyzed the MO optical system and effects of the medium. Both the optical system transfer function and effects of the medium of this development are discussed.

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

    NASA Astrophysics Data System (ADS)

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

    2016-04-01

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

  14. Intramolecular Charge Transfer States in the Condensed Phase

    NASA Astrophysics Data System (ADS)

    Williams, C. F.; Herbert, J. M.

    2009-06-01

    Time-Dependent Density Functional Theory (TDDFT) with long range corrected functionals can give accurate results for the energies of electronically excited states involving Intramolecular Charge Transfer (ICT) in large molecules. If this is combined with a Molecular Mechanics (MM) representation of the surrounding solvent this technique can be used to interpret the results of condensed phase UV-Vis Spectroscopy. Often the MM region is represented by a set of point charges, however this means that the solvent cannot repolarize to adapt to the new charge distribution as a result of ICT and so the excitation energies to ICT states are overestimated. To solve this problem an algorithm that interfaces TDDFT with the polarizable force-field AMOEBA is presented; the effect of solvation on charge transfer in species such as 4,4'dimethylaminobenzonitrile (DMABN) is discussed. M.A. Rohrdanz, K.M. Martins, and J.M. Herbert, J. Chem. Phys. 130 034107 (2008).

  15. Charge transfer properties of pentacene adsorbed on silver: DFT study

    SciTech Connect

    N, Rekha T.; Rajkumar, Beulah J. M.

    2015-06-24

    Charge transfer properties of pentacene adsorbed on silver is investigated using DFT methods. Optimized geometry of pentacene after adsorption on silver indicates distortion in hexagonal structure of the ring close to the silver cluster and deviations in co-planarity of carbon atoms due to the variations in bond angles and dihedral angles. Theoretically simulated absorption spectrum has a symmetric surface plasmon resonance peak around 486nm corresponding to the transfer of charge from HOMO-2 to LUMO. Theoretical SERS confirms the process of adsorption, tilted orientation of pentacene on silver surface and the charge transfers reported. Localization of electron density arising from redistribution of electrostatic potential together with a reduced bandgap of pentacene after adsorption on silver suggests its utility in the design of electro active organic semiconducting devices.

  16. Charge transfer in helium-rich supernova plasma

    NASA Technical Reports Server (NTRS)

    Swartz, Douglas A.

    1994-01-01

    Charge transfer rate coefficients are estimated using Landau-Zener and modified Demkov approximations. The coefficients, augmented by those available from the literature, are used in statistical equilibrium equations describing the state of helium-rich supernova plasma. Such a plasma may describe both Type Ib and Type Ic supernova ejecta. The hypothesis that extensive mixing of metals with helium in Type Ic supernovae may provide a catalyst for rapid charge transfer that weakens the helium line emission by altering the excitation balance is tested. It is shown that charge transfer as a mechanism for suppressing helium line emission is ineffective unless the metal abundance is comparable to or larger than the helium abundance. This result supports an earlier conclusion that Type Ic supernovae must be helium poor relative to Type Ib events.

  17. Charge transfer to a semi-esterified bifunctional phenol

    NASA Astrophysics Data System (ADS)

    Brede, O.; Hermann, R.; Orthner, H.

    1996-03-01

    The charge transfer from solvent radical cations of n-butyl chloride and cyclohexane to 2-butyl-6(3'-t-butyl-2'-hydroxy-5'-methylbenzyl)-4-methyl-phenylacrylate (GM) yields in the first step phenoxyl radicals as well as acrylate radical cations of this semi-acrylated bifunctional phenol. Subsequently an intramolecular charge transfer from the acrylate radical cation to the phenol group takes place. Because of the instability of phenol radical cations, under our experimental conditions (nanosecond pulse radiolysis, non-polar solvents, room temperature) phenoxyl radicals are the only observable products of phenol ionization.

  18. Transfer ionization in collisions with a fast highly charged ion.

    PubMed

    Voitkiv, A B

    2013-07-26

    Transfer ionization in fast collisions between a bare ion and an atom, in which one of the atomic electrons is captured by the ion whereas another one is emitted, crucially depends on dynamic electron-electron correlations. We show that in collisions with a highly charged ion a strong field of the ion has a very profound effect on the correlated channels of transfer ionization. In particular, this field weakens (strongly suppresses) electron emission into the direction opposite (perpendicular) to the motion of the ion. Instead, electron emission is redirected into those parts of the momentum space which are very weakly populated in fast collisions with low charged ions.

  19. Electrostatic sensors applied to the measurement of electric charge transfer in gas solids pipelines

    NASA Astrophysics Data System (ADS)

    Woodhead, S. R.; Denham, J. C.; Armour-Chelu, D. I.

    2005-01-01

    This paper describes the development of a number of electric charge sensors. The sensors have been developed specifically to investigate triboelectric charge transfer which takes place between particles and the pipeline wall, when powdered materials are conveyed through a pipeline using air. A number of industrial applications exist for such gas solids pipelines, including pneumatic conveyors, vacuum cleaners and dust extraction systems. The build-up of electric charge on pipelines and powdered materials can lead to electrostatic discharge and so is of interest from a safety viewpoint. The charging of powders can also adversely affect their mechanical handling characteristics and so is of interest to handling equipment engineers. The paper presents the design of the sensors, the design of the electric charge test rig and electric charge measurement test results.

  20. Ultrafast investigation of photoinduced charge transfer in aminoanthraquinone pharmaceutical product

    NASA Astrophysics Data System (ADS)

    Zhang, Song; Sun, Simei; Zhou, Miaomiao; Wang, Lian; Zhang, Bing

    2017-02-01

    We investigated the mechanism of intramolecular charge transfer and the following radiationless dynamics of the excited states of 1-aminoanthraquinone using steady state and time-resolved absorption spectroscopy combined with quantum chemical calculations. Following photoexcitation with 460 nm, conformational relaxation via twisting of the amino group, charge transfer and the intersystem crossing (ISC) processes have been established to be the major relaxation pathways responsible for the ultrafast nonradiative of the excited S1 state. Intramolecular proton transfer, which could be induced by intramolecular hydrogen bonding is inspected and excluded. Time-dependent density functional theory (TDDFT) calculations reveal the change of the dipole moments of the S0 and S1 states along the twisted coordinate of the amino group, indicating the mechanism of twisted intra-molecular charge transfer (TICT). The timescale of TICT is measured to be 5 ps due to the conformational relaxation and a barrier on the S1 potential surface. The ISC from the S1 state to the triplet manifold is a main deactivation pathway with the decay time of 28 ps. Our results observed here have yield a physically intuitive and complete picture of the photoinduced charge transfer and radiationless dynamics in anthraquinone pharmaceutial products.

  1. Ultrafast investigation of photoinduced charge transfer in aminoanthraquinone pharmaceutical product

    PubMed Central

    Zhang, Song; Sun, Simei; Zhou, Miaomiao; Wang, Lian; Zhang, Bing

    2017-01-01

    We investigated the mechanism of intramolecular charge transfer and the following radiationless dynamics of the excited states of 1-aminoanthraquinone using steady state and time-resolved absorption spectroscopy combined with quantum chemical calculations. Following photoexcitation with 460 nm, conformational relaxation via twisting of the amino group, charge transfer and the intersystem crossing (ISC) processes have been established to be the major relaxation pathways responsible for the ultrafast nonradiative of the excited S1 state. Intramolecular proton transfer, which could be induced by intramolecular hydrogen bonding is inspected and excluded. Time-dependent density functional theory (TDDFT) calculations reveal the change of the dipole moments of the S0 and S1 states along the twisted coordinate of the amino group, indicating the mechanism of twisted intra-molecular charge transfer (TICT). The timescale of TICT is measured to be 5 ps due to the conformational relaxation and a barrier on the S1 potential surface. The ISC from the S1 state to the triplet manifold is a main deactivation pathway with the decay time of 28 ps. Our results observed here have yield a physically intuitive and complete picture of the photoinduced charge transfer and radiationless dynamics in anthraquinone pharmaceutial products. PMID:28233835

  2. Charge transfer in multi-component low-dimensional materials stacks (Conference Presentation)

    NASA Astrophysics Data System (ADS)

    Bersuker, Gennadi

    2016-09-01

    Advanced electronics, energy storage and harvesting, etc. applications employ devices combining nano-thick layers of dielectric, semiconductor and metal materials. Electrical characteristics of such highly-scaled materials stacks are found to be strongly influenced by the charge transfer across the layers. Charge transfer processes are controlled, to a great degree, by the interface regions, their structure and composition being modified by the inter-materials interaction affected by stack fabrication conditions. These complex systems pose new challenges for analyzing charge transfer processes, which are sensitive to even extremely small concentrations of electrically active defects. In order to identify these defects, the critical task is to link the atomic-level structural features of multicomponent ultra-thin material stacks to their electrical characteristics affected by charge transfer. We focus on analyzing oxide structural features responsible for the charge transfer by combining a variety of electrical measurement techniques with high time and spatial resolutions that allow capturing fast transient charging processes and differentiating signals from different regions through the depth of the multi-layer stacks. These data are used to fit the results of simulations of the physical processes underlying the electrical measurements in order to extract spatial and energy profiles of electrically active centers. The extracted characteristics are, in turn, compared to the atomic-level material modeling data to pinpoint atomic and energy material characteristics responsible for the electrical properties, thus, providing a helpful feedback to optimize the device fabrication process. We discuss examples of implementations of this approach for analysis and optimization of a variety of ultra-thin layers devices.

  3. [Dynamics of charge transfer along an oligonucleotide at finite temperature].

    PubMed

    Lakhno, V D; Fialko, N S

    2004-01-01

    The quantum-statistical approach was used to describe the charge transfer in nucleotide sequences. The results of numerical modeling for hole transfer in the GTTGGG sequence with background temperature noise are given. It was shown that, since guanine has an oxidation potential lower than thymine, the hole created at the G donor in this sequence passes through the thymine barrier into the guanine triplet (acceptor) at a time of approximately 10 ps at a temperature of 37 degrees C.

  4. A two-dimensional position sensitive gas chamber with scanned charge transfer readout

    NASA Astrophysics Data System (ADS)

    Gómez, F.; Iglesias, A.; Lobato, R.; Mosquera, J.; Pardo, J.; Pena, J.; Pazos, A.; Pombar, M.; Rodríguez, A.

    2003-10-01

    We have constructed and tested a two-dimensional position sensitive parallel-plate gas ionization chamber with scanned charge transfer readout. The scan readout method described here is based on the development of a new position-dependent charge transfer technique. It has been implemented by using gate strips perpendicularly oriented to the collector strips. This solution reduces considerably the number of electronic readout channels needed to cover large detector areas. The use of a 25 μm thick kapton etched circuit allows high charge transfer efficiency with a low gating voltage, consequently needing a very simple commutating circuit. The present prototype covers 8×8 cm2 with a pixel size of 1.27×1.27 mm2. Depending on the intended use and beam characteristics a smaller effective pixel is feasible and larger active areas are possible. This detector can be used for X-ray or other continuous beam intensity profile monitoring.

  5. Enhancing SERS by Means of Supramolecular Charge Transfer

    NASA Technical Reports Server (NTRS)

    Wong, Eric; Flood, Amar; Morales, Alfredo

    2009-01-01

    In a proposed method of sensing small quantities of molecules of interest, surface enhanced Raman scattering (SERS) spectroscopy would be further enhanced by means of intermolecular or supramolecular charge transfer. There is a very large potential market for sensors based on this method for rapid detection of chemical and biological hazards. In SERS, the Raman signals (vibrational spectra) of target molecules become enhanced by factors of the order of 108 when those molecules are in the vicinities of nanostructured substrate surfaces that have been engineered to have plasmon resonances that enhance local electric fields. SERS, as reported in several prior NASA Tech Briefs articles and elsewhere, has remained a research tool and has not yet been developed into a practical technique for sensing of target molecules: this is because the short range (5 to 20 nm) of the field enhancement necessitates engineering of receptor molecules to attract target molecules to the nanostructured substrate surfaces and to enable reliable identification of the target molecules in the presence of interferants. Intermolecular charge-transfer complexes have been used in fluorescence-, photoluminescence-, and electrochemistry-based techniques for sensing target molecules, but, until now, have not been considered for use in SERS-based sensing. The basic idea of the proposed method is to engineer receptor molecules that would be attached to nanostructured SERS substrates and that would interact with the target molecules to form receptor-target supramolecular charge-transfer complexes wherein the charge transfer could be photoexcited.

  6. Charge transfer devices. Citations from the NTIS data base

    NASA Astrophysics Data System (ADS)

    Reed, W. E.

    1980-04-01

    The technology, design, fabrication, and applications of charge transfer devices are presented in the cited research reports. Applications include imaging, signal processing, detectors, filters, amplifiers, and memory devices. This updated bibliography contains 107 abstracts, all of which are new entries to the previous edition.

  7. 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.

  8. 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.

  9. Variable nonlinear transfer characteristics of MSLM

    NASA Astrophysics Data System (ADS)

    Kobayashi, Yuji; Hara, Tsutomu; Suzuki, Yoshiji

    1990-08-01

    Variable nonlinear transfer characteristics (gamma characteristics) of microchannel spatial light modulator (MSLM) are investigated theoretically and experimentally. The MSLM structure and the principle of operation are discussed, and experimental results are presented. It is shown that the thresholding nonlinearities of the MSLM can be controlled by either the mesh voltage or by writing the time change in the thresholding operation. The resulting variable nonlinear transfer characteristics can be used in various optical processings such as a sigmoid function on optical neural networks and an analog operating on optical information processing.

  10. Infrared Spectroscopy of Charge Transfer Complexes of Purines and Pyrimidines

    SciTech Connect

    Rathod, Pravinsinh I.; Oza, A. T.

    2011-10-20

    The FTIR spectra of charge transfer complexes of purines and pyrimidines with organic acceptors such as TCNQ, TCNE, DDQ, chloranil and iodine are obtained and studied in the present work. Adenine, guanine, thymine, cytosine and uracil are the purines and pyrimidines which are found as constituent of DNA and RNA. Charge transfer induced hydrogen bonding is concluded on the basis of indirect transitions observed in the infrared range in these CTCs. Some CTCs show gaussian bands revealing delocalization of charge carriers. The CTCs show interband transition in three-dimensions rather than two-dimensions unlike CTCs of amino acids. There is no extended hydrogen bonded network spanning the whole crystal. This leads to indirect transition due to locally deformed lattice furnishing a phonon-assisted transition.

  11. Effect of Aperiodicity on the Charge Transfer Through DNA Molecules

    NASA Astrophysics Data System (ADS)

    Ghosh, Angsula; Chaudhuri, Puspitapallab

    The effect of aperiodicity on the charge transfer process through DNA molecules is investigated using a tight-binding model. Single-stranded aperiodic Fibonacci polyGC and polyAT sequences along with aperiodic Rudin-Shapiro poly(GCAT) sequences are used in the study. Based on the tight-binding model, molecular orbital calculations of the DNA chains are performed and ionization potentials compared, as this might be relevant to understanding the charge transfer process. Charges migrate through the sequences in a multistep hopping process. Results for current conduction through aperiodic sequences are compared with those for the corresponding periodic sequences. We find that dinucleotide aperiodic Fibonacci sequences decrease the current while tetranucleotide aperiodic Rudin-Shapiro sequences increase the current when compared with the corresponding periodic sequences. The conductance in all cases decays exponentially as the sequence length increases.

  12. Radiative charge transfer in collisions of C with He+

    NASA Astrophysics Data System (ADS)

    Babb, James F.; McLaughlin, B. M.

    2017-02-01

    Radiative charge exchange collisions between a carbon atom {{C}}({}3P) and a helium ion {{He}}+({}2S), both in their ground state, are investigated theoretically. Detailed quantum chemistry calculations are carried out to obtain potential energy curves and transition dipole matrix elements for doublet and quartet molecular states of the HeC+ cation. Radiative charge transfer cross sections and rate coefficients are calculated and are found at thermal and lower energies to be large compared to those for direct charge transfer. The present results might be applicable to modelling the complex interplay of [{{C}} {{II}}] (or {{{C}}}+), {{C}}, and {CO} at the boundaries of interstellar photon dominated regions and in x-ray dominated regions, where the abundance of {{He}}+ affects the abundance of {CO}.

  13. Infrared Spectroscopy of Charge Transfer Complexes of Purines and Pyrimidines

    NASA Astrophysics Data System (ADS)

    Rathod, Pravinsinh I.; Oza, A. T.

    2011-10-01

    The FTIR spectra of charge transfer complexes of purines and pyrimidines with organic acceptors such as TCNQ, TCNE, DDQ, chloranil and iodine are obtained and studied in the present work. Adenine, guanine, thymine, cytosine and uracil are the purines and pyrimidines which are found as constituent of DNA and RNA. Charge transfer induced hydrogen bonding is concluded on the basis of indirect transitions observed in the infrared range in these CTCs. Some CTCs show gaussian bands revealing delocalization of charge carriers. The CTCs show interband transition in three-dimensions rather than two-dimensions unlike CTCs of amino acids. There is no extended hydrogen bonded network spanning the whole crystal. This leads to indirect transition due to locally deformed lattice furnishing a phonon-assisted transition.

  14. Graphene nonvolatile memory prototype based on charge-transfer mechanism

    NASA Astrophysics Data System (ADS)

    Lv, Hongming; Wu, Huaqiang; Huang, Can; Wang, Yuda; Qian, He

    2014-04-01

    A graphene nonvolatile memory (GNVM) prototype based on charge transfer between the graphene layer and the NH2(CH2)3Si(OEt)3 (APTES) self-assembled monolayer (SAM) is demonstrated. Graphene was transferred to an APTES-SAM-engineered SiO2 substrate and patterned into bottom-gate transistors. Owing to the charge trapping/detrapping property of the nitrogen atoms in APTES, a significant and reproducible transfer curve hysteresis is observed. Memory performance metrics, including retention and endurance, are reported. Comparisons between vacuum and ambient environment test results indicate air absorbates’ detrimental effect. Loss of nonvolatile storage is explained on the basis of a two-layer tunneling junction model, which sheds light on further device improvement through aminosilane molecule structure optimization.

  15. 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.

  16. Active pixel sensor with intra-pixel charge transfer

    NASA Technical Reports Server (NTRS)

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

    2003-01-01

    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.

  17. Active pixel sensor with intra-pixel charge transfer

    NASA Technical Reports Server (NTRS)

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

    2004-01-01

    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.

  18. Charge-transfer crystallites as molecular electrical dopants

    PubMed Central

    Méndez, Henry; Heimel, Georg; Winkler, Stefanie; Frisch, Johannes; Opitz, Andreas; Sauer, Katrein; Wegner, Berthold; Oehzelt, Martin; Röthel, Christian; Duhm, Steffen; Többens, Daniel; Koch, Norbert; Salzmann, Ingo

    2015-01-01

    Ground-state integer charge transfer is commonly regarded as the basic mechanism of molecular electrical doping in both, conjugated polymers and oligomers. Here, we demonstrate that fundamentally different processes can occur in the two types of organic semiconductors instead. Using complementary experimental techniques supported by theory, we contrast a polythiophene, where molecular p-doping leads to integer charge transfer reportedly localized to one quaterthiophene backbone segment, to the quaterthiophene oligomer itself. Despite a comparable relative increase in conductivity, we observe only partial charge transfer for the latter. In contrast to the parent polymer, pronounced intermolecular frontier-orbital hybridization of oligomer and dopant in 1:1 mixed-stack co-crystallites leads to the emergence of empty electronic states within the energy gap of the surrounding quaterthiophene matrix. It is their Fermi–Dirac occupation that yields mobile charge carriers and, therefore, the co-crystallites—rather than individual acceptor molecules—should be regarded as the dopants in such systems. PMID:26440403

  19. Charge transfer induced polarity switching in carbon nanotube transistors.

    PubMed

    Klinke, Christian; Chen, Jia; Afzali, Ali; Avouris, Phaedon

    2005-03-01

    We probed the charge transfer interaction between the amine-containing molecules hydrazine, polyaniline, and aminobutyl phosphonic acid and carbon nanotube field effect transistors (CNTFETs). We successfully converted p-type CNTFETs to n-type and drastically improved the device performance in both the ON- and OFF-transistor states, utilizing hydrazine as dopant. We effectively switched the transistor polarity between p- and n- type by accessing different oxidation states of polyaniline. We also demonstrated the flexibility of modulating the threshold voltage (Vth) of a CNTFET by engineering various charge-accepting and -donating groups in the same molecule.

  20. What is the "best" atomic charge model to describe through-space charge-transfer excitations?

    PubMed

    Jacquemin, Denis; Le Bahers, Tangui; Adamo, Carlo; Ciofini, Ilaria

    2012-04-28

    We investigate the efficiency of several partial atomic charge models (Mulliken, Hirshfeld, Bader, Natural, Merz-Kollman and ChelpG) for investigating the through-space charge-transfer in push-pull organic compounds with Time-Dependent Density Functional Theory approaches. The results of these models are compared to benchmark values obtained by determining the difference of total densities between the ground and excited states. Both model push-pull oligomers and two classes of "real-life" organic dyes (indoline and diketopyrrolopyrrole) used as sensitisers in solar cell applications have been considered. Though the difference of dipole moments between the ground and excited states is reproduced by most approaches, no atomic charge model is fully satisfactory for reproducing the distance and amount of charge transferred that are provided by the density picture. Overall, the partitioning schemes fitting the electrostatic potential (e.g. Merz-Kollman) stand as the most consistent compromises in the framework of simulating through-space charge-transfer, whereas the other models tend to yield qualitatively inconsistent values.

  1. Laboratory Studies of Thermal Energy Charge Transfer of Multiply Charged Ions in Astrophysical Plasmas

    NASA Technical Reports Server (NTRS)

    Kwong, Victor H. S.

    2003-01-01

    The laser ablation/ion storage facility at the UNLV Physics Department has been dedicated to the study of atomic and molecular processes in low temperature plasmas. Our program focuses on the charge transfer (electron capture) of multiply charged ions and neutrals important in astrophysics. The electron transfer reactions with atoms and molecules is crucial to the ionization condition of neutral rich photoionized plasmas. With the successful deployment of the Far Ultraviolet Spectroscopic Explorer (FUSE) and the Chandra X-ray Observatory by NASA high resolution VUV and X-ray emission spectra fiom various astrophysical objects have been collected. These spectra will be analyzed to determine the source of the emission and the chemical and physical environment of the source. The proper interpretation of these spectra will require complete knowledge of all the atomic processes in these plasmas. In a neutral rich environment, charge transfer can be the dominant process. The rate coefficients need to be known accurately. We have also extended our charge transfer measurements to KeV region with a pulsed ion beam. The inclusion of this facility into our current program provides flexibility in extending the measurement to higher energies (KeV) if needed. This flexibility enables us to address issues of immediate interest to the astrophysical community as new observations are made by high resolution space based observatories.

  2. Charge transfer to ground-state ions produces free electrons

    NASA Astrophysics Data System (ADS)

    You, D.; Fukuzawa, H.; Sakakibara, Y.; Takanashi, T.; Ito, Y.; Maliyar, G. G.; Motomura, K.; Nagaya, K.; Nishiyama, T.; Asa, K.; Sato, Y.; Saito, N.; Oura, M.; Schöffler, M.; Kastirke, G.; Hergenhahn, U.; Stumpf, V.; Gokhberg, K.; Kuleff, A. I.; Cederbaum, L. S.; Ueda, K.

    2017-01-01

    Inner-shell ionization of an isolated atom typically leads to Auger decay. In an environment, for example, a liquid or a van der Waals bonded system, this process will be modified, and becomes part of a complex cascade of relaxation steps. Understanding these steps is important, as they determine the production of slow electrons and singly charged radicals, the most abundant products in radiation chemistry. In this communication, we present experimental evidence for a so-far unobserved, but potentially very important step in such relaxation cascades: Multiply charged ionic states after Auger decay may partially be neutralized by electron transfer, simultaneously evoking the creation of a low-energy free electron (electron transfer-mediated decay). This process is effective even after Auger decay into the dicationic ground state. In our experiment, we observe the decay of Ne2+ produced after Ne 1s photoionization in Ne-Kr mixed clusters.

  3. Charge transfer to ground-state ions produces free electrons

    PubMed Central

    You, D.; Fukuzawa, H.; Sakakibara, Y.; Takanashi, T.; Ito, Y.; Maliyar, G. G.; Motomura, K.; Nagaya, K.; Nishiyama, T.; Asa, K.; Sato, Y.; Saito, N.; Oura, M.; Schöffler, M.; Kastirke, G.; Hergenhahn, U.; Stumpf, V.; Gokhberg, K.; Kuleff, A. I.; Cederbaum, L. S.; Ueda, K

    2017-01-01

    Inner-shell ionization of an isolated atom typically leads to Auger decay. In an environment, for example, a liquid or a van der Waals bonded system, this process will be modified, and becomes part of a complex cascade of relaxation steps. Understanding these steps is important, as they determine the production of slow electrons and singly charged radicals, the most abundant products in radiation chemistry. In this communication, we present experimental evidence for a so-far unobserved, but potentially very important step in such relaxation cascades: Multiply charged ionic states after Auger decay may partially be neutralized by electron transfer, simultaneously evoking the creation of a low-energy free electron (electron transfer-mediated decay). This process is effective even after Auger decay into the dicationic ground state. In our experiment, we observe the decay of Ne2+ produced after Ne 1s photoionization in Ne–Kr mixed clusters. PMID:28134238

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

    SciTech Connect

    Pavanello, Michele; Neugebauer, Johannes

    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.

  5. Exciton strings in an organic charge-transfer crystal

    NASA Astrophysics Data System (ADS)

    Kuwata-Gonokami, M.; Peyghambarian, N.; Meissner, K.; Fluegel, B.; Sato, Y.; Ema, K.; Shimano, R.; Mazumdar, S.; Guo, F.; Tokihiro, T.; Ezaki, H.; Hanamura, E.

    1994-01-01

    COLLECTIVE excitations resulting from many-body Coulomb interactions have been studied extensively in the solid state1: for example, the exchange interaction between the electrons in two excitons (bound electron-hole pairs) can bind the excitons together, forming a biexciton. At the other extreme, if the number of excitons is sufficiently large (~106), they can condense into a degenerate 'liquid' phase known as an electron-hole drop. But in conventional semiconductors, intermediate bound states, consisting of more than two excitons, are not formed. We show here, both theoretically and experimentally, that bound states of multiple excitons can form in the organic charge-transfer solid anthracene-(pyromellitic acid dianhydride). Coulomb interactions along the one-dimensional stacks of this material can stabilize trains of several charge-transfer excitons, and we refer to the resulting collective excitations as exciton strings.

  6. 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.

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

    PubMed

    Pavanello, Michele; Neugebauer, Johannes

    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 π-stacked nucleobase dimers of B-DNA: 5'-GG-3' and 5'-GT-3'. 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.

  8. Raman scattering from molecular conduction junctions: Charge transfer mechanism

    NASA Astrophysics Data System (ADS)

    Oren, Michal; Galperin, Michael; Nitzan, Abraham

    2012-03-01

    We present a model for the charge transfer contribution to surface-enhanced Raman spectroscopy (SERS) in a molecular junction. The model is a generalization of the equilibrium scheme for SERS of a molecule adsorbed on a metal surface [B. N. J. Persson. Chem. Phys. Lett.CHPLBC0009-261410.1016/0009-2614(81)85441-3 82, 561 (1981)]. We extend the same physical consideration to a nonequilibrium situation in a biased molecular junction and to nonzero temperatures. Two approaches are considered and compared: a semiclassical approach appropriate for nonresonance Raman scattering, and a quantum approach based on the nonequilibrium Green's function method. Nonequilibrium effects on this contribution to SERS are demonstrated with numerical examples. It is shown that the semiclassical approach provides an excellent approximation to the full quantum calculation as long as the molecular electronic state is outside the Fermi window, that is, as long as the field-induced charge transfer is small.

  9. Charge transfer and interface properties in inorganic superstructures and composites

    NASA Astrophysics Data System (ADS)

    Flyagina, I. S.; Petrov, A. A.; Pervov, V. S.

    2016-06-01

    The processes of charge transfer and electronic reconstruction at interfaces of inorganic superstructures and composites have not yet been adequately investigated. This review integrates and analyzes the results of theoretical and experimental studies of structural and electronic effects at interfaces of metal oxide or chalcogenide superstructures and composites. Charge transfer and, hence, change in interface properties compared to the properties of substructures are shown to be determined by the preparation method of composites and chemical nature of the superstructures, incommensurability of structural parameters and valence states of the constituent metals. The changes are maximal for nanoheterostructures, and the degree of change is related to electronic conductivity of substructures. The macroscopic properties of the composite materials depend on the amount of interfaces in their bulk. The bibliography includes 66 references.

  10. Charge-Transfer Interactions between Transition Metal Hexafluorides and Xenon

    DTIC Science & Technology

    1977-10-01

    HEXAFLUORIDES AND XENON’. by J. D./Webb M E. R./Bernstein\\ Prepared for Publication in the Journal of the American Chemical Society DTIE Department of...Metal Hexafluorides ar. Xenon" " 6. PERFORMIKG ORG REPk)RT NUMODE . CONTRACT OR GNANT NUMBLR(e) J. D. Webb and E. R. Bernstein N00014-75-C-1179 9...neceoswy and Idenifil by block numbet) charge transfer electron affinities Transitio Metal Hexafluorides Xencn electronegativities 4,AGSTRACT Coninue an

  11. Momentum transfer in relativistic heavy ion charge-exchange reactions

    NASA Technical Reports Server (NTRS)

    Townsend, L. W.; Wilson, J. W.; Khan, F.; Khandelwal, G. S.

    1991-01-01

    Relativistic heavy ion charge-exchange reactions yield fragments (Delta-Z = + 1) whose longitudinal momentum distributions are downshifted by larger values than those associated with the remaining fragments (Delta-Z = 1, -2,...). Kinematics alone cannot account for the observed downshifts; therefore, an additional contribution from collision dynamics must be included. In this work, an optical model description of collision momentum transfer is used to estimate the additional dynamical momentum downshift. Good agreement between theoretical estimates and experimental data is obtained.

  12. Interfacial Charge Transfer States in Condensed Phase Systems

    NASA Astrophysics Data System (ADS)

    Vandewal, Koen

    2016-05-01

    Intermolecular charge transfer (CT) states at the interface between electron-donating (D) and electron-accepting (A) materials in organic thin films are characterized by absorption and emission bands within the optical gap of the interfacing materials. CT states efficiently generate charge carriers for some D-A combinations, and others show high fluorescence quantum efficiencies. These properties are exploited in organic solar cells, photodetectors, and light-emitting diodes. This review summarizes experimental and theoretical work on the electronic structure and interfacial energy landscape at condensed matter D-A interfaces. Recent findings on photogeneration and recombination of free charge carriers via CT states are discussed, and relations between CT state properties and optoelectronic device parameters are clarified.

  13. Direct detection of photoinduced charge transfer complexes in polymer fullerene blends

    NASA Astrophysics Data System (ADS)

    Behrends, Jan; Sperlich, Andreas; Schnegg, Alexander; Biskup, Till; Teutloff, Christian; Lips, Klaus; Dyakonov, Vladimir; Bittl, Robert

    2012-03-01

    We report transient electron paramagnetic resonance (trEPR) measurements with submicrosecond time resolution performed on a polymer:fullerene blend consisting of poly(3-hexylthiophene) (P3HT) and [6,6]-phenyl C61-butyric acid methyl ester (PCBM) at low temperatures. The trEPR spectrum immediately following photoexcitation reveals signatures of spin-correlated polaron pairs. The pair partners (positive polarons in P3HT and negative polarons in PCBM) can be identified by their characteristic g values. The fact that the polaron pair states exhibit strong non-Boltzmann population unambiguously shows that the constituents of each pair are geminate, i.e., originate from one exciton. We demonstrate that coupled polaron pairs are present even several microseconds after charge transfer and suggest that they embody the intermediate charge transfer complexes that form at the donor/acceptor interface and mediate the conversion from excitons into free charge carriers.

  14. Accumulative electron transfer: multiple charge separation in artificial photosynthesis.

    PubMed

    Karlsson, Susanne; Boixel, Julien; Pellegrin, Yann; Blart, Errol; Becker, Hans-Christian; Odobel, Fabrice; Hammarström, Leif

    2012-01-01

    To achieve artificial photosynthesis it is necessary to couple the single-electron event of photoinduced charge separation with the multi-electron reactions of fuel formation and water splitting. Therefore, several rounds of light-induced charge separation are required to accumulate enough redox equivalents at the catalytic sites for the target chemistry to occur, without any sacrificial donors or acceptors other than the catalytic substrates. Herein, we discuss the challenges of such accumulative electron transfer in molecular systems. We present a series of closely related systems base on a Ru(II)-polypyridine photosensitizer with appended triaryl-amine or oligo-triaryl-amine donors, linked to nanoporous TiO2 as the acceptor. One of the systems, based on dye 4, shows efficient accumulative electron transfer in high overall yield resulting in the formation of a two-electron charge-separated state upon successive excitation by two photons. In contrast, the other systems do not show accumulative electron transfer because of different competing reactions. This illustrates the difficulties in designing successful systems for this still largely unexplored type of reaction scheme.

  15. Energy and charge transfer in ionized argon coated water clusters.

    PubMed

    Kočišek, J; Lengyel, J; Fárník, M; Slavíček, P

    2013-12-07

    We investigate the electron ionization of clusters generated in mixed Ar-water expansions. The electron energy dependent ion yields reveal the neutral cluster composition and structure: water clusters fully covered with the Ar solvation shell are formed under certain expansion conditions. The argon atoms shield the embedded (H2O)n clusters resulting in the ionization threshold above ≈15 eV for all fragments. The argon atoms also mediate more complex reactions in the clusters: e.g., the charge transfer between Ar(+) and water occurs above the threshold; at higher electron energies above ~28 eV, an excitonic transfer process between Ar(+)* and water opens leading to new products Ar(n)H(+) and (H2O)(n)H(+). On the other hand, the excitonic transfer from the neutral Ar* state at lower energies is not observed although this resonant process was demonstrated previously in a photoionization experiment. Doubly charged fragments (H2O)(n)H2(2+) and (H2O)(n)(2+) ions are observed and Intermolecular Coulomb decay (ICD) processes are invoked to explain their thresholds. The Coulomb explosion of the doubly charged cluster formed within the ICD process is prevented by the stabilization effect of the argon solvent.

  16. 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 π-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.

  17. Energy and charge transfer in ionized argon coated water clusters

    SciTech Connect

    Kočišek, J. E-mail: michal.farnik@jh-inst.cas.cz Lengyel, J.; Fárník, M. E-mail: michal.farnik@jh-inst.cas.cz; Slavíček, P. E-mail: michal.farnik@jh-inst.cas.cz

    2013-12-07

    We investigate the electron ionization of clusters generated in mixed Ar-water expansions. The electron energy dependent ion yields reveal the neutral cluster composition and structure: water clusters fully covered with the Ar solvation shell are formed under certain expansion conditions. The argon atoms shield the embedded (H{sub 2}O){sub n} clusters resulting in the ionization threshold above ≈15 eV for all fragments. The argon atoms also mediate more complex reactions in the clusters: e.g., the charge transfer between Ar{sup +} and water occurs above the threshold; at higher electron energies above ∼28 eV, an excitonic transfer process between Ar{sup +}* and water opens leading to new products Ar{sub n}H{sup +} and (H{sub 2}O){sub n}H{sup +}. On the other hand, the excitonic transfer from the neutral Ar* state at lower energies is not observed although this resonant process was demonstrated previously in a photoionization experiment. Doubly charged fragments (H{sub 2}O){sub n}H{sub 2}{sup 2+} and (H{sub 2}O){sub n}{sup 2+} ions are observed and Intermolecular Coulomb decay (ICD) processes are invoked to explain their thresholds. The Coulomb explosion of the doubly charged cluster formed within the ICD process is prevented by the stabilization effect of the argon solvent.

  18. Efficient charge generation by relaxed charge-transfer states at organic interfaces

    NASA Astrophysics Data System (ADS)

    Vandewal, Koen; Albrecht, Steve; Hoke, Eric T.; Graham, Kenneth R.; Widmer, Johannes; Douglas, Jessica D.; Schubert, Marcel; Mateker, William R.; Bloking, Jason T.; Burkhard, George F.; Sellinger, Alan; Fréchet, Jean M. J.; Amassian, Aram; Riede, Moritz K.; McGehee, Michael D.; Neher, Dieter; Salleo, Alberto

    2014-01-01

    Interfaces between organic electron-donating (D) and electron-accepting (A) materials have the ability to generate charge carriers on illumination. Efficient organic solar cells require a high yield for this process, combined with a minimum of energy losses. Here, we investigate the role of the lowest energy emissive interfacial charge-transfer state (CT1) in the charge generation process. We measure the quantum yield and the electric field dependence of charge generation on excitation of the charge-transfer (CT) state manifold via weakly allowed, low-energy optical transitions. For a wide range of photovoltaic devices based on polymer:fullerene, small-molecule:C60 and polymer:polymer blends, our study reveals that the internal quantum efficiency (IQE) is essentially independent of whether or not D, A or CT states with an energy higher than that of CT1 are excited. The best materials systems show an IQE higher than 90% without the need for excess electronic or vibrational energy.

  19. Efficient charge generation by relaxed charge-transfer states at organic interfaces.

    PubMed

    Vandewal, Koen; Albrecht, Steve; Hoke, Eric T; Graham, Kenneth R; Widmer, Johannes; Douglas, Jessica D; Schubert, Marcel; Mateker, William R; Bloking, Jason T; Burkhard, George F; Sellinger, Alan; Fréchet, Jean M J; Amassian, Aram; Riede, Moritz K; McGehee, Michael D; Neher, Dieter; Salleo, Alberto

    2014-01-01

    Interfaces between organic electron-donating (D) and electron-accepting (A) materials have the ability to generate charge carriers on illumination. Efficient organic solar cells require a high yield for this process, combined with a minimum of energy losses. Here, we investigate the role of the lowest energy emissive interfacial charge-transfer state (CT1) in the charge generation process. We measure the quantum yield and the electric field dependence of charge generation on excitation of the charge-transfer (CT) state manifold via weakly allowed, low-energy optical transitions. For a wide range of photovoltaic devices based on polymer:fullerene, small-molecule:C60 and polymer:polymer blends, our study reveals that the internal quantum efficiency (IQE) is essentially independent of whether or not D, A or CT states with an energy higher than that of CT1 are excited. The best materials systems show an IQE higher than 90% without the need for excess electronic or vibrational energy.

  20. Quantum information transfer between topological and conventional charge qubits

    NASA Astrophysics Data System (ADS)

    Jun, Li; Yan, Zou

    2016-02-01

    We propose a scheme to realize coherent quantum information transfer between topological and conventional charge qubits. We first consider a hybrid system where a quantum dot (QD) is tunnel-coupled to a semiconductor Majorana-hosted nanowire (MNW) via using gated control as a switch, the information encoded in the superposition state of electron empty and occupied state can be transferred to each other through choosing the proper interaction time to make measurements. Then we consider another system including a double QDs and a pair of parallel MNWs, it is shown that the entanglement information transfer can be realized between the two kinds of systems. We also realize long distance quantum information transfer between two quantum dots separated by an MNW, by making use of the nonlocal fermionic level formed with the pared Majorana feimions (MFs) emerging at the two ends of the MNW. Furthermore, we analyze the teleportationlike electron transfer phenomenon predicted by Tewari et al. [Phys. Rev. Lett. 100, 027001 (2008)] in our considered system. Interestingly, we find that this phenomenon exactly corresponds to the case that the information encoded in one QD just returns back to its original place during the dynamical evolution of the combined system from the perspective of quantum state transfer. Project supported by the National Natural Science Foundation of China (Grant No. 11304031).

  1. Dual Fluorescence in GFP Chromophore Analogues: Chemical Modulation of Charge Transfer and Proton Transfer Bands.

    PubMed

    Chatterjee, Tanmay; Mandal, Mrinal; Das, Ananya; Bhattacharyya, Kalishankar; Datta, Ayan; Mandal, Prasun K

    2016-04-14

    Dual fluorescence of GFP chromophore analogues has been observed for the first time. OHIM (o-hydroxy imidazolidinone) shows only a charge transfer (CT) band, CHBDI (p-cyclicamino o-hydroxy benzimidazolidinone) shows a comparable intensity CT and PT (proton transfer) band, and MHBDI (p-methoxy o-hydroxy benzimidazolidinone) shows a higher intensity PT band. It could be shown that the differential optical behavior is not due to conformational variation in the solid or solution phase. Rather, control of the excited state electronic energy level and excited state acidity constant by functional group modification could be shown to be responsible for the differential optical behavior. Chemical modification-induced electronic control over the relative intensity of the charge transfer and proton transfer bands could thus be evidenced. Support from single-crystal X-ray structure, NMR, femtosecond to nanosecond fluorescence decay analysis, and TDDFT-based calculation provided important information and thus helped us understand the photophysics better.

  2. Theory of ultrafast heterogeneous electron transfer: Contributions of direct charge transfer excitations to the absorbance

    SciTech Connect

    Wang, Luxia; Willig, Frank; May, Volkhard

    2007-04-07

    Absorption spectra related to heterogeneous electron transfer are analyzed with the focus on direct charge transfer transition from the surface attached molecule into the semiconductor band states. The computations are based on a model of reduced dimensionality with a single intramolecular vibrational coordinate but a complete account for the continuum of conduction band states. The applicability of this model to perylene on TiO{sub 2} has been demonstrated in a series of earlier papers. Here, based on a time-dependent formulation, the absorbance is calculated with the inclusion of charge transfer excitations. A broad parameter set inspired by the perylene TiO{sub 2} systems is considered. In particular, the description generalizes the Fano effect to heterogeneous electron transfer reactions. Preliminary simulations of measured spectra are presented for perylene-catechol attached to TiO{sub 2}.

  3. Quantifying through-space charge transfer dynamics in π-coupled molecular systems.

    PubMed

    Batra, Arunabh; Kladnik, Gregor; Vázquez, Héctor; Meisner, Jeffrey S; Floreano, Luca; Nuckolls, Colin; Cvetko, Dean; Morgante, Alberto; Venkataraman, Latha

    2012-01-01

    Understanding the role of intermolecular interaction on through-space charge transfer characteristics in π-stacked molecular systems is central to the rational design of electronic materials. However, a quantitative study of charge transfer in such systems is often difficult because of poor control over molecular morphology. Here we use the core-hole clock implementation of resonant photoemission spectroscopy to study the femtosecond charge-transfer dynamics in cyclophanes, which consist of two precisely stacked π-systems held together by aliphatic chains. We study two systems, [2,2]paracyclophane (22PCP) and [4,4]paracyclophane (44PCP), with inter-ring separations of 3.0 and 4.0 Å, respectively. We find that charge transfer across the π-coupled system of 44PCP is 20 times slower than in 22PCP. We attribute this difference to the decreased inter-ring electronic coupling in 44PCP. These measurements illustrate the use of core-hole clock spectroscopy as a general tool for quantifying through-space coupling in π-stacked systems.

  4. 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.

    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

  5. Super-iron Nanoparticles with Facile Cathodic Charge Transfer

    SciTech Connect

    M Farmand; D Jiang; B Wang; S Ghosh; D Ramaker; S Licht

    2011-12-31

    Super-irons contain the + 6 valence state of iron. One advantage of this is that it provides a multiple electron opportunity to store additional battery charge. A decrease of particle size from the micrometer to the nanometer domain provides a higher surface area to volume ratio, and opportunity to facilitate charge transfer, and improve the power, voltage and depth of discharge of cathodes made from such salts. However, super-iron salts are fragile, readily reduced to the ferric state, with both heat and contact with water, and little is known of the resultant passivating and non-passivating ferric oxide products. A pathway to decrease the super-iron particle size to the nano-domain is introduced, which overcomes this fragility, and retains the battery capacity advantage of their Fe(VI) valence state. Time and power controlled mechanosynthesis, through less aggressive, dry ball milling, leads to facile charge transfer of super-iron nanoparticles. Ex-situ X-ray Absorption Spectroscopy is used to explore the oxidation state and structure of these iron oxides during discharge and shows the significant change in stability of the ferrate structure to lower oxidation state when the particle size is in the nano-domain.

  6. Polaron assisted charge transfer in model biological systems

    NASA Astrophysics Data System (ADS)

    Li, Guangqi; Movaghar, Bijan

    2016-11-01

    We use a tight binding Hamiltonian to simulate the electron transfer from an initial charge-separating exciton to a final target state through a two-arm transfer model. The structure is copied from the model frequently used to describe electron harvesting in photosynthesis (photosystems I). We use this network to provide proof of principle for dynamics, in quantum system/bath networks, especially those involving interference pathways, and use these results to make predictions on artificially realizable systems. Each site is coupled to the phonon bath via several electron-phonon couplings. The assumed large energy gaps and weak tunneling integrals linking the last 3 sites give rise to"Stark Wannier like" quantum localization; electron transfer to the target cluster becomes impossible without bath coupling. As a result of the electron-phonon coupling, local electronic energies relax when the site is occupied, and transient polaronic states are formed as photo-generated electrons traverse the system. For a symmetric constructively interfering two pathway network, the population is shared equally between two sets of equivalent sites and therefore the polaron energy shift is smaller. The smaller energy shift however makes the tunnel transfer to the last site slower or blocks it altogether. Slight disorder (or thermal noise) can break the symmetry, permitting essentially a "one path", and correspondingly more efficient transfer.

  7. Stark spectroscopy of charge-transfer transitions in catechol-sensitized TiO 2 nanoparticles

    NASA Astrophysics Data System (ADS)

    Nawrocka, Agnieszka; Zdyb, Agata; Krawczyk, Stanisław

    2009-06-01

    Electronic excited states of catechol bound to titanium dioxide nanoparticles were investigated using electroabsorption (Stark effect) spectroscopy. The electronic transition at about 400 nm, characteristic for catechol bound to TiO 2 is associated with a change in permanent dipole moment by f · |Δ μ| = 15.7 D (where f is the local field correction factor), and a small negative change in the polarizability. Electron transfer distance points to the strong charge-transfer character of this transition. The electroabsorption spectra show also another electronic transition 7000 cm -1 higher energy, partially masked by the TiO 2 absorption.

  8. 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.

  9. Dielectric Properties of Organic Charge-Transfer Salts

    NASA Astrophysics Data System (ADS)

    Fischer, J. K. H.; Lunkenheimer, P.; Krohns, S.; Manna, R. S.; Hartmann, B.; Schubert, H.; Lang, M.; Müller, J.; Schlueter, J. A.; Mézière, C.; Batail, P.; Loidl, A.

    The BEDT-TTF-based charge-transfer salts have attracted considerable attention due to their often intriguing dielectric properties. An example is κ-(BEDT-TTF)2Cu[N(CN)2]Cl. It was recently found to exhibit multiferroicity, for which a new electric-dipole driven mechanism was proposed. The polar moment in this system was suggested to arise from the dimerization of the BEDT-TTF molecules, combined with charge order. Another interesting recent example is α-(BEDT-TTF)2I3, which shows the signature of relaxor-ferroelectric behavior. Here, we will present an overview of the dielectric properties of the above systems and provide new results on κ-(BEDT-TTF)2Hg(SCN)2Cl, which also seems to show relaxor-ferroelectric behavior in its charge-ordered state. In addition, we present measurements of δ-(EDT-TTF-CONMe2)2Br. This compound lacks dimerization, but exhibits charge order already at room temperature.

  10. Enhancement of IR and VCD intensities due to charge transfer.

    PubMed

    Nicu, Valentin Paul; Autschbach, Jochen; Baerends, Evert Jan

    2009-03-14

    Donor-acceptor interactions such as the one between the Cl(-) base and the N-H sigma* acceptor orbitals encountered in the complexation of Cl(-) counterions to the [Co(en)(3)](3+) transition metal complex, have been shown to cause huge enhancement (between 1 and 2 orders of magnitude) of the VCD intensities of N-H stretching modes. This effect has been fully analyzed, and could be attributed to increased charge flow from the Cl(-) donors when the N-H bonds become stretched. The transfer of charge counteracts the movement of negative electronic charge that happens along with the motion of the H nuclei, effectively reversing the electronic part of the electric dipole transition moment (EDTM) in the direction of the charge flow (z, say), and of the magnetic transition dipole moment (MDTM) in the perpendicular direction. The consequences for the IR and VCD intensity follow: IR intensity is strongly increased if the EDTM is polarized in the z direction, e.g. in A(2) modes, but not so much if it is polarized in the xy plane (E modes), the VCD is strongly enhanced if the EDTM and MTDM are polarized in the xy plane (in E modes), but less so when they are polarized in the z direction (in A(2) modes). The explanation holds generally for complexation phenomena of this sort, including the donor-acceptor part of hydrogen bonding interactions, e.g. with solvent molecules.

  11. Heat Transfer Characteristics of SHS Reactions

    DTIC Science & Technology

    1990-07-01

    A+R?0 Qt43 =5 -YA co ,/A FINAL REPORT AD- A225 769-=-_ HEAT TRANSFER CHARACTERISTICS OF SHS REACTIONS K. V. Logan, G. R. Villalobos, J. N. Harris, P...2741 Ta 180.9 3287 5731 Cr 52.0 2130 2945 lNb 95.9 2890 4919 W 183.8 3683 >6000 Mli 54.9 1518 2335 Fe 55.8 1808 3135 Co 58.9 1768 3201 Ni 58.7 1726

  12. Charge transfer in proton-hydrogen collisions under Debye plasma

    SciTech Connect

    Bhattacharya, Arka; Kamali, M. Z. M.; Ghoshal, Arijit; Ratnavelu, K.

    2015-02-15

    The effect of plasma environment on the 1s → nlm charge transfer, for arbitrary n, l, and m, in proton-hydrogen collisions has been investigated within the framework of a distorted wave approximation. The effect of external plasma has been incorporated using Debye screening model of the interacting charge particles. Making use of a simple variationally determined hydrogenic wave function, it has been possible to obtain the scattering amplitude in closed form. A detailed study has been made to investigate the effect of external plasma environment on the differential and total cross sections for electron capture into different angular momentum states for the incident energy in the range of 20–1000 keV. For the unscreened case, our results are in close agreement with some of the most accurate results available in the literature.

  13. Morphology Effects on Space Charge Characteristics of Low Density Polyethylene

    NASA Astrophysics Data System (ADS)

    Zhou; Yuanxiang; Wang; Yunshan; Zahn, Markus; Wang; Ninghua; Sun; Qinghua; Liang; Xidong; Guan; Zhichen

    2011-01-01

    Low density polyethylene (LDPE) film samples with different morphology were prepared by three kinds of annealing methods which were different in cooling rates in this study. A pulsed electro-acoustic (PEA) space charge measurement system was improved to solve the surface discharge problems for small samples applied with a high voltage. Negative direct current (DC) fields from 50 to above 220 kV/mm were applied to the samples. The influences of morphologies on space charge and space charge packet characteristics were measured by the improved high voltage withstand (HVW) PEA system. Mobility and trap depth of released charges were calculated by space charge decay. It was found that there is a different probability of space charge packet initiation under applied field from -60 to -100 kV/mm. Average velocity and mobility of the space charge packets were calculated by space charge packet dynamics. It was found that the lower cooling rate samples have higher crystallinity, more homo-charge accumulation, lower mobility and deeper trap depth. The mechanism of morphological effects on space charge phenomena have been presumed to give a plausible explanation for their inherent relationships. The morphology in the metal-dielectric interface and in the bulk is convincingly suggested to be responsible for the injection and propagation processes of space charge. A model of positive space charge initiation in LDPE samples was also suggested and analyzed. The mechanism of morphological effects and the charge injection model are well fit with the injection and propagation processes of space charge. The different effects of morphology in the metal-dielectric interface and in the bulk of polymers are stressed.

  14. Polarization and charge transfer in the hydration of chloride ions

    SciTech Connect

    Zhao Zhen; Rogers, David M.; Beck, Thomas L.

    2010-01-07

    A theoretical study of the structural and electronic properties of the chloride ion and water molecules in the first hydration shell is presented. The calculations are performed on an ensemble of configurations obtained from molecular dynamics simulations of a single chloride ion in bulk water. The simulations utilize the polarizable AMOEBA force field for trajectory generation and MP2-level calculations are performed to examine the electronic structure properties of the ions and surrounding waters in the external field of more distant waters. The ChelpG method is employed to explore the effective charges and dipoles on the chloride ions and first-shell waters. The quantum theory of atoms in molecules (QTAIM) is further utilized to examine charge transfer from the anion to surrounding water molecules. The clusters extracted from the AMOEBA simulations exhibit high probabilities of anisotropic solvation for chloride ions in bulk water. From the QTAIM analysis, 0.2 elementary charges are transferred from the ion to the first-shell water molecules. The default AMOEBA model overestimates the average dipole moment magnitude of the ion compared to the quantum mechanical value. The average magnitude of the dipole moment of the water molecules in the first shell treated at the MP2-level, with the more distant waters handled with an AMOEBA effective charge model, is 2.67 D. This value is close to the AMOEBA result for first-shell waters (2.72 D) and is slightly reduced from the bulk AMOEBA value (2.78 D). The magnitude of the dipole moment of the water molecules in the first solvation shell is most strongly affected by the local water-water interactions and hydrogen bonds with the second solvation shell, rather than by interactions with the ion.

  15. Modulating unimolecular charge transfer by exciting bridge vibrations.

    PubMed

    Lin, Zhiwei; Lawrence, Candace M; Xiao, Dequan; Kireev, Victor V; Skourtis, Spiros S; Sessler, Jonathan L; Beratan, David N; Rubtsov, Igor V

    2009-12-23

    Ultrafast UV-vibrational spectroscopy was used to investigate how vibrational excitation of the bridge changes photoinduced electron transfer between donor (dimethylaniline) and acceptor (anthracene) moieties bridged by a guanosine-cytidine base pair (GC). The charge-separated (CS) state yield is found to be lowered by high-frequency bridge mode excitation. The effect is linked to a dynamic modulation of the donor-acceptor coupling interaction by weakening of H-bonding and/or by disruption of the bridging base-pair planarity.

  16. Intramolecular charge transfer in donor-acceptor molecules

    SciTech Connect

    Slama-Schwok, A.; Blanchard-Desce, M.; Lehn, J.M. )

    1990-05-17

    The photophysical properties of donor-acceptor molecules, push-pull polyenes and carotenoids, have been studied by absorption and fluorescence spectroscopy. The compounds bear various acceptor and donor groups, linked together by chains of different length and structure. The position of the absorption and fluorescence maxima and their variation in solvents of increasing polarity are in agreement with long-distance intramolecular charge-transfer processes, the linker acting as a molecular wire. The effects of the linker length and structure and of the nature of acceptor and donor are presented.

  17. Negative thermal expansion induced by intermetallic charge transfer.

    PubMed

    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-x Mn x O12, 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.

  18. 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.

  19. Characterization and control of charge transfer in a tunnel junction

    NASA Astrophysics Data System (ADS)

    Gabelli, Julien; Thibault, Karl; Gasse, Gabriel; Lupien, Christian; Reulet, Bertrand

    2017-03-01

    Charge transfer in a tunnel junction is studied under dc and ac voltage bias using quantum shot noise. Under dc voltage bias $V$, spectral density of noise measured within a very large bandwidth enables to deduce the current-current correlator in the time domain by Fourier transform. This correlator exhibits regular oscillations proving that electrons try to cross the junction regularly, every $h/eV$. Using harmonic and bi-harmonic ac voltage bias, we then show that quasiparticles excitations can be transferred through the junction in a controlled way. By measuring the reduction of the excess shot noise, we are able to determine the number of electron-hole pairs surrounding the injected electrons and demonstrate that bi-harmonic voltage pulses realize an on-demand electron source with a very small admixture of electron-hole pairs.

  20. Development of a charge-transfer distribution model for stack simulation of solid oxide fuel cells

    NASA Astrophysics Data System (ADS)

    Onaka, H.; Iwai, H.; Kishimoto, M.; Saito, M.; Yoshida, H.; Brus, G.; Szmyd, J. S.

    2016-09-01

    An overpotential model for planar solid oxide fuel cells (SOFCs) is developed and applied to a stack numerical simulation. Charge-transfer distribution within the electrodes are approximated using an exponential function, based on which the Ohmic loss and activation overpotential are evaluated. The predicted current-voltage characteristics agree well with the experimental results, and also the overpotentials within the cell can reproduce the results obtained from a numerical analysis where the distribution of the charge-transfer current within the electrodes is fully solved. The proposed model is expected to be useful to maintain the accuracy of SOFC simulations when the cell components, consisting of anode, electrolyte and cathode, are simplified into one layer element.

  1. Competition between covalent bonding and charge transfer at complex-oxide interfaces.

    PubMed

    Salafranca, Juan; Rincón, Julián; Tornos, Javier; León, Carlos; Santamaria, Jacobo; Dagotto, Elbio; Pennycook, Stephen J; Varela, Maria

    2014-05-16

    Here we study the electronic properties of cuprate-manganite interfaces. By means of atomic resolution electron microscopy and spectroscopy, we produce a subnanometer scale map of the transition metal oxidation state profile across the interface between the high Tc superconductor YBa2Cu3O7-δ and the colossal magnetoresistance compound (La,Ca)MnO3. A net transfer of electrons from manganite to cuprate with a peculiar nonmonotonic charge profile is observed. Model calculations rationalize the profile in terms of the competition between standard charge transfer tendencies (due to band mismatch), strong chemical bonding effects across the interface, and Cu substitution into the Mn lattice, with different characteristic length scales.

  2. Radiative charge transfer and association in slow Li- + H collisions

    NASA Astrophysics Data System (ADS)

    Lin, Xiaohe; Peng, Yigeng; Wu, Yong; Wang, Jianguo; Janev, Ratko; Shao, Bin

    2017-02-01

    Aims: The radiative charge transfer and association processes in Li- + H collisions are studied in the 10-10-10 eV center-of-mass energy range. Methods: we carried out total and ν-resolved state-selective cross sections have been carried out by using the fully quantum, optical potential, and semiclassical methods. Results: In the energy region below 0.8 eV, the radiative association process is the dominant decay channel, while radiative charge transfer dominates at higher energies. Rich resonance structures are observed in the cross sections of both processes in the 0.1-1.5 eV energy range; These structures are associated with the quasi-bound states below the top of the centrifugal barrier of the effective potential in the entrance channel for specific vibrational and angular momentum states. It is found that with the increase of collision energy, the resonances occur for higher angular momentum states and lower vibrational states. Besides the cross sections for the studied processes we also present their reaction rate coefficients in the 10-6-106K temperature range.

  3. Ultrafast charge transfer via a conical intersection in dimethylaminobenzonitrile.

    PubMed

    Fuss, Werner; Pushpa, Kumbil Kuttan; Rettig, Wolfgang; Schmid, Wolfram E; Trushin, Sergei A

    2002-04-01

    The L(a)-like S2 state (2A) of 4-(dimethylamino)benzonitrile was pumped at 267 nm in the gas phase at 130 degrees C. Nonresonant multiphoton ionization at 800 nm with mass-selective detection then probed the subsequent processes. Whereas ionization at the Franck-Condon geometry only gave rise to the parent ion, fragmentation increased on motion towards the charge-transfer (CT) state. This useful difference is ascribed to a geometry-dependent resonance in the ion. The time constants found are interpreted by ultrafast (approximately 68 fs) relaxation through a conical intersection to both the CT and the L(b)-type S1 state (1B). Then the population equilibrates between these two states within 1 ps. From there the molecule relaxes within 90 ps to a lower excited state which can only be a triplet state (T(n)) and then decomposes within 300 ps. Previous experiments either investigated only 1B --> CT relaxation-which does not take place in the gas phase or nonpolar solvents for energetic reasons--or, starting from S2 excitation, typically had insufficient time resolution (>1 ps) to detect the temporary charge transfer. Only recently temporary population of the CT state was found in a nonpolar solvent (Kwok et al., J. Phys. Chem. A. 2000, 104, 4188), a result fully consistent with our mechanism. We also show that S2 --> S1 relaxation does not occur vertically but involves an intermediate strong geometrical distortion, passing through a conical intersection.

  4. Charge transfer interactions in oligomer coated gold nanoclusters

    NASA Astrophysics Data System (ADS)

    Newmai, M. Boazbou; Kumar, Pandian Senthil

    2016-05-01

    Gold nanoclusters were synthesized by a bottom-up synergistic approach of in-situ oligomerization of the monomer, N-vinyl pyrrolidone (NVP) and simultaneous weak reduction of Au-NVP complexes in the absence of any other external energy sources, thereby making these tiny gold clusters as the most elemental building blocks to construct further novel nano/microstructures with application potentials. It is well-known that metal clusters with less than 2 nm size do not show the usual surface plasmon band, because of the presence of a band-gap at the fermi level. Nevertheless, our present oligomer coated gold clusters show a discrete intense band at around 630 nm, which could very well be attributed to the charge transfer between the oligomer chain and the surface Au atoms. Such kind of sacrificial plasmon induced charge transfer interaction, observed for the very first time to the best of our knowledge, were also strongly corroborated through the enhancement / shifting of specific vibrational / rotational peaks as observed from the FTIR and Raman measurements as a function of the metal oxidation states, thus representing a new prototype for an efficient solar energy conversion probe.

  5. Mutation induction by charged particles of defined linear energy transfer.

    PubMed

    Hei, T K; Chen, D J; Brenner, D J; Hall, E J

    1988-07-01

    The mutagenic potential of charged particles of defined linear energy transfer (LET) was assessed using the hypoxanthine-guanine phosphoribosyl transferase locus (HGPRT) in primary human fibroblasts. Exponentially growing cultures of early passaged fibroblasts were grown as monolayers on thin mylar sheets and were irradiated with accelerated protons, deuterons or helium-3 ions. The mutation rates were compared with those generated by 137Cs gamma-rays. LET values for charged particles accelerated at the Radiological Research Accelerator Facility, using the track segment mode, ranged from 10 to 150 keV/micron. After irradiation, cells were trypsinized, subcultured and assayed for both cytotoxicity and 6-thioguanine resistance. For gamma-rays, and for the charged particles of lower LET, the dose-response curves for cell survival were characterized by a marked initial shoulder, but approximated to an exponential function of dose for higher LETs. Mutation frequencies, likewise, showed a direct correlation to LET over the dose range examined. Relative biological effectiveness (RBE) for mutagenesis, based on the initial slopes of the dose-response curves, ranged from 1.30 for 10 keV/micron protons to 9.40 for 150 keV/micron helium-3 ions. Results of the present studies indicate that high-LET radiations, apart from being efficient inducers of cell lethality, are even more efficient in mutation induction as compared to low-LET ionizing radiation. These data are consistent with results previously obtained with both rodent and human fibroblast cell lines.

  6. Research progress on space charge characteristics in polymeric insulation

    NASA Astrophysics Data System (ADS)

    Zhang, Yibo; Christen, Thomas; Meng, Xing; Chen, Jiansheng; Rocks, Jens

    2016-03-01

    Due to their excellent electrical insulation properties and processability, polymer materials are used in many electrical products. It is widely believed that space charge plays an important role for the electric field distribution, conduction, ageing, and electric breakdown of polymeric insulation. This paper reviews measurements and characteristics of space charge behavior which mainly determined by the pulsed electro-acoustic (PEA) measurement technique. Particular interests are the effects of the applied voltage, the electrodes, temperature, humidity, microstructure, additives, and filler materials on accumulation, distribution, transport, and the decay of space charge in polymeric materials. This review paper is to provide an overview on various space charge effects under different conditions, and also to summarize the information for polymeric materials with suppressed space charge and improved electrical behavior.

  7. Transfer RNA: a dancer between charging and mis-charging for protein biosynthesis.

    PubMed

    Zhou, Xiaolong; Wang, Enduo

    2013-10-01

    Transfer RNA plays a fundamental role in the protein biosynthesis as an adaptor molecule by functioning as a biological link between the genetic nucleotide sequence in the mRNA and the amino acid sequence in the protein. To perform its role in protein biosynthesis, it has to be accurately recognized by aminoacyl-tRNA synthetases (aaRSs) to generate aminoacyl-tRNAs (aa-tRNAs). The correct pairing between an amino acid with its cognate tRNA is crucial for translational quality control. Production and utilization of mis-charged tRNAs are usually detrimental for all the species, resulting in cellular dysfunctions. Correct aa-tRNAs formation is collectively controlled by aaRSs with distinct mechanisms and/or other trans-factors. However, in very limited instances, mis-charged tRNAs are intermediate for specific pathways or essential components for the translational machinery. Here, from the point of accuracy in tRNA charging, we review our understanding about the mechanism ensuring correct aa-tRNA generation. In addition, some unique mis-charged tRNA species necessary for the organism are also briefly described.

  8. Charging and Discharging Characteristic on PI Films Irradiated by Protons

    NASA Astrophysics Data System (ADS)

    Uchiyama, Ryo; Miyake, Hiroaki; Tanaka, Yasuhiro; Takada, Tatuo

    We evaluate the dielectric characteristic of polymeric materials for MLI (Multi Layer Insulator, a kind of thermal insulation material) for spacecraft under high energy proton irradiation using results of space charge distribution. Spacecrafts have a serious damage due to the electro-static discharge accident. The electric charges are accumulated in the polymeric materials due to radioactive rays, especially electrons and protons. The charge accumulation is the origin of aging and discharging phenomena, furthermore those become trigger for spacecraft operation anomaly. Therefore, we need to obtain the space charge distribution in the bulks. In this study, we especially focused polyimide films for MLI irradiated by high energy proton. We measured the space charge distribution in the bulks during and after proton beam irradiation. From the results, it is found that positive charges accumulate in the bulk at the position of proton penetration depth. We also obtained same tendency from the results of conductivity measurement treated by ASTM method. From the above reason, we have studied the dielectric characteristics of MLI materials irradiated by radioactive rays, especially we focused the condition of proton irradiation. In this paper, we discuss the dielectric phenomena and the relationship between conductivity and charge accumulation in bulks.

  9. Boiling heat transfer characteristics of liquid xenon

    NASA Astrophysics Data System (ADS)

    Haruyama, T.

    2002-05-01

    Liquid xenon is one of the excellent media for high-energy particle calorimeter. In order to detect a scintillation light effectively, a large number of photo-multipliers (PMTs) will be immersed in liquid xenon. Many chip-resistors equipped with the PMTs dissipate heat into liquid and possibly generate thermal turbulence, such as bubbles, convection flow under a certain operating condition. There is, however, no heat transfer curve (q-ΔT curve) in the literature. Boiling heat transfer characteristics of liquid xenon were measured at a saturated pressure of 0.1 MPa for the first time by using a small pulse tube refrigerator. The heat transfer surface is a thin platinum wire of 0.1 mm diameter and 25 mm long. The measured results were in good agreement with the calculated values both in natural convection and nucleate boiling condition. The film boiling state was difficult to obtain due to its poor reproducibility, and only one data was obtained. The relationship between the heat flux q and temperature difference ΔT was in good agreement with the Morgan's empirical equation in the natural convection region, and with the Kutateladze's equation in the nucleate boiling region.

  10. Luminescent charge-transfer platinum(II) metallacycle.

    PubMed

    Hua, Fei; Kinayyigit, Solen; Rachford, Aaron A; Shikhova, Elena A; Goeb, Sébastien; Cable, John R; Adams, Christopher J; Kirschbaum, Kristin; Pinkerton, A Alan; Castellano, Felix N

    2007-10-15

    The photophysical and electrochemical properties of a platinum(II) diimine complex bearing the bidentate diacetylide ligand tolan-2,2'-diacetylide (tda), Pt(dbbpy)(tda) [dbbpy = 4,4'-di-tert-butyl-2,2'-bipyridine] (1), are compared with two reference compounds, Pt(dbbpy)(C[triple bond]CPh)(2) (2) and Pt(dppp)tda [dppp = 1,3-bis(diphenylphosphino)propane] (3), respectively. The X-ray crystal structure of 1 is reported, which illustrates the nearly perfect square planarity exhibited by this metallacycle. Chromophore 2 possesses low-lying charge-transfer excited states analogous to 1, whereas structure 3 lacks such excited states but features a low-lying platinum-perturbed tda intraligand triplet manifold. In CH(2)Cl(2), 1 exhibits a broad emission centered at 562 nm at ambient temperature, similar to 2, but with a higher photoluminescence quantum yield and longer excited-state lifetime. In both instances, the photoluminescence is consistent with triplet-charge-transfer excited-state parentage. The rigidity imposed by the cyclic diacetylide ligand in 1 leads to a reduction in nonradiative decay, which enhances its room-temperature photophysical properties. By comparison, 3 radiates highly structured tda-localized triplet-state phosphorescence at room temperature. The 77 K emission spectrum of 1 in 4:1 EtOH/MeOH becomes structured and is quantitatively similar to that measured for 3 under the same conditions. Because the 77 K spectra are nearly identical, the emissions are assigned as (3)tda in nature, implying that the charge-transfer states are raised in energy, relative to the (3)tda levels in 1 in the low-temperature glass. Nanosecond transient absorption spectrometry and ultrafast difference spectra were determined for 1-3 in CH(2)Cl(2) and DMF at ambient temperature. In 1 and 2, the major absorption transients are consistent with the one-electron reduced complexes, corroborated by reductive spectroelectrochemical measurements performed at room temperature. As 3

  11. Negative thermal expansion induced by intermetallic charge transfer

    PubMed Central

    Azuma, Masaki; Oka, Kengo; Nabetani, Koichiro

    2015-01-01

    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. PMID:27877801

  12. Hydrogen Ion-Molecule Isotopomer Collisions: Charge Transfer and Rearrangement

    NASA Astrophysics Data System (ADS)

    Wang, J. G.; Stancil, P. C.

    A survey of existing data for collisions of isotopes of hydrogen atoms, ions, and molecules is presented. The survey was limited to atom - diatom ionic collisions and to energies generally less than about 10 keV/u. The processes include particle-rearrangement and charge transfer, including both dissociative and non-dissociative channels, with an emphasis on state-to-state (or state-selected) data, where available. Since the last survey (Linder, Janev and Botero 1995), a small number of investigations for deuterium and tritium ion-diatom systems have been performed, with some involving state-resolved data, which include the initial-state-resolved and state-to-state processes. While some progress has been made since the last survey, the database involving hydrogen isotope collisional processes, both total and state- resolved, is far from complete.

  13. The charge-transfer complex trans-STB-TCNQF4.

    PubMed

    Sato, A; Okada, M; Saito, K; Sorai, M

    2001-05-01

    In the crystal structure of the title charge-transfer complex, namely trans-stilbene-2,2'-(2,3,5,6-tetrafluorobenzene-1,4-diylidene)propanedinitrile (1/1) (trans-STB-TCNQF(4)), C(14)H(12).C(12)F(4)N(4), the planar STB and TCNQF(4) molecules are stacked alternately. The structure is not isostructural with that of STB-TCNQ. No anomaly was found in the displacement parameters of any atoms, while the bond length of the central C=C moiety was shorter than the corresponding bond in ethylene. This suggests that the central C=C moiety of the STB molecule vibrates with a large amplitude, similar to the case in free STB and STB-TCNQ.

  14. Charge transfer in heterostructures of strongly correlated materials

    SciTech Connect

    Gonzalez Lopez Del Castillo, Ivan; Okamoto, Satoshi; Yunoki, Seiji; Moreo, Adriana; Dagotto, Elbio R

    2008-01-01

    In this work, recent theoretical investigations by the authors in the area of oxide multilayers are briefly reviewed. The calculations were carried out using model Hamiltonians and a variety of non-perturbative techniques. Moreover, new results are also included here. They correspond to the generation of a metallic state by mixing insulators in a multilayer geometry, using the Hubbard and double-exchange models. For the latter, the resulting metallic state is also ferromagnetic. This illustrates how electron or hole doping via transfer of charge in multilayers can lead to the study of phase diagrams of transition metal oxides in the clean limit. Currently, these phase diagrams are much affected by the disordering standard chemical doping procedure, which introduces quenched disorder in the material.

  15. Charge transfer in heterostructures of strongly correlated materials.

    PubMed

    González, I; Okamoto, S; Yunoki, S; Moreo, A; Dagotto, E

    2008-07-02

    In this work, recent theoretical investigations by the authors in the area of oxide multilayers are briefly reviewed. The calculations were carried out using model Hamiltonians and a variety of non-perturbative techniques. Moreover, new results are also included here. They correspond to the generation of a metallic state by mixing insulators in a multilayer geometry, using the Hubbard and double-exchange models. For the latter, the resulting metallic state is also ferromagnetic. This illustrates how electron or hole doping via transfer of charge in multilayers can lead to the study of phase diagrams of transition metal oxides in the clean limit. Currently, these phase diagrams are much affected by the disordering standard chemical doping procedure, which introduces quenched disorder in the material.

  16. Charge transfer between O{sup +} ions and helium

    SciTech Connect

    Zhao, L.B.; Stancil, P.C.; Liebermann, H.P.; Funke, P.; Buenker, R.J.

    2005-06-15

    The charge-transfer processes O{sup +}({sup 4}S{sup 0},{sup 2}D{sup 0},{sup 2}P{sup 0})+He{yields}O({sup 3}P)+He{sup +} have been investigated by using a fully quantal molecular-orbital close-coupling (QMOCC) approach. Cross sections are presented for ion energies from 0.5 to 10 keV and compared with those from recent experiments and semiclassical theory. Good agreement is found between the QMOCC results and the measurements. Particular attention is given to addressing the metastable component of the experimental ion beams. We further argue that the so-called 'suppressed electron-capture effect' for metastable ions proposed by Wolfrum et al. is not a viable mechanism to explain their measurements. However, the current QMOCC calculations were found to reproduce neither the ground-state nor metastable-state cross sections predicted by the semiclassical method.

  17. HST WFC3/UVIS: charge transfer efficiency monitoring and mitigation

    NASA Astrophysics Data System (ADS)

    Baggett, Sylvia M.; Sosey, Megan L.; Anderson, Jay; Gosmeyer, Catherine; Bourque, Matthew; Bajaj, Varun; Khandrika, Harish G.; Martlin, Catherine; Kozhurina-Platais, Vera; Sabbi, Elena; WFC3 Team

    2016-01-01

    The harsh low-earth orbit environment is known to damage CCD devices and the HST WFC3/UVIS camera is no exception. One consequence of the radiation damage is charge-transfer efficiency (CTE) loss over time. We summarize the level of the CTE losses, the effect on science data, and the pre- and post-observation mitigation options available. Among them is the pixel-based CTE correction, which has been incorporated into the HST automatic data processing pipeline. The pipeline now provides both standard and CTE-corrected data products; observers with older data can re-retrieve their images via the the Mikulski Archive for Space Telescopes (MAST) to obtain the new products.

  18. Charge transfer emission of ytterbium-doped oxyborates.

    PubMed

    Sablayrolles, J; Jubera, V; Guillen, F; Garcia, A

    2008-03-01

    The ultraviolet spectroscopic properties of trivalent ytterbium have been studied at low temperature in one borate and two oxyborates in the ternary diagram Li(2)O-Y(2)O(3)-B(2)O(3). The UV luminescence was detected in the two ytterbium-doped oxyborates. The evolution of these emissions was studied as a function of the temperature. A determination of the configurational coordinate diagrams based on the Struck and Fonger model is proposed to calculate the position in energy of the charge transfer band afforded by the simulation of spectral distribution of these excitation and emission bands. The strong correlation between the luminescent properties and the environments of the rare earth is pointed out.

  19. 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

  20. Charge-Transfer Emitting Triarylborane π-Electron Systems.

    PubMed

    Li, Sheng-Yong; Sun, Zuo-Bang; Zhao, Cui-Hua

    2017-02-06

    Triarylboranes have attracted significantly increasing research interest as a remarkable class of photoelectronic π-electron materials. Because of the presence of vacant p orbital on the B center, the boryl group is a very unique electron acceptor that exhibits not only electron-accepting ability through p-π* conjugation but also high Lewis acidity to coordinate with Lewis bases and steric bulk arising from the aryl substituent on the B center to get enough kinetic stability. Thus, the incorporation of a trivalent B element into π-conjugated systems is an efficient strategy to tune the electronic and stereo structures and thus the photoelectronic properties of π-electron systems. When an electron-donating group, such as amino, is present, triarylboranes would likely display intramolecular charge-transfer transitions. These kinds of molecules are often highly emissive. In addition, the geometry of the molecules has a great impact on the emission properties. In this Forum Article, we herein describe our recent progress on the charge-transfer emitting triarylborane π-electron systems with novel geometries, which include the lateral boryl-substituted π-system with amino groups at the terminal positions, the o,o'-substituted biaryl π-system with boryl and amino groups at the o,o'-positions, a triarylborane-based BODIPY system, and a B,N/S-bridged ladder-type π-system. We mainly put the emphasis on the molecular design concept, structure-property relationships, intriguing emission properties and great applications of the corresponding triarylborane π-systems.

  1. Heat transfer characteristics of igniter output plumes

    NASA Astrophysics Data System (ADS)

    Evans, N. A.; Durand, N. A.

    Seven types of pyrotechnic igniters were each mounted at one end of a closed cylindrical bore hole representative of the center hole in a thermal battery. Measurements of local bore wall temperature, T(sub w), using commercially available, fast response (10 microsec) sheathed chromel-constantan thermocouples allowed calculation of local heat transfer rates, q, and wall heat flows, Q. The principal charge constituents of all these igniters were titanium and potassium perchlorate, while three types also contained barium styphnate as an ignition sensitizer. Igniter closure disc materials included glass-ceramic, glass, metal (plain, scored, with and without capture cone), and kapton/RTV. All igniters produced the lowest values of T(sub w) and q at the beginning of the bore, and, except for the igniter with the kapton/RTV closure disc, these quantities increased with distance along the bore. For igniters containing only titanium/potassium perchlorate, the rates of increase of Q along the bore length, compared with those for T(sub w) and q, were generally lower and more variable. The inclusion of barium styphnate produced rates of change in Q that were essentially constant to the end of the bore. The highest overall average wall temperatures were achieved by two igniter types with metal closure discs and no capture cone. No clear correlation was established between peak bore pressure and maximum wall temperature.

  2. Laser Studies of - and Charge-Transfer Dynamics

    NASA Astrophysics Data System (ADS)

    Goldman, Jay Robert

    This thesis presents the results of three experiments which use lasers to investigate energy-transfer and charge -transfer dynamics. The dynamical processes studied include nanosecond vibrational energy transfer in molecules, subpicosecond electron relaxation in semiconductors, and subpicosecond initiation of surface bimolecular reactions on a metal crystal. In experiments using time-resolved coherent Raman spectroscopy to probe infrared multiphoton excited molecules, we study CO_2-laser excited SO _2 and SF_6. In SO _2 we observe direct nu _1-mode excitation and distinguish between this process and excitation of the nearly resonant nu_2-mode overtone. In SF _6, we directly observe nu _3-mode excitation followed by collisional energy redistribution to a heat bath of non-pumped modes. Quantitative modeling of the SF_6^ectra yields excited vibrational population distributions and resolves some long-standing inconsistencies between different previously published reports. In an experiment using time-resolved photoelectron spectroscopy, we observe the subpicosecond evolution of an optically-excited nonequilibrium electron distribution in silicon. We observe an electron thermalization time of less than 120 fs, electron equilibration with the lattice in 1 ps, and an energy-dependent electron cooling rate consistent with published calculations of the electron -phonon scattering rate. The results indicate the formation, in 1 ps, of a surface space-charge electron layer with an electron density two orders of magnitude greater than the bulk electron density. In an experiment using 100-fs laser pulses to induce desorption of O_2 and reaction of O_2+CO to form CO_2 on a Pt(111) surface, we present desorption and reaction data obtained over an absorbed fluence range of 1-20 mJ/cm_2 at wavelengths of 800, 400, and 266 nm. We observe a highly nonlinear desorption and reaction yield fluence dependence; the data are fit by a power law model in which the yield is proportional to

  3. Charge Transfer and Support Effects in Heterogeneous Catalysis

    SciTech Connect

    Hervier, Antoine

    2011-12-21

    The kinetic, electronic and spectroscopic properties of two-dimensional oxide-supported catalysts were investigated in order to understand the role of charge transfer in catalysis. Pt/TiO2 nanodiodes were fabricated and used as catalysts for hydrogen oxidation. During the reaction, the current through the diode, as well as its I-V curve, were monitored, while gas chromatography was used to measure the reaction rate. The current and the turnover rate were found to have the same temperature dependence, indicating that hydrogen oxidation leads to the non-adiabatic excitation of electrons in Pt. A fraction of these electrons have enough energy to ballistically transport through Pt and overcome the Schottky barrier at the interface with TiO2. The yield for this phenomenon is on the order of 10-4 electrons per product molecule formed, similar to what has been observed for CO oxidation and for the adsorption of many different molecules. The same Pt/TiO2 system was used to compare currents in hydrogen oxidation and deuterium oxidation. The current through the diode under deuterium oxidation was found to be greater than under hydrogen oxidation by a factor of three. Weighted by the difference in turnover frequencies for the two isotopes, this would imply a chemicurrent yield 5 times greater for D2 compared to H2, contrary to what is expected given the higher mass of D2. Reversible changes in the rectification factor of the diode are observed when switching between D2 and H2. These changes are a likely cause for the differences in current between the two isotopes. In the nanodiode experiments, surface chemistry leads to charge flow, suggesting the possibility of creating charge flow to tune surface chemistry. This was done first by exposing a Pt/Si diode to visible light while using it as a catalyst for H2 oxidation. Absorption of the light in the Si, combined with

  4. Correlation between charge transfer exciton recombination and photocurrent in polymer/fullerene solar cells

    SciTech Connect

    Hallermann, Markus; Da Como, Enrico; Feldmann, Jochen; Izquierdo, Marta; Filippone, Salvatore; Martin, Nazario; Juechter, Sabrina; Hauff, Elizabeth von

    2010-07-12

    We correlate carrier recombination via charge transfer excitons (CTEs) with the short circuit current, J{sub sc}, in polymer/fullerene solar cells. Near infrared photoluminescence spectroscopy of CTE in three blends differing for the fullerene acceptor, gives unique insights into solar cell characteristics. The energetic position of the CTE is directly correlated with the open-circuit voltage, V{sub oc}, and more important J{sub sc} decreases with increasing CTE emission intensity. CTE emission intensity is discussed from the perspective of blend morphology. The work points out the fundamental role of CTE recombination and how optical spectroscopy can be used to derive information on solar cell performances.

  5. Charge-transfer photodissociation of adsorbed molecules via electron image states

    SciTech Connect

    Jensen, E. T.

    2008-01-28

    The 248 and 193 nm photodissociations of submonolayer quantities of CH{sub 3}Br and CH{sub 3}I adsorbed on thin layers of n-hexane indicate that the dissociation is caused by dissociative electron attachment from subvacuum level photoelectrons created in the copper substrate. The characteristics of this photodissociation-translation energy distributions and coverage dependences show that the dissociation is mediated by an image potential state which temporarily traps the photoelectrons near the n-hexane-vacuum interface, and then the charge transfers from this image state to the affinity level of a coadsorbed halomethane which then dissociates.

  6. Analysis of charge transfer effects in molecular complexes based on absolutely localized molecular orbitals

    SciTech Connect

    Khaliullin, Rustam Z.; Head-Gordon, Martin; Bell, Alexis T.

    2008-05-14

    A new method based on absolutely localized molecular orbitals (ALMOs) is proposed to measure the degree of intermolecular electron density delocalization (charge transfer) in molecular complexes. ALMO charge transfer analysis (CTA) enables separation of the forward and backward charge transfer components for each pair of molecules in the system. The key feature of ALMO CTA is that all charge transfer terms have corresponding well defined energetic effects that measure the contribution of the given term to the overall energetic stabilization of the system. To simplify analysis of charge transfer effects, the concept of chemically significant complementary occupied-virtual orbital pairs (COVPs) is introduced. COVPs provide a simple description of intermolecular electron transfer effects in terms of just a few localized orbitals. ALMO CTA is applied to understand fundamental aspects of donor-acceptor interactions in borane adducts, synergic bonding in classical and nonclassical metal carbonyls, and multiple intermolecular hydrogen bonds in a complex of isocyanuric acid and melamine. These examples show that the ALMO CTA results are generally consistent with the existing conceptual description of intermolecular bonding. The results also show that charge transfer and the energy lowering due to charge transfer are not proportional to each other, and some interesting differences emerge which are discussed. Additionally, according to ALMO CTA, the amount of electron density transferred between molecules is significantly smaller than charge transfer estimated from various population analysis methods.

  7. Analysis of charge transfer effects in molecular complexes based on absolutely localized molecular orbitals.

    PubMed

    Khaliullin, Rustam Z; Bell, Alexis T; Head-Gordon, Martin

    2008-05-14

    A new method based on absolutely localized molecular orbitals (ALMOs) is proposed to measure the degree of intermolecular electron density delocalization (charge transfer) in molecular complexes. ALMO charge transfer analysis (CTA) enables separation of the forward and backward charge transfer components for each pair of molecules in the system. The key feature of ALMO CTA is that all charge transfer terms have corresponding well defined energetic effects that measure the contribution of the given term to the overall energetic stabilization of the system. To simplify analysis of charge transfer effects, the concept of chemically significant complementary occupied-virtual orbital pairs (COVPs) is introduced. COVPs provide a simple description of intermolecular electron transfer effects in terms of just a few localized orbitals. ALMO CTA is applied to understand fundamental aspects of donor-acceptor interactions in borane adducts, synergic bonding in classical and nonclassical metal carbonyls, and multiple intermolecular hydrogen bonds in a complex of isocyanuric acid and melamine. These examples show that the ALMO CTA results are generally consistent with the existing conceptual description of intermolecular bonding. The results also show that charge transfer and the energy lowering due to charge transfer are not proportional to each other, and some interesting differences emerge which are discussed. Additionally, according to ALMO CTA, the amount of electron density transferred between molecules is significantly smaller than charge transfer estimated from various population analysis methods.

  8. Analysis of charge transfer effects in molecular complexes based on absolutely localized molecular orbitals

    NASA Astrophysics Data System (ADS)

    Khaliullin, Rustam Z.; Bell, Alexis T.; Head-Gordon, Martin

    2008-05-01

    A new method based on absolutely localized molecular orbitals (ALMOs) is proposed to measure the degree of intermolecular electron density delocalization (charge transfer) in molecular complexes. ALMO charge transfer analysis (CTA) enables separation of the forward and backward charge transfer components for each pair of molecules in the system. The key feature of ALMO CTA is that all charge transfer terms have corresponding well defined energetic effects that measure the contribution of the given term to the overall energetic stabilization of the system. To simplify analysis of charge transfer effects, the concept of chemically significant complementary occupied-virtual orbital pairs (COVPs) is introduced. COVPs provide a simple description of intermolecular electron transfer effects in terms of just a few localized orbitals. ALMO CTA is applied to understand fundamental aspects of donor-acceptor interactions in borane adducts, synergic bonding in classical and nonclassical metal carbonyls, and multiple intermolecular hydrogen bonds in a complex of isocyanuric acid and melamine. These examples show that the ALMO CTA results are generally consistent with the existing conceptual description of intermolecular bonding. The results also show that charge transfer and the energy lowering due to charge transfer are not proportional to each other, and some interesting differences emerge which are discussed. Additionally, according to ALMO CTA, the amount of electron density transferred between molecules is significantly smaller than charge transfer estimated from various population analysis methods.

  9. Scaling laws for charge transfer in multiply bridged donor/acceptor molecules in a dissipative environment.

    PubMed

    Goldsmith, Randall H; Wasielewski, Michael R; Ratner, Mark A

    2007-10-31

    The ability of multiple spatial pathways to sum coherently and facilitate charge transfer is examined theoretically. The role of multiple spatial pathways in mediating charge transfer has been invoked several times in the recent literature while discussing charge transfer in proteins, while multiple spatial pathways are known to contribute to charge transport in metal-molecule-metal junctions. We look at scaling laws for charge transfer in donor-bridge-acceptor (D-B-A) molecules and show that these scaling laws change significantly when environment-induced dephasing is included. In some cases, D-B-A systems are expected to show no enhancement in the rate of charge transfer with the addition of multiple degenerate pathways. The origins of these different scaling laws are investigated by looking at which Liouville space pathways are active in different dephasing regimes.

  10. Laboratory Studies of Thermal Energy Charge Transfer of Silicon and Iron Ions in Astrophysical Plasmas

    NASA Technical Reports Server (NTRS)

    Kwong, Victor H. S.

    1996-01-01

    Charge transfer at electron-volt energies between multiply charged atomic ions and neutral atoms and molecules is of considerable importance in astrophysics, plasma physics, and in particular, fusion plasmas. In the year covered by this report, several major tasks were completed. These include: (1) the re-calibration of the ion gauge to measure the absolute particle densities of H2, He, N2, and CO for our current measurements; (2) the analysis of data for charge transfer reactions of N(exp 2 plus) ion and He, H2, N2, and CO; (3) measurement and data analysis of the charge transfer reaction of (Fe(exp 2 plus) ion and H2; (4) charge transfer measurement of Fe(exp 2 plus) ion and H2; and (5) redesign and modification of the ion detection and data acquisition system for the low energy beam facility (reflection time of flight mass spectrometer) dedicated to the study of state select charge transfer.

  11. Mechanisms of proton transfer in proteins: Localized charge transfer versus delocalized soliton transfer

    PubMed Central

    Stuchebrukhov, Alexei A.

    2010-01-01

    Proton translocation coupled to redox chemistry is ubiquitous for membrane enzymes involved in energy generation in cells. In such enzymes, proton transport occurs in special proton conducting channels, which consist of a series of protonatable groups of the protein connected by chains of mobile water molecules. Here we discuss two possible mechanisms of proton transport along such structures: diffusion of a localized charge and delocalized soliton transitions, in which several protons are collectively shifted along a chain of hydrogen bonds. PMID:19391991

  12. Charging characteristics of materials: Comparison of experimental results with simple analytical models

    NASA Technical Reports Server (NTRS)

    Purvis, C. K.; Stevens, N. J.; Oglebay, J. C.

    1977-01-01

    A one-dimensional model for charging of samples is used in conjunction with experimental data taken to develop material charging characteristics for silvered Teflon. These characteristics are then used in a one dimensional model for charging in space to examine expected response. Relative charging rates as well as relative charging levels for silvered Teflon and metal are discussed.

  13. Charge transfer and electronic transitions in polycrystalline BiFeO3

    NASA Astrophysics Data System (ADS)

    Ramachandran, B.; Dixit, A.; Naik, R.; Lawes, G.; Rao, M. S. Ramachandra

    2010-07-01

    We report on the electronic energy-level diagram of polycrystalline BiFeO3 using the elemental, optical, and current-density-electric field (J-E) characteristics. The elemental, electronic composition, and valence-band structure of BiFeO3 ceramics were studied using x-ray photoelectron spectroscopy. The diffuse reflectance spectrum of a mixture of BiFeO3 and BaSO4 , used as a standard, was recorded to test the Kubelka-Munk model. From the graph of the Kubelka-Munk function versus wavelength, two charge-transfer bands and two doubly degenerated d-d transitions ( A61g→T42g and A61g→T41g ) were observed in polycrystalline BiFeO3 . The J-E curves measured on the BiFeO3 ceramics showed space-charge-limited conduction mechanism.

  14. Bond patterns and charge-order amplitude in quarter-filled charge-transfer solids

    NASA Astrophysics Data System (ADS)

    Clay, R. T.; Ward, A. B.; Gomes, N.; Mazumdar, S.

    2017-03-01

    Most quasi-one-dimensional (quasi-1D) quarter-filled organic charge-transfer solids (CTS) with insulating ground states have two thermodynamic transitions: a high-temperature metal-insulator transition followed by a low-temperature magnetic transition. This sequence of transitions can be understood within the 1D Peierls-extended Hubbard (PEH) model. However, in some quasi-1D CTS both transitions occur simultaneously in a direct metal to spin-gapped insulator transition. In this second class of materials the organic stack bond distortion pattern does not follow the pattern of a second dimerization of a dimer lattice. These materials also display charge ordering of a large amplitude below the transition. Using quantum Monte Carlo methods we show that the same PEH model can be used to understand both classes of materials, however, within different parameter regions. We discuss the relevance of our work to experiments on several quarter-filled conductors, focusing in particular on the materials (EDO-TTF)2X and (DMEDO-TTF)2X .

  15. Ab initio Determination of Formation Energies and Charge Transfer Levels of Charged Ions in Water

    NASA Astrophysics Data System (ADS)

    Vatti, Anoop Kishore; Todorova, Mira; Neugebauer, Joerg

    The ability to describe the complex atomic and electronic structure of liquid water and hydrated ions on a microscopic level is a key requirement to understand and simulate electro-chemical and biological processes. Identifying theoretical concepts which enable us to achieve an accurate description in a computationally efficient way is thereby of central importance. Aiming to unravel the importance and influence of different contributions on the hydration energy of ions we perform extensive ab-initio molecular dynamics simulations for charged and neutral cations (Zn, Mg) and anions (Cl, Br, I) in water. The structural correlations and electronic properties of the studied ions are analysed and compared to experimental observations. Following an approach inspired by the defect chemistry in semiconductors and aligning the water band edges on an absolute scale allows us to benchmark the calculated formation energies, identify transition states and compare the results to experiment. Based on these results we discuss the performance of various DFT xc-functionals to predict charge transfer levels and photo-emission experiments.

  16. Synthesis of Stable Interfaces on SnO2 Surfaces for Charge-Transfer Applications

    NASA Astrophysics Data System (ADS)

    Benson, Michelle C.

    The commercial market for solar harvesting devices as an alternative energy source requires them to be both low-cost and efficient to replace or reduce the dependence on fossil fuel burning. Over the last few decades there has been promising efforts towards improving solar devices by using abundant and non-toxic metal oxide nanomaterials. One particular metal oxide of interest has been SnO2 due to its high electron mobility, wide-band gap, and aqueous stability. However SnO2 based solar cells have yet to reach efficiency values of other metal oxides, like TiO2. The advancement of SnO2 based devices is dependent on many factors, including improved methods of surface functionalization that can yield stable interfaces. This work explores the use of a versatile functionalization method through the use of the Cu(I)-catalyzed azide-alkyne cycloaddition (CuAAC) reaction. The CuAAC reaction is capable of producing electrochemically, photochemically, and electrocatalytically active surfaces on a variety of SnO2 materials. The resulting charge-transfer characteristics were investigated as well as an emphasis on understanding the stability of the resulting molecular linkage. We determined the CuAAC reaction is able to proceed through both azide-modified and alkyne-modified surfaces. The resulting charge-transfer properties showed that the molecular tether was capable of supporting charge separation at the interface. We also investigated the enhancement of electron injection upon the introduction of an ultra-thin ZrO2 coating on SnO2. Several complexes were used to fully understand the charge-transfer capabilities, including model systems of ferrocene and a ruthenium coordination complex, a ruthenium mononuclear water oxidation catalyst, and a commercial ruthenium based dye.

  17. The thermodynamics of charge transfer in DNA photolyase: using thermodynamic integration calculations to analyse the kinetics of electron transfer reactions.

    PubMed

    Krapf, Sebastian; Koslowski, Thorsten; Steinbrecher, Thomas

    2010-08-28

    DNA Photolyases are light sensitive oxidoreductases present in many organisms that participate in the repair of photodamaged DNA. They are capable of electron transfer between a bound cofactor and a chain of tryptophan amino acid residues. Due to their unique mechanism and important function, photolyases have been subject to intense study in recent times, with both experimental and computational efforts. In this work, we present a novel application of classical molecular dynamics based free energy calculations, combined with quantum mechanical computations, to biomolecular charge transfer. Our approach allows for the determination of all reaction parameters in Marcus' theory of charge transport. We were able to calculate the free energy profile for the movement of a positive charge along protein sidechains involved in the biomolecule's function as well as charge-transfer rates that are in good agreement with experimental results. Our approach to simulate charge-transfer reactions explicitly includes the influence of protein flexibility and solvent dynamics on charge-transfer energetics. As applied here to a biomolecular system of considerable scientific interest, we believe the method to be easily adaptable to the study of charge-transfer phenomena in biochemistry and other fields.

  18. Satellite lines at the ionization threshold in charge transfer systems

    NASA Astrophysics Data System (ADS)

    Wardermann, W.; von Niessen, W.

    1992-01-01

    This article deals with the possibility of low-energy ionizations of reduced intensity for larger organic molecules. Possible mechanisms which may lead to this phenomenon are outlined and the necessary structural features are discussed. The lowest ionization energies of some organic unsaturated nitro and nitroso compounds are calculated by the ADC(3) ab initio many-body Green's function method. The π-electron system consists either of fused five- and six-membered rings or of two fused five-membered rings with a variable number of heteroatoms. Some of the molecules contain exocylic double bonds and some are substituted with the donor groups -NH 2, -OH and -NHOH. The strongest many-body effects are found for the nitroso compounds, where in one case the spectral line at the ionization threshold has lost more than 40% of its intensity to satellites. We study the many-body effects at or close to the ionization threshold for these compounds. A particular mechanism which involves the screening of localized valence holes by charge transfer excitations appears to be capable of influencing the profile and intensities of the ionization spectrum already at the ionization threshold. The effect leads to strongly reduced relative intensities of the bands and may cause the appearance of satellite bands nearly at the ionization threshold. The spectral changes in the outermost valence region are discussed by using a simple model calculation in terms of ground-state electronic properties of the molecules.

  19. Dynamic Peptide Library for the Discovery of Charge Transfer Hydrogels.

    PubMed

    Berdugo, Cristina; Nalluri, Siva Krishna Mohan; Javid, Nadeem; Escuder, Beatriu; Miravet, Juan F; Ulijn, Rein V

    2015-11-25

    Coupling of peptide self-assembly to dynamic sequence exchange provides a useful approach for the discovery of self-assembling materials. In here, we demonstrate the discovery and optimization of aqueous, gel-phase nanostructures based on dynamically exchanging peptide sequences that self-select to maximize charge transfer of n-type semiconducting naphthalenediimide (NDI)-dipeptide bioconjugates with various π-electron-rich donors (dialkoxy/hydroxy/amino-naphthalene or pyrene derivatives). These gel-phase peptide libraries are characterized by spectroscopy (UV-vis and fluorescence), microscopy (TEM), HPLC, and oscillatory rheology and it is found that, of the various peptide sequences explored (tyrosine Y-NDI with tyrosine Y, phenylalanine F, leucine L, valine V, alanine A or glycine G-NH2), the optimum sequence is tyrosine-phenylalanine in each case; however, both its absolute and relative yield amplification is dictated by the properties of the donor component, indicating cooperativity of peptide sequence and donor/acceptor pairs in assembly. The methodology provides an in situ discovery tool for nanostructures that enable dynamic interfacing of supramolecular electronics with aqueous (biological) systems.

  20. Charge transfer vibronic transitions in uranyl tetrachloride compounds;

    SciTech Connect

    Liu, G. K.; Deifel, N. P.; Cahill, C. L.

    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.

  1. Charge transfer vibronic transitions in uranyl tetrachloride compounds

    SciTech Connect

    Liu, Guokui; Deifel, Nicholas P.; Cahill, Christopher L.; Zhurov, Vladimir V.; Pinkerton, A. Alan

    2012-01-01

    The electronic and vibronic interactions of uranyl (UO₂)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 3σ ground state into the fδ,Φ 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.

  2. 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

  3. The role of collective motion in the ultrafast charge transfer in van der Waals heterostructures

    DOE PAGES

    Wang, Han; Bang, Junhyeok; Sun, Yiyang; ...

    2016-05-10

    Here, the success of van der Waals (vdW) heterostructures, made of graphene, metal dichalcogenides, and other layered materials, hinges on the understanding of charge transfer across the interface as the foundation for new device concepts and applications. In contrast to conventional heterostructures, where a strong interfacial coupling is essential to charge transfer, recent experimental findings indicate that vdW heterostructues can exhibit ultra-fast charge transfer despite the weak binding of the heterostructure. Using time-dependent density functional theory molecular dynamics, we identify a strong dynamic coupling between the vdW layers associated with charge transfer. This dynamic coupling results in rapid nonlinear coherentmore » charge oscillations which constitute a purely electronic phenomenon and are shown to be a general feature of vdW heterostructures provided they have a critical minimum dipole coupling. Application to MoS2/WS2 heterostructure yields good agreement with experiment, indicating near complete charge transfer within a timescale of 100 fs.The success of van der Waals heterostructures made of graphene, metal dichalcogenides and other layered materials, hinges on the understanding of charge transfer across the interface as the foundation for new device concepts and applications. In contrast to conventional heterostructures, where a strong interfacial coupling is essential to charge transfer, recent experimental findings indicate that van der Waals heterostructues can exhibit ultrafast charge transfer despite the weak binding of these heterostructures. Here we find, using time-dependent density functional theory molecular dynamics, that the collective motion of excitons at the interface leads to plasma oscillations associated with optical excitation. By constructing a simple model of the van der Waals heterostructure, we show that there exists an unexpected criticality of the oscillations, yielding rapid charge transfer across the

  4. The role of collective motion in the ultrafast charge transfer in van der Waals heterostructures

    SciTech Connect

    Wang, Han; Bang, Junhyeok; Sun, Yiyang; West, Damien; Meunier, Vincent; Zhang, Shengbai; Liang, Linagbo

    2016-05-10

    Here, the success of van der Waals (vdW) heterostructures, made of graphene, metal dichalcogenides, and other layered materials, hinges on the understanding of charge transfer across the interface as the foundation for new device concepts and applications. In contrast to conventional heterostructures, where a strong interfacial coupling is essential to charge transfer, recent experimental findings indicate that vdW heterostructues can exhibit ultra-fast charge transfer despite the weak binding of the heterostructure. Using time-dependent density functional theory molecular dynamics, we identify a strong dynamic coupling between the vdW layers associated with charge transfer. This dynamic coupling results in rapid nonlinear coherent charge oscillations which constitute a purely electronic phenomenon and are shown to be a general feature of vdW heterostructures provided they have a critical minimum dipole coupling. Application to MoS2/WS2 heterostructure yields good agreement with experiment, indicating near complete charge transfer within a timescale of 100 fs.The success of van der Waals heterostructures made of graphene, metal dichalcogenides and other layered materials, hinges on the understanding of charge transfer across the interface as the foundation for new device concepts and applications. In contrast to conventional heterostructures, where a strong interfacial coupling is essential to charge transfer, recent experimental findings indicate that van der Waals heterostructues can exhibit ultrafast charge transfer despite the weak binding of these heterostructures. Here we find, using time-dependent density functional theory molecular dynamics, that the collective motion of excitons at the interface leads to plasma oscillations associated with optical excitation. By constructing a simple model of the van der Waals heterostructure, we show that there exists an unexpected criticality of the oscillations, yielding rapid charge transfer across the interface

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

    NASA Astrophysics Data System (ADS)

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

    2013-12-01

    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.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. Electronic supplementary information (ESI) available: AFM line scans of the substrate before and after functionalization; scheme for measuring amorphous carbon coverage from TEM images; diameter comparisons of ac-TEM image and simulation of C60 molecule; Raman spectra D peak comparison; optical response of transfer properties of pristine devices; comparison between swept and pulsed Vg measurements

  6. Quantum Plasmonics: Optical Monitoring of DNA-Mediated Charge Transfer in Plasmon Rulers.

    PubMed

    Lerch, Sarah; Reinhard, Björn M

    2016-03-09

    Plasmon coupling between DNA-tethered gold nanoparticles is investigated by correlated single-particle spectroscopy and transmission electron microscopy for interparticle separations between 0.5 and 41 nm. Spectral characterization reveals a weakening of the plasmon coupling due to DNA-mediated charge transfer for separations up to 2.8 nm. Electromagnetic simulations indicate a coherent charge transfer across the DNA.

  7. The role of collective motion in the ultrafast charge transfer in van der Waals heterostructures.

    PubMed

    Wang, Han; Bang, Junhyeok; Sun, Yiyang; Liang, Liangbo; West, Damien; Meunier, Vincent; Zhang, Shengbai

    2016-05-10

    The success of van der Waals heterostructures made of graphene, metal dichalcogenides and other layered materials, hinges on the understanding of charge transfer across the interface as the foundation for new device concepts and applications. In contrast to conventional heterostructures, where a strong interfacial coupling is essential to charge transfer, recent experimental findings indicate that van der Waals heterostructues can exhibit ultrafast charge transfer despite the weak binding of these heterostructures. Here we find, using time-dependent density functional theory molecular dynamics, that the collective motion of excitons at the interface leads to plasma oscillations associated with optical excitation. By constructing a simple model of the van der Waals heterostructure, we show that there exists an unexpected criticality of the oscillations, yielding rapid charge transfer across the interface. Application to the MoS2/WS2 heterostructure yields good agreement with experiments, indicating near complete charge transfer within a timescale of 100 fs.

  8. Crystal growth of new charge-transfer salts based on π-conjugated donor molecules

    NASA Astrophysics Data System (ADS)

    Morherr, Antonia; Witt, Sebastian; Chernenkaya, Alisa; Bäcker, Jan-Peter; Schönhense, Gerd; Bolte, Michael; Krellner, Cornelius

    2016-09-01

    New charge transfer crystals of π-conjugated, aromatic molecules (phenanthrene and picene) as donors were obtained by physical vapor transport. The melting behavior, optimization of crystal growth and the crystal structure are reported for charge transfer salts with (fluorinated) tetracyanoquinodimethane (TCNQ-Fx, x=0, 2, 4), which was used as acceptor material. The crystal structures were determined by single-crystal X-ray diffraction. Growth conditions for different vapor pressures in closed ampules were applied and the effect of these starting conditions for crystal size and quality is reported. The process of charge transfer was investigated by geometrical analysis of the crystal structure and by infrared spectroscopy on single crystals. With these three different acceptor strengths and the two sets of donor materials, it is possible to investigate the distribution of the charge transfer systematically. This helps to understand the charge transfer process in this class of materials with π-conjugated donor molecules.

  9. The role of collective motion in the ultrafast charge transfer in van der Waals heterostructures

    PubMed Central

    Wang, Han; Bang, Junhyeok; Sun, Yiyang; Liang, Liangbo; West, Damien; Meunier, Vincent; Zhang, Shengbai

    2016-01-01

    The success of van der Waals heterostructures made of graphene, metal dichalcogenides and other layered materials, hinges on the understanding of charge transfer across the interface as the foundation for new device concepts and applications. In contrast to conventional heterostructures, where a strong interfacial coupling is essential to charge transfer, recent experimental findings indicate that van der Waals heterostructues can exhibit ultrafast charge transfer despite the weak binding of these heterostructures. Here we find, using time-dependent density functional theory molecular dynamics, that the collective motion of excitons at the interface leads to plasma oscillations associated with optical excitation. By constructing a simple model of the van der Waals heterostructure, we show that there exists an unexpected criticality of the oscillations, yielding rapid charge transfer across the interface. Application to the MoS2/WS2 heterostructure yields good agreement with experiments, indicating near complete charge transfer within a timescale of 100 fs. PMID:27160484

  10. Heat transfer performance of a pulsating heat pipe charged with acetone-based mixtures

    NASA Astrophysics Data System (ADS)

    Wang, Wenqing; Cui, Xiaoyu; Zhu, Yue

    2016-12-01

    Pulsating heat pipes (PHPs) are used as high efficiency heat exchangers, and the selection of working fluids in PHPs has a great impact on the heat transfer performance. This study investigates the thermal resistance characteristics of the PHP charged with acetone-based binary mixtures, where deionized water, methanol and ethanol were added to and mixed with acetone, respectively. The volume mixing ratios were 2:1, 4:1 and 7:1, and the heating power ranged from 10 to 100 W with filling ratios of 45, 55, 62 and 70%. At a low filling ratio (45%), the zeotropic characteristics of the binary mixtures have an influence on the heat transfer performance of the PHP. Adding water, which has a substantially different boiling point compared with that of acetone, can significantly improve the anti-dry-out ability inside the PHP. At a medium filling ratio (55%), the heat transfer performance of the PHP is affected by both phase transition characteristics and physical properties of working fluids. At high heating power, the thermal resistance of the PHP with acetone-water mixture is between that with pure acetone and pure water, whereas the thermal resistance of the PHP with acetone-methanol and acetone-ethanol mixtures at mixing ratios of 2:1 and 4:1 is less than that with the corresponding pure fluids. At high filling ratios (62 and 70%), the heat transfer performance of the PHP is mainly determined by the properties of working fluids that affects the flow resistance. Thus, the PHP with acetone-methanol and acetone-ethanol mixtures that have a lower flow resistance shows better heat transfer performance than that with acetone-water mixture.

  11. Heat Transfer Characteristics in Crank-Shape Thermosyphons

    NASA Astrophysics Data System (ADS)

    Imura, Hedeaki; Koito, Yasushi

    A two-phase closed thermosyphon is applied to gas-to-gas heat exchangers, the cooling of heat generation devices, the melting of snow, the prevention from icing of water on roads and so on. Generally, straight tubes are used as the thermosyphon. However, because of the limited space for the straight thermosyphon to be installed, it is considered that a bent thermosyphon is enforced to employ. In response to this, fundamental experiments are conducted on the heat transfer characteristics in a two-phase crank shape closed thermosyphon, in which an evaporator and a condenser are vertically positioned, and a connecting adiabatic section is horizontal. Ethylene glycol aqueous solutions which have lower freezing points and hydrofluoroether 7100 and 7200 which do not contain chloride are used as the working fluids Heat transfer coefficients and critical heat fluxes in the thermosyphon are measured by changing the amount of charged working fluid (0.30,0.40,0.50 and 0.60 of the evaporator volume),the temperature of the adiabatic section (40,50,60,70 and 80°C) and heat flux (from 4.0 kW /m2 to critical). The experimental results are shown and compared with those taken using water as the working fluid.

  12. Carbon-, sulfur-, and phosphorus-based charge transfer reactions in inductively coupled plasma-atomic emission spectrometry

    NASA Astrophysics Data System (ADS)

    Grindlay, Guillermo; Gras, Luis; Mora, Juan; de Loos-Vollebregt, Margaretha T. C.

    2016-01-01

    In this work, the influence of carbon-, sulfur-, and phosphorus-based charge transfer reactions on the emission signal of 34 elements (Ag, Al, As, Au, B, Ba, Be, Ca, Cd, Co, Cr, Cu, Fe, Ga, Hg, I, In, Ir, K, Li, Mg, Mn, Na, Ni, P, Pb, Pd, Pt, S, Sb, Se, Sr, Te, and Zn) in axially viewed inductively coupled plasma-atomic emission spectrometry has been investigated. To this end, atomic and ionic emission signals for diluted glycerol, sulfuric acid, and phosphoric acid solutions were registered and results were compared to those obtained for a 1% w w- 1 nitric acid solution. Experimental results show that the emission intensities of As, Se, and Te atomic lines are enhanced by charge transfer from carbon, sulfur, and phosphorus ions. Iodine and P atomic emission is enhanced by carbon- and sulfur-based charge transfer whereas the Hg atomic emission signal is enhanced only by carbon. Though signal enhancement due to charge transfer reactions is also expected for ionic emission lines of the above-mentioned elements, no experimental evidence has been found with the exception of Hg ionic lines operating carbon solutions. The effect of carbon, sulfur, and phosphorus charge transfer reactions on atomic emission depends on (i) wavelength characteristics. In general, signal enhancement is more pronounced for electronic transitions involving the highest upper energy levels; (ii) plasma experimental conditions. The use of robust conditions (i.e. high r.f. power and lower nebulizer gas flow rates) improves carbon, sulfur, and phosphorus ionization in the plasma and, hence, signal enhancement; and (iii) the presence of other concomitants (e.g. K or Ca). Easily ionizable elements reduce ionization in the plasma and consequently reduce signal enhancement due to charge transfer reactions.

  13. Charge-recombination processes in organic solar cells: the impact of charge-transfer states (Conference Presentation)

    NASA Astrophysics Data System (ADS)

    Coropceanu, Veaceslav

    2016-09-01

    We study the role of electron-vibration coupling, electronic polarization, molecular packing, system size and electron delocalization on the nature of the charge-transfer states in model donor-acceptor systems. The morphologies we consider range from a bilayer with flat interface to a bilayer with rough interface and bulk heterojunctions with coarse and fine intercalated domains of donor and acceptor molecules. The implications of the charge-transfer states, active material morphology, density of states and charge carrier concentration on non-geminate recombination kinetics is investigated by means of a three-dimensional reaction-diffusion lattice model with the charge carrier hopping rate described by the Miller-Abrahams formalism.

  14. Charge delocalization characteristics of regioregular high mobility polymers

    DOE PAGES

    Coughlin, J. E.; Zhugayevych, A.; Wang, M.; ...

    2017-01-01

    Controlling the regioregularity among the structural units of narrow bandgap conjugated polymer backbones has led to improvements in optoelectronic properties, for example in the mobilities observed in field effect transistor devices. To investigate how the regioregularity affects quantities relevant to hole transport, regioregular and regiorandom oligomers representative of polymeric structures were studied using density functional theory. Several structural and electronic characteristics of the oligomers were compared, including chain planarity, cation spin density, excess charges on molecular units and internal reorganizational energy. The main difference between the regioregular and regiorandom oligomers is found to be the conjugated backbone planarity, while themore » reorganizational energies calculated are quite similar across the molecular family. Lastly, this work constitutes the first step on understanding the complex interplay of atomistic changes and an oligomer backbone structure toward modeling the charge transport properties.« less

  15. Charge delocalization characteristics of regioregular high mobility polymers

    SciTech Connect

    Coughlin, J. E.; Zhugayevych, A.; Wang, M.; Bazan, G. C.; Tretiak, S.

    2017-01-01

    Controlling the regioregularity among the structural units of narrow bandgap conjugated polymer backbones has led to improvements in optoelectronic properties, for example in the mobilities observed in field effect transistor devices. To investigate how the regioregularity affects quantities relevant to hole transport, regioregular and regiorandom oligomers representative of polymeric structures were studied using density functional theory. Several structural and electronic characteristics of the oligomers were compared, including chain planarity, cation spin density, excess charges on molecular units and internal reorganizational energy. The main difference between the regioregular and regiorandom oligomers is found to be the conjugated backbone planarity, while the reorganizational energies calculated are quite similar across the molecular family. Lastly, this work constitutes the first step on understanding the complex interplay of atomistic changes and an oligomer backbone structure toward modeling the charge transport properties.

  16. A three-step kinetic model for electrochemical charge transfer in the hopping regime.

    PubMed

    Yin, Xing; Wierzbinski, Emil; Lu, Hao; Bezer, Silvia; de Leon, Arnie R; Davis, Kathryn L; Achim, Catalina; Waldeck, David H

    2014-09-04

    Single-step nonadiabatic electron tunneling models are widely used to analyze electrochemical rates through self-assembled monolayer films (SAMs). For some systems, such as nucleic acids, long-range charge transfer can occur in a "hopping" regime that involves multiple charge transfer events and intermediate states. This report describes a three-step kinetic scheme to model charge transfer in this regime. Some of the features of the three-step model are probed experimentally by changing the chemical composition of the SAM. This work uses the three-step model and a temperature dependence of the charge transfer rate to extract the charge injection barrier for a SAM composed of a 10-mer peptide nucleic acid that operates in the hopping regime.

  17. Using quantum dynamics simulations to follow the competition between charge migration and charge transfer in polyatomic molecules

    NASA Astrophysics Data System (ADS)

    Spinlove, K. E.; Vacher, M.; Bearpark, M.; Robb, M. A.; Worth, G. A.

    2017-01-01

    Recent work, particularly by Cederbaum and co-workers, has identified the phenomenon of charge migration, whereby charge flow occurs over a static molecular framework after the creation of an electronic wavepacket. In a real molecule, this charge migration competes with charge transfer, whereby the nuclear motion also results in the re-distribution of charge. To study this competition, quantum dynamics simulations need to be performed. To break the exponential scaling of standard grid-based algorithms, approximate methods need to be developed that are efficient yet able to follow the coupled electronic-nuclear motion of these systems. Using a simple model Hamiltonian based on the ionisation of the allene molecule, the performance of different methods based on Gaussian Wavepackets is demonstrated.

  18. Spectral properties of molecular charge-transfer probe QMOM

    NASA Astrophysics Data System (ADS)

    Tomin, V. I.; Jaworski, R.; Yushchenko, D. A.

    2010-09-01

    The spectral characteristics of solutions of a dye with dual fluorescence, 1-methyl-2-(4-methoxy)phenyl-3-hydroxy-4(1H)-quinolone, in acetonitrile are studied upon selective excitation. This dye is a structural analogue of 3-hydroxyflavone and also exhibits excited-state proton transfer, which, as well as in the case of 3-hydroxyflavone, has a kinetic nature. The fluorescence spectra are studied upon excitation by photons of various energies, and the excitation spectra are recorded at wavelengths of different fluorescence bands. It is found that the intensity ratio of the emission of the normal and tautomeric forms (at wavelength of 415 and 518 nm, respectively) is almost the same (0.23-0.25) for excitation in the regions of the main and the second absorption bands. At the same time, in the case of excitation between these bands, this ratio decreases to 0.19. The second interesting feature is the existence of a third latent emission band peaked at about 480 nm, which is reliably detected upon excitation at wavelengths in the region of 400-450 nm. This study shows that this emission belongs to the anionic form of the dye. This form is also responsible for a decrease in the intensity ratio of the emission of the two main forms in the case of excitation between the first and second absorption bands.

  19. Experimental and theoretical studies of charge transfer and deuterium ion transfer between D2O+ and C2H4

    NASA Astrophysics Data System (ADS)

    Liu, Li; Cai, Xiaohui; Li, Yue; Richards O'Grady, Elizabeth; Farrar, James M.

    2004-08-01

    The charge transfer and deuterium ion transfer reactions between D2O+ and C2H4 have been studied using the crossed beam technique at relative collision energies below one electron volt and by density functional theory (DFT) calculations. Both direct and rearrangement charge transfer processes are observed, forming C2H4+ and C2H3D+, respectively. Independent of collision energy, deuterium ion transfer accounts for approximately 20% of the reactive collisions. Between 22 and 36 % of charge transfer collisions occur with rearrangement. In both charge transfer processes, comparison of the internal energy distributions of products with the photoelectron spectrum of C2H4 shows that Franck-Condon factors determine energy disposal in these channels. DFT calculations provide evidence for transient intermediates that undergo H/D migration with rearrangement, but with minimal modification of the product energy distributions determined by long range electron transfer. The cross section for charge transfer with rearrangement is approximately 103 larger than predicted from the Rice-Ramsperger-Kassel-Marcus isomerization rate in transient complexes, suggesting a nonstatistical mechanism for H/D exchange. DFT calculations suggest that reactive trajectories for deuterium ion transfer follow a pathway in which a deuterium atom from D2O+ approaches the π-cloud of ethylene along the perpendicular bisector of the C-C bond. The product kinetic energy distributions exhibit structure consistent with vibrational motion of the D-atom in the bridged C2H4D+ product perpendicular to the C-C bond. The reaction quantitatively transforms the reaction exothermicity into internal excitation of the products, consistent with mixed energy release in which the deuterium ion is transferred in a configuration in which both the breaking and the forming bonds are extended.

  20. Lead-iodide nanowire perovskite with methylviologen showing interfacial charge-transfer absorption: a DFT analysis.

    PubMed

    Fujisawa, Jun-ichi; Giorgi, Giacomo

    2014-09-07

    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.

  1. Reptation Quantum Monte Carlo Calculation of Charge Transfer in The Na-Cl Dimer

    NASA Astrophysics Data System (ADS)

    Yao, Yi; Kanai, Yosuke

    2015-03-01

    Reptation Quantum Monte Carlo (QMC) calculations are performed to describe the charge transfer behavior in a NaCl dimer. Influence of fixed node approximation on the charge transfer was examined by obtaining electron density via reputation QMC. We employ Slater-Jastrow wavefunction as the trial wavefunction, and the fermion nodes are obtained from single particle orbitals of Hartree-Fock and Density Functional Theory (DFT) with several exchange-correlation approximations. We will discuss our QMC results together with DFT calculations to give insights into observed dependence of the charge transfer behavior on the fixed-node approximation.

  2. 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

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

    SciTech Connect

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

    2015-05-14

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

  4. Improved Charge Transfer by Thin Metal Oxide Films

    NASA Astrophysics Data System (ADS)

    Irfan

    The field of electronics has an immense impact on our day to day life. Efficient charge transfer at the semiconductor and electrode interface is one of the most crucial issues for the performance of any electronic device. A lot of effort has been spent to address this issue. A counter intuitive phenomenon of insertion of a thin metal oxide film at the semiconductor and electrode interface has gained momentum recently. In the current thesis, based on results of several experiments, I will propose a prominent mechanism of performance improvement with such insertions. I will also demonstrate the applicability of such metal oxide thin films in many other systems. First, I will introduce the scope of the thesis in detail. I will also introduce the background to understand the electronic structure of organic semiconductors, along with the interface formation at the semiconductor/metal interface. Then, I will discuss the measurement techniques. I will start the discussion on results with the insertion of a thin layer of MoOx (a transition metal oxide) between indium tin oxide (ITO) and two well studied organic semiconductors. I will also demonstrate that the optimum insertion layer thickness is just a few nanometers. I will illustrate the importance of high vacuum during the deposition of such insertion layers. I will also discuss the method to recover work function of air exposed MoOx films. I will further demonstrate that a thin layer of MoOx can be utilized to dope C60 strongly p-type. Then, I will discuss the application of MoO x insertion layer in CdTe based solar cells. I will further show the application of MoOx and organic double-inter-layer in organic devices. At the end, I will discuss an intense oxygen plasma treatment on ITO films and demonstrate a method to achieve high work function ITO films. The mechanism of high work function and application in devices will also be explained in detail. Finally, I will summarize the thesis.

  5. Modeling the electrical conduction in DNA nanowires: charge transfer and lattice fluctuation theories.

    PubMed

    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.

  6. Proton-transfer mediated quenching of pyrene/indole charge-transfer states in isooctane solutions.

    PubMed

    Altamirano, Marcela S; Bohorquez, María del Valle; Previtali, Carlos M; Chesta, Carlos A

    2008-01-31

    The fluorescence quenching of pyrene (Py) by a series of N-methyl and N-H substituted indoles was studied in isooctane at 298 K. The fluorescence quenching rate constants were evaluated by mean of steady-state and time-resolved measurements. In all cases, the quenching process involves a charge-transfer (CT) mechanism. The I(o)/I and tau(o)/tau Stern-Volmer plots obtained for the N-H indoles show a very unusual upward deviation with increasing concentration of the quenchers. This behavior is attributed to the self-quenching of the CT intermediates by the free indoles in solution. The efficiency of quenching of the polyaromatic by the N-H indoles increases abruptly in the presence of small amount of added pyridine (or propanol). A detailed analysis of the experimental data obtained in the presence of pyridine provides unambiguous evidence that the self-quenching process involves proton transfer from the CT states to indoles.

  7. Ultrafast dynamics of a charge-transfer dimer as a model for the photoinduced phase transition of charge-transfer compounds.

    PubMed

    Lüer, Larry; Manzoni, Cristian; Cerullo, Giulio; Lanzani, Guglielmo; Meneghetti, Moreno

    2007-07-13

    By applying ultrafast pump-probe spectroscopy with 15 fs temporal resolution to (TMTTF(+))(2) dimers we provide a full picture of the structural relaxation following photoexcitation of their CT transition. Both population and coherent phonon dynamics allow tracking wave packet motion onto the multidimensional excited state potential energy surface, as obtained by density functional theory calculations. We show that the vibrations that are strongly coupled to the charge-transfer transition of the dimer correspond to those driving the photoinduced phase transition occurring in charge-transfer crystalline solids.

  8. Deep-hole transfer leads to ultrafast charge migration in DNA hairpins.

    PubMed

    Renaud, Nicolas; Harris, Michelle A; Singh, Arunoday P N; Berlin, Yuri A; Ratner, Mark A; Wasielewski, Michael R; Lewis, Frederick D; Grozema, Ferdinand C

    2016-11-01

    Charge transport through the DNA double helix is of fundamental interest in chemistry and biochemistry, but also has potential technological applications such as for DNA-based nanoelectronics. For the latter, it is of considerable interest to explore ways to influence or enhance charge transfer. In this Article we demonstrate a new mechanism for DNA charge transport, namely 'deep-hole transfer', which involves long-range migration of a hole through low-lying electronic states of the nucleobases. Here, we demonstrate, in a combined experimental and theoretical study, that it is possible to achieve such transfer behaviour by changing the energetics of charge injection. This mechanism leads to an enhancement in transfer rates by up to two orders of magnitude and much weaker distance dependence. This transfer is faster than relaxation to the lowest-energy state, setting this mechanism apart from those previously described. This opens up a new direction to optimize charge transfer in DNA with unprecedented charge-transfer rates.

  9. Dissociation heat transfer characteristics of methane hydrates

    SciTech Connect

    Kamath, V.A.; Holder, G.D.

    1987-02-01

    Knowledge of the interfacial heat transfer phenomenon during the dissociation of gas hydrates is essential in modeling the hydrate dissociation process. Such knowledge has applications in natural gas processing, storage, or transportation; in the drilling and recovery of oil and gas in the presence of gas hydrates; in the desalination of sea water; and in the production of natural gas from hydrate reservoirs. The process of hydrate dissociation is a unique phenomenon in which gas and water are simultaneously produced at the dissociated hydrate surface and play an important role in the mechanism of heat transfer to hydrates. An earlier study of propane hydrate dissociation showed that hydrate dissociation is a heat-transfer-limited process and somewhat similar to the nucleate boiling of liquids. In the present study, heat transfer limitations for methane hydrate dissociation were studied for two reasons. First, a comparison of the results of this study with propane hydrate was desired. Second, the effect of hydrate structure and gas molecule type on the rate of heat transfer during hydrate dissociation was sought.

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

    PubMed Central

    2015-01-01

    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

  11. Topological Effects of Charge Transfer in Telomere G-Quadruplex Mechanism on Telomerase Activation and Inhibition

    NASA Astrophysics Data System (ADS)

    Wang, Xin; Liang, Shi-Dong

    2013-02-01

    We explore the charge transfer in the telomere G-Quadruplex (TG4) DNA theoretically by the nonequilibrium Green's function method, and reveal the topological effect of the charge transport in TG4 DNA. The consecutive TG4 (CTG4) is semiconducting with 0.2 0.3 eV energy gap. Charges transfer favorably in the CTG4, but are trapped in the nonconsecutive TG4 (NCTG4). The global conductance is inversely proportional to the local conductance for NCTG4. The topological structure transition from NCTG4 to CTG4 induces abruptly 3nA charge current, which provide a microscopic clue to understand the telomerase activated or inhibited by TG4. Our findings reveal the fundamental property of charge transfer in TG4 and its relationship with the topological structure of TG4.

  12. Proposal of Simplified Method of Analysis of Charge Transfer Associated with Return Strokes

    NASA Astrophysics Data System (ADS)

    Michishita, Koji; Umehara, Satoshi; Kawamoto, Shinji; Maeda, Koji

    Charge transfer is one of the most important parameters when one discusses the damage to the equipments on a power line due to the energy of the lightning. The amount of charge transfer associated with a lightning flash or individual strokes can be estimated by using the electric field change measured with a slow antenna. In this letter, the authors propose a simplified method of analysis of charge transfer associated with cloud-to-ground strokes along with estimation of the height of a charge in the point charge model. The height is evaluated by the product of the average speed of the downward propagating stepped leader and the time difference between the beginning of the preliminary breakdown and the onset of a return stroke.

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

    NASA Technical Reports Server (NTRS)

    Chakraverty, B. K.

    1990-01-01

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

  14. Charge transfer between sensing and targeted metal nanoparticles in indirect nanoplasmonic sensors

    NASA Astrophysics Data System (ADS)

    Zhdanov, Vladimir P.; Langhammer, Christoph

    2017-03-01

    In indirect nanoplasmonic sensors, the plasmonic metal nanoparticles are adjacent to the material of interest, and the material-related changes of their optical properties are used to probe that material. If the latter itself represents another metal in the form of nanoparticles, its deposition is accompanied by charge transfer to or from the plasmonic nanoparticles in order to equalize the Fermi levels. We estimate the value of the transferred charge and show on the two examples, nanoparticle sintering and hydride formation, that the charge transfer has negligible influence on the probed processes, because the effect of charge transfer is less important than that of nanoparticle surface energy. This further corroborates the non-invasive nature of nanoplasmonic sensors.

  15. 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.

  16. Observations of the Bowen fluorescence mechanism and charge transfer in planetary nebulae. II

    NASA Astrophysics Data System (ADS)

    Liu, Xiao-Wei; Danziger, John; Murdin, Paul

    1993-06-01

    The study compares measurements of O(2+) Bowen fluorescence and charge transfer lines in nine planetary nebulae with theoretical predictions, taking into account contributions from the Bowen fluorescence mechanism, the charge transfer reaction between O(3+) and H(0), and radiative and dielectronic recombination. In general, good agreement is found. It is shown that excitation by absorption of the stellar continuum UV radiation is negligible for these lines. There is a good positive correlation between the strength of the charge transfer reaction and the degree of excitation of the nebulae. The relative charge transfer rate coefficients into singlet and triplet levels of O(2+), k(2p3p3DJ)/k(2p3p1P)(J = 1, 2, 3), are derived and on average are equal to 1.2, independent of the statistical weight 2J + 1 of the fine-structure level.

  17. Lowest energy Frenkel and charge transfer exciton intermixing in one-dimensional copper phthalocyanine molecular lattice

    NASA Astrophysics Data System (ADS)

    Bondarev, I. V.; Popescu, A.; Younts, R. A.; Hoffman, B.; McAfee, T.; Dougherty, D. B.; Gundogdu, K.; Ade, H. W.

    2016-11-01

    We report the results of the combined experimental and theoretical studies of the low-lying exciton states in crystalline copper phthalocyanine. We derive the eigen energy spectrum for the two lowest intramolecular Frenkel excitons coupled to the intermolecular charge transfer exciton state and compare it with temperature dependent optical absorption spectra measured experimentally, to obtain the parameters of the Frenkel-charge-transfer exciton intermixing. The two Frenkel exciton states are spaced apart by 0.26 eV, and the charge transfer exciton state is 50 meV above the lowest Frenkel exciton. Both Frenkel excitons are strongly mixed with the charge transfer exciton, showing the coupling constant 0.17 eV which agrees with earlier experimental measurements. These results can be used for the proper interpretation of the physical properties of crystalline phthalocyanines.

  18. Modeling noncovalent radical-molecule interactions using conventional density-functional theory: beware erroneous charge transfer.

    PubMed

    Johnson, Erin R; Salamone, Michela; Bietti, Massimo; DiLabio, Gino A

    2013-02-07

    Conventional density-functional theory (DFT) has the potential to overbind radical-molecule complexes because of erroneous charge transfer. We examined this behavior by exploring the ability of various DFT approximations to predict fractional charge transfer and by quantifying the overbinding in a series of complexes. It is demonstrated that too much charge is transferred from molecules to radicals when the radical singly unoccupied molecular orbitals are predicted to be erroneously too low in energy relative to the molecule highest occupied molecular orbitals, leading to excessive Coulombic attraction. In this respect, DFT methods formulated with little or no Hartree-Fock exchange perform most poorly. The present results illustrate that the charge-transfer problem is much broader than may have been previously expected and is not limited to conventional (i.e., molecule-molecule) donor-acceptor complexes.

  19. On the HSAB based estimate of charge transfer between adsorbates and metal surfaces

    NASA Astrophysics Data System (ADS)

    Kokalj, Anton

    2012-01-01

    The applicability of the HSAB based electron charge transfer parameter, Δ N, is analyzed for molecular and atomic adsorbates on metal surfaces by means of explicit DFT calculations. For molecular adsorbates Δ N gives reasonable trends of charge transfer if work function is used for electronegativity of metal surface. For this reason, calculated work functions of low Miller index surfaces for 11 different metals are reported. As for reactive atomic adsorbates, e.g., N, O, and Cl, the charge transfer is proportional to the adatom valence times the electronegativity difference between the metal surface and the adatom, where the electronegativity of metal is represented by a linear combination of atomic Mulliken electronegativity and the work function of metal surface. It is further shown that the adatom-metal bond strength is linearly proportional to the metal-to-adatom charge transfer thus making the Δ N parameter a useful indicator to anticipate the corresponding adsorption energy trends.

  20. Regressed relations for forced convection heat transfer in a direct injection stratified charge rotary engine

    NASA Technical Reports Server (NTRS)

    Lee, Chi M.; Schock, Harold J.

    1988-01-01

    Currently, the heat transfer equation used in the rotary combustion engine (RCE) simulation model is taken from piston engine studies. These relations have been empirically developed by the experimental input coming from piston engines whose geometry differs considerably from that of the RCE. The objective of this work was to derive equations to estimate heat transfer coefficients in the combustion chamber of an RCE. This was accomplished by making detailed temperature and pressure measurements in a direct injection stratified charge (DISC) RCE under a range of conditions. For each specific measurement point, the local gas velocity was assumed equal to the local rotor tip speed. Local physical properties of the fluids were then calculated. Two types of correlation equations were derived and are described in this paper. The first correlation expresses the Nusselt number as a function of the Prandtl number, Reynolds number, and characteristic temperature ratio; the second correlation expresses the forced convection heat transfer coefficient as a function of fluid temperature, pressure and velocity.

  1. 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.

  2. Intramolecular charge transfer in the excited state of 4-dimethylaminobenzaldehyde and 4-dimethylaminoacetophenone

    NASA Astrophysics Data System (ADS)

    Fujiwara, Takashige; Lee, Jae-Kwang; Zgierski, Marek Z.; Lim, Edward C.

    2009-10-01

    TDDFT calculations and time-resolved transient absorption (TA) studies of the low-lying excited states of 4-dimethylaminobenzaldehyde (4-DMABA) and 4-dimethylaminoacetophenone (4-DMAAP) have been carried out to probe the mechanism of photoinduced intramolecular charge transfer (ICT). In polar acetonitrile, where dual fluorescence appears, both 4-DMABA and 4-DMAAP exhibit a TA band at about 510 nm and 490 nm, which correspond to the absorption spectra of the twisted ICT (TICT) state, with spectral characteristics that correspond to the radical anion absorptions of benzaldehyde or acetophenone. The decay time of the TICT-state absorption corresponds to that of the ICT fluorescence, indicating that the fluorescent ICT state is the TICT states.

  3. When hole extraction determines charge transfer across metal-organic-metal structure

    NASA Astrophysics Data System (ADS)

    Govor, L. V.; Reiter, G.; Parisi, J.

    2016-03-01

    We examined the charge transfer in metal-organic-metal structure, where the contact resistance of the extracting interface is larger than the resistance of the organic crystalline material and the resistance of the injecting interface. If direct tunneling (low voltage) and Fowler-Nordheim tunnelling (high voltage) across both interfaces take place, part of the injected holes remains located in the organic crystal because of the blocking action of the extracting interface, but not because of traps within the organic crystalline material (which was negligible). If Fowler-Nordheim tunneling across the injecting interface and direct tunneling across the extracting interface take place for high voltages, the latter leads to the deviation of the total current-voltage characteristic from the power law I∼ Vγ with γ>2 to Ohm's law with γ≃1.0 .

  4. Excited state two photon absorption of a charge transfer radical dimer in the near infrared.

    PubMed

    Schiccheri, Nicola; Meneghetti, Moreno

    2005-06-02

    Nonlinear transmission measurements of a solution of radical dimers of tetramethyl-tetrathiafulvalene, (TMTTF+)2, recorded with 9 ns laser pulses at 1064 nm are reported and interpreted on the basis of a multiphoton absorption process. One finds that the process can be interpreted with a sequence of three photon absorption, the first being a one photon absorption related to the intermolecular charge transfer process characteristic of the dimers and the second a two photon absorption from the excited state created with the first process. A model calculation allows one to obtain the value of the two photon absorption cross section which is found to be several orders of magnitude larger than those usually found for two photon absorbing systems excited from the ground state. These results show the importance of an excited-state population for obtaining large nonlinear optical responses.

  5. On the structure of iodine charge-transfer complexes in solution

    NASA Astrophysics Data System (ADS)

    Walker, Larry A., II; Pullen, Stuart; Donovan, Brent; Sension, Roseanne J.

    1995-08-01

    Femtosecond transient absorption studies of charge-transfer complexes of I 2 with hexamethylbenzene have been performed in a series of noncomplexing solvents. Anisotropy measurements of the bleach of the charge-transfer absorption band indicate that the geometry and electronic structure of the complex is dependent upon the solvent environment. The results are interpreted as favoring an oblique, nearly axial, geometry in alkanes and a resting geometry in chlorinated methanes.

  6. Charge Compensation and Electrostatic Transferability in Three Entropy Stabilized Oxides: Results from Density Functional Theory Calculations

    DTIC Science & Technology

    2016-09-06

    Charge compensation and electrostatic transferability in three entropy-stabilized oxides: Results from density functional theory calculations Zs. Rak...North Carolina State University, Raleigh, North Carolina 27695-7907, USA 2Department of Mechanical Engineering and Materials Science and Center for...random structures. For J14, Bader charges are transferable between the binary, ternary, and random structures. For J14þSc and J14þLi, average Bader

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

    SciTech Connect

    Yates, G.J.; Gallegos, R.; Pena, C.; Zagarino, P.

    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.

  8. Environment effect on spectral and charge distribution characteristics of some drugs of folate derivatives

    NASA Astrophysics Data System (ADS)

    Khadem Sadigh, M.; Zakerhamidi, M. S.; Seyed Ahmadian, S. M.; Johari-Ahar, M.; Zare Haghighi, L.

    2017-01-01

    Molecular surrounding media as an important factor can effect on the operation of wide variety of drugs. For more study in this paper, spectral properties of Methotrexate and Folinic acid have been studied in various solvents. Our results show that the photo-physical of solute molecules depend strongly on solute-solvent interactions and active groups in their chemical structures. In order to investigate the contribution of specific and nonspecific interactions on the various properties of drug molecules, the linear solvation energy relationships concept is used. Moreover, charge distribution characteristics of used samples with various resonance structures in solvent environments were calculated by means of solvatochromic method. The high value of dipole moments in excited state show that local intramolecular charge transfer can occur by excitation. These results about molecular interactions can be extended to biological systems and can indicate completely the behaviors of Methotrexate and Folinic acid in polar solvents such as water in body system.

  9. Molecular Structures and Momentum Transfer Cross Sections: The Influence of the Analyte Charge Distribution

    NASA Astrophysics Data System (ADS)

    Young, Meggie N.; Bleiholder, Christian

    2017-03-01

    Structure elucidation by ion mobility spectrometry-mass spectrometry methods is based on the comparison of an experimentally measured momentum transfer cross-section to cross-sections calculated for model structures. Thus, it is imperative that the calculated cross-section must be accurate. However, it is not fully understood how important it is to accurately model the charge distribution of an analyte ion when calculating momentum transfer cross-sections. Here, we calculate and compare momentum transfer cross-sections for carbon clusters that differ in mass, charge state, and mode of charge distribution, and vary temperature and polarizability of the buffer gas. Our data indicate that the detailed distribution of the ion charge density is intimately linked to the contribution of glancing collisions to the momentum transfer cross-section. The data suggest that analyte ions with molecular mass 3 kDa or momentum transfer cross-section 400-500 Å2 would be significantly influenced by the charge distribution in nitrogen buffer gas. Our data further suggest that accurate structure elucidation on the basis of IMS-MS data measured in nitrogen buffer gas must account for the molecular charge distribution even for systems as large as C960 ( 12 kDa) when localized charges are present and/or measurements are conducted under cryogenic temperatures. Finally, our data underscore that accurate structure elucidation is unlikely if ion mobility data recorded in one buffer gas is converted into other buffer gases when electronic properties of the buffer gases differ.

  10. Spectroscopy of equilibrium and nonequilibrium charge transfer in semiconductor quantum structures

    NASA Astrophysics Data System (ADS)

    Rössler, C.; Burkhard, S.; Krähenmann, T.; Röösli, M.; Märki, P.; Basset, J.; Ihn, T.; Ensslin, K.; Reichl, C.; Wegscheider, W.

    2014-08-01

    We investigate equilibrium and nonequilibrium charge-transfer processes by performing high-resolution transport spectroscopy. Using electrostatically defined quantum dots for energy-selective emission and detection, we achieved very high 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 hΓ 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 hΓ≫kBT. By performing spectroscopy below the Fermi energy, we furthermore observe elastic and inelastic transfer of holes.

  11. Deep-hole transfer leads to ultrafast charge migration in DNA hairpins

    NASA Astrophysics Data System (ADS)

    Renaud, Nicolas; Harris, Michelle A.; Singh, Arunoday P. N.; Berlin, Yuri A.; Ratner, Mark A.; Wasielewski, Michael R.; Lewis, Frederick D.; Grozema, Ferdinand C.

    2016-11-01

    Charge transport through the DNA double helix is of fundamental interest in chemistry and biochemistry, but also has potential technological applications such as for DNA-based nanoelectronics. For the latter, it is of considerable interest to explore ways to influence or enhance charge transfer. In this Article we demonstrate a new mechanism for DNA charge transport, namely ‘deep-hole transfer’, which involves long-range migration of a hole through low-lying electronic states of the nucleobases. Here, we demonstrate, in a combined experimental and theoretical study, that it is possible to achieve such transfer behaviour by changing the energetics of charge injection. This mechanism leads to an enhancement in transfer rates by up to two orders of magnitude and much weaker distance dependence. This transfer is faster than relaxation to the lowest-energy state, setting this mechanism apart from those previously described. This opens up a new direction to optimize charge transfer in DNA with unprecedented charge-transfer rates.

  12. Proton transfer to charged platinum electrodes. A molecular dynamics trajectory study.

    PubMed

    Wilhelm, Florian; Schmickler, Wolfgang; Spohr, Eckhard

    2010-05-05

    A recently developed empirical valence bond (EVB) model for proton transfer on Pt(111) electrodes (Wilhelm et al 2008 J. Phys. Chem. C 112 10814) has been applied in molecular dynamics (MD) simulations of a water film in contact with a charged Pt surface. A total of seven negative surface charge densities σ between -7.5 and -18.9 µC cm(-2) were investigated. For each value of σ, between 30 and 84 initial conditions of a solvated proton within a water slab were sampled, and the trajectories were integrated until discharge of a proton occurred on the charged surfaces. We have calculated the mean rates for discharge and for adsorption of solvated protons within the adsorbed water layer in contact with the metal electrode as a function of surface charge density. For the less negative values of σ we observe a Tafel-like exponential increase of discharge rate with decreasing σ. At the more negative values this exponential increase levels off and the discharge process is apparently transport limited. Mechanistically, the Tafel regime corresponds to a stepwise proton transfer: first, a proton is transferred from the bulk into the contact water layer, which is followed by transfer of a proton to the charged surface and concomitant discharge. At the more negative surface charge densities the proton transfer into the contact water layer and the transfer of another proton to the surface and its discharge occur almost simultaneously.

  13. Time delay and integration detectors using charge transfer devices

    NASA Astrophysics Data System (ADS)

    McCann, D. H.; White, M. H.; Turly, A. P.

    1981-07-01

    An imaging system comprises a multi-channel matrix array of CCD devices wherein a number of sensor cells (pixels) in each channel are subdivided and operated in discrete intercoupled groups of subarrays with a readout CCD shift register terminating each end of the channels. Clock voltages, applied to the subarrays, selectively cause charge signal flow in each subarray in either direction independent of the other subarrays. By selective application of four phase clock voltages, either one, two or all three of the sections subarray sections cause charge signal flow in one direction, while the remainder cause charge signal flow in the opposite direction. This creates a form of selective electronic exposure control which provides an effective variable time delay and integration of three, six or nine sensor cells or integration stages. The device is constructed on a semiconductor sustrate with a buried channel and is adapted for front surface imaging through transparent doped tin oxide gates.

  14. Charging characteristics of materials: Comparison of experimental results with simple analytical models

    NASA Technical Reports Server (NTRS)

    Purvis, C. K.; Stevens, N. J.; Oglebay, J. C.

    1977-01-01

    An understanding of the behavior of materials, of dielectrics in particular, under charged particle bombardment is essential to the prediction and prevention of the adverse effects of spacecraft charging. A one-dimensional model for charging of samples in a test facility was used in conjunction with experimental data taken to develop "material charging characteristics" for silvered Teflon. These characteristics were then used in a one-dimensional model for charging in space to examine expected response. Relative charging rates as well as relative charging levels for silvered Teflon and metal are discussed.

  15. Charge transfer emission in coumarin 343 sensitized TiO{sub 2} nanoparticle: A direct measurement of back electron transfer

    SciTech Connect

    Ghosh, H.N.

    1999-11-25

    Electron injection and back electron transfer dynamics in coumarin 343 (C-343) adsorbed on TiO{sub 2} nanoparticles are studied by picosecond transient absorption and time-resolved fluorescence spectroscopy. The direct detection of electrons in the nanoparticles and the parent cation are monitored using picosecond transient absorption spectroscopy, and the corresponding dynamics of the adsorbate are monitored by time-resolved absorption spectra of the cation radical of C-343 in the visible region. When the electron returns from the nanoparticles to the present cation, a low quantum yield red-shifted charge transfer emission is observed. Measuring the charge transfer emission lifetimes by a picosecond time-resolved fluorimeter, the author gets an exact rate of back electron transfer reaction from the nanoparticle to the parent cation.

  16. Photoemission Experiments for Charge Characteristics of Individual Dust Grains

    NASA Technical Reports Server (NTRS)

    Abbas, M. M.; Craven, P. D.; Spann, J. F.; West, E.; Pratico, J.; Tankosic, D.; Venturini, C. C.; Six, N. Frank (Technical Monitor)

    2001-01-01

    Photoemission experiments with UV radiation have been performed to investigate the microphysics and charge characteristics of individual isolated dust grains of various compositions and sizes by using the electrodynamic balance facility at NASA Marshall Space Flight Center. Dust particles of 2-10 gm diameter are levitated in a vacuum chamber at pressures approximately 10(exp-5) torr and exposed to a collimated beam of UV radiation in the 120-200 nm spectral range from a deuterium lamp source with a MgF2 window. A monochromator is used to select the UV wavelength with a spectral resolution of 8 nm. The electrodynamic facility permits measurements of the charge and diameters of particles of known composition, and monitoring of photoemission rates with the incident UV radiation. Experiments have been conducted on test particles of silica and polystyrene to determine the photoelectric yields and surface equilibrium potentials when exposed to UV radiation. A brief description of an experimental procedure for photoemission studies is given and some preliminary laboratory measurements of the photoelectric yields of individual dust particles are presented.

  17. Photoemission Experiments for Charge Characteristics of Individual Dust Grains

    NASA Technical Reports Server (NTRS)

    Abbas, M. M.; Spann, James F., Jr.; Craven, Paul D.; West, E.; Pratico, Jared; Scheianu, D.; Tankosic, D.; Venturini, C. C.; Whitaker, Ann F. (Technical Monitor)

    2001-01-01

    Photoemission experiments with UV radiation have been performed to investigate the microphysics and charge characteristics of individual isolated dust grains of various compositions and sizes by using the electrodynamic balance facility at NASA Marshall Space Flight Center. Dust particles of 1 - 100 micrometer diameter are levitated in a vacuum chamber at pressures approx. 10(exp -5) torr and exposed to a collimated beam of UV radiation in the 120-300 nanometers spectral range from a deuterium lamp source with a MgF2 window. A monochromator is used to select the UV radiation wavelength with a spectral resolution of 8 nanometers. The electrodynamic facility permits measurements of the charge and diameters of particles of known composition, and monitoring of photoemission rates with the incident UV radiation. Experiments have been conducted on Al2O3 and silicate particles, and in particular on JSC-1 Mars regolith simulants, to determine the photoelectron yields and surface equilibrium potentials of dust particles when exposed to UV radiation in the 120-250 micrometers spectral range. A brief discussion of the experimental procedure, the results of photoemission experiments, and comparisons with theoretical models will be presented.

  18. The simplest equivalent circuit of a pulsed dielectric barrier discharge and the determination of the gas gap charge transfer

    NASA Astrophysics Data System (ADS)

    Pipa, A. V.; Koskulics, J.; Brandenburg, R.; Hoder, T.

    2012-11-01

    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 qmax, and (iii) the development of a graphical method for the determination of qmax from charge-voltage characteristics (Q-V plots, often referred as Lissajous figures) measured under pulsed excitation. The method of graphical presentation of qmax is demonstrated with an example of a Q-V plot measured under pulsed excitation. The relations between the discharge current jR(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 Cd. Whereas for quantitative evaluation of electrical measurements, the accurate estimation of the Cd is important.

  19. 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.

  20. 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

  1. [Combined hopping-superexchange mechanism of charge transfer in DNA; a model with nearest interactions].

    PubMed

    Lakhno, V D; Sultanov, V B

    2007-01-01

    In the framework of the earlier developed combined hopping-superexchange mechanism of charge transfer in DNA, a model with all nearest interactions between nucleobases is proposed. It is shown that the transfer rates for various types of nucleotide sequences calculated within this model are in a good agreement with experimental data.

  2. 33 CFR 127.301 - Persons in charge of shoreside transfer operations: Qualifications and certification.

    Code of Federal Regulations, 2010 CFR

    2010-07-01

    ... LNG may not use the services of any person, as a person in charge of shoreside transfer operations, unless that person— (1) Has at least 48 hours of LNG transfer experience; (2) Knows the hazards of LNG... at the waterfront facility handling LNG....

  3. 33 CFR 127.301 - Persons in charge of shoreside transfer operations: Qualifications and certification.

    Code of Federal Regulations, 2012 CFR

    2012-07-01

    ... LNG may not use the services of any person, as a person in charge of shoreside transfer operations, unless that person— (1) Has at least 48 hours of LNG transfer experience; (2) Knows the hazards of LNG... at the waterfront facility handling LNG....

  4. 33 CFR 127.301 - Persons in charge of shoreside transfer operations: Qualifications and certification.

    Code of Federal Regulations, 2011 CFR

    2011-07-01

    ... LNG may not use the services of any person, as a person in charge of shoreside transfer operations, unless that person— (1) Has at least 48 hours of LNG transfer experience; (2) Knows the hazards of LNG... at the waterfront facility handling LNG....

  5. 33 CFR 127.301 - Persons in charge of shoreside transfer operations: Qualifications and certification.

    Code of Federal Regulations, 2014 CFR

    2014-07-01

    ... LNG may not use the services of any person, as a person in charge of shoreside transfer operations, unless that person— (1) Has at least 48 hours of LNG transfer experience; (2) Knows the hazards of LNG... at the waterfront facility handling LNG....

  6. 33 CFR 127.301 - Persons in charge of shoreside transfer operations: Qualifications and certification.

    Code of Federal Regulations, 2013 CFR

    2013-07-01

    ... LNG may not use the services of any person, as a person in charge of shoreside transfer operations, unless that person— (1) Has at least 48 hours of LNG transfer experience; (2) Knows the hazards of LNG... at the waterfront facility handling LNG....

  7. Review on charge transfer and chemical activity of TiO2: Mechanism and applications

    NASA Astrophysics Data System (ADS)

    Cai, Yongqing; Feng, Yuan Ping

    2016-12-01

    Charge separation and transfer at the interface between two materials play a significant role in various atomic-scale processes and energy conversion systems. In this review, we present the mechanism and outcome of charge transfer in TiO2, which is extensively explored for photocatalytic applications in the field of environmental science. We list several experimental and computational methods to estimate the amount of charge transfer. The effects of the work function, defects and doping, and employment of external electric field on modulating the charge transfer are presented. The interplay between the band bending and carrier transport across the surface and interface consisting of TiO2 is discussed. We show that the charge transfer can also strongly affect the behavior of deposited nanoparticles on TiO2 through built-in electric field that it creates. This review encompasses several advances of composite materials where TiO2 is combined with two-dimensional materials like graphene, MoS2, phosphorene, etc. The charge transport in the TiO2-organohalide perovskite with respect to the electron-hole separation at the interface is also discussed.

  8. Giant quantum Hall plateaus generated by charge transfer in epitaxial graphene

    PubMed Central

    Alexander-Webber, J. A.; Huang, J.; Maude, D. K.; Janssen, T. J. B. M.; Tzalenchuk, A.; Antonov, V.; Yager, T.; Lara-Avila, S.; Kubatkin, S.; Yakimova, R.; Nicholas, R. J.

    2016-01-01

    Epitaxial graphene has proven itself to be the best candidate for quantum electrical resistance standards due to its wide quantum Hall plateaus with exceptionally high breakdown currents. However one key underlying mechanism, a magnetic field dependent charge transfer process, is yet to be fully understood. Here we report measurements of the quantum Hall effect in epitaxial graphene showing the widest quantum Hall plateau observed to date extending over 50 T, attributed to an almost linear increase in carrier density with magnetic field. This behaviour is strong evidence for field dependent charge transfer from charge reservoirs with exceptionally high densities of states in close proximity to the graphene. Using a realistic framework of broadened Landau levels we model the densities of donor states and predict the field dependence of charge transfer in excellent agreement with experimental results, thus providing a guide towards engineering epitaxial graphene for applications such as quantum metrology. PMID:27456765

  9. Altering intra- to inter-molecular hydrogen bonding by dimethylsulfoxide: A TDDFT study of charge transfer for coumarin 343

    NASA Astrophysics Data System (ADS)

    Liu, Xiaochun; Yin, Hang; Li, Hui; Shi, Ying

    2017-04-01

    DFT and TDDFT methods were carried out to investigate the influences of intramolecular and intermolecular hydrogen bonding on excited state charge transfer for coumarin 343 (C343). Intramolecular hydrogen bonding is formed between carboxylic acid group and carbonyl group in C343 monomer. However, in dimethylsulfoxide (DMSO) solution, DMSO 'opens up' the intramolecular hydrogen bonding and forms solute-solvent intermolecular hydrogen bonded C343-DMSO complex. Analysis of frontier molecular orbitals reveals that intramolecular charge transfer (ICT) occurs in the first excited state both for C343 monomer and complex. The results of optimized geometric structures indicate that the intramolecular hydrogen bonding interaction is strengthened while the intermolecular hydrogen bonding is weakened in excited state, which is confirmed again by monitoring the shifts of characteristic peaks of infrared spectra. We demonstrated that DMSO solvent can not only break the intramolecular hydrogen bonding to form intermolecular hydrogen bonding with C343 but also alter the mechanism of excited state hydrogen bonding strengthening.

  10. Oxygen Transfer Characteristics of Miniaturized Bioreactor Systems

    PubMed Central

    Kirk, Timothy V; Szita, Nicolas

    2013-01-01

    Since their introduction in 2001 miniaturized bioreactor systems have made great advances in function and performance. In this article the dissolved oxygen (DO) transfer performance of submilliliter microbioreactors, and 1–10 mL minibioreactors was examined. Microbioreactors have reached kLa values of 460 h-1, and are offering instrumentation and some functionality comparable to production systems, but at high throughput screening volumes. Minibioreactors, aside from one 1,440 h-1 kLa system, have not offered as high rates of DO transfer, but have demonstrated superior integration with automated fluid handling systems. Microbioreactors have been typically limited to studies with E. coli, while minibioreactors have offered greater versatility in this regard. Further, mathematical relationships confirming the applicability of kLa measurements across all scales have been derived, and alternatives to fluorescence lifetime DO sensors have been evaluated. Finally, the influence on reactor performance of oxygen uptake rate (OUR), and the possibility of its real-time measurement have been explored. Biotechnol. Bioeng. 2013; 110: 1005–1019. © 2012 Wiley Periodicals, Inc. PMID:23280578

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

    SciTech Connect

    Soniat, Marielle; Rick, Steven W.

    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.

  12. Analysis of incomplete charge transfer effects in a CMOS image sensor

    NASA Astrophysics Data System (ADS)

    Liqiang, Han; Suying, Yao; Jiangtao, Xu; Chao, Xu; Zhiyuan, Gao

    2013-05-01

    A method to judge complete charger transfer is proposed for a four-transistor CMOS image sensor with a large pixel size. Based on the emission current theory, a qualitative photoresponse model is established to the preliminary prediction. Further analysis of noise for incomplete charge transfer predicts the noise variation. The test pixels were fabricated in a specialized 0.18 μm CMOS image sensor process and two different processes of buried N layer implantation are compared. The trend prediction corresponds with the test results, especially as it can distinguish an unobvious incomplete charge transfer. The method helps us judge whether the charge transfer time satisfies the requirements of the readout circuit for the given process especially for pixels of a large size.

  13. Spectrophotometric study of the charge transfer complexation of some porphyrin derivatives as electron donors with tetracyanoethylene.

    PubMed

    El-Zaria, Mohamed E

    2008-01-01

    Charge transfer complexes (CTC) of 5,10,15,20-tetraphenylporphyrin (TPP), 5,10,15,20-tetra(4-tolyl)porphyrin (TTP), 5,10,15,20-tetra(4-methoxyphenyl)porphyrin (TMP), Zn-5,10,15,20-tetraphenylporphyrin (Zn-TPP), and Zn-5,10,15,20-tetra(4-tolyl)porphyrin (Zn-TTP) with tetracyanoethylene (TCNE) have been studied at various temperatures in CH(2)Cl(2) and CCl(4). The data are discussed in terms of equilibrium constant (K(CT)), molar extinction coefficient (epsilon(CT)), thermodynamic standard reaction quantities (DeltaG degrees , DeltaH degrees and DeltaS degrees ), oscillator strength (f), and transition dipole moment (mu). The spectrum obtained for TPP/TCNE, TTP/TCNE, and TMP/TCNE systems shows two main absorption bands at 475 and 690nm, which are not due to the absorption of any of the reactants. These bands are characteristic of an intermolecular charge transfer involving the overlap of the lowest unoccupied molecular orbital (LUMO) of the acceptor with the highest occupied molecular orbital (HOMO) of the donor. The results reveal that the interaction between the donors and acceptor is due to pi-pi(*) transitions by the formation of radical ion pairs. The stoichiometry of the complexes was found to be 1:1 ratio by the Job and straight line methods between donors and acceptor with the maximum absorption bands at wavelengths of 475 and 690nm. The observed data show salvation effects on the spectral and thermodynamics properties of CTC. The ionization potential of the donors and the dissociation energy of the CTC were also determined and are found to be constant.

  14. Spectrophotometric study of the charge transfer complexation of some porphyrin derivatives as electron donors with tetracyanoethylene

    NASA Astrophysics Data System (ADS)

    El-Zaria, Mohamed E.

    2008-01-01

    Charge transfer complexes (CTC) of 5,10,15,20-tetraphenylporphyrin (TPP), 5,10,15,20-tetra(4-tolyl)porphyrin (TTP), 5,10,15,20-tetra(4-methoxyphenyl)porphyrin (TMP), Zn-5,10,15,20-tetraphenylporphyrin (Zn-TPP), and Zn-5,10,15,20-tetra(4-tolyl)porphyrin (Zn-TTP) with tetracyanoethylene (TCNE) have been studied at various temperatures in CH 2Cl 2 and CCl 4. The data are discussed in terms of equilibrium constant ( KCT), molar extinction coefficient ( ɛCT), thermodynamic standard reaction quantities (Δ G°, Δ H° and Δ S°), oscillator strength ( f), and transition dipole moment ( μ). The spectrum obtained for TPP/TCNE, TTP/TCNE, and TMP/TCNE systems shows two main absorption bands at 475 and 690 nm, which are not due to the absorption of any of the reactants. These bands are characteristic of an intermolecular charge transfer involving the overlap of the lowest unoccupied molecular orbital (LUMO) of the acceptor with the highest occupied molecular orbital (HOMO) of the donor. The results reveal that the interaction between the donors and acceptor is due to π-π * transitions by the formation of radical ion pairs. The stoichiometry of the complexes was found to be 1:1 ratio by the Job and straight line methods between donors and acceptor with the maximum absorption bands at wavelengths of 475 and 690 nm. The observed data show salvation effects on the spectral and thermodynamics properties of CTC. The ionization potential of the donors and the dissociation energy of the CTC were also determined and are found to be constant.

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

    NASA Astrophysics Data System (ADS)

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

    2016-10-01

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

  16. Ultrafast charge transfer in nickel phthalocyanine probed by femtosecond Raman-induced Kerr effect spectroscopy.

    PubMed

    Balakrishnan, Gurusamy; Soldatova, Alexandra V; Reid, Philip J; Spiro, Thomas G

    2014-06-18

    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 ν10 (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.

  17. Hyperbolic metamaterial nanostructures to tune charge-transfer dynamics (Conference Presentation)

    NASA Astrophysics Data System (ADS)

    Lee, Kwang Jin; Xiao, Yiming; Woo, Jae Heun; Kim, Eun Sun; Kreher, David; Attias, André-Jean; Mathevet, Fabrice; Ribierre, Jean-Charles; Wu, Jeong Weon; André, Pascal

    2016-09-01

    Charge transfer (CT) is an essential phenomenon relevant to numerous fields including biology, physics and chemistry.1-5 Here, we demonstrate that multi-layered hyperbolic metamaterial (HMM) substrates alter organic semiconductor CT dynamics.6 With triphenylene:perylene diimide dyad supramolecular self-assemblies prepared on HMM substrates, we show that both charge separation (CS) and charge recombination (CR) characteristic times are increased by factors of 2.5 and 1.6, respectively, resulting in longer-lived CT states. We successfully rationalize the experimental data by extending Marcus theory framework with dipole image interactions tuning the driving force. The number of metal-dielectric pairs alters the HMM interfacial effective dielectric constant and becomes a solid analogue to solvent polarizability. Based on the experimental results and extended Marcus theory framework, we find that CS and CR processes are located in normal and inverted regions on Marcus parabola diagram, respectively. The model and further PH3T:PCBM data show that the phenomenon is general and that molecular and substrate engineering offer a wide range of kinetic tailoring opportunities. This work opens the path toward novel artificial substrates designed to control CT dynamics with potential applications in fields including optoelectronics, organic solar cells and chemistry. 1. Marcus, Rev. Mod. Phys., 1993, 65, 599. 2. Marcus, Phys. Chem. Chem. Phys., 2012, 14, 13729. 3. Lambert, et al., Nat. Phys., 2012, 9, 10. 4. C. Clavero, Nat. Photon., 2014, 8, 95. 5. A. Canaguier-Durand, et al., Angew. Chem. Int. Ed., 2013, 52, 10533. 6. K. J. Lee, et al., Submitted, 2015, arxiv.org/abs/1510.08574.

  18. Charge-Transfer Dynamics of Fluorescent Dye-Sensitized Electrodes under Applied Biases.

    PubMed

    Godin, Robert; Sherman, Benjamin D; Bergkamp, Jesse J; Chesta, Carlos A; Moore, Ana L; Moore, Thomas A; Palacios, Rodrigo E; Cosa, Gonzalo

    2015-07-16

    The development of dye-sensitized solar cells requires an in-depth understanding of the interfacial charge-transfer dynamics that take place between dye sensitizers and semiconductors. Here, we describe a prototype system to probe these dynamics by monitoring in real time the fluorescence of two organic sensitizers, a perylene and a squaraine, bound to a SnO2 semiconductor thin film as a function of potentiostatic control of the Fermi level. The two different sensitizer fluorophores characterized by vastly different redox potentials undergo similar fluorescence modulation with applied bias, an indication that the density of states of the semiconductor largely influences the charge-transfer dynamics while energetics play a minimal role. We further show that the rate of photodegradation of the perylene sensitizer with applied bias provides a suitable marker to study the rate of charge injection and charge recombination. Taken together, our results demonstrate a suitable platform to visualize and study charge-transfer dynamics on films and constitute a step toward achieving single-molecule resolution in our quest to decipher the static and dynamic heterogeneity of charge-transfer dynamics in dye-sensitized photoanodes.

  19. Characteristics and Development of Children with CHARGE Association/Syndrome

    ERIC Educational Resources Information Center

    Salem-Hartshorne, Nancy; Jacob, Susan

    2004-01-01

    CHARGE association/syndrome refers to a group of congenital anomalies occurring together more often than chance. Parents of children with CHARGE were surveyed and asked to indicate whether their child had various features commonly found among individuals with CHARGE (e.g., vision or hearing impairment) and to complete an adaptive behavior scale…

  20. Characteristics And Development Of Children With CHARGE Association-Syndrome

    ERIC Educational Resources Information Center

    Salem-Hartshorne, Nancy; Jacob, Susan

    2004-01-01

    CHARGE association-syndrome refers to a group of congenital anomalies occurring together more often than chance. Parents of children with CHARGE were surveyed and asked to indicate whether their child had various features commonly found among individuals with CHARGE (e.g., vision or hearing impairment) and to complete an adaptive behavior scale…

  1. 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.

  2. 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

  3. Ultrafast charge- and energy-transfer dynamics in conjugated polymer: cadmium selenide nanocrystal blends.

    PubMed

    Morgenstern, Frederik S F; Rao, Akshay; Böhm, Marcus L; Kist, René J P; Vaynzof, Yana; Greenham, Neil C

    2014-02-25

    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.

  4. 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.

  5. Spectrophotometric study of the charge transfer complex between 2-amino-4-picoline with chloranilic acid

    NASA Astrophysics Data System (ADS)

    Alghanmi, Reem M.; Al-Attas, Amirah S.; Habeeb, Moustafa M.

    2013-02-01

    Charge transfer complex formation between 2-amino-4-picoline (2A4P) as the electron donor with chloranilic acid (CLA) as the electron acceptor has been studied spectrophotometrically in different polar solvents included acetone (AcN), ethanol (EtOH) and acetonitrile (AN). The molecular composition of the formed complex was recognized utilizing Job's, photometric and conductometric titration methods to be 1:1. The formation constants and molecular extinction coefficients were estimated using Benesi-Hildebrand equation; they recorded high values confirming high stability of the formed complex. Moreover, the results showed that the complex is more stable in acetone with lower electric permittivity compared with ethanol or acetonitrile of higher ones. The values of some spectroscopic physical parameters like oscillator strength f, transition dipole moment μ, resonance energy RN, charge transfer energy ECT, dissociation energy W, ionization potential IP and standard free energy ΔGo were determined and evaluated. The solid complex was isolated and its molecular composition was determined by elemental analysis to be 1:1. Furthermore, the solid complex was characterized using FTIR and 1H NMR measurements. They confirmed the presence of proton transfer beside charge transfer in the obtained complex. Molecular orbital calculations utilizing GAMESS computations were carried out to predict infrared spectra. They also confirmed the presence of proton transfer beside charge transfer in the formed complex.

  6. The Characteristic of Residual Charge for Water-tree Degraded XLPE and the Measurement Method

    NASA Astrophysics Data System (ADS)

    Ebinuma, Yasumitsu; Masui, Noriaki

    Recently the measurement of residual charge has been studying as insulation deterioration diagnosis of XLPE insulated cables. Authors have studied the measurement process and the charge characteristic. The specimens are XLPE sheets of 1mm which are degraded with water-trees. There are four processes of charge removal, charge injection, ground and charge release in the measurement. The process of charge removal was introduced to measure a little charge successfully. In the process of charge injection, it was confirmed that the relation between the applied dc voltage and the charge was examined, and the higher dc voltage was, more the charge was. In addition, it has been showed that the applied process of the dc voltage greatly influences the measured charge. In the process of ground, the grounding period is changed and the charge is measured. It has been showed that the grounding period doesn't influence the measured charge greatly. In the process of charge release, the frequency and the period of applied ac voltage were changed and the charge was measured. It has been showed that neither the frequency nor the period of ac voltage greatly influence the charge measured. In addition, the dc voltage was superimposed to ac voltage, and the charge was measured. It has been showed that the charge measured changes greatly even if the dc voltage is low. The method of the insulation deterioration measurement of cable was examined from these results, and the measurement conditions and a newer method were suggested.

  7. Charge transfer and electronic doping in nitrogen-doped graphene

    PubMed Central

    Joucken, Frédéric; Tison, Yann; Le Fèvre, Patrick; Tejeda, Antonio; Taleb-Ibrahimi, Amina; Conrad, Edward; Repain, Vincent; Chacon, Cyril; Bellec, Amandine; Girard, Yann; Rousset, Sylvie; Ghijsen, Jacques; Sporken, Robert; Amara, Hakim; Ducastelle, François; Lagoute, Jérôme

    2015-01-01

    Understanding the modification of the graphene’s electronic structure upon doping is crucial for enlarging its potential applications. We present a study of nitrogen-doped graphene samples on SiC(000) combining angle-resolved photoelectron spectroscopy, scanning tunneling microscopy and spectroscopy and X-ray photoelectron spectroscopy (XPS). The comparison between tunneling and angle-resolved photoelectron spectra reveals the spatial inhomogeneity of the Dirac energy shift and that a phonon correction has to be applied to the tunneling measurements. XPS data demonstrate the dependence of the N 1s binding energy of graphitic nitrogen on the nitrogen concentration. The measure of the Dirac energy for different nitrogen concentrations reveals that the ratio usually computed between the excess charge brought by the dopants and the dopants’ concentration depends on the latter. This is supported by a tight-binding model considering different values for the potentials on the nitrogen site and on its first neighbors. PMID:26411651

  8. Precursor charge state prediction for electron transfer dissociation tandem mass spectra.

    PubMed

    Sharma, Vagisha; Eng, Jimmy K; Feldman, Sergey; von Haller, Priska D; MacCoss, Michael J; Noble, William S

    2010-10-01

    Electron-transfer dissociation (ETD) induces fragmentation along the peptide backbone by transferring an electron from a radical anion to a protonated peptide. In contrast with collision-induced dissociation, side chains and modifications such as phosphorylation are left intact through the ETD process. Because the precursor charge state is an important input to MS/MS sequence database search tools, the ability to accurately determine the precursor charge is helpful for the identification process. Furthermore, because ETD can be applied to large, highly charged peptides, the need for accurate precursor charge state determination is magnified. Otherwise, each spectrum must be searched repeatedly using a large range of possible precursor charge states. To address this problem, we have developed an ETD charge state prediction tool based on support vector machine classifiers that is demonstrated to exhibit superior classification accuracy while minimizing the overall number of predicted charge states. The tool is freely available, open source, cross platform compatible, and demonstrated to perform well when compared with an existing charge state prediction tool. The program is available from http://code.google.com/p/etdz/.

  9. Charge transfer and mobility enhancement at CdO/SnTe heterointerfaces

    SciTech Connect

    Nishitani, Junichi; Yu, Kin Man; Walukiewicz, Wladek

    2014-09-29

    We report a study of the effects of charge transfer on electrical properties of CdO/SnTe heterostructures. A series of structures with variable SnTe thicknesses were deposited by RF magnetron sputtering. Because of an extreme type III band offset with the valence band edge of SnTe located at 1.5 eV above the conduction band edge of CdO, a large charge transfer is expected at the interface of the CdO/SnTe heterostructure. The electrical properties of the heterostructures are analyzed using a multilayer charge transport model. The analysis indicates a large 4-fold enhancement of the CdO electron mobility at the interface with SnTe. The mobility enhancement is attributed to reduction of the charge center scattering through neutralization of the donor-like defects responsible for the Fermi level pinning at the CdO/SnTe interface.

  10. NEW APPROACHES: Students' understanding of the transfer of charge between conductors

    NASA Astrophysics Data System (ADS)

    Guruswamy, Chitra; Somers, Mark D.; Hussey, R. G.

    1997-03-01

    This paper describes an investigation into students' understanding of the transfer of charge between two charged conductors. The research is based on interviews conducted with students in an algebra and trigonometry based physics course and on written tests administered both before and after instruction. Results from two tasks are reported, both of which involve a pair of identical conductors that are given an initial charge, are made to touch each other and are then separated. The test was also administered as a post test to other populations at the pre-college and college levels. It was found that a considerable number of students from the eighth grader to the college student in an advanced physics course were unable to predict the transfer of charge correctly from one conductor to another. Implications for instruction are also discussed.

  11. Charge transfer in strongly correlated systems: an exact diagonalization approach to model Hamiltonians.

    PubMed

    Schöppach, Andreas; Gnandt, David; Koslowski, Thorsten

    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' π 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.

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

    SciTech Connect

    Schöppach, Andreas; Gnandt, David; Koslowski, Thorsten

    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' π 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.

  13. Spectrophotometric study of the charge-transfer complexes of iodine with antipyrine in organic solvents

    NASA Astrophysics Data System (ADS)

    Hasani, Masoumeh; Rezaei, Alireza

    2006-12-01

    The charge-transfer complex formation of iodine with antipyrine has been studied spectrophotometrically in chloroform, dichloromethane (DCM) and 1,2-dichloroethane (DCE) solutions at 25 °C. The results indicate the formation of 1:1 charge-transfer complexes. The observed time dependence of the charge-transfer band and subsequent formation of I 3- in solution were related to the slow transformation of the initially formed 1:1 antipyrine:I 2 outer complex to an inner electron donor-acceptor (EDA) complex, followed by fast reaction of the inner complex with iodine to form a triiodide ion. The values of the equilibrium constant, K, are calculated for each complex and the influence of the solvent properties on the formation of EDA complexes and the rates of subsequent reaction is evaluated.

  14. Spectrophotometric study of the charge-transfer complexes of iodine with antipyrine in organic solvents.

    PubMed

    Hasani, Masoumeh; Rezaei, Alireza

    2006-12-01

    The charge-transfer complex formation of iodine with antipyrine has been studied spectrophotometrically in chloroform, dichloromethane (DCM) and 1,2-dichloroethane (DCE) solutions at 25 degrees C. The results indicate the formation of 1:1 charge-transfer complexes. The observed time dependence of the charge-transfer band and subsequent formation of I(3)(-) in solution were related to the slow transformation of the initially formed 1:1 antipyrine:I(2) outer complex to an inner electron donor-acceptor (EDA) complex, followed by fast reaction of the inner complex with iodine to form a triiodide ion. The values of the equilibrium constant, K, are calculated for each complex and the influence of the solvent properties on the formation of EDA complexes and the rates of subsequent reaction is evaluated.

  15. Engineering the Charge Transfer in all 2D Graphene-Nanoplatelets Heterostructure Photodetectors

    PubMed Central

    Robin, A.; Lhuillier, E.; Xu, X. Z.; Ithurria, S.; Aubin, H.; Ouerghi, A.; Dubertret, B.

    2016-01-01

    Two dimensional layered (i.e. van der Waals) heterostructures open up great prospects, especially in photodetector applications. In this context, the control of the charge transfer between the constituting layers is of crucial importance. Compared to bulk or 0D system, 2D materials are characterized by a large exciton binding energy (0.1–1 eV) which considerably affects the magnitude of the charge transfer. Here we investigate a model system made from colloidal 2D CdSe nanoplatelets and epitaxial graphene in a phototransistor configuration. We demonstrate that using a heterostructured layered material, we can tune the magnitude and the direction (i.e. electron or hole) of the charge transfer. We further evidence that graphene functionalization by nanocrystals only leads to a limited change in the magnitude of the 1/f noise. These results draw some new directions to design van der Waals heterostructures with enhanced optoelectronic properties. PMID:27143413

  16. Charge transfer and excitation in H++CH3 collisions below 10keV

    NASA Astrophysics Data System (ADS)

    Nagao, Masatoshi; Hida, Ken-Nosuke; Kimura, Mineo; Rai, Sachchida N.; Liebermann, Heinz-Peter; Buenker, Robert J.; Suno, Hiroya; Stancil, Phillip C.

    2008-07-01

    Charge transfer and electronic excitation in collisions of H+ ions with CH3 from a few tens of eV up to 10keV are theoretically investigated. The adiabatic potential energy curves and corresponding wave functions are calculated by using the multireference single- and double-excitation configuration interaction method, and the scattering dynamics is studied based on the semiclassical impact parameter molecular-orbital close-coupling approach. Charge-transfer cross sections are found to be large and rather energy-dependent over the entire energy region studied. Electronic excitation is also energy-dependent with a sharp increase from below 10-17to10-16cm2 . Most of the molecular products produced through charge transfer or excitation are known to be unstable and undergo fragmentation producing various hydrocarbon radical species. Hence, identification of fragmented species and their production mechanism are important for spectroscopic analysis.

  17. Near resonant charge transfer in the reaction F(+) + CO - F + CO(+)

    NASA Astrophysics Data System (ADS)

    Kusunoki, I.; Ishikawa, T.

    1985-06-01

    Charge transfer reactions in the F(+) + CO system were investigated using a F(+) ion beam in the energy range 10-300 eVlab. The electronically excited product CO(+) A2Pi(i) was observed by the emission from the A-X transitions. At low collisional energy the dominant product is in the vibrational level v' = 5. The reaction cross section sigma(5) is about 1 A-sq at 12 eVc.m. and decreases with increasing collision energy. The large cross section at v' = 5 can be interpreted by near-resonant charge-transfer reactions. The rotational temperature of the product is about 300 K, which is the temperature of the reactant CO gas. For the resonant charge transfer, the translational energy is not effective, but the electronic and vibrational energy couple with each other strongly.

  18. Engineering the Charge Transfer in all 2D Graphene-Nanoplatelets Heterostructure Photodetectors

    NASA Astrophysics Data System (ADS)

    Robin, A.; Lhuillier, E.; Xu, X. Z.; Ithurria, S.; Aubin, H.; Ouerghi, A.; Dubertret, B.

    2016-05-01

    Two dimensional layered (i.e. van der Waals) heterostructures open up great prospects, especially in photodetector applications. In this context, the control of the charge transfer between the constituting layers is of crucial importance. Compared to bulk or 0D system, 2D materials are characterized by a large exciton binding energy (0.1–1 eV) which considerably affects the magnitude of the charge transfer. Here we investigate a model system made from colloidal 2D CdSe nanoplatelets and epitaxial graphene in a phototransistor configuration. We demonstrate that using a heterostructured layered material, we can tune the magnitude and the direction (i.e. electron or hole) of the charge transfer. We further evidence that graphene functionalization by nanocrystals only leads to a limited change in the magnitude of the 1/f noise. These results draw some new directions to design van der Waals heterostructures with enhanced optoelectronic properties.

  19. 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.

  20. Polyoxometalate active charge-transfer material for mediated redox flow battery

    DOEpatents

    Anderson, Travis Mark; Hudak, Nicholas; Staiger, Chad; Pratt, Harry

    2017-01-17

    Redox flow batteries including a half-cell electrode chamber coupled to a current collecting electrode are disclosed herein. In a general embodiment, a separator is coupled to the half-cell electrode chamber. The half-cell electrode chamber comprises a first redox-active mediator and a second redox-active mediator. The first redox-active mediator and the second redox-active mediator are circulated through the half-cell electrode chamber into an external container. The container includes an active charge-transfer material. The active charge-transfer material has a redox potential between a redox potential of the first redox-active mediator and a redox potential of the second redox-active mediator. The active charge-transfer material is a polyoxometalate or derivative thereof. The redox flow battery may be particularly useful in energy storage solutions for renewable energy sources and for providing sustained power to an electrical grid.

  1. Laboratory Studies of Thermal Energy Charge Transfer of Silicon and Iron Ions in Astrophysical Plasmas

    NASA Technical Reports Server (NTRS)

    Kwong, Victor H. S.

    1997-01-01

    The laser ablation/ion storage facility at the UNLV Physics Department is dedicated to the study of atomic processes in low temperature plasmas. Our current program is directed to the study of charge transfer of multiply charged ions and neutrals that are of importance to astrophysics at energies less than 1 eV (about 10(exp 4) K). Specifically, we measure the charge transfer rate coefficient of ions such as N(2+), Si(3+), Si(3+), with helium and Fe(2+) with molecular and atomic hydrogen. All these ions are found in a variety of astrophysical plasmas. Their electron transfer reactions with neutral atoms can affect the ionization equilibrium of the plasma.

  2. Fermi level pinning and the charge transfer contribution to the energy of adsorption at semiconducting surfaces

    SciTech Connect

    Krukowski, Stanisław; Kempisty, Paweł; Strak, Paweł; Sakowski, Konrad

    2014-01-28

    It is shown that charge transfer, the process analogous to formation of semiconductor p-n junction, contributes significantly to adsorption energy at semiconductor surfaces. For the processes without the charge transfer, such as molecular adsorption of closed shell systems, the adsorption energy is determined by the bonding only. In the case involving charge transfer, such as open shell systems like metal atoms or the dissociating molecules, the energy attains different value for the Fermi level differently pinned. The Density Functional Theory (DFT) simulation of species adsorption at different surfaces, such as SiC(0001) or GaN(0001) confirms these predictions: the molecular adsorption is independent on the coverage, while the dissociative process adsorption energy varies by several electronvolts.

  3. Molecular Structures and Momentum Transfer Cross Sections: The Influence of the Analyte Charge Distribution.

    PubMed

    Young, Meggie N; Bleiholder, Christian

    2017-04-01

    Structure elucidation by ion mobility spectrometry-mass spectrometry methods is based on the comparison of an experimentally measured momentum transfer cross-section to cross-sections calculated for model structures. Thus, it is imperative that the calculated cross-section must be accurate. However, it is not fully understood how important it is to accurately model the charge distribution of an analyte ion when calculating momentum transfer cross-sections. Here, we calculate and compare momentum transfer cross-sections for carbon clusters that differ in mass, charge state, and mode of charge distribution, and vary temperature and polarizability of the buffer gas. Our data indicate that the detailed distribution of the ion charge density is intimately linked to the contribution of glancing collisions to the momentum transfer cross-section. The data suggest that analyte ions with molecular mass ~3 kDa or momentum transfer cross-section 400-500 Å(2) would be significantly influenced by the charge distribution in nitrogen buffer gas. Our data further suggest that accurate structure elucidation on the basis of IMS-MS data measured in nitrogen buffer gas must account for the molecular charge distribution even for systems as large as C960 (~12 kDa) when localized charges are present and/or measurements are conducted under cryogenic temperatures. Finally, our data underscore that accurate structure elucidation is unlikely if ion mobility data recorded in one buffer gas is converted into other buffer gases when electronic properties of the buffer gases differ. Graphical Abstract ᅟ.

  4. Violation of detailed balance for charge-transfer statistics in Coulomb-blockade systems

    NASA Astrophysics Data System (ADS)

    Stegmann, Philipp; König, Jürgen

    2017-03-01

    We discuss the possibility to generate in Coulomb-blockade systems steady states that violate detailed balance. This includes both voltage biased and non-biased scenarios. The violation of detailed balance yields that the charge-transfer statistics for electrons tunneling into an island experiencing strong Coulomb interaction is different from the statistics for tunneling out. This can be experimentally tested by time-resolved measurement of the island's charge state. We demonstrate this claim for two model systems.

  5. Proton-Coupled Electron Transfer: Moving Together and Charging Forward

    PubMed Central

    2016-01-01

    Proton-coupled electron transfer (PCET) is ubiquitous throughout chemistry and biology. This Perspective discusses recent advances and current challenges in the field of PCET, with an emphasis on the role of theory and computation. The fundamental theoretical concepts are summarized, and expressions for rate constants and kinetic isotope effects are provided. Computational methods for calculating reduction potentials and pKa’s for molecular electrocatalysts, as well as insights into linear correlations and non-innocent ligands, are also described. In addition, computational methods for simulating the nonadiabatic dynamics of photoexcited PCET are discussed. Representative applications to PCET in solution, proteins, electrochemistry, and photoinduced processes are presented, highlighting the interplay between theoretical and experimental studies. The current challenges and suggested future directions are outlined for each type of application, concluding with an overall view to the future. PMID:26110700

  6. Heat transfer characteristics of a linear solar collector.

    PubMed

    Seraphin, B O

    1973-02-01

    The heat transfer characteristics of a linear solar energy collector are calculated as functions of dimensions, spectral quality of the selective absorber surface, optical flux concentration of the optical configuration, and thermal parameters and flow rate of the heat transfer medium. Carnot efficiency, exit temperature, and an upper limit to the amount of heat extracted are determined for systems in which liquid sodium serves as the heat transfer medium. The performance is evaluated for selective absorber surfaces representing the state of the art as well as for surfaces requiring a more mature thin-film technology.

  7. Photoinduced charge transfer involving a MoMo quadruply bonded complex to a perylene diimide.

    PubMed

    Alberding, Brian G; Brown-Xu, Samantha E; Chisholm, Malcolm H; Epstein, Arthur J; Gustafson, Terry L; Lewis, Sharlene A; Min, Yong

    2013-04-21

    Evidence, based on femtosecond transient absorption and time resolved infrared spectroscopy, is presented for photoinduced charge transfer from the Mo2δ orbital of the quadruply bonded molecule trans-Mo2(T(i)PB)2(BTh)2, where T(i)PB = 2,4,6-triisopropyl benzoate and BTh = 2,2'-bithienylcarboxylate, to di-n-octyl perylene diimide and di-n-hexylheptyl perylene diimide in thin films and solutions of the mixtures. The films show a long-lived charge separated state while slow back electron transfer, τBET ~ 500 ps, occurs in solution.

  8. UV Vis spectrum of simple hydrocarbons in a zeolite cavity. A supramolecular charge transfer

    NASA Astrophysics Data System (ADS)

    Montero, Luis A.; Díaz, Lourdes A.; Castillo, Norberto

    2002-09-01

    Experimental findings show that ethylene included in a zeolite cavity absorbs visible light to allow photochemical reactions. This evident supramolecular effect is explained in this Letter in terms of a charge transfer transition upon excitation. According a priori NDOL calculations the charge transfer of ethylene occurs between the HOMO, localized on the trapped molecule, and electronic states distributed on the zeolite network, together with a very perturbed intramolecular transition in ethylene. The cases of methane and ethane were also studied and a drop of about 4 eV is always observed in the first electronic transition energy when included in the zeolite cage with respect to the isolated molecules.

  9. Spectral and photophysical properties of intramolecular charge transfer fluorescence probe: 4'-Dimethylamino-2,5-dihydroxychalcone

    NASA Astrophysics Data System (ADS)

    Xu, Zhicheng; Bai, Guan; Dong, Chuan

    2005-12-01

    The spectral and photophysical properties of a new intramolecular charge transfer (ICT) probe, namely 4'-dimethylamino-2,5-dihydroxychalcone (DMADHC) were studied in different solvents by using steady-state absorption and emission spectroscopy. Whereas the absorption spectrum undergoes minor change with increasing polarity of the solvents, the fluorescence spectrum experiences a distinct bathochromic shift in the band position and the fluorescence quantum yield increases reaching a maximum before decrease with increasing the solvent polarity. The magnitude of change in the dipole moment was calculated based on the Lippert-Mataga equation. These results give the evidence about the intramolecular charge transfer character in the emitting singlet state of this compound.

  10. Ultrafast Charge Transfer and Hybrid Exciton Formation in 2D/0D Heterostructures

    SciTech Connect

    Boulesbaa, Abdelaziz; Wang, Kai; Mahjouri-Samani, Masoud; Tian, Mengkun; Puretzky, Alexander A.; Ivanov, Ilia; Rouleau, Christopher M.; Xiao, Kai; Sumpter, Bobby G.; Geohegan, David B.

    2016-10-18

    We report that photoinduced interfacial charge transfer is at the heart of many applications, including photovoltaics, photocatalysis, and photodetection. With the emergence of a new class of semiconductors such as monolayer two-dimensional transition metal dichalcogenides (2D-TMDs), charge transfer at the 2D/2D heterojunctions attracted several efforts due to the remarkable optical and electrical properties of 2D-TMDs. Unfortunately, in 2D/2D heterojunctions, for a given combination of two materials, the relative energy band alignment and the charge transfer efficiency are locked. Due to their large variety and broad size tunability, semiconductor quantum dots (0D-QDs) interfaced with 2D-TMDs may become an attractive heterostructure for optoelectronic applications. Here, we incorporate femtosecond pump-probe spectroscopy to reveal the sub-45 fs charge transfer at a 2D/0D heterostructure composed of tungsten disulfide monolayers (2D-WS2) and a single layer of cadmium selenide (CdSe)/zinc sulfide (ZnS) core/shell 0D-QDs. Furthermore, ultrafast dynamics and steady-state measurements suggested that following electron transfer from the 2D to the 0D, hybrid excitons (HXs), wherein the electron resides in the 0D and hole resides in the 2D-TMD monolayer, are formed with a binding energy on the order of ~140 meV, which is several times lower than that of tightly bound excitons in 2D-TMDs.

  11. Ultrafast Charge Transfer and Hybrid Exciton Formation in 2D/0D Heterostructures

    DOE PAGES

    Boulesbaa, Abdelaziz; Wang, Kai; Mahjouri-Samani, Masoud; ...

    2016-10-18

    We report that photoinduced interfacial charge transfer is at the heart of many applications, including photovoltaics, photocatalysis, and photodetection. With the emergence of a new class of semiconductors such as monolayer two-dimensional transition metal dichalcogenides (2D-TMDs), charge transfer at the 2D/2D heterojunctions attracted several efforts due to the remarkable optical and electrical properties of 2D-TMDs. Unfortunately, in 2D/2D heterojunctions, for a given combination of two materials, the relative energy band alignment and the charge transfer efficiency are locked. Due to their large variety and broad size tunability, semiconductor quantum dots (0D-QDs) interfaced with 2D-TMDs may become an attractive heterostructure formore » optoelectronic applications. Here, we incorporate femtosecond pump-probe spectroscopy to reveal the sub-45 fs charge transfer at a 2D/0D heterostructure composed of tungsten disulfide monolayers (2D-WS2) and a single layer of cadmium selenide (CdSe)/zinc sulfide (ZnS) core/shell 0D-QDs. Furthermore, ultrafast dynamics and steady-state measurements suggested that following electron transfer from the 2D to the 0D, hybrid excitons (HXs), wherein the electron resides in the 0D and hole resides in the 2D-TMD monolayer, are formed with a binding energy on the order of ~140 meV, which is several times lower than that of tightly bound excitons in 2D-TMDs.« less

  12. Ultrafast Charge Transfer and Hybrid Exciton Formation in 2D/0D Heterostructures.

    PubMed

    Boulesbaa, Abdelaziz; Wang, Kai; Mahjouri-Samani, Masoud; Tian, Mengkun; Puretzky, Alexander A; Ivanov, Ilia; Rouleau, Christopher M; Xiao, Kai; Sumpter, Bobby G; Geohegan, David B

    2016-11-09

    Photoinduced interfacial charge transfer is at the heart of many applications, including photovoltaics, photocatalysis, and photodetection. With the emergence of a new class of semiconductors, i.e., monolayer two-dimensional transition metal dichalcogenides (2D-TMDs), charge transfer at the 2D/2D heterojunctions has attracted several efforts due to the remarkable optical and electrical properties of 2D-TMDs. Unfortunately, in 2D/2D heterojunctions, for a given combination of two materials, the relative energy band alignment and the charge-transfer efficiency are locked. Due to their large variety and broad size tunability, semiconductor quantum dots (0D-QDs) interfaced with 2D-TMDs may become an attractive heterostructure for optoelectronic applications. Here, we incorporate femtosecond pump-probe spectroscopy to reveal the sub-45 fs charge transfer at a 2D/0D heterostructure composed of tungsten disulfide monolayers (2D-WS2) and a single layer of cadmium selenide/zinc sulfide core/shell 0D-QDs. Furthermore, ultrafast dynamics and steady-state measurements suggested that, following electron transfer from the 2D to the 0D, hybrid excitons, wherein the electron resides in the 0D and the hole resides in the 2D-TMD monolayer, are formed with a binding energy on the order of ∼140 meV, which is several times lower than that of tightly bound excitons in 2D-TMDs.

  13. Fluorinated aminoanthranilamides: non-native amino acids for bringing proteomic approaches to charge-transfer systems.

    PubMed

    Larsen-Clinton, Jillian M; Espinoza, Eli M; F Mayther, Maximillian; Clark, John; Tao, Christina; Bao, Duoduo; Larino, Christa M; Wurch, Michelle; Lara, Stephanie; Vullev, Valentine I

    2017-03-15

    The ability to control charge transfer at molecular and nanometer scales represents the ultimate level of electronic mastery, and its impacts cannot be overstated. As electrostatic analogues of magnets, electrets possess ordered electric dipoles that present key paradigms for directing transduction of electrons and holes. Herein we describe the design and development of fluorinated aminoanthranilamides, derivatives of non-native aromatic beta-amino acids, as building blocks for hole-transfer molecular electrets. A highly regio-selective nucleophilic aromatic substitution of difluorinated nitrobenzoic acid provides the underpinnings for an array of unprecedented anthranilamide structures. Spin density distribution and electrochemical analyses reveal that fluorine induces about 200 mV positive shifts in reduction potentials without compromising the stability of the oxidized residues, making them invaluable building blocks for hole-transfer systems. These findings open unexplored routes to novel amino-acid structures, setting a foundation for bringing principles of proteomics to designs of charge-transfer systems.

  14. A 190 by 244 charge-coupled area image sensor with interline transfer organization

    NASA Technical Reports Server (NTRS)

    Walsh, L. R.

    1975-01-01

    A 190 x 244 element charge coupled area image sensor has been designed, fabricated and tested. This sensor employs an interline transfer organization and buried n-channel technology. It features a novel on-chip charge integrator and a distributed floating gate amplifier for high and low light level applications. The X-Y element count has been chosen to establish the capability of producing an NTSC compatible video signal. The array size is also compatible with the Super 8 lens format. The first few sample devices have been successfully operated at full video bandwidth for both high and low light levels with the charge amplifier system.

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

    NASA Astrophysics Data System (ADS)

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

    2014-02-01

    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.

  16. Evidence of Delocalization in Charge-Transfer State Manifold for Donor:Acceptor Organic Photovoltaics.

    PubMed

    Guan, Zhiqiang; Li, Ho-Wa; Zhang, Jinfeng; Cheng, Yuanhang; Yang, Qingdan; Lo, Ming-Fai; Ng, Tsz-Wai; Tsang, Sai-Wing; Lee, Chun-Sing

    2016-08-24

    How charge-transfer states (CTSs) assist charge separation of a Coulombically bound exciton in organic photovoltaics has been a hot topic. It is believed that the delocalization feature of a CTS plays a crucial role in the charge separation process. However, the delocalization of the "hot" and the "relaxed" CTSs is still under debate. Here, with a novel frequency dependent charge-modulated electroabsorption spectroscopy (CMEAS) technique, we elucidate clearly that both "hot" and "relaxed" CTSs are loosely bound and delocalized states. This is confirmed by comparing the CMEAS results of CTSs with those of localized polaron states. Our results reveal the role of CTS delocalization on charge separation and indicate that no substantial delocalization gradient exists in CTSs.

  17. Structural dynamics of a noncovalent charge transfer complex from femtosecond stimulated Raman spectroscopy.

    PubMed

    Fujisawa, Tomotsumi; Creelman, Mark; Mathies, Richard A

    2012-09-06

    Femtosecond stimulated Raman spectroscopy is used to examine the structural dynamics of photoinduced charge transfer within a noncovalent electron acceptor/donor complex of pyromellitic dianhydride (PMDA, electron acceptor) and hexamethylbenzene (HMB, electron donor) in ethylacetate and acetonitrile. The evolution of the vibrational spectrum reveals the ultrafast structural changes that occur during the charge separation (Franck-Condon excited state complex → contact ion pair) and the subsequent charge recombination (contact ion pair → ground state complex). The Franck-Condon excited state is shown to have significant charge-separated character because its vibrational spectrum is similar to that of the ion pair. The charge separation rate (2.5 ps in ethylacetate and ∼0.5 ps in acetonitrile) is comparable to solvation dynamics and is unaffected by the perdeuteration of HMB, supporting the dominant role of solvent rearrangement in charge separation. On the other hand, the charge recombination slows by a factor of ∼1.4 when using perdeuterated HMB, indicating that methyl hydrogen motions of HMB mediate the charge recombination process. Resonance Raman enhancement of the HMB vibrations in the complex reveals that the ring stretches of HMB, and especially the C-CH(3) deformations are the primary acceptor modes promoting charge recombination.

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

    SciTech Connect

    Mirkin, Noemi G.; Krimm, Samuel

    2014-01-28

    Charge transfer in a hydrogen-bonded N-methylacetamide(H{sub 2}O){sub 3} system is obtained from ωB97X-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.

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

    SciTech Connect

    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.

  20. Proton-Coupled Electron Transfer: Moving Together and Charging Forward

    SciTech Connect

    Hammes-Schiffer, Sharon

    2015-07-22

    Proton-coupled electron transfer (PCET) is ubiquitous throughout chemistry and biology. This Perspective discusses recent advances and current challenges in the field of PCET, with an emphasis on the role of theory and computation. The fundamental theoretical concepts are summarized, and expressions for rate constants and kinetic isotope effects are provided. Computational methods for calculating reduction potentials and pKa’s for molecular electrocatalysts, as well as methods for simulating the nonadiabatic dynamics of photoinduced processes, are also described. Representative applications to PCET in solution, proteins, electrochemistry, and photoinduced processes are presented, highlighting the interplay between theoretical and experimental studies. The current challenges and suggested future directions are outlined for each type of application, concluding with an overall view to the future. The work described herein was supported by National Science Foundation Grant CHE-13-61293 (theory development), National Institutes of Health Grant GM056207 (soybean lipoxygenase), Center for Chemical Innovation of the National Science Foundation Solar Fuels Grant CHE-1305124 (cobalt catalysts), Center for Molecular Electrocatalysis, an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences (nickel catalysts), and Air Force Office of Scientific Research Award No. FA9550-14-1-0295 (photoinduced PCET).

  1. Determination of layer-charge characteristics of smectites

    USGS Publications Warehouse

    Christidis, G.E.; Eberl, D.D.

    2003-01-01

    A new method for calculation of layer charge and charge distribution of smectites is proposed. The method is based on comparisons between X-ray diffraction (XRD) patterns of K-saturated, ethylene glycol-solvated, oriented samples and calculated XRD patterns for three-component, mixed-layer systems. For the calculated patterns it is assumed that the measured patterns can be modeled as random interstratifications of fully expanding 17.1 A?? layers, partially expanding 13.5 A?? layers and non-expanding 9.98 A?? layers. The technique was tested using 29 well characterized smectites. According to their XRD patterns, smectites were classified as group 1 (low-charge smectites) and group 2 (high-charge smectites). The boundary between the two groups is at a layer charge of -0.46 equivalents per half unit-cell. Low-charge smectites are dominated by 17.1 A?? layers, whereas high-charge smectites contain only 20% fully expandable layers on average. Smectite properties and industrial applications may be dictated by the proportion of 17.1 A?? layers present. Non-expanding layers may control the behavior of smectites during weathering, facilitating the formation of illite layers after subsequent cycles of wetting and drying. The precision of the method is better than 3.5% at a layer charge of -0.50; therefore the method should be useful for basic research and for industrial purposes.

  2. [Time-resolved optical studies of charge relaxation and charge transfer at electrode interfaces

    SciTech Connect

    Not Available

    1992-01-01

    Key components were identified in a quantitative model of carrier relaxation in semiconductor electrodes: nonlinear aspects of nonradiative and radiative recombination, effect of space charge field on carrier dynamics, self-absorption effects in direct gas semiconductors, and influence of surface state population kinetics on charge carrier recombination. For CdSe, the first three are operative (no direct proof of the last one). A realistic kinetic model for carrier recombination in the bulk of CdSe was used which includes important nonlinear effects, both radiative and nonradiative. The change in interfacial recombination velocity with the chemical nature of the sinterface was studied (n-CdSe/silane interfaces). Temperature effect (278 to 328 K) on fluorescence decay of n-CdSe in contact with 0.5 M KOH was found to be weak. An analytical solution was obtained for time-resolved fluoresence from electrodes under potential bias, and is being tested. Fluorescence work on a different material, CdS, indicate different recombination kinetics; this material was used to directly pump an optical transition of a surface state.

  3. [Time-resolved optical studies of charge relaxation and charge transfer at electrode interfaces

    SciTech Connect

    Not Available

    1992-12-31

    Key components were identified in a quantitative model of carrier relaxation in semiconductor electrodes: nonlinear aspects of nonradiative and radiative recombination, effect of space charge field on carrier dynamics, self-absorption effects in direct gas semiconductors, and influence of surface state population kinetics on charge carrier recombination. For CdSe, the first three are operative (no direct proof of the last one). A realistic kinetic model for carrier recombination in the bulk of CdSe was used which includes important nonlinear effects, both radiative and nonradiative. The change in interfacial recombination velocity with the chemical nature of the sinterface was studied (n-CdSe/silane interfaces). Temperature effect (278 to 328 K) on fluorescence decay of n-CdSe in contact with 0.5 M KOH was found to be weak. An analytical solution was obtained for time-resolved fluoresence from electrodes under potential bias, and is being tested. Fluorescence work on a different material, CdS, indicate different recombination kinetics; this material was used to directly pump an optical transition of a surface state.

  4. Energetics of charge transfer reactions in solvents of dipolar and higher order multipolar character. II. Results

    NASA Astrophysics Data System (ADS)

    Perng, Baw-Ching; Newton, Marshall D.; Raineri, Fernando O.; Friedman, Harold L.

    1996-05-01

    We apply the theories developed in the preceding paper (paper I) to calculate various energy quantities of charge transfer (CT) reactions in nine solvents that cover a wide range of polarity, and for which interaction site models (ISM's) may be found in the literature. Besides the two surrogate Hamiltonian theories developed in paper I, the renormalized site-density theory (RST) and the renormalized dielectric theory (RDT), we also investigate a simple harmonic approximation (HXA) for the diabatic free energy profiles, whose characteristic parameters are calculated taking specific advantage of the expression given by the extended reference interaction site method (XRISM) for the free energy of solvation. For each CT process we analyze (a) the solvent reorganization energy λ, (b) the shift of the absorption transition energy due to the solvatochromic effect, and (c) the solvent contribution to the free energy change ΔA. In addition, for a few selected examples, we also report the detailed diabatic free energy profiles. The calculations reported rely on solute-solvent and solvent-solvent pair correlation functions obtained with the XRISM integral equation method applied to nonpolarizable (with fixed mean partial charges) ISM representations of the solute and solvent molecules. To rectify the omission of the solvent electronic degrees of freedom, we correct the dielectric part of the solvent reorganization energy with an additive term designed to compensate for the use of fixed charge ISM models. Contact with theories in which the solvent is represented as a dielectric continuum medium (with or without spatial dispersion) and the solute as a set of charges inside spherical cavities carved out of the dielectric is made straightforwardly within the RDT theory by considering a particularly simple form of the solute-solvent RISM site-site direct correlation functions. Using simple ISM models for several solute species, including Reichardt's betaine-30 dye and a

  5. Space charge and charge trapping characteristics of cross-linked polyethylene subjected to ac electric stresses

    NASA Astrophysics Data System (ADS)

    Chong, Y. L.; Chen, G.; Miyake, H.; Matsui, K.; Tanaka, Y.; Takada, T.

    2006-04-01

    This paper reports on the result of space charge evolution in cross-linked polyethylene (XLPE) planar samples approximately 220 µm thick. The space charge measurement technique used in this study is the pulsed electroacoustic method. There are two phases to this experiment. In the first phase, the samples were subjected to dc 30 kVdc mm-1 and ac (sinusoidal) electric stress levels of 30 kVpk mm-1 at frequencies of 1, 10 and 50 Hz ac. In addition, ac space charge under 30 kVrms mm-1 and 60 kVpk mm-1 electric stress at 50 Hz was also investigated. The volts-off results showed that the amount of charge trapped in XLPE sample under dc electric stress is significantly bigger than samples under ac stress even when the applied ac stresses are substantially higher. The second phase of the experiment involves studying the dc space charge evolution in samples that were tested under ac stress during the first phase of the experiment. Ac ageing causes positive charge to become more dominant over negative charge. It was also discovered that ac ageing creates deeper traps, particularly for negative charge. This paper also gives a brief overview of the data processing methods used to analyse space charge under ac electric stress.

  6. Camptothecins guanine interactions: mechanism of charge transfer reaction upon photoactivation

    NASA Astrophysics Data System (ADS)

    Steenkeste, K.; Guiot, E.; Tfibel, F.; Pernot, P.; Mérola, F.; Georges, P.; Fontaine-Aupart, M. P.

    2002-01-01

    The potent activity exhibited by the antitumoral camptothecin (CPT) and its analog irinotecan (CPT-11) is known to be related to a close contact between the drug and the nucleic acid base guanine. This specificity of interaction between these two chromophores was examined by following changes in the photophysical properties of the drug using steady-state as well as time-resolved absorption and fluorescence methods. The observed effects on absorption, fluorescence emission and singlet excited state lifetimes give evidence for the occurrence of a stacking complex formation restricted to the quinoline part of CPT or CPT-11 and the guanine base but also with the adenine base. The triplet excited state properties of the drugs have been also characterized in absence and in presence of guanosine monophosphate and reveal the occurrence of an electron transfer from the guanine base to the drug. Support for this conclusion was obtained from the studies of a set of biological targets of various oxido-reduction potentials, adenosine monophosphate, cytidine, cytosine, tryptophan, tyrosine and phenylalanine. This finding gives an interpretation of the CPT-induced guanine photolesions previously reported in the literature. These data taken together are discussed in connection with the drug activity. The stacking complex CPT/guanine is necessary but not sufficient to explain the role of the chirality and of the lactone structure in the function of the drug. A stereospecific interaction with the enzyme topoisomerase I seems necessary to stabilize the stacking complex. The first experiments using time-resolved fluorescence by two-photon excitation confirms that CPT does not bind to the isolated enzyme.

  7. 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.

  8. 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.

  9. Hybridization-controlled charge transfer and induced magnetism at correlated oxide interfaces.

    PubMed

    Grisolia, M N; Varignon, J; Sanchez-Santolino, G; Arora, A; Valencia, S; Varela, M; Abrudan, R; Weschke, E; Schierle, E; Rault, J E; Rueff, J-P; Barthélémy, A; Santamaria, J; Bibes, M

    2016-05-01

    At interfaces between conventional materials, band bending and alignment are classically controlled by differences in electrochemical potential. Applying this concept to oxides in which interfaces can be polar and cations may adopt a mixed valence has led to the discovery of novel two-dimensional states between simple band insulators such as LaAlO3 and SrTiO3. However, many oxides have a more complex electronic structure, with charge, orbital and/or spin orders arising from strong Coulomb interactions between transition metal and oxygen ions. Such electronic correlations offer a rich playground to engineer functional interfaces but their compatibility with the classical band alignment picture remains an open question. Here we show that beyond differences in electron affinities and polar effects, a key parameter determining charge transfer at correlated oxide interfaces is the energy required to alter the covalence of the metal-oxygen bond. Using the perovskite nickelate (RNiO3) family as a template, we probe charge reconstruction at interfaces with gadolinium titanate GdTiO3. X-ray absorption spectroscopy shows that the charge transfer is thwarted by hybridization effects tuned by the rare-earth (R) size. Charge transfer results in an induced ferromagnetic-like state in the nickelate, exemplifying the potential of correlated interfaces to design novel phases. Further, our work clarifies strategies to engineer two-dimensional systems through the control of both doping and covalence.

  10. Hybridization-controlled charge transfer and induced magnetism at correlated oxide interfaces

    NASA Astrophysics Data System (ADS)

    Grisolia, M. N.; Varignon, J.; Sanchez-Santolino, G.; Arora, A.; Valencia, S.; Varela, M.; Abrudan, R.; Weschke, E.; Schierle, E.; Rault, J. E.; Rueff, J.-P.; Barthélémy, A.; Santamaria, J.; Bibes, M.

    2016-05-01

    At interfaces between conventional materials, band bending and alignment are classically controlled by differences in electrochemical potential. Applying this concept to oxides in which interfaces can be polar and cations may adopt a mixed valence has led to the discovery of novel two-dimensional states between simple band insulators such as LaAlO3 and SrTiO3. However, many oxides have a more complex electronic structure, with charge, orbital and/or spin orders arising from strong Coulomb interactions at and between transition metal and oxygen ions. Such electronic correlations offer a rich playground to engineer functional interfaces but their compatibility with the classical band alignment picture remains an open question. Here we show that beyond differences in electron affinities and polar effects, a key parameter determining charge transfer at correlated oxide interfaces is the energy required to alter the covalence of the metal-oxygen bond. Using the perovskite nickelate (RNiO3) family as a template, we probe charge reconstruction at interfaces with gadolinium titanate GdTiO3. X-ray absorption spectroscopy shows that the charge transfer is thwarted by hybridization effects tuned by the rare-earth (R) size. Charge transfer results in an induced ferromagnetic-like state in the nickelate, exemplifying the potential of correlated interfaces to design novel phases. Further, our work clarifies strategies to engineer two-dimensional systems through the control of both doping and covalence.

  11. Hybridization-controlled charge transfer and induced magnetism at correlated oxide interfaces

    PubMed Central

    Grisolia, M.N.; Arora, A.; Valencia, S.; Varela, M.; Abrudan, R.; Weschke, E.; Schierle, E.; Rault, J.E.; Rueff, J.-P.; Barthélémy, A.; Santamaria, J.; Bibes, M.

    2015-01-01

    At interfaces between conventional materials, band bending and alignment are classically controlled by differences in electrochemical potential. Applying this concept to oxides in which interfaces can be polar and cations may adopt a mixed valence has led to the discovery of novel two-dimensional states between simple band insulators such as LaAlO3 and SrTiO3. However, many oxides have a more complex electronic structure, with charge, orbital and/or spin orders arising from strong Coulomb interactions between transition metal and oxygen ions. Such electronic correlations offer a rich playground to engineer functional interfaces but their compatibility with the classical band alignment picture remains an open question. Here we show that beyond differences in electron affinities and polar effects, a key parameter determining charge transfer at correlated oxide interfaces is the energy required to alter the covalence of the metal-oxygen bond. Using the perovskite nickelate (RNiO3) family as a template, we probe charge reconstruction at interfaces with gadolinium titanate GdTiO3. X-ray absorption spectroscopy shows that the charge transfer is thwarted by hybridization effects tuned by the rare-earth (R) size. Charge transfer results in an induced ferromagnetic-like state in the nickelate, exemplifying the potential of correlated interfaces to design novel phases. Further, our work clarifies strategies to engineer two-dimensional systems through the control of both doping and covalence. PMID:27158255

  12. Charge transfer dynamics between photoexcited CdS nanorods and mononuclear Ru water-oxidation catalysts.

    PubMed

    Tseng, Huan-Wei; Wilker, Molly B; Damrauer, Niels H; Dukovic, Gordana

    2013-03-06

    We describe the charge transfer interactions between photoexcited CdS nanorods and mononuclear water oxidation catalysts derived from the [Ru(bpy)(tpy)Cl](+) parent structure. Upon excitation, hole transfer from CdS oxidizes the catalyst (Ru(2+) → Ru(3+)) on a 100 ps to 1 ns timescale. This is followed by 10-100 ns electron transfer (ET) that reduces the Ru(3+) center. The relatively slow ET dynamics may provide opportunities for the accumulation of multiple holes at the catalyst, which is necessary for water oxidation.

  13. Engineering and Probing Topological Properties of Dirac Semimetal Films by Asymmetric Charge Transfer.

    PubMed

    Villanova, John W; Barnes, Edwin; Park, Kyungwha

    2017-02-08

    Dirac semimetals (DSMs) have topologically robust three-dimensional Dirac (doubled Weyl) nodes with Fermi-arc states. In heterostructures involving DSMs, charge transfer occurs at the interfaces, which can be used to probe and control their bulk and surface topological properties through surface-bulk connectivity. Here we demonstrate that despite a band gap in DSM films, asymmetric charge transfer at the surface enables one to accurately identify locations of the Dirac-node projections from gapless band crossings and to examine and engineer properties of the topological Fermi-arc surface states connecting the projections, by simulating adatom-adsorbed DSM films using a first-principles method with an effective model. The positions of the Dirac-node projections are insensitive to charge transfer amount or slab thickness except for extremely thin films. By varying the amount of charge transfer, unique spin textures near the projections and a separation between the Fermi-arc states change, which can be observed by gating without adatoms.

  14. 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.

  15. Molecular orbital (SCF-Xα-SW) theory of metal-metal charge transfer processes in minerals

    USGS Publications Warehouse

    Sherman, David M.

    1987-01-01

    Electronic transitions between the Fe-Fe bonding and Fe-Fe antibonding orbitals results in the optically-induced intervalence charge transfer bands observed in the electronic spectra of mixed valence minerals. Such transitions are predicted to be polarized along the metal-metal bond direction, in agreement with experimental observations.

  16. Quantum-Classical Path Integral Simulation of Ferrocene-Ferrocenium Charge Transfer in Liquid Hexane.

    PubMed

    Walters, Peter L; Makri, Nancy

    2015-12-17

    We employ the quantum-classical path integral methodology to simulate the outer sphere charge-transfer process of the ferrocene-ferrocenium pair in liquid hexane with unprecedented accuracy. Comparison of the simulation results to those obtained by mapping the solvent on an effective harmonic bath demonstrates the accuracy of linear response theory in this system.

  17. Charge transfer polarisation wave in high Tc oxides and superconductive pairing

    NASA Technical Reports Server (NTRS)

    Chakraverty, B. K.

    1991-01-01

    A general formalism of quantized charge transfer polarization waves was developed. The nature of possible superconductive pairing between oxygen holes is discussed. Unlike optical phonons, these polarization fields will give rise to dielectric bipolarons or bipolaron bubbles. In the weak coupling limit, a new class of superconductivity is to be expected.

  18. The influence of the HGMF on mass-charge transfer in gravisensing cells.

    PubMed

    Kondrachuk, A; Belyavskaya, N

    2001-07-01

    The present work is focused on the influence of the high-gradient-magnetic field (HGMF) on spatial distribution of ion fluxes along the roots (a), cytoplasmic streaming (b), and the processes of plant cell growth connected with intracellular mass and charge transfer (c).

  19. Ground-state charge transfer as a mechanism for surface-enhanced Raman scattering

    NASA Astrophysics Data System (ADS)

    Lippitsch, Max E.

    1984-03-01

    A model is presented for the contribution of ground-state charge transfer between a metal and adsorbate to surface-enhanced Raman scattering (SERS). It is shown that this contribution can be understood using the vibronic theory for calculating Raman intensities. The enhancement is due to vibronic coupling of the molecular ground state to the metal states, the coupling mechanism being a modulation of the ground-state charge-transfer energy by the molecular vibrations. An analysis of the coupling operator gives the selection rules for this process, which turn out to be dependent on the overall symmetry of the adsorbate-metal system, even if the charge transfer is small enough for the symmetry of the adsorbate to remain the same as that of the free molecule. It is shown that the model can yield predictions on the properties of SERS, e.g., specificity to adsorption geometry, appearance of forbidden bands, dependence on the applied potential, and dependence on the excitation wavelength. The predictions are in good agreement with experimental results. It is also deduced from this model that in many cases atomic-scale roughness is a prerequisite for the observation of SERS. A result on the magnitude of the enhancement can only be given in a crude approximation. Although in most cases an additional electromagnetic enhancement seems to be necessary to give an observable signal, this charge-transfer mechanism should be important in many SERS systems.

  20. 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.

  1. Failures of TDDFT in describing the lowest intramolecular charge-transfer excitation in para-nitroaniline

    NASA Astrophysics Data System (ADS)

    Eriksen, Janus J.; Sauer, Stephan P. A.; Mikkelsen, Kurt V.; Christiansen, Ove; Jensen, Hans Jørgen Aa.; Kongsted, Jacob

    2013-07-01

    We investigate the failure of time-dependent density functional theory (TDDFT) with the CAM-B3LYP exchange-correlation (xc) functional coupled to the polarisable embedding (PE) scheme (PE-CAM-B3LYP) in reproducing the solvatochromic shift of the lowest intense charge-transfer excitation in para-nitroaniline (pNA) in water by comparing with results obtained with the coupled cluster singles and doubles (CCSD) model also coupled to the polarisable embedding scheme (PE-CCSD). We determine the amount of charge separation in the ground and excited charge-transfer state with both methods by calculating the electric dipole moments in the gas phase and for 100 solvent configurations. We find that CAM-B3LYP overestimates the amount of charge separation inherent in the ground state and TDDFT/CAM-B3LYP drastically underestimates this amount in the excited charge-transfer state. As the errors in the solvatochromatic shift are found to be inverse proportional to the change in dipole moment upon excitation, we conclude that the flaws in the description of the solvatochromic shift of this excitation are related to TDDFT itself and how it responds to the solvent effects modelled by the PE scheme. We recommend therefore to benchmark results of TDDFT calculations with CAM-B3LYP for intramolecular charge-transfer excitations in molecular systems similar to pNA against higher level ab initio wave function methods, like, e.g. CCSD, prior to their use. Using the calculated change in dipole moment upon excitation as a measure for charge-transfer character, we furthermore confirm that the difference between excitation energies calculated with TDDFT and with the Tamm-Dancoff approximation (TDA) to TDDFT is indeed correlated with the charge-transfer character of a given electronic transition both in vacuo and in solution. This is supported by a corresponding correlation between the change in dipole moment and the size of the Λ index diagnostic for the investigated CT excitation.

  2. Pseudogap and superconductivity in two-dimensional doped charge-transfer insulators

    NASA Astrophysics Data System (ADS)

    Fratino, L.; Sémon, P.; Sordi, G.; Tremblay, A.-M. S.

    2016-06-01

    High-temperature superconductivity emerges upon doping a state of matter that is insulating because of interactions. A widely studied model considers one orbital per CuO2 unit cell on a square lattice with a strong intraorbital repulsion that leads to a so-called Mott-Hubbard insulator. Here we solve a model that takes into account, within each unit cell, two oxygen orbitals where there is no electron-electron repulsion and a copper orbital with strong electron-electron repulsion. The insulating phase is a so-called charge-transfer insulator, not a Mott-Hubbard insulator. Using cluster dynamical mean-field theory with continuous-time quantum Monte Carlo as an impurity solver and 12 atoms per cluster, we report the normal and superconducting phase diagram of this model as a function of doping, interaction strength, and temperature. As expected, the three-orbital model is consistent with the experimental observation that doped holes are located predominantly on oxygens, a result that goes beyond the one-orbital model. Nevertheless, the phase boundary between pseudogap and correlated metal, the Widom line, and the origin of the pairing energy (kinetic vs potential) are similar to the one-orbital model, demonstrating that these are emergent phenomena characteristic of doped Mott insulators, independently of many microscopic details. Broader implications are discussed.

  3. Fullerene-Assisted Photoinduced Charge Transfer of Single-Walled Carbon Nanotubes through a Flavin Helix.

    PubMed

    Mollahosseini, Mehdi; Karunaratne, Erandika; Gibson, George N; Gascón, Jose A; Papadimitrakopoulos, Fotios

    2016-05-11

    One of the greatest challenges with single-walled carbon nanotube (SWNT) photovoltaics and nanostructured devices is maintaining the nanotubes in their pristine state (i.e., devoid of aggregation and inhomogeneous doping) so that their unique spectroscopic and transport characteristics are preserved. To this effect, we report on the synthesis and self-assembly of a C60-functionalized flavin (FC60), composed of PCBM and isoalloxazine moieties attached on either ends of a linear, C-12 aliphatic spacer. Small amounts of FC60 (up to 3 molar %) were shown to coassembly with an organic soluble derivative of flavin (FC12) around SWNTs and impart effective dispersion and individualization. A key annealing step was necessary to perfect the isoalloxazine helix and expel the C60 moiety away from the nanotubes. Steady-state and transient absorption spectroscopy illustrate that 1% or higher incorporation of FC60 allows for an effective photoinduced charge transfer quenching of the encased SWNTs through the seamless helical encase. This is enabled via the direct π-π overlap between the graphene sidewalls, isoalloxazine helix, and the C60 cage that facilitates SWNT exciton dissociation and electron transfer to the PCBM moiety. Atomistic molecular simulations indicate that the stability of the complex originates from enhanced van der Waals interactions of the flexible spacer wrapped around the fullerene that brings the C60 in π-π overlap with the isoalloxazine helix. The remarkable spectral purity (in terms of narrow E(S)ii line widths) for the resulting ground-state complex signals a new class of highly organized supramolecular nanotube architecture with profound importance for advanced nanostructured devices.

  4. Mechanism of charge separation in DNA by hole transfer through consecutive adenines.

    PubMed

    Kawai, Kiyohiko; Osakada, Yasuko; Fujitsuka, Mamoru; Majima, Tetsuro

    2008-01-01

    To investigate the mechanism of charge separation in DNA with consecutive adenines adjacent to a photosensitizer (Sens), a series of naphthalimide (NI) and 5-bromouracil ((br)U)-modified DNAs were prepared, and the quantum yields of formation of the charge-separated states (Phi) upon photo-excitation of the Sens NI in DNA were measured. The Phi was modulated by the incorporation site of (br)U, which changes the oxidation potential of its complementary A through hydrogen bonding and the hole-transfer rates between adenines. The results were interpreted as charge separation by means of the initial charge transfer between NI in the singlet excited state and the second- and third-nearest adenine to the NI. In addition, the oxidation of the A nearest to NI leads to the rapid charge recombination within a contact ion pair. This suggests that the charge-separation process can be refined to maximize the Phi by putting a redox-inactive spacer base pair between a photosensitizer and an A-T stretch.

  5. Charge transfer to a dielectric target by guided ionization waves using electric field measurements

    NASA Astrophysics Data System (ADS)

    Slikboer, Elmar; Garcia-Caurel, Enric; Guaitella, Olivier; Sobota, Ana

    2017-03-01

    A kHz-operated atmospheric pressure plasma jet is investigated by measuring charge transferred to a dielectric electro-optic surface (BSO crystal) allowing for the measurement of electric field by exploiting the Pockels effect. The electric field values, distribution of the surface discharge and amount of deposited charge are obtained for various parameters, including gas flow, applied voltage, target distance and the length of the capillary from ground to the end. A newly formed surface discharge emerges at the target when enough charge is deposited at the impact point and electric fields are high enough, i.e. 200 pC and 9 ± 2 kV cm‑1. The maximum amount of charge transferred by a single ionization wave (‘plasma bullet’) is 350 ± 40 pC. Due to the emerging new surface discharge behind the impact point, the total charge deposited on the surface of the dielectric target can increase up to 950 pC. The shape of the secondary discharge on the target is found to be mainly driven by gas flow, while the applied voltage allows us to utilize longer distances within the boundaries set by this gas mixing. Finally the ionization wave is found to lose charge along its propagation on the inner walls of the capillary. The loss is estimated to be approximately 7.5 pC mm‑1 of travel distance inside the capillary.

  6. Molecular dynamics and charge transport in organic semiconductors: a classical approach to modeling electron transfer

    DOE PAGES

    Pelzer, Kenley M.; Vázquez-Mayagoitia, Álvaro; Ratcliff, Laura E.; ...

    2017-01-01

    Organic photovoltaics (OPVs) are a promising carbon-neutral energy conversion technology, with recent improvements pushing power conversion efficiencies over 10%. A major factor limiting OPV performance is inefficiency of charge transport in organic semiconducting materials (OSCs). Due to strong coupling with lattice degrees of freedom, the charges form polarons, localized quasi-particles comprised of charges dressed with phonons. These polarons can be conceptualized as pseudo-atoms with a greater effective mass than a bare charge. Here we propose that due to this increased mass, polarons can be modeled with Langevin molecular dynamics (LMD), a classical approach with a computational cost much lower thanmore » most quantum mechanical methods. Here we present LMD simulations of charge transfer between a pair of fullerene molecules, which commonly serve as electron acceptors in OSCs. We find transfer rates consistent with experimental measurements of charge mobility, suggesting that this method may provide quantitative predictions of efficiency when used to simulate materials on the device scale. Our approach also offers information that is not captured in the overall transfer rate or mobility: in the simulation data, we observe exactly when and why intermolecular transfer events occur. In addition, we demonstrate that these simulations can shed light on the properties of polarons in OSCs. In conclusion, much remains to be learned about these quasi-particles, and there are no widely accepted methods for calculating properties such as effective mass and friction. Lastly, our model offers a promising approach to exploring mass and friction as well as providing insight into the details of polaron transport in OSCs.« less

  7. Molecular dynamics and charge transport in organic semiconductors: a classical approach to modeling electron transfer

    SciTech Connect

    Pelzer, Kenley M.; Vázquez-Mayagoitia, Álvaro; Ratcliff, Laura E.; Tretiak, Sergei; Bair, Raymond A.; Gray, Stephen K.; Van Voorhis, Troy; Larsen, Ross E.; Darling, Seth B.

    2017-01-01

    Organic photovoltaics (OPVs) are a promising carbon-neutral energy conversion technology, with recent improvements pushing power conversion efficiencies over 10%. A major factor limiting OPV performance is inefficiency of charge transport in organic semiconducting materials (OSCs). Due to strong coupling with lattice degrees of freedom, the charges form polarons, localized quasi-particles comprised of charges dressed with phonons. These polarons can be conceptualized as pseudo-atoms with a greater effective mass than a bare charge. Here we propose that due to this increased mass, polarons can be modeled with Langevin molecular dynamics (LMD), a classical approach with a computational cost much lower than most quantum mechanical methods. Here we present LMD simulations of charge transfer between a pair of fullerene molecules, which commonly serve as electron acceptors in OSCs. We find transfer rates consistent with experimental measurements of charge mobility, suggesting that this method may provide quantitative predictions of efficiency when used to simulate materials on the device scale. Our approach also offers information that is not captured in the overall transfer rate or mobility: in the simulation data, we observe exactly when and why intermolecular transfer events occur. In addition, we demonstrate that these simulations can shed light on the properties of polarons in OSCs. In conclusion, much remains to be learned about these quasi-particles, and there are no widely accepted methods for calculating properties such as effective mass and friction. Lastly, our model offers a promising approach to exploring mass and friction as well as providing insight into the details of polaron transport in OSCs.

  8. Anomalous charge and negative-charge-transfer insulating state in cuprate chain compound KCuO2

    NASA Astrophysics Data System (ADS)

    Choudhury, D.; Rivero, P.; Meyers, D.; Liu, X.; Cao, Y.; Middey, S.; Whitaker, M. J.; Barraza-Lopez, S.; Freeland, J. W.; Greenblatt, M.; Chakhalian, J.

    2015-11-01

    Using a combination of x-ray absorption spectroscopy (XAS) experiments and first-principles calculations, we demonstrate that insulating KCuO2 contains Cu in an unusually high formal 3+ valence state, and the ligand-to-metal (O-to-Cu) charge-transfer energy is intriguingly negative (Δ ˜-1.5 eV) and has a dominant (˜60 % ) ligand-hole character in the ground state akin to the high Tc cuprate Zhang-Rice state. Unlike most other formal Cu3 + compounds, the Cu 2 p XAS spectra of KCuO2 exhibit pronounced 3 d8 (Cu3 +) multiplet structures, which account for ˜40 % of its ground state wave function. Ab initio calculations elucidate the origin of the band gap in KCuO2 as arising primarily from strong intracluster Cu 3 d -O 2 p hybridizations (tpd); the value of the band gap decreases with a reduced value of tpd. Further, unlike conventional negative-charge-transfer insulators, the band gap in KCuO2 persists even for vanishing values of Coulomb repulsion U , underscoring the importance of single-particle band-structure effects connected to the one-dimensional nature of the compound.

  9. Charge and Heat Transfer Mechanism in Directly Coupled CdSe-Metal Nanohybrids

    NASA Astrophysics Data System (ADS)

    Augustine, Anju K.; Girijavallabhan, C. P.; Nampoori, V. P. N.; Kailasnath, M.

    2015-10-01

    The charge and heat energy transfer dynamics of directly coupled mixtures of CdSe quantum dots with metal nanoparticles have been studied using thermal lens and photoluminescence (PL) techniques, respectively. The PL of such nanohybrids is found to be quenched dramatically at a particular threshold. Fluorescence decay curves of the Au-CdSe nanohybrids and Ag-CdSe nanohybrids show distinct decay channels with the fastest one associated with transfer of electrons from the CdSe portion to the metal portion. A study on the influence of this charge transfer on the thermal diffusivity with respect to the emission wavelength of quantum dots has been carried out, which could lead to the design of modern photocatalysts and solar cells constructed from nanoscale metal-semiconductor hybrids.

  10. [Diffusion and diffusion-osmosis models of the charged macromolecule transfer in barriers of biosystems].

    PubMed

    Varakin, A I; Mazur, V V; Arkhipova, N V; Serianov, Iu V

    2009-01-01

    Mathematical models of the transfer of charged macromolecules have been constructed on the basis of the classical equations of electromigration diffusion of Helmholtz-Smolukhovskii, Goldman, and Goldman-Hodgkin-Katz. It was shown that ion transfer in placental (mimicking lipid-protein barriers) and muscle barriers occurs by different mechanisms. In placental barriers, the electromigration diffusion occurs along lipid-protein channels formed due to the conformational deformation of phospholipid and protein molecules with the coefficients of diffusion D = (2.6-3.6) x 10(-8) cm2/s. The transfer in muscle barriers is due to the migration across charged interfibrillar channels with the negative diffusion activation energy, which is explained by changes in the structure of muscle fibers and expenditures of thermal energy for the extrusion of Cl- from channel walls with the diffusion coefficient D = (6.0-10.0) x 10(-6) cm2/s.

  11. Charge transfer in dissociating iodomethane and fluoromethane molecules ionized by intense femtosecond X-ray pulses

    PubMed Central

    Boll, Rebecca; Erk, Benjamin; Coffee, Ryan; Trippel, Sebastian; Kierspel, Thomas; Bomme, Cédric; Bozek, John D.; Burkett, Mitchell; Carron, Sebastian; Ferguson, Ken R.; Foucar, Lutz; Küpper, Jochen; Marchenko, Tatiana; Miron, Catalin; Patanen, Minna; Osipov, Timur; Schorb, Sebastian; Simon, Marc; Swiggers, Michelle; Techert, Simone; Ueda, Kiyoshi; Bostedt, Christoph; Rolles, Daniel; Rudenko, Artem

    2016-01-01

    Ultrafast electron transfer in dissociating iodomethane and fluoromethane molecules was studied at the Linac Coherent Light Source free-electron laser using an ultraviolet-pump, X-ray-probe scheme. The results for both molecules are discussed with respect to the nature of their UV excitation and different chemical properties. Signatures of long-distance intramolecular charge transfer are observed for both species, and a quantitative analysis of its distance dependence in iodomethane is carried out for charge states up to I21+. The reconstructed critical distances for electron transfer are in good agreement with a classical over-the-barrier model and with an earlier experiment employing a near-infrared pump pulse. PMID:27051675

  12. Charge-transfer dynamics in multilayered PbS and PbSe quantum dot architectures

    SciTech Connect

    Xu, F.; Ma, X.; Haughn, C. R.; Doty, M. F.; Cloutier, S. G.

    2014-02-03

    We demonstrate control of the charge transfer process in PbS and PbSe quantum dot assemblies. We first demonstrate efficient charge transfer from donor quantum dots to acceptor quantum dots in a multi-layer PbSe cascade structure. Then, we assemble type-I and type-II heterostructures using both PbS and PbSe quantum dots via careful control of the band alignment. In type-I structures, photo-generated carriers are transferred and localized in the smaller bandgap (acceptor) quantum dots, resulting in a significant luminescence enhancement. In contrast, a significant luminescence quenching and shorter emission lifetime confirms an efficient separation of photo-generated carriers in the type-II architecture.

  13. Coordination structure and charge transfer in microsolvated transition metal hydroxide clusters [MOH](+)(H2O)1-4.

    PubMed

    Marsh, Brett M; Voss, Jonathan M; Zhou, Jia; Garand, Etienne

    2015-09-21

    Infrared vibrational predissociation spectra of transition metal hydroxide clusters, [MOH](+)(H2O)1-4·D2 with M = Mn, Fe, Co, Ni, Cu, and Zn, are presented and analyzed with the aid of density functional theory calculations. For the [MnOH](+), [FeOH](+), [CoOH](+) and [ZnOH](+) species, we find that the first coordination shell contains three water molecules and the four ligands are arranged in a distorted tetrahedral geometry. [CuOH](+) can have either two or three water molecules in the first shell arranged in a planar arrangement, while [NiOH](+) has an octahedral ligand geometry with the first shell likely closed with five water molecules. Upon closure of the first coordination shell, characteristic stretch frequencies of hydrogen-bonded OH in the 2500-3500 cm(-1) region are used to pinpoint the location of the water molecule in the second shell. The relative energetics of different binding sites are found to be metal dependent, dictated by the first-shell coordination geometry and the charge transfer between the hydroxide and the metal center. Finally, the frequency of the hydroxide stretch is found to be sensitive to the vibrational Stark shift induced by the charged metal center, as observed previously for the smaller [MOH](+)(H2O) species. Increasing solvation modulates this frequency by reducing the extent of the charge transfer while elongating the M-OH bond.

  14. Ground and excited state intramolecular proton transfer controlled intramolecular charge separation and recombination: A new type of charge and proton transfer reaction

    NASA Astrophysics Data System (ADS)

    Nie, Daobo; Bian, Zuqiang; Yu, Anchi; Chen, Zhuqi; Liu, Zhiwei; Huang, Chunhui

    2008-06-01

    A novel β-diketone 1-(4-(9-carbazol)phenyl)-3-phenyl-1,3-propanedione (CDBM) has been synthesized. When excited at 380 nm, this molecule shows single fluorescence. However, when excited at 338 nm, it shows dual fluorescence. A Al 3+ complex Al(CDBM) 3 has been synthesized to investigate the dual fluorescence of CDBM. It is found that this complex shows single fluorescence under all excitation. This result indicated that the dual fluorescence of CDBM may relate to the intramolecular proton transfer reaction. Based on the experimental and theoretical studies of CDBM, N-(4-cyanophenyl)carbazole (CBN) and Al(CDBM) 3, a "ground and excited state intramolecular proton transfer controlled intramolecular charge separation and recombination" mechanism is proposed to explain the unusual excitation-dependent dual fluorescence of CDBM.

  15. Heat Transfer Characteristics of Slush Nitrogen in Turbulent Pipe Flows

    NASA Astrophysics Data System (ADS)

    Ohira, K.; Ishimoto, J.; Nozawa, M.; Kura, T.; Takahashi, N.

    2008-03-01

    Slush fluids, such as slush hydrogen and slush nitrogen, are two-phase (solid-liquid) single-component cryogenic fluids containing solid particles in a liquid, and consequently their density and refrigerant capacity are greater than for liquid state fluid alone. This paper reports on the experimental results of the forced convection heat transfer characteristics of slush nitrogen flowing in a pipe. Heat was supplied to slush nitrogen by a heater wound around the copper pipe wall. The local heat transfer coefficient was measured in conjunction with changes in the velocity and the solid fraction. The differences in heat transfer characteristics between two-phase slush and single phase liquid nitrogen were obtained, and the decrease in heat transfer to slush nitrogen caused by the previously observed pressure drop reduction was confirmed by this study. Furthermore, for the purpose of establishing the thermal design criteria for slush nitrogen in the case of pressure drop reduction, the heat transfer correlation between the experimental results and the Sieder-Tate Equation was obtained.

  16. Understanding charge transfer processes on metal oxides: a laser-flash-photolysis study

    NASA Astrophysics Data System (ADS)

    Sieland, Fabian; Schneider, Jenny; Lippmann, Thorsten; Bahnemann, Detlef W.

    2016-09-01

    In the focus of this study, mixtures of commercially available TiO2 powders were created and their photocatalytic activity concerning the acetaldehyde degradation in the gas phase was tested. Further, the lifetime of the photogenerated charge carriers was analyzed by Laser-Flash-Photolysis-Spectroscopy. The acetaldehyde degradation experiments of the mixed powders lead to positive and negative deviations from the expected weighted mean. Nevertheless, their photocatalytic activity could be correlated with the lifetime of the charge carriers. A longer charge carrier lifetime at ambient conditions correlated with a lower fractional conversion of acetaldehyde. The advantageous activities of the samples were associated with a charge transfer reaction between larger and smaller particles comparable to the antenna mechanism.1

  17. 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)

    2003-01-01

    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.

  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.

  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. 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

  1. 29 CFR 102.33 - Transfer of charge and proceeding from region to region; consolidation of proceedings in same...

    Code of Federal Regulations, 2010 CFR

    2010-07-01

    ... 29 Labor 2 2010-07-01 2010-07-01 false Transfer of charge and proceeding from region to region; consolidation of proceedings in same region; severance. 102.33 Section 102.33 Labor Regulations Relating to... § 102.33 Transfer of charge and proceeding from region to region; consolidation of proceedings in...

  2. Charge Transfer Dynamics in Complexes of Light-Absorbing CdS Nanorods and Redox Catalysts

    NASA Astrophysics Data System (ADS)

    Wilker, Molly Bea

    The use of photoexcited electrons and holes in semiconductor nanocrystals as reduction and oxidation reagents is an intriguing way of harvesting photon energy to drive chemical reactions. This dissertation describes research efforts to understand the photoexcited charge transfer kinetics in complexes of colloidal CdS nanorods coupled with either a water oxidation or reduction catalyst. The first project focuses on the charge transfer interactions between photoexcited CdS nanorods and a mononuclear water oxidation catalyst derived from the [Ru(bpy)(tpy)Cl]+ parent structure. The second project details the electron transfer kinetics in complexes of CdS nanorods coupled with [FeFe]-hydrogenase, which catalyzes H+ reduction. These complexes photochemically produce H2 with quantum yields of up to 20%. Kinetics of electron transfer from CdS nanorods to hydrogenase play a critical role in the overall photochemical reactivity, as the quantum efficiency of electron transfer defines the upper limit on the quantum yield of H 2 generation. Insights from these time-resolved spectroscopic studies are used to discuss the intricate kinetic pathways involved in photochemical H2 generation and the mechanism for electron transfer from photoexcited nanorods to hydrogenase in photocatalytic complexes.

  3. Calculation of rates of exciton dissociation into hot charge-transfer states in model organic photovoltaic interfaces

    NASA Astrophysics Data System (ADS)

    Vázquez, Héctor; Troisi, Alessandro

    2013-11-01

    We investigate the process of exciton dissociation in ordered and disordered model donor/acceptor systems and describe a method to calculate exciton dissociation rates. We consider a one-dimensional system with Frenkel states in the donor material and states where charge transfer has taken place between donor and acceptor. We introduce a Green's function approach to calculate the generation rates of charge-transfer states. For disorder in the Frenkel states we find a clear exponential dependence of charge dissociation rates with exciton-interface distance, with a distance decay constant β that increases linearly with the amount of disorder. Disorder in the parameters that describe (final) charge-transfer states has little effect on the rates. Exciton dissociation invariably leads to partially separated charges. In all cases final states are “hot” charge-transfer states, with electron and hole located far from the interface.

  4. Communication: Modeling of concentration dependent water diffusivity in ionic solutions: Role of intermolecular charge transfer

    SciTech Connect

    Yao, Yi; Berkowitz, Max L. E-mail: ykanai@unc.edu; Kanai, Yosuke E-mail: ykanai@unc.edu

    2015-12-28

    The translational diffusivity of water in solutions of alkali halide salts depends on the identity of ions, exhibiting dramatically different behavior even in solutions of similar salts of NaCl and KCl. The water diffusion coefficient decreases as the salt concentration increases in NaCl. Yet, in KCl solution, it slightly increases and remains above bulk value as salt concentration increases. Previous classical molecular dynamics simulations have failed to describe this important behavior even when polarizable models were used. Here, we show that inclusion of dynamical charge transfer among water molecules produces results in a quantitative agreement with experiments. Our results indicate that the concentration-dependent diffusivity reflects the importance of many-body effects among the water molecules in aqueous ionic solutions. Comparison with quantum mechanical calculations shows that a heterogeneous and extended distribution of charges on water molecules around the ions due to ion-water and also water-water charge transfer plays a very important role in controlling water diffusivity. Explicit inclusion of the charge transfer allows us to model accurately the difference in the concentration-dependent water diffusivity between Na{sup +} and K{sup +} ions in simulations, and it is likely to impact modeling of a wide range of systems for medical and technological applications.

  5. Communication: Modeling of concentration dependent water diffusivity in ionic solutions: Role of intermolecular charge transfer

    NASA Astrophysics Data System (ADS)

    Yao, Yi; Berkowitz, Max L.; Kanai, Yosuke

    2015-12-01

    The translational diffusivity of water in solutions of alkali halide salts depends on the identity of ions, exhibiting dramatically different behavior even in solutions of similar salts of NaCl and KCl. The water diffusion coefficient decreases as the salt concentration increases in NaCl. Yet, in KCl solution, it slightly increases and remains above bulk value as salt concentration increases. Previous classical molecular dynamics simulations have failed to describe this important behavior even when polarizable models were used. Here, we show that inclusion of dynamical charge transfer among water molecules produces results in a quantitative agreement with experiments. Our results indicate that the concentration-dependent diffusivity reflects the importance of many-body effects among the water molecules in aqueous ionic solutions. Comparison with quantum mechanical calculations shows that a heterogeneous and extended distribution of charges on water molecules around the ions due to ion-water and also water-water charge transfer plays a very important role in controlling water diffusivity. Explicit inclusion of the charge transfer allows us to model accurately the difference in the concentration-dependent water diffusivity between Na+ and K+ ions in simulations, and it is likely to impact modeling of a wide range of systems for medical and technological applications.

  6. Communication: Modeling of concentration dependent water diffusivity in ionic solutions: Role of intermolecular charge transfer.

    PubMed

    Yao, Yi; Berkowitz, Max L; Kanai, Yosuke

    2015-12-28

    The translational diffusivity of water in solutions of alkali halide salts depends on the identity of ions, exhibiting dramatically different behavior even in solutions of similar salts of NaCl and KCl. The water diffusion coefficient decreases as the salt concentration increases in NaCl. Yet, in KCl solution, it slightly increases and remains above bulk value as salt concentration increases. Previous classical molecular dynamics simulations have failed to describe this important behavior even when polarizable models were used. Here, we show that inclusion of dynamical charge transfer among water molecules produces results in a quantitative agreement with experiments. Our results indicate that the concentration-dependent diffusivity reflects the importance of many-body effects among the water molecules in aqueous ionic solutions. Comparison with quantum mechanical calculations shows that a heterogeneous and extended distribution of charges on water molecules around the ions due to ion-water and also water-water charge transfer plays a very important role in controlling water diffusivity. Explicit inclusion of the charge transfer allows us to model accurately the difference in the concentration-dependent water diffusivity between Na(+) and K(+) ions in simulations, and it is likely to impact modeling of a wide range of systems for medical and technological applications.

  7. Site-specific probing of charge transfer dynamics in organic photovoltaics

    SciTech Connect

    Arion, Tiberiu; Roth, Friedrich; Hussain, Zahid; Eberhardt, Wolfgang

    2015-03-23

    We report the site-specific probing of charge-transfer dynamics in a prototype system for organic photovoltaics (OPVs) by picosecond time-resolved X-ray photoelectron spectroscopy. A layered system consisting of approximately two monolayers of C{sub 60} deposited on top of a thin film of Copper-Phthalocyanine (CuPC) is excited by an optical pump pulse and the induced electronic dynamics are probed with 590 eV X-ray pulses. Charge transfer from the electron donor (CuPC) to the acceptor (C{sub 60}) and subsequent charge carrier dynamics are monitored by recording the time-dependent C 1s core level photoemission spectrum of the system. The arrival of electrons in the C{sub 60} layer is readily observed as a completely reversible, transient shift of the C{sub 60} associated C 1s core level, while the C 1s level of the CuPC remains unchanged. The capability to probe charge transfer and recombination dynamics in OPV assemblies directly in the time domain and from the perspective of well-defined domains is expected to open additional pathways to better understand and optimize the performance of this emerging technology.

  8. Ultrafast exciton dynamics in 2D in-plane hetero-nanostructures: delocalization and charge transfer.

    PubMed

    Cassette, E; Pedetti, S; Mahler, B; Ithurria, S; Dubertret, B; Scholes, G D

    2017-03-10

    In this article we study the ultrafast dynamics of excitons and charge carriers photogenerated in two-dimensional in-plane heterostructures, namely, CdSe-CdTe nanoplatelets. We combine transient absorption and two-dimensional electronic spectroscopy to study charge transfer and delocalization from a few tens of femtoseconds to several nanoseconds. In contrast with spherical nanocrystals, the relative alignment of the electron and hole states of CdSe and CdTe in thin 2D nanoplatelets does not lead to a type-II heterostructure. Following the excitation in CdSe or CdTe materials, the electron preferentially delocalises instantaneously over the whole heterostructure. In addition, depending on the crown material (CdTe versus CdTeSe), the hole transfers either to trap states or to the crown, within a few hundreds of femtoseconds. We conclude that the photoluminescence band, at lower energy than the CdSe and CdTe first exciton transition, does not result from the recombination of the charge carriers at the charge transfer state but involves localised hole states.

  9. 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.

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

    PubMed Central

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

    2010-01-01

    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 4s2 and 4s13d1 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 π system: (i) a van der Waals complex with a doubly occupied highest molecular orbital, denoted , 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 ϕ1ϕ2, where ϕ2 is an orbital showing significant charge transfer form Ca to the π-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 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-π complexes. PMID:21037111

  11. Phosphine passivated gold clusters: how charge transfer affects electronic structure and stability.

    PubMed

    Mollenhauer, Doreen; Gaston, Nicola

    2016-11-02

    A systematic evaluation of small phosphine ligand-protected gold clusters with six to nine gold atoms using density functional theory with dispersion correction has been performed in order to understand the major factors determining stability, including its size, shape, and charge dependence. We show that the charge per atom of the cluster is much more important for the interaction between the ligand shell and gold cluster than the system size. Thus, strong charge transfer effects determine the binding strength between the ligand shell and cluster. The clusters in this series are all non-spherical and exhibit large HOMO-LUMO gaps (above 2.7 eV). Analysis of the delocalized nature of the electronic states at the centre of the clusters demonstrates the presence of nascent superatomic states. However the number of delocalized electrons in these systems is significantly influenced by the charge transfer from the phosphine ligands, contrary to the usual accounting rule for superatom complex systems. Thus, not only electron withdrawing but also charge transfer effects should be considered to influence the superatomic structure of charged ligand surrounded clusters. In consequence in the phosphine gold cluster series under consideration the systems Au7(PPh3)7(+) and Au8(PPh3)8(2+) exhibit nearly fully filled S and P states and the HOMO-LUMO gap increases by 0.2 eV and 0.9 eV, respectively. The interpretation for the stability of the gold phosphine systems is in agreement with experimental results and demonstrates the importance of the superatomic concept.

  12. Charge-dependent dissociation of insulin cations via ion/ion electron transfer

    NASA Astrophysics Data System (ADS)

    Liu, Jian; Gunawardena, Harsha P.; Huang, Teng-Yi; McLuckey, Scott A.

    2008-10-01

    The dissociation reactions of various charge states of insulin cations obtained directly from nano-electrospray were investigated as a result of ion/ion electron transfer from azobenzene anions. Data were collected with and without simultaneous ion trap collisional excitation of the first generation charge-reduced product during the ion/ion reaction period. Neither separation of the two constituent chains nor cleavages within the loop defined by the disulfide bridges were observed under normal electron transfer dissociation (ETD) conditions for any of the charge states studied. However, substantial sequence coverage (exocyclic region: 82.6%; entire protein: 38.8%) outside the ring structure was obtained for insulin +6, while only limited coverage (exocyclic: 43.5%; entire protein: 20.4%) was observed for insulin +5 and no dissociation, aside from low abundance side-chain losses, was noted for insulin +4 and +3 in the normal ETD spectra. When the first generation charge-reduced precursor ions were subjected to collisional activation during the ion/ion reaction period, higher sequence coverages were obtained for both insulin +5 (entire protein: 34.7%) and +4 (entire protein: 20.4%) with backbone cleavages occurring within the loop defined by the disulfide bonds. Dissociation of insulin +3 was not significantly improved by the additional activation. Separation of the two constituent chains resulting from cleavages of both of the two disulfide bridges that link the chains was observed for insulin +6, +5, and +4 when the charge-reduced species were activated. The dissociation of disulfide linkages in this study suggests that as the charge state decreases, disulfide bond cleavages dominate over N-C[alpha] bond cleavages in the electron transfer dissociation process.

  13. Intermolecular electron transfer from intramolecular excitation and coherent acoustic phonon generation in a hydrogen-bonded charge-transfer solid

    NASA Astrophysics Data System (ADS)

    Rury, Aaron S.; Sorenson, Shayne; Dawlaty, Jahan M.

    2016-03-01

    Organic materials that produce coherent lattice phonon excitations in response to external stimuli may provide next generation solutions in a wide range of applications. However, for these materials to lead to functional devices in technology, a full understanding of the possible driving forces of coherent lattice phonon generation must be attained. To facilitate the achievement of this goal, we have undertaken an optical spectroscopic study of an organic charge-transfer material formed from the ubiquitous reduction-oxidation pair hydroquinone and p-benzoquinone. Upon pumping this material, known as quinhydrone, on its intermolecular charge transfer resonance as well as an intramolecular resonance of p-benzoquinone, we find sub-cm-1 oscillations whose dispersion with probe energy resembles that of a coherent acoustic phonon that we argue is coherently excited following changes in the electron density of quinhydrone. Using the dynamical information from these ultrafast pump-probe measurements, we find that the fastest process we can resolve does not change whether we pump quinhydrone at either energy. Electron-phonon coupling from both ultrafast coherent vibrational and steady-state resonance Raman spectroscopies allows us to determine that intramolecular electronic excitation of p-benzoquinone also drives the electron transfer process in quinhydrone. These results demonstrate the wide range of electronic excitations of the parent of molecules found in many functional organic materials that can drive coherent lattice phonon excitations useful for applications in electronics, photonics, and information technology.

  14. Comparative study of convective heat transfer characteristics of nanofluids

    NASA Astrophysics Data System (ADS)

    Muryam, Hina; Ramzan, Naveed; Umer, Asim; Awan, Gul Hameed; Hassan, Ali

    2017-02-01

    The present research is about to draw a comparison between heat transfer characteristics of gold/deionized water (DIW) and silver/DIW based nanofluid under same heat flux for laminar flow. Experiments are performed on both nanofluid by using different concentrations (0.015, 0.045, 0.0667%) of nano-particles (NPs) in DIW as a base fluid. The experimental study concludes that an appreciable intensification in heat transfer coefficient (HTC) of both nanofluid has been attained as compare to base fluid. However, gold/DIW based nanofluid exhibit better convective heat transfer intensification compared with silver/DIW based nanofluid but Shah correlation cannot predict as much augmentation as in experimental work for both nanofluid. It is also noticed that the anomalous enhancement in Nusselt number and HTC is not only due to the accession in thermal properties but also by the formation of thinner thermal boundary layer at the entrance of the tube due to NPs.

  15. Boosting the efficiency of quantum dot sensitized solar cells through modulation of interfacial charge transfer.

    PubMed

    Kamat, Prashant V

    2012-11-20

    The demand for clean energy will require the design of nanostructure-based light-harvesting assemblies for the conversion of solar energy into chemical energy (solar fuels) and electrical energy (solar cells). Semiconductor nanocrystals serve as the building blocks for designing next generation solar cells, and metal chalcogenides (e.g., CdS, CdSe, PbS, and PbSe) are particularly useful for harnessing size-dependent optical and electronic properties in these nanostructures. This Account focuses on photoinduced electron transfer processes in quantum dot sensitized solar cells (QDSCs) and discusses strategies to overcome the limitations of various interfacial electron transfer processes. The heterojunction of two semiconductor nanocrystals with matched band energies (e.g., TiO(2) and CdSe) facilitates charge separation. The rate at which these separated charge carriers are driven toward opposing electrodes is a major factor that dictates the overall photocurrent generation efficiency. The hole transfer at the semiconductor remains a major bottleneck in QDSCs. For example, the rate constant for hole transfer is 2-3 orders of magnitude lower than the electron injection from excited CdSe into oxide (e.g., TiO(2)) semiconductor. Disparity between the electron and hole scavenging rate leads to further accumulation of holes within the CdSe QD and increases the rate of electron-hole recombination. To overcome the losses due to charge recombination processes at the interface, researchers need to accelerate electron and hole transport. The power conversion efficiency for liquid junction and solid state quantum dot solar cells, which is in the range of 5-6%, represents a significant advance toward effective utilization of nanomaterials for solar cells. The design of new semiconductor architectures could address many of the issues related to modulation of various charge transfer steps. With the resolution of those problems, the efficiencies of QDSCs could approach those of dye

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

    SciTech Connect

    Theophilou, Iris; Tassi, M.; Thanos, S.

    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.

  17. Direct Observation of Charge Transfer in Double-Perovskite-Like RbMn[Fe(CN)6

    NASA Astrophysics Data System (ADS)

    Kato, K.; Moritomo, Y.; Takata, M.; Sakata, M.; Umekawa, M.; Hamada, N.; Ohkoshi, S.; Tokoro, H.; Hashimoto, K.

    2003-12-01

    The charge density distribution has been determined for a transition metal cyanide, RbMn[Fe(CN)6], by means of the maximum entropy Rietveld method combined with the highly angularly resolved synchrotron radiation x-ray powder diffraction at SPring-8 BL02B2. We directly observed a charge transfer from the Mn site to the Fe site in the low-temperature phase. On the basis of a local density approximation calculation, we discuss the origin for the anisotropic bonding electron distribution around the Mn3+ ion in the low-temperature phase.

  18. Infrared light irradiation diminishes effective charge transfer in slow sodium channel gating system

    NASA Astrophysics Data System (ADS)

    Plakhova, Vera B.; Bagraev, Nikolai T.; Klyachkin, Leonid E.; Malyarenko, Anna M.; Romanov, Vladimir V.; Krylov, Boris V.

    2001-02-01

    Effects of infrared light irradiation (IR) on cultured dorsal root ganglia cells were studied by the whole-cell patch-clamp technique. The IR field is demonstrated to diminish the effective charge transfer in the activation system from 6.2 +-0.6 to 4.5 +-0.4 in units of electron charge per e-fold change in membrane potential. The effects was blocked with ouabain. Our data is the first indication that sodium pump might be the molecular sensor of infrared irradiation in animal kingdom.

  19. Infrared light irradiation diminishes effective charge transfer in slow sodium channel gating system

    NASA Astrophysics Data System (ADS)

    Plakhova, Vera B.; Bagraev, Nikolai T.; Klyachkin, Leonid E.; Malyarenko, Anna M.; Romanov, Vladimir V.; Krylov, Boris V.

    2000-02-01

    Effects of infrared light irradiation (IR) on cultured dorsal root ganglia cells were studied by the whole-cell patch-clamp technique. The IR field is demonstrated to diminish the effective charge transfer in the activation system from 6.2 +-0.6 to 4.5 +-0.4 in units of electron charge per e-fold change in membrane potential. The effects was blocked with ouabain. Our data is the first indication that sodium pump might be the molecular sensor of infrared irradiation in animal kingdom.

  20. State-selective charge transfer cross sections for light ion impact of atomic hydrogen

    SciTech Connect

    Schultz, D. R.; Stancil, Phillip C.; Havener, C. C.

    2015-01-01

    Owing to the utility of diagnosing plasma properties such as impurity concentration and spatial distribution, and plasma temperature and rotation, by detection of photon emission following capture of electrons from atomic hydrogen to excited states of multiply charged ions, new calculations of state-selective charge transfer involving light ions have been carried out using the atomic orbital close-coupling and the classical trajectory Monte Carlo methods. By comparing these with results of other approaches applicable in a lower impact energy regime, and by benchmarking them using key experimental data, knowledge of the cross sections can be made available across the range parameters needed by fusion plasma diagnostics.

  1. Photoinduced intramolecular charge transfer process of betaine pyridinium: A theoretical spectroscopic study

    NASA Astrophysics Data System (ADS)

    Perrier, Aurélie; Aloïse, Stéphane; Pawlowska, Zuzanna; Sliwa, Michel; Maurel, François; Abe, Jiro

    2011-10-01

    Using Time-Dependent Density Functional Theory and taking into account bulk solvent effects, we investigate the absorption and emission spectra of a betaine pyridinium molecule, the 2-(1-pyridinio) benzimidazolate (SBPa). This molecule exhibits strong photoinduced intramolecular charge transfer (ICT). We have identified two different electronic states involved, respectively, in the strong bathochromic ICT absorption band (S 2) and in the moderate emission band (S 1). The ICT process is analyzed in terms of charge distribution and dipole moment evolutions upon photoexcitation. These results are compared with steady-state spectroscopic measurements.

  2. Flow Visualization and Heat Transfer Characteristics of Liquid Jet Impingement

    NASA Astrophysics Data System (ADS)

    Jafar, Farial A.; Thorpe, Graham R.; Turan, Özden F.

    2012-07-01

    Equipment used to cool horticultural produce often involves three-phase porous media. The flow field and heat transfer processes that occur in such equipment are generally quantified by means of empirical relationships amongst dimensionless groups. This work represents a first step towards the goal of harnessing the power of computational fluid dynamics (CFD) to better understand the heat transfer processes that occur in beds of irrigated horticultural produce. The primary objective of the present study is to use numerical predictions towards reducing the energy and cooling water requirement in cooling horticultural produce. In this paper, flow and heat transfer predictions are presented of a single slot liquid jet impinging on flat and curved surfaces using a CFD code (FLUENT) for 2D configurations. The effects of Reynolds number, nozzle to plate spacing, nozzle width, and target surface configuration have been studied. Reynolds numbers of 250, 375, 500, 700, 1000, 1500, 1800, and 1900 are studied where the liquid medium is water. Here, the Reynolds number is defined in terms of the hydraulic nozzle diameter, inlet jet velocity, and fluid kinematic viscosity. The results show that Reynolds numbers, nozzle to plate spacing, and nozzle width have a significant effect on the flow field and heat transfer characteristics, whereas the target surface configuration at the stagnation area has no substantial impact. The use of a numerical tool has resulted in a detailed investigation of these characteristics, which has not been available in the literature previously.

  3. Charge transfer kinetics at the solid-solid interface in porous electrodes

    NASA Astrophysics Data System (ADS)

    Bai, Peng; Bazant, Martin Z.

    2014-04-01

    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 electrodes. Here we report a simple method to extract the charge transfer rates in carbon-coated LiFePO4 porous electrodes from chronoamperometry experiments, obtaining curved Tafel plots that contradict the Butler-Volmer equation but fit the Marcus-Hush-Chidsey prediction over a range of temperatures. The fitted reorganization energy matches the Born solvation energy for electron transfer from carbon to the iron redox site. The kinetics are thus limited by electron transfer at the solid-solid (carbon-LixFePO4) interface rather than by ion transfer at the liquid-solid interface, as previously assumed. The proposed experimental method generalizes Chidsey’s method for phase-transforming particles and porous electrodes, and the results show the need to incorporate Marcus kinetics in modelling batteries and other electrochemical systems.

  4. Modeling of Transient Absorption Spectra in Exciton-Charge-Transfer Systems.

    PubMed

    Kramer, Tobias; Rodríguez, Mirta; Zelinskyy, Yaroslav

    2017-01-26

    Time-resolved spectroscopy provides the main tool for analyzing the dynamics of excitonic energy transfer in light-harvesting complexes. Inferring the time scales and effective coupling parameters from experimental data requires the development of numerically exact theoretical models. The finite duration of the laser-molecule interactions and the reorganization process during the exciton migration affect the location and strength of spectroscopic signals. We show that the nonperturbative hierarchical equations of motion method captures these processes in a model exciton system, including the charge-transfer state.

  5. 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.

  6. Charge-transfer contributions to the excitonic coupling matrix element in BODIPY-based energy transfer cassettes

    NASA Astrophysics Data System (ADS)

    Spiegel, J. Dominik; Lyskov, Igor; Kleinschmidt, Martin; Marian, Christel M.

    2017-01-01

    BODIPY-based dyads serve as model systems for the investigation of excitation energy transfer (EET). Through-space EET is brought about by direct and exchange interactions between the transition densities of donor and acceptor localized states. The presence of a molecular linker gives rise to additional charge transfer (CT) contributions. Here, we present a novel approach for the calculation of the excitonic coupling matrix element (ECME) including CT contributions which is based on supermolecular one-electron transition density matrices (STD). The validity of the approach is assessed for a model system of two π -stacked ethylene molecules at varying intermolecular separation. Wave functions and electronic excitation energies of five EET cassettes comprising anthracene as exciton donor and BODIPY as exciton acceptor are obtained by the redesigned combined density functional theory and multireference configuration interaction (DFT/MRCI-R) method. CT contributions to the ECME are shown to be important in the covalently linked EET cassettes.

  7. Dependence of charge transfer phenomena during solid-air two-phase flow on particle disperser

    NASA Astrophysics Data System (ADS)

    Tanoue, Ken-ichiro; Suedomi, Yuuki; Honda, Hirotaka; Furutani, Satoshi; Nishimura, Tatsuo; Masuda, Hiroaki

    2012-12-01

    An experimental investigation of the tribo-electrification of particles has been conducted during solid-air two-phase turbulent flow. The current induced in a metal plate by the impact of polymethylmethacrylate (PMMA) particles in a high-speed air flow was measured for two different plate materials. The results indicated that the contact potential difference between the particles and a stainless steel plate was positive, while for a nickel plate it was negative. These results agreed with theoretical contact charge transfer even if not only the particle size but also the kind of metal plate was changed. The specific charge of the PMMA particles during solid-air two-phase flow using an ejector, a stainless steel branch pipe, and a stainless steel straight pipe was measured using a Faraday cage. Although the charge was negative in the ejector, the particles had a positive specific charge at the outlet of the branch pipe, and this positive charge increased in the straight pipe. The charge decay along the flow direction could be reproduced by the charging and relaxation theory. However, the proportional coefficients in the theory changed with the particle size and air velocity. Therefore, an unexpected charge transfer occurred between the ejector and the branch pipe, which could not be explained solely by the contact potential difference. In the ejector, an electrical current in air might have been produced by self-discharge of particles with excess charge between the nickel diffuser in the ejector and the stainless steel nozzle or the stainless steel pipe due to a reversal in the contact potential difference between the PMMA and the stainless steel. The sign of the current depended on the particle size, possibly because the position where the particles impacted depended on their size. When dual coaxial glass pipes were used as a particle disperser, the specific charge of the PMMA particles became more positive along the particle flow direction due to the contact

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

    SciTech Connect

    Miller, John M.; Onar, Omer C.; Chinthavali, Madhu

    2014-12-22

    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. Lastly, this paper also provides an experimental evidence for frequency selection, fringe field assessment, and the need for low-latency communications in the feedback path.

  9. Combining intra- and intermolecular charge-transfer: a new strategy towards molecular ferromagnets and multiferroics

    PubMed Central

    Di Maiolo, Francesco; Sissa, Cristina; Painelli, Anna

    2016-01-01

    Organic ferroelectric materials are currently a hot research topic, with mixed stack charge transfer crystals playing a prominent role with their large, electronic-in-origin polarization and the possibility to tune the transition temperature down to the quantum limit and/or to drive the ferroelectric transition via an optical stimulus. By contrast, and in spite of an impressive research effort, organic ferromagnets are rare and characterized by very low transition temperatures. Coexisting magnetic and electric orders in multiferroics offer the possibility to control magnetic (electric) properties by an applied electric (magnetic) field with impressive technological potential. Only few examples of multiferroics are known today, based on inorganics materials. Here we demonstrate that, by decorating mixed stack charge transfer crystals with organic radicals, a new family of robust molecular ferromagnets can be designed, stable up to ambient temperature, and with a clear tendency towards multiferroic behaviour. PMID:26790963

  10. Charge-transfer-directed radical substitution enables para-selective C-H functionalization

    NASA Astrophysics Data System (ADS)

    Boursalian, Gregory B.; Ham, Won Seok; Mazzotti, Anthony R.; Ritter, Tobias

    2016-08-01

    Efficient C-H functionalization requires selectivity for specific C-H bonds. Progress has been made for directed aromatic substitution reactions to achieve ortho and meta selectivity, but a general strategy for para-selective C-H functionalization has remained elusive. Herein we introduce a previously unappreciated concept that enables nearly complete para selectivity. We propose that radicals with high electron affinity elicit arene-to-radical charge transfer in the transition state of radical addition, which is the factor primarily responsible for high positional selectivity. We demonstrate with a simple theoretical tool that the selectivity is predictable and show the utility of the concept through a direct synthesis of aryl piperazines. Our results contradict the notion, widely held by organic chemists, that radical aromatic substitution reactions are inherently unselective. The concept of radical substitution directed by charge transfer could serve as the basis for the development of new, highly selective C-H functionalization reactions.

  11. Interaction and charge transfer between dielectric spheres: Exact and approximate analytical solutions.

    PubMed

    Lindén, Fredrik; Cederquist, Henrik; Zettergren, Henning

    2016-11-21

    We present exact analytical solutions for charge transfer reactions between two arbitrarily charged hard dielectric spheres. These solutions, and the corresponding exact ones for sphere-sphere interaction energies, include sums that describe polarization effects to infinite orders in the inverse of the distance between the sphere centers. In addition, we show that these exact solutions may be approximated by much simpler analytical expressions that are useful for many practical applications. This is exemplified through calculations of Langevin type cross sections for forming a compound system of two colliding spheres and through calculations of electron transfer cross sections. We find that it is important to account for dielectric properties and finite sphere sizes in such calculations, which for example may be useful for describing the evolution, growth, and dynamics of nanometer sized dielectric objects such as molecular clusters or dust grains in different environments including astrophysical ones.

  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. Double charge transfer in low-energy H{sup +}+H{sup -} collisions

    SciTech Connect

    Mezei, J. Zs.; Stenrup, M.; Elander, N.; Larson, A.

    2010-07-15

    The cross section for double charge transfer between H{sup +} and H{sup -} at low collision energies (E{<=}90 eV) is calculated using a many-state molecular close-coupling model. The wave function is expanded in a diabatic representation of the seven lowest {sup 1{Sigma}}{sub g}{sup +} and the six lowest {sup 1{Sigma}}{sub u}{sup +} states of the hydrogen molecule. The calculated cross section shows clear oscillations as a function of the collision energy, similar to those observed experimentally. However, the magnitude of the calculated cross section is larger than found in experiments. Also, the cross section for double charge transfer in collisions between D{sup +} and H{sup -} is calculated.

  14. Short-Range Charge Transfer Between Oxide Based Superconductor-Ferromagnetic Metal Interfaces

    NASA Astrophysics Data System (ADS)

    Chien, Te-Yu; Kourkoutis, L. F.; Chakhalian, J.; Muller, D.; Freeland, J. W.

    2014-03-01

    Unlike the conventional superconductor (S) and ferromagnetic metal (F) interface, the understanding of the proximity effect between oxide-based S and F is still unclear. One particular question relates to the charge transfer length scale between S and F layers, which resulted from the lack of an appropriate experimental tool. In this talk, we show that by combining the cross-sectional scanning tunneling microscopy and spectroscopy (XSTM/S) along with scanning transmission electron microscopy (STEM) and electron energy loss spectroscopy (EELS), the charge transfer length scale at the interfaces between YBa Cu O -δ(YBCO) and La3Ca3MnO (LCMO) was revealed to have upper limit of 1 nm.

  15. Combining intra- and intermolecular charge-transfer: a new strategy towards molecular ferromagnets and multiferroics

    NASA Astrophysics Data System (ADS)

    di Maiolo, Francesco; Sissa, Cristina; Painelli, Anna

    2016-01-01

    Organic ferroelectric materials are currently a hot research topic, with mixed stack charge transfer crystals playing a prominent role with their large, electronic-in-origin polarization and the possibility to tune the transition temperature down to the quantum limit and/or to drive the ferroelectric transition via an optical stimulus. By contrast, and in spite of an impressive research effort, organic ferromagnets are rare and characterized by very low transition temperatures. Coexisting magnetic and electric orders in multiferroics offer the possibility to control magnetic (electric) properties by an applied electric (magnetic) field with impressive technological potential. Only few examples of multiferroics are known today, based on inorganics materials. Here we demonstrate that, by decorating mixed stack charge transfer crystals with organic radicals, a new family of robust molecular ferromagnets can be designed, stable up to ambient temperature, and with a clear tendency towards multiferroic behaviour.

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

    SciTech Connect

    Zanni, Martin Thomas

    1999-12-01

    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. Isotope effect in charge-transfer collisions of H with He{sup +}

    SciTech Connect

    Loreau, J.; Dalgarno, A.; Ryabchenko, S.

    2011-11-15

    We present a theoretical study of the isotope effect arising from the replacement of H by T in the charge-transfer collision H(n=2) + He{sup +}(1s) at low energy. Using a quasimolecular approach and a time-dependent wave-packet method, we compute the cross sections for the reaction including the effects of the nonadiabatic radial and rotational couplings. For H(2s) + He{sup +}(1s) collisions, we find a strong isotope effect at energies below 1 eV/amu for both singlet and triplet states. We find a much smaller isotopic dependence of the cross section for H(2p) + He{sup +}(1s) collisions in triplet states, and no isotope effect in singlet states. We explain the isotope effect on the basis of the potential energy curves and the nonadiabatic couplings, and we evaluate the importance of the isotope effect on the charge-transfer rate coefficients.

  18. A novel spectrophotometric determination of trace copper based on charge transfer complex

    NASA Astrophysics Data System (ADS)

    Di, Junwei; Wu, Ying; Ma, Yun

    2005-03-01

    A new type of colored complex, the charge transfer complex, was used to develop the spectrophotometric determination of copper. The method was based on the formation of a colored product, the charge transfer complex of copper substituted tungstophosphate with 3,3',5,5'-tetramethybenzidine (TMB), which was stabilized and sensitized by the addition of polyvinyl alcohol (PVA) in aqueous solution. The structure of copper substituted tungstophosphate was Keggin-type according to the results of infrared (IR) spectra. The optimum reaction conditions and other important analytic parameters had been investigated. Beer's law was obeyed in the copper(II) concentration range of 0.003-0.1 μg mL -1, and the molar absorptivity at 660 nm is 2.54×10 5 L mol -1 cm -1. The proposed method was simple, selective, and sensitive. It was applied to the analytic samples with satisfactory results.

  19. 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 μl per 1.5 ml sensor volume.

  20. Resonant charge transfer in slow Li+-Li(2s) collisions

    NASA Astrophysics Data System (ADS)

    Li, Tie-Cheng; Liu, Chun-Hua; Qu, Yi-Zhi; Liu, Ling; Wu, Yong; Wang, Jian-Guo; P. Liebermann, H.; J. Buenker, R.

    2015-10-01

    The resonant charge transfer process for Li+-Li(2s) collision is investigated by the quantum-mechanical molecular orbital close-coupling (QMOCC) method and the two-center atomic-orbital close-coupling (AOCC) method in an energy range of 1.0 eV/u-104 eV/u. Accurate molecular structure data and charge transfer cross sections are given. Both the all-electron model (AEM) and one-electron model (OEM) are used in the QMOCC calculations, and the discrepancies between the two models are analyzed. The OEM calculation can also give a reliable prediction of the cross sections for energies below 1 keV/u. Project supported by the National Natural Science Foundation of China (Grant Nos. 11179041, 11474032, and 11474033) and the NSAF (Grant No. U1330117).

  1. Spectrophotometric and some thermodynamic parameters of the charge transfer complexation between chloranilic acid and chlorpheniramine.

    PubMed

    Ofoefule, S I; Ajali, U

    2001-01-01

    The principle of charge transfer complexation involving a pi-acceptor (chloranilic acid) and an n-donor (chlorpheniramine) was utilized in the assay of the later in its pure form and in its tablet dosage forms. Some thermodynamic parameters of the complex such as association constant (Kc), molar absorptivity (epsilon c), free energy change (delta G degree), enthalpy (delta H degree) and entropy (delta S degree) changes were determined to establish the stability of the complex and the optimum conditions for the complex formation. The values obtained for these thermodynamic parameters indicated that the complex formed between this two chemical entities is highly stable. Assay of chlorpheniramine in its pure form and in its tablet dosage forms gave high percentage recoveries. The principle of charge transfer complexation could therefore be employed in the colorimetric assay of chlorpheniramine in its tablet dosage forms.

  2. Charge Transfer Directed Radical Substitution Enables para-Selective C–H Functionalization

    PubMed Central

    Boursalian, Gregory B.; Ham, Won Seok; Mazzotti, Anthony R.; Ritter, Tobias

    2016-01-01

    Efficient C–H functionalization requires selectivity for specific C–H bonds. Progress has been made for directed aromatic substitution reactions to achieve ortho- and meta- selectivity, but a general strategy for para-selective C–H functionalization has remained elusive. Herein, we introduce a previously unappreciated concept which enables nearly complete para selectivity. We propose that radicals with high electron affinity elicit areneto-radical charge transfer in the transition state of radical addition, which is the factor primarily responsible for high positional selectivity. We demonstrate that the selectivity is predictable by a simple theoretical tool and show the utility of the concept through a direct synthesis of aryl piperazines. Our results contradict the notion, widely held by organic chemists, that radical aromatic substitution reactions are inherently unselective. The concept of charge transfer directed radical substitution could serve as the basis for the development of new, highly selective C–H functionalization reactions. PMID:27442288

  3. Symmetry-Breaking Charge Transfer of Visible Light Absorbing Systems: Zinc Dipyrrins

    PubMed Central

    2015-01-01

    Zinc dipyrrin complexes with two identical dipyrrin ligands absorb strongly at 450–550 nm and exhibit high fluorescence quantum yields in nonpolar solvents (e.g., 0.16–0.66 in cyclohexane) and weak to nonexistent emission in polar solvents (i.e., <10–3, in acetonitrile). The low quantum efficiencies in polar solvents are attributed to the formation of a nonemissive symmetry-breaking charge transfer (SBCT) state, which is not formed in nonpolar solvents. Analysis using ultrafast spectroscopy shows that in polar solvents the singlet excited state relaxes to the SBCT state in 1.0–5.5 ps and then decays via recombination to the triplet or ground states in 0.9–3.3 ns. In the weakly polar solvent toluene, the equilibrium between a localized excited state and the charge transfer state is established in 11–22 ps. PMID:25270268

  4. Interfaces between strongly correlated oxides: controlling charge transfer and induced magnetism by hybridization

    NASA Astrophysics Data System (ADS)

    Bibes, Manuel

    At interfaces between conventional materials, band bending and alignment are controlled by differences in electrochemical potential. Applying this concept to oxides in which interfaces can be polar and cations may adopt a mixed valence has led to the discovery of novel two-dimensional states between simple band insulators such as LaAlO3 and SrTiO3. However, many oxides have a more complex electronic structure, with charge, orbital and/or spin orders arising from correlations between transition metal and oxygen ions. Strong correlations thus offer a rich playground to engineer functional interfaces but their compatibility with the classical band alignment picture remains an open question. In this talk we will show that beyond differences in electron affinities and polar effects, a key parameter determining charge transfer at correlated oxide interfaces is the energy required to alter the covalence of the metal-oxygen bond. Using the perovskite nickelate (RNiO3) family as a template, we have probed charge reconstruction at interfaces with gadolinium titanate GdTiO3 using soft X-ray absorption spectroscopy and hard X-ray photoemission spectroscopy. We show that the charge transfer is thwarted by hybridization effects tuned by the rare-earth (R) size. Charge transfer results in an induced ferromagnetic-like state in the nickelate (observed by XMCD), exemplifying the potential of correlated interfaces to design novel phases. Further, our work clarifies strategies to engineer two-dimensional systems through the control of both doping and covalence. Work supported by ERC CoG MINT #615759.

  5. Electronic structure, charge distribution, and charge transfer in α- and β-Si3N4 and at the Si(111)/Si3N4(001) interface

    NASA Astrophysics Data System (ADS)

    Zhao, G. L.; Bachlechner, M. E.

    1997-02-01

    The electronic structure, charge distribution, and charge transfer in α- and β- Si3N4 and at the Si(111)/Si3N4(001) interface have been studied using a self-consistent first-principles LCAO method. The calculated charge transfer suggests that both in α- and β-phases, the ionic formula may be written as Si3+1.24N4-0.93. For the Si(111)/Si3N4(001) interface, the silicon atoms from the Si(111) side give some electrons to the N atoms of Si3N4 forming the Si-N bonds at the interface. One Si-N bond is associated with a charge transfer of about 0.31 electrons.

  6. Highly Efficient and Anomalous Charge Transfer in van der Waals Trilayer Semiconductors.

    PubMed

    Ceballos, Frank; Ju, Ming-Gang; Lane, Samuel D; Zeng, Xiao Cheng; Zhao, Hui

    2017-03-08

    Two-dimensional materials, such as graphene and monolayer transition metal dichalcogenides, allow the fabrication of multilayer structures without lattice matching restriction. A central issue in developing such artificial materials is to understand and control the interlayer electron transfer process, which plays a key role in harnessing their emergent properties. Recent photoluminescence and transient absorption measurements revealed that the electron transfer in heterobilayers occurs on ultrafast time scales. However, there is still a lack of fundamental understanding on how this process can be so efficient at van der Waals interfaces. Here we show evidence suggesting the coherent nature of such interlayer electron transfer. In a trilayer of MoS2-WS2-MoSe2, electrons excited in MoSe2 transfer to MoS2 in about one picosecond. Surprisingly, these electrons do not populate the middle WS2 layer during this process. Calculations showed the coherent nature of the charge transfer and reproduced the measured electron transfer time. The hole transfer from MoS2 to MoSe2 is also found to be efficient and ultrafast. The separation of electrons and holes extends their lifetimes to more than one nanosecond, suggesting potential applications of such multilayer structures in optoelectronics.

  7. Ligand-induced dependence of charge transfer in nanotube–quantum dot heterostructures

    SciTech Connect

    Wang, Lei; Han, Jinkyu; Sundahl, Bryan; Thornton, Scott; Zhu, Yuqi; Zhou, Ruiping; Jaye, Cherno; Liu, Haiqing; Li, Zhuo-Qun; Taylor, Gordon T.; Fischer, Daniel A.; Appenzeller, Joerg; Harrison, Robert J.; Wong, Stanislaus S.

    2016-07-01

    As a model system to probe ligand-dependent charge transfer in complex composite heterostructures, we fabricated double-walled carbon nanotube (DWNT) – CdSe quantum dot (QD) composites. Whereas the average diameter of the QDs probed was kept fixed at ~4.1 nm and the nanotubes analyzed were similarly oxidatively processed, by contrast, the ligands used to mediate the covalent attachment between the QDs and DWNTs were systematically varied to include p-phenylenediamine (PPD), 2-aminoethanethiol (AET), and 4-aminothiophenol (ATP). Herein, we have put forth a unique compilation of complementary data from experiment and theory, including results from transmission electron microscopy (TEM), near-edge X-ray absorption fine structure (NEXAFS) spectroscopy, Raman spectroscopy, electrical transport measurements, and theoretical modeling studies, in order to fundamentally assess the nature of the charge transfer between CdSe QDs and DWNTs, as a function of the structure of various, intervening bridging ligand molecules. Specifically, we correlated evidence of charge transfer as manifested by changes and shifts associated with NEXAFS intensities, Raman peak positions, and threshold voltages both before and after CdSe QD deposition onto the underlying DWNT surface. Importantly, for the first time ever in these types of nanoscale composite systems, we have sought to use theoretical modeling to justify and account for our experimental results. Finally, our overall data suggest that (i) QD coverage density on the DWNTs varies, based upon the different ligand pendant groups used and that (ii) the presence of a π-conjugated carbon framework within the ligands themselves and the electron affinity of the pendant groups collectively play important roles in the resulting charge transfer from QDs to the underlying CNTs.

  8. Charge transfer in collisions of Be3+ ions with H atoms

    NASA Astrophysics Data System (ADS)

    Liu, C. H.; Wang, J. G.

    2013-04-01

    The nonradiative charge-transfer processes for the Be3+(1s)+H(1s) collisions are investigated by the quantum-mechanical molecular orbital close-coupling method in the energy range of 0.01-10 keV/u. The radiative charge-transfer cross sections are calculated by the optical potential and semiclassical methods in the energy range 10-6-103 eV/u. The needed molecular data are obtained by the ab initio multireference single- and double-excitation configuration interaction method. Total and state-selective cross sections are presented and compared with other available theoretical data. Our calculation agrees well with the atomic orbital close-coupling results of Liu [L. Liu, D. Jakimovski, J. G. Wang, and R. K. Janev, J. Phys. BJPAPEH0953-407510.1088/0953-4075/43/14/144005 43, 144005 (2010)], but there exist some discrepancies with the semiclassical molecular orbital close-coupling results of Shimakura [N. Shimakura, J. Phys. BJPAMA40953-407510.1088/0953-4075/21/13/015 21, 2485 (1988)]. The present results show that the capture to Si2+(1s3l) states is dominant in the whole energy range with the exception of a narrow range of 2-4 keV/u. Rotational couplings play an important role not only in the state-selective cross sections, but also in the total charge-transfer results. At energies below 40 eV/u, the radiative charge transfer exceeds the nonradiative process.

  9. 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.

  10. Ligand-induced dependence of charge transfer in nanotube–quantum dot heterostructures

    DOE PAGES

    Wang, Lei; Han, Jinkyu; Sundahl, Bryan; ...

    2016-07-01

    As a model system to probe ligand-dependent charge transfer in complex composite heterostructures, we fabricated double-walled carbon nanotube (DWNT) – CdSe quantum dot (QD) composites. Whereas the average diameter of the QDs probed was kept fixed at ~4.1 nm and the nanotubes analyzed were similarly oxidatively processed, by contrast, the ligands used to mediate the covalent attachment between the QDs and DWNTs were systematically varied to include p-phenylenediamine (PPD), 2-aminoethanethiol (AET), and 4-aminothiophenol (ATP). Herein, we have put forth a unique compilation of complementary data from experiment and theory, including results from transmission electron microscopy (TEM), near-edge X-ray absorption finemore » structure (NEXAFS) spectroscopy, Raman spectroscopy, electrical transport measurements, and theoretical modeling studies, in order to fundamentally assess the nature of the charge transfer between CdSe QDs and DWNTs, as a function of the structure of various, intervening bridging ligand molecules. Specifically, we correlated evidence of charge transfer as manifested by changes and shifts associated with NEXAFS intensities, Raman peak positions, and threshold voltages both before and after CdSe QD deposition onto the underlying DWNT surface. Importantly, for the first time ever in these types of nanoscale composite systems, we have sought to use theoretical modeling to justify and account for our experimental results. Finally, our overall data suggest that (i) QD coverage density on the DWNTs varies, based upon the different ligand pendant groups used and that (ii) the presence of a π-conjugated carbon framework within the ligands themselves and the electron affinity of the pendant groups collectively play important roles in the resulting charge transfer from QDs to the underlying CNTs.« less

  11. Oxidation and metal-insertion in molybdenite surfaces: evaluation of charge-transfer mechanisms and dynamics

    PubMed Central

    Ramana, CV; Becker, U; Shutthanandan, V; Julien, CM

    2008-01-01

    Molybdenum disulfide (MoS2), a layered transition-metal dichalcogenide, has been of special importance to the research community of geochemistry, materials and environmental chemistry, and geotechnical engineering. Understanding the oxidation behavior and charge-transfer mechanisms in MoS2 is important to gain better insight into the degradation of this mineral in the environment. In addition, understanding the insertion of metals into molybdenite and evaluation of charge-transfer mechanism and dynamics is important to utilize these minerals in technological applications. Furthermore, a detailed investigation of thermal oxidation behavior and metal-insertion will provide a basis to further explore and model the mechanism of adsorption of metal ions onto geomedia. The present work was performed to understand thermal oxidation and metal-insertion processes of molybdenite surfaces. The analysis was performed using atomic force microscopy (AFM), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Rutherford backscattering spectrometry (RBS), and nuclear reaction analysis (NRA). Structural studies using SEM and TEM indicate the local-disordering of the structure as a result of charge-transfer process between the inserted lithium and the molybdenite layer. Selected area electron diffraction measurements indicate the large variations in the diffusivity of lithium confirming that the charge-transfer is different along and perpendicular to the layers in molybdenite. Thermal heating of molybenite surface in air at 400°C induces surface oxidation, which is slow during the first hour of heating and then increases significantly. The SEM results indicate that the crystals formed on the molybdenite surface as a result of thermal oxidation exhibit regular thin-elongated shape. The average size and density of the crystals on the surface is dependent on the time of annealing; smaller size and high density during the first one-hour and significant increase in

  12. The Mean Trajectory Approximation for Charge and Energy Transfer Processes at Surfaces.

    DTIC Science & Technology

    1985-03-01

    surface. The simplest process of this kind is the ionization/neutralization of an atom/ ion incident on a metal surface. 1-7 More complicated examples...charge transfer process. 1 2 Auger neutralization of an incident ion - 3 is a still more involved example. Other important orocesses that may be described... ion scattering work is carried out at high kinetic energy the low kinetic energy regime is very important in electron stimulated desorption and in the

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

    NASA Astrophysics Data System (ADS)

    Sun, Baichuan; Barnard, Amanda S.

    2016-07-01

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

  14. Luminescence Measurements of Xe+ + N2 and Xe2+ + N2 Hyperthermal Charge Transfer Collisions (Postprint)

    DTIC Science & Technology

    2012-04-10

    Landau - Zener curve-crossing models,18 where CT proba- bilities are maximum at intermediate coupling distances. Lindinger16 studied charge-transfer rate...tran- sition probability approaches a maximum in the high en- ergy limit, unlike the Landau - Zener CT probability which ap- proaches zero. Thus, at the...the cross sections remain constant with energy at high energies is further support for a Rosen- Zener /Demkov over a Landau - Zener curve-crossing

  15. Computational models of an inductive power transfer system for electric vehicle battery charge

    NASA Astrophysics Data System (ADS)

    Anele, A. O.; Hamam, Y.; Chassagne, L.; Linares, J.; Alayli, Y.; Djouani, K.

    2015-09-01

    One of the issues to be solved for electric vehicles (EVs) to become a success is the technical solution of its charging system. In this paper, computational models of an inductive power transfer (IPT) system for EV battery charge are presented. Based on the fundamental principles behind IPT systems, 3 kW single phase and 22 kW three phase IPT systems for Renault ZOE are designed in MATLAB/Simulink. The results obtained based on the technical specifications of the lithium-ion battery and charger type of Renault ZOE show that the models are able to provide the total voltage required by the battery. Also, considering the charging time for each IPT model, they are capable of delivering the electricity needed to power the ZOE. In conclusion, this study shows that the designed computational IPT models may be employed as a support structure needed to effectively power any viable EV.

  16. Ultrafast excitonic and charge transfer dynamics in nanostructured organic polymer materials

    NASA Astrophysics Data System (ADS)

    Polkehn, Matthias; Eisenbrandt, Pierre; Tamura, Hiroyuki; Haacke, Stefan; Méry, Stéphane; Burghardt, Irene

    2016-04-01

    We present theoretical studies of elementary exciton and charge transfer processes in functional organic materials, in view of understanding the key microscopic factors that lead to efficient charge generation in photovoltaics applications. As highlighted by recent experiments, these processes can be guided by quantum coherence, despite the presence of static and dynamic disorder. Our approach combines first-principles parametrized Hamiltonians, based on Time-Dependent Density Functional Theory (TDDFT) and/or high-level electronic structure calculations, with accurate quantum dynamics simulations using the Multi-Configuration Time-Dependent Hartree (MCTDH) method. This contribution specifically addresses charge generation in a novel class of highly ordered oligothiophene-perylene diimide type co-oligomer assemblies, highlighting that chemical design of donor/acceptor combinations needs to be combined with a detailed understanding of the effects of molecular packing.

  17. 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

    ... market value of the property when the transfer involves property meeting conditions in § 102-36.285(a)(1... for excess personal property on a transfer with reimbursement? 102-36.290 Section 102-36.290 Public... Personal Property Transfers with Reimbursement § 102-36.290 How much do we charge for excess...

  18. Manipulating charge transfer excited state relaxation and spin crossover in iron coordination complexes with ligand substitution

    DOE PAGES

    Zhang, Wenkai; Kjaer, Kasper S.; Alonso-Mori, Roberto; ...

    2016-08-25

    Developing light-harvesting and photocatalytic molecules made with iron could provide a cost effective, scalable, and environmentally benign path for solar energy conversion. To date these developments have been limited by the sub-picosecond metal-to-ligand charge transfer (MLCT) electronic excited state lifetime of iron based complexes due to spin crossover – the extremely fast intersystem crossing and internal conversion to high spin metal-centered excited states. We revitalize a 30 year old synthetic strategy for extending the MLCT excited state lifetimes of iron complexes by making mixed ligand iron complexes with four cyanide (CN–) ligands and one 2,2'-bipyridine (bpy) ligand. This enables MLCTmore » excited state and metal-centered excited state energies to be manipulated with partial independence and provides a path to suppressing spin crossover. We have combined X-ray Free-Electron Laser (XFEL) Kβ hard X-ray fluorescence spectroscopy with femtosecond time-resolved UV-visible absorption spectroscopy to characterize the electronic excited state dynamics initiated by MLCT excitation of [Fe(CN)4(bpy)]2–. The two experimental techniques are highly complementary; the time-resolved UV-visible measurement probes allowed electronic transitions between valence states making it sensitive to ligand-centered electronic states such as MLCT states, whereas the Kβ fluorescence spectroscopy provides a sensitive measure of changes in the Fe spin state characteristic of metal-centered excited states. Here, we conclude that the MLCT excited state of [Fe(CN)4(bpy)]2– decays with roughly a 20 ps lifetime without undergoing spin crossover, exceeding the MLCT excited state lifetime of [Fe(2,2'-bipyridine)3]2+ by more than two orders of magnitude.« less

  19. Manipulating charge transfer excited state relaxation and spin crossover in iron coordination complexes with ligand substitution

    SciTech Connect

    Zhang, Wenkai; Kjaer, Kasper S.; Alonso-Mori, Roberto; Bergmann, Uwe; Chollet, Matthieu; Fredin, Lisa A.; Hadt, Ryan G.; Hartsock, Robert W.; Harlang, Tobias; Kroll, Thomas; Kubicek, Katharina; Lemke, Henrik T.; Liang, Huiyang W.; Liu, Yizhu; Nielsen, Martin M.; Persson, Petter; Robinson, Joseph S.; Solomon, Edward I.; Sun, Zheng; Sokaras, Dimosthenis; van Driel, Tim B.; Weng, Tsu -Chien; Zhu, Diling; Warnmark, Kenneth; Sundstrom, Villy; Gaffney, Kelly J.

    2016-08-25

    Developing light-harvesting and photocatalytic molecules made with iron could provide a cost effective, scalable, and environmentally benign path for solar energy conversion. To date these developments have been limited by the sub-picosecond metal-to-ligand charge transfer (MLCT) electronic excited state lifetime of iron based complexes due to spin crossover – the extremely fast intersystem crossing and internal conversion to high spin metal-centered excited states. We revitalize a 30 year old synthetic strategy for extending the MLCT excited state lifetimes of iron complexes by making mixed ligand iron complexes with four cyanide (CN) ligands and one 2,2'-bipyridine (bpy) ligand. This enables MLCT excited state and metal-centered excited state energies to be manipulated with partial independence and provides a path to suppressing spin crossover. We have combined X-ray Free-Electron Laser (XFEL) Kβ hard X-ray fluorescence spectroscopy with femtosecond time-resolved UV-visible absorption spectroscopy to characterize the electronic excited state dynamics initiated by MLCT excitation of [Fe(CN)4(bpy)]2–. The two experimental techniques are highly complementary; the time-resolved UV-visible measurement probes allowed electronic transitions between valence states making it sensitive to ligand-centered electronic states such as MLCT states, whereas the Kβ fluorescence spectroscopy provides a sensitive measure of changes in the Fe spin state characteristic of metal-centered excited states. Here, we conclude that the MLCT excited state of [Fe(CN)4(bpy)]2– decays with roughly a 20 ps lifetime without undergoing spin crossover, exceeding the MLCT excited state lifetime of [Fe(2,2'-bipyridine)3]2+ by more than two orders of magnitude.

  20. Dependence of radiative stabilization on the projectile charge state after double-electron-transfer processes in slow, highly charged ion-molecule collisions

    NASA Astrophysics Data System (ADS)

    Krok, Franciszek; Tolstikhina, Inga Yu.; Sakaue, Hiroyuki A.; Yamada, Ichihiro; Hosaka, Kazumoto; Kimura, Masahiro; Nakamura, Nobuyuki; Ohtani, Shunsuke; Tawara, Hiroyuki

    1997-12-01

    We have measured the radiative stabilization probabilities after double-electron-transfer processes in slow (1.5q keV) Iq++CO collisions in the charge-state regime 8<=q<=26 by using the charge-selected-projectile-recoil-ion-coincidence method. It was found that the radiative stabilization probabilities Prad, defined as Prad=TDC/(TDC+ADC) (TDC is true double capture, and ADC autoionizing double capture), increases from about 1% at the lowest charge up to about 10% at the highest charge as the charge state of the projectile increases. A model is proposed which can explain such a feature, by incorporating a slight modification of the initial population of the transferred levels in the projectile predicted in the extended classical over-barrier model. Based upon the present model, theoretical radiative and autoionization decay rates have been calculated, using the Cowan code. Fairly good agreement between the measured and calculated results has been obtained.

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

    NASA Astrophysics Data System (ADS)

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

    2014-02-01

    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.

  2. Host-Guest Engineering of Coordination Polymers for Highly Tunable Luminophores Based on Charge Transfer Emissions.

    PubMed

    Zhao, Bei; Li, Na; Wang, Xi; Chang, Ze; Bu, Xian-He

    2017-01-25

    Aiming at the targeted construction of coordination polymer luminophores, the engineering of host-guest architectures with charge transfer based emissions is performed by utilizing the interactions between the electron-deficient 2,4,6-tri(pyridin-4-yl)-1,3,5-triazine (tpt) and electron-rich polycyclic aromatic hydrocarbons (PAHs) motifs as acceptors and donors, respectively. Through guest modulation of a prototype coordination polymer [Cd(tpt)(1,4-pda)(H2O)2]·(tpt)·(H2O)2 (1) (1,4-H2pda = 1,4-phenylenediacetic acid), a series of coordination polymers with different PAHs as guests, [Cd2(tpt)2(1,4-pda)2]·guest (2-5) (guest = triphenylene for 2, pyrene for 3, coronene for 4, and perylene for 5), are successfully fabricated. Distinct from 1, coordination polymers 2-5 reveal unique bilayer structures with PAHs interlayer and good stability, owing to the enhanced stacking interactions between tpt motifs and PAH guests. Moreover, their emissions cover a wide range of wavelength due to the effective guest to host charge transfer interactions between donor and acceptor motifs. Their readily tunable host-guest charge transfer based emissions make them good candidates as potential luminophores.

  3. Influence of microhydration on the structures and proton-induced charge transfer in RNA intermediates.

    PubMed

    Bacchus-Montabonel, M C; Calvo, F

    2016-11-01

    Solvation effects are of major interest in the context of radiation damage, due to their potential applications in cancer therapy. Reliable modeling of the solvent is, however, quite challenging, and numerous studies have been devoted to isolated biomolecules and stepwise-hydrated molecules in which the amount of solvent is controlled one molecule at a time. The influence of stepwise hydration on radiation damage is investigated here using the example of proton-induced charge transfer in two biomolecular targets. Uracil has been widely investigated both experimentally and theoretically in this context, and 2-aminooxazole was recently shown to be a potentially important intermediate in prebiotic chemistry. Focusing here on doubly hydrated biomolecules, stable structures and infrared spectra were obtained by combining the results of molecular dynamics simulations with those of quantum chemistry calculations performed at the density-functional theory level with the double hybrid M06-2X functional. The charge-transfer cross-sections upon proton impact were obtained from ab initio molecular calculations and after applying a semi-classical approach to investigate the collision. Our results suggest a significant relationship between the detailed hydration structure and the efficacy of proton-induced charge transfer, highlighting the competing roles of inter- and intramolecular hydrogen bonding.

  4. Charge-transfer complexes of 4-nitrocatechol with some amino alcohols

    NASA Astrophysics Data System (ADS)

    Baniyaghoob, Sahar; Najafpour, Mohammad Mahdi; Boghaei, Davar M.

    2010-03-01

    Charge-transfer (CT) complexes formed from the reactions of 4-nitropyrocatechol (4-nCat) as an electron acceptor with four amino alcohols: 2-aminoethanol, 1-amino-2-propanol, 4-aminobutanol and N-(2-hydroxyethyl)-1,3-diaminopropane (NHEDAP) as electron donors, have been studied spectrophotometrically in H 2O and H 2O/EtOH at 20, 25, 30, 35 and 40 °C. The calculated values of the oscillator strength and transition moment confirm the formation of CT-complexes. The thermodynamic and spectroscopic parameters were also evaluated for the formation of CT-complexes. The equilibrium constants ranged from 9.00 to 2.20 l mol -1 (M -1). These interactions are exothermic and have relatively large standard enthalpy and entropy changes (Δ H values ranged from -15.58 to -3.10 kJ mol -1; Δ S ranged from 26.81 to -3.25 J K -1 mol -1). The solid CT-complexes have been synthesized and characterized by IR, NMR, mass spectrometry and thermal analysis. The photometric titration curves and other spectrometric data for the reactions indicated that the data obtained refer to the formation of 1:1 charge-transfer complex of [(4-nCat) (NHEDAP)] and 1:2 charge-transfer complexes of other amino alcohols [(4-nCat) (amino alcohol) 2]. The effect of alkali and alkaline earth metals on increasing the equilibrium constant of the CT-complexation was also investigated.

  5. Development of highly accurate approximate scheme for computing the charge transfer integral

    NASA Astrophysics Data System (ADS)

    Pershin, Anton; Szalay, Péter G.

    2015-08-01

    The charge transfer integral is a key parameter required by various theoretical models to describe charge transport properties, e.g., in organic semiconductors. The accuracy of this important property depends on several factors, which include the level of electronic structure theory and internal simplifications of the applied formalism. The goal of this paper is to identify the performance of various approximate approaches of the latter category, while using the high level equation-of-motion coupled cluster theory for the electronic structure. The calculations have been performed on the ethylene dimer as one of the simplest model systems. By studying different spatial perturbations, it was shown that while both energy split in dimer and fragment charge difference methods are equivalent with the exact formulation for symmetrical displacements, they are less efficient when describing transfer integral along the asymmetric alteration coordinate. Since the "exact" scheme was found computationally expensive, we examine the possibility to obtain the asymmetric fluctuation of the transfer integral by a Taylor expansion along the coordinate space. By exploring the efficiency of this novel approach, we show that the Taylor expansion scheme represents an attractive alternative to the "exact" calculations due to a substantial reduction of computational costs, when a considerably large region of the potential energy surface is of interest. Moreover, we show that the Taylor expansion scheme, irrespective of the dimer symmetry, is very accurate for the entire range of geometry fluctuations that cover the space the molecule accesses at room temperature.

  6. Development of highly accurate approximate scheme for computing the charge transfer integral.

    PubMed

    Pershin, Anton; Szalay, Péter G

    2015-08-21

    The charge transfer integral is a key parameter required by various theoretical models to describe charge transport properties, e.g., in organic semiconductors. The accuracy of this important property depends on several factors, which include the level of electronic structure theory and internal simplifications of the applied formalism. The goal of this paper is to identify the performance of various approximate approaches of the latter category, while using the high level equation-of-motion coupled cluster theory for the electronic structure. The calculations have been performed on the ethylene dimer as one of the simplest model systems. By studying different spatial perturbations, it was shown that while both energy split in dimer and fragment charge difference methods are equivalent with the exact formulation for symmetrical displacements, they are less efficient when describing transfer integral along the asymmetric alteration coordinate. Since the "exact" scheme was found computationally expensive, we examine the possibility to obtain the asymmetric fluctuation of the transfer integral by a Taylor expansion along the coordinate space. By exploring the efficiency of this novel approach, we show that the Taylor expansion scheme represents an attractive alternative to the "exact" calculations due to a substantial reduction of computational costs, when a considerably large region of the potential energy surface is of interest. Moreover, we show that the Taylor expansion scheme, irrespective of the dimer symmetry, is very accurate for the entire range of geometry fluctuations that cover the space the molecule accesses at room temperature.

  7. Rate limiting activity of charge transfer during lithiation from ionic liquids

    NASA Astrophysics Data System (ADS)

    Rodrigues, Marco-Tulio F.; Lin, Xinrong; Gullapalli, Hemtej; Grinstaff, Mark W.; Ajayan, Pulickel M.

    2016-10-01

    Given the increased use of room temperature ionic liquid electrolytes in Li-ion batteries, due to their non-flammability and negligible volatility, this study evaluates the lithiation kinetics to understand and improve the rate performance of Li-ion batteries. Lithium titanate spinel is used as a model electrode and the electrolyte is composed of LiTFSI and TFSI-coordinated alkoxy-modified phosphonium ionic liquid. Based on the analysis of activation energies for each process, we report that the charge-transfer reaction at the electrode/electrolyte interface is the rate-limiting step for cell operation. This finding is further supported by the observation that a 50-fold decrease in charge-transfer resistance at higher temperatures leads to a significant performance improvement over that of a traditional organic electrolyte at room temperature. Charge-transfer resistance and electrolyte wetting on the electrode surface are critical processes for optimal battery performance, and such processes need to be included when designing new ionic liquids in order to exceed the power density obtained with the use of current carbonate-based electrolytes.

  8. Observation of vibrationally resolved charge transfer in H + +H2 at ECM=20 eV

    NASA Astrophysics Data System (ADS)

    Niedner, G.; Noll, M.; Toennies, J. P.; Schlier, Ch.

    1987-09-01

    The doubly differential cross sections for both the scattered protons and H atoms have been measured at ELAB=30 eV (ECM=20 eV) from θLAB=0° to 12° (θCM=0° to 18°) for the reactions H++H2(v=0)→H++H2(vf) and →H+H+2(vf) . The energy resolution is sufficient to resolve final vibrational states in both channels. The comparison of both the angular and energy loss distributions for the two product channels provides the first clear experimental evidence of a two-step charge transfer mechanism: Vibrational excitation on the lower H++H2 surface is followed by charge transfer in the outgoing collision for only those H2 molecules which are excited vibrationally high enough (vf≥4) to overcome the endoergic barrier (ΔE=1.83 eV). The final vibrational distributions of H+2 appear to be very similar to those of H2 for vf≥4 indicating that for the angular range observed the charge transfer probability is the same for all vibrational states with vf≥4. The comparison with classical trajectory surface hopping (TSH) calculations points to some disagreement which probably can be attributed to the potential surface used.

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

    SciTech Connect

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

    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.

  10. Charge-transfer states and optical transitions at the pentacene-TiO2 interface

    NASA Astrophysics Data System (ADS)

    Ljungberg, M. P.; Vänskä, O.; Koval, P.; Koch, S. W.; Kira, M.; Sánchez-Portal, D.

    2017-03-01

    Pentacene molecules have recently been observed to form a well-ordered monolayer on the (110) surface of rutile TiO2, with the molecules adsorbed lying flat, head to tail. With the geometry favorable for direct optical excitation and given its ordered character, this interface seems to provide an intriguing model to study charge-transfer excitations where the optically excited electrons and holes reside on different sides of the organic–inorganic interface. In this work, we theoretically investigate the structural and electronic properties of this system by means of ab initio calculations and compute its excitonic absorption spectrum. Molecular states appear in the band gap of the clean TiO2 surface, which enables charge-transfer excitations directly from the molecular HOMO to the TiO2 conduction band. The calculated optical spectrum shows a strong polarization dependence and displays excitonic resonances corresponding to the charge-transfer states, which could stimulate new experimental work on the optical response of this interface.

  11. Observation of Ground- and Excited-State Charge Transfer at the C60/Graphene Interface.

    PubMed

    Jnawali, Giriraj; Rao, Yi; Beck, Jonathan H; Petrone, Nicholas; Kymissis, Ioannis; Hone, James; Heinz, Tony F

    2015-07-28

    We examine charge transfer interactions in the hybrid system of a film of C60 molecules deposited on single-layer graphene using Raman spectroscopy and Terahertz (THz) time-domain spectroscopy. In the absence of photoexcitation, we find that the C60 molecules in the deposited film act as electron acceptors for graphene, yielding increased hole doping in the graphene layer. Hole doping of the graphene film by a uniform C60 film at a level of 5.6 × 10(12)/cm(2) or 0.04 holes per interfacial C60 molecule was determined by the use of both Raman and THz spectroscopy. We also investigate transient charge transfer occurring upon photoexcitation by femtosecond laser pulses with a photon energy of 3.1 eV. The C60/graphene hybrid exhibits a short-lived (ps) decrease in THz conductivity, followed by a long-lived increase in conductivity. The initial negative photoconductivity transient, which decays within 2 ps, reflects the intrinsic photoresponse of graphene. The longer-lived positive conductivity transient, with a lifetime on the order of 100 ps, is attributed to photoinduced hole doping of graphene by interfacial charge transfer. We discuss possible microscopic pathways for hot carrier processes in the hybrid system.

  12. Importance of Correctly Describing Charge-Transfer Excitations for Understanding the Chemical Effect in SERS

    SciTech Connect

    Moore, Justin E.; Morton, Seth M.; Jensen, Lasse

    2012-09-06

    The enhancement mechanism due to the molecule-surface chemical coupling in surface-enhanced Raman scattering (SERS) is governed to a large extent by the energy difference between the highest occupied molecular orbital (HOMO) of the metal and the lowest unoccupied molecular orbital (LUMO) of the molecule. Here, we investigate the importance of correctly describing charge-transfer excitations, using time dependent density functional theory (TDDFT), when calculating the chemical coupling in SERS. It is well-known that TDDFT, using traditional functionals, underestimates the position of charge-transfer excitations. Here, we show that this leads to a significant overestimation of the chemical coupling mechanism in SERS. Significantly smaller enhancements are found using long-range corrected (LC) functionals as compared with a traditional generalized gradient approximation (GGA) and hybrid functionals. Enhancement factors are found to be smaller than 530 and typically less than 50. Our results show that it is essential to correctly describe charge-transfer excitations for predicting the chemical enhancement in SERS.

  13. Development of highly accurate approximate scheme for computing the charge transfer integral

    SciTech Connect

    Pershin, Anton; Szalay, Péter G.

    2015-08-21

    The charge transfer integral is a key parameter required by various theoretical models to describe charge transport properties, e.g., in organic semiconductors. The accuracy of this important property depends on several factors, which include the level of electronic structure theory and internal simplifications of the applied formalism. The goal of this paper is to identify the performance of various approximate approaches of the latter category, while using the high level equation-of-motion coupled cluster theory for the electronic structure. The calculations have been performed on the ethylene dimer as one of the simplest model systems. By studying different spatial perturbations, it was shown that while both energy split in dimer and fragment charge difference methods are equivalent with the exact formulation for symmetrical displacements, they are less efficient when describing transfer integral along the asymmetric alteration coordinate. Since the “exact” scheme was found computationally expensive, we examine the possibility to obtain the asymmetric fluctuation of the transfer integral by a Taylor expansion along the coordinate space. By exploring the efficiency of this novel approach, we show that the Taylor expansion scheme represents an attractive alternative to the “exact” calculations due to a substantial reduction of computational costs, when a considerably large region of the potential energy surface is of interest. Moreover, we show that the Taylor expansion scheme, irrespective of the dimer symmetry, is very accurate for the entire range of geometry fluctuations that cover the space the molecule accesses at room temperature.

  14. Electronic structure and charge transfer excitation energies of three endohedral fullerene- ZnTPP/ZnPc dyads

    NASA Astrophysics Data System (ADS)

    Amerikheirabadi, Fatemeh; Basurto, Luis; Zope, Rajendra; Baruah, Tunna

    2015-03-01

    Organic donor-acceptor (D-A) moieties make up the main component of organic photovoltaics (OPVs). It has been proved that the open circuit voltage of these devices which is a parameter in efficiency determination, is directly related to the charge transfer excited states of the D-A pairs. Fullerenes having lots of interesting acceptor properties and porphyrins as well as phthalocyanines possessing intriguing donor characteristics, are shown to be promising nominees. In this work, we computationally analyze three donor-acceptor dyads of Zn-tetraphenyl porphyrin and Zn-phthalocyanine with novel endohedral fullerenes: Sc3N@C80_ZnTPP, Y3N@C80_ZnTPPandSc3N@C80_ZnPc.TheSc3N@C80_and Y3N@C80 belong to a particular class of fullerenes called trimetallic nitride endohedral fullerenes where the trimellatic nitrides form the endohedral units. Density functional theory, as implemented in NRLMOL code, is used to study the electronic structure and the related properties of these D-A complexes. The charge transfer excitation energies are calculated using the perturbative delta self-consistent field method recently developed in our group. We find that the CT excitation energies are larger for endohedral fullerene based dyads compared to similar C60 based dyads.

  15. The Role of πσ* State in Intramolecular Charge Transfer of 4-(DIMETHYLAMINO){-}BENZONITRILE and Related Molecules

    NASA Astrophysics Data System (ADS)

    Fujiwara, Takashige; Zgierski, Marek Z.; Lim, Edward C.

    2011-06-01

    The solvent-polarity dependence and temporal characteristics of the transient absorption of 4-(dimethylamino)-benzonitrile, DMABN, and 4-(dimethylamino)benzethyne, DMABE, demonstrate the presence of the πσ*-state absorption at about 700 nm and the ππ* (LE)-state absorption at about 520 nm and 450 nm. The rise and decay times of the πσ*-state transient differ from those of the ππ*-state transients in both compounds. Moreover, the peak position of the πσ*-state absorption is blue-shifted and more intense in acetonitrile as compared to n-hexane, whereas the band positions of the ππ*-state absorptions are essentially the same in the two solvents. For DMABN in acetonitrile, the rise time (˜ 4.3 ps) of the twisted intramolecular charge transfer (TICT)-state transient at 330 nm is identical to the decay time of the πσ*-state transient. The 4.8 ns decay time of the TICT-state absorption of DMABN is longer than the 2.9 ns decay time of the intramolecular charge-transfer (ICT) fluorescence, indicating that the fluorescent ICT state differs from the TICT state observed in transient absorption. These results are consistent with the presence of a low-lying πσ* state in DMABN (and DMABE), and the role the πσ* state plays in the formation of the TICT state of DMABN.

  16. Ultrafast Investigation of Intramolecular Charge Transfer and Solvation Dynamics of Tetrahydro[5]-helicene-Based Imide Derivatives

    NASA Astrophysics Data System (ADS)

    Zhu, Huaning; Li, Meng; Hu, Jiangpu; Wang, Xian; Jie, Jialong; Guo, Qianjin; Chen, Chuanfeng; Xia, Andong

    2016-04-01

    We report the excited-state intramolecular charge transfer (ICT) characteristics of four tetrahydro[5] helicene-based imide (THHBI) derivatives with various electron-donating substitutes in different polarity of solvents using steady-state, time-resolved transient absorption (TA) spectroscopy. It is found that, the small bathochromic-shift of the absorption spectra but large red shift of the emission spectra for all dyes with increasing solvent polarity indicates the larger dipole moment of the excited state compared to ground state. The results of theoretical calculations exhibit the charge transfer from the terminal donors to helical backbone, which accounts for the degrees of red shift of the emission spectra from different extent of ICT nature. Time-resolved TA spectra recorded as a function of electron-donating substitutes and solvent polarity show the dye with stronger donors (THHBI-PhNPh2) in more polar solvent behaves faster excited-state ICT relaxation, leading to the formation of solvent-stabilized ICT state (ICT’ state) from the excited ICT state; The dyes (THHBI-Ph, THHBI-PhCF3 and THHBI-PhOMe) with relative weaker donors show weaker dependence on solvent polarity, and instead of that intersystem crossing (ISC) becomes possible from ICT state to triplet state.

  17. On the effect of demographic characteristics on the formulation of solid waste charging policy.

    PubMed

    Karagiannidis, A; Xirogiannopoulou, A; Moussiopoulos, N

    2006-01-01

    This paper presents the results from an analysis of municipal charges in Greece, as the fees paid by municipal waste producers to the municipal authorities are included in these charges and constitute a major part of them. The aim is to determine whether and how some of the demographic characteristics of a municipality influence the formulation of municipal waste charges and specifically the level of the charge. The study included 339 Hellenic municipalities, which comprised approximately 62% of the overall population in the country.

  18. 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 π-π* transition in the chloranil is also observed.

  19. Charge transfer dissociation (CTD) mass spectrometry of peptide cations using kiloelectronvolt helium cations.

    PubMed

    Hoffmann, William D; Jackson, Glen P

    2014-11-01

    A kiloelectronvolt beam of helium ions is used to ionize and fragment precursor peptide ions starting in the 1+ charge state. The electron affinity of helium cations (24.6 eV) exceeds the ionization potential of protonated peptides and can therefore be used to abstract an electron from--or charge exchange with--the isolated precursor ions. Kiloelectronvolt energies are used, (1) to overcome the Coulombic repulsion barrier between the cationic reactants, (2) to overcome ion-defocussing effects in the ion trap, and (3) to provide additional activation energy. Charge transfer dissociation (CTD) of the [M+H](+) precursor of Substance P gives product ions such as [M+H](2+•) and a dominant series of a ions in both the 1+ and 2+ charge states. These observations, along with the less-abundant a + 1 ions, are consistent with ultraviolet photodissociation (UVPD) results of others and indicate that C-C(α) cleavages are possible through charge exchange with helium ions. Although the efficiencies and timescale of CTD are not yet suitable for on-line chromatography, this new approach to ion activation provides an additional potential tool for the interrogation of gas phase ions.

  20. Charge Transfer as a Probe for the Interfacial Properties of Quantum Dot-Ligand Complexes

    NASA Astrophysics Data System (ADS)

    Weinberg, David Joseph

    This dissertation describes the study of charge transfer interactions between colloidal quantum dots (QDs) and molecular redox partners in the context of both fundamental investigations of charge recombination mechanisms in nanocrystal-molecule systems, and as a technique to probe the properties of the QD ligand shell. Charge separation in a system of CdS nanocrystals and organic hole acceptors results in the formation of a spin-correlated radical ion pair. Interrogating this photogenerated species with EPR and magnetic field effect transient absorption techniques reveals that the charge recombination dynamics of this donor-acceptor system are dictated by the radical pair intersystem crossing mechanism on the nanosecond timescale. These experiments also indicate that the photoinjected electron localizes at a CdS QD surface trap state, and the coupling between the electron and hole in this spin-correlated system is low. Additional studies involving the CdS QDs and organic hole acceptors are proposed which would investigate the exchange of charge and energy within the nanocrystal organic adlayer. Collisional charge transfer interactions between substituted benzoquinone molecules and PbS QDs coated with mixed monolayers of oleic acid and perfluorodecanethiol are monitored via photoluminescence and transient absorption spectroscopies. These experiments reveal that partially fluorinated ligand shells are less permeable to solution phase molecules and offer greater protection of the nanocrystal surface than their aliphatic counterparts. Only a small amount of fluorinated surfactant ( 20% surface coverage) is necessary to profoundly change the permeability of the ligand shell, and the protective nature of these fluorinated molecules is likely a combination of the molecular volume and oleophobicity of these ligands. Follow up work is discussed which would elucidate the influence of solvent and extent of surfactant fluorination on the permeability of these ligand shells, as

  1. Ion imaging study of dissociative charge transfer in the N2(+) + CH4 system.

    PubMed

    Pei, Linsen; Farrar, James M

    2013-03-28

    The velocity map ion imaging method is applied to the dissociative charge transfer reactions of N2(+) with CH4 studied in crossed beams. The velocity space images are collected at four collision energies between 0.5 and 1.5 eV, providing both product kinetic energy and angular distributions for the reaction products CH3(+) and CH2(+). The general shapes of the images are consistent with long range electron transfer from CH4 to N2(+) preceding dissociation, and product kinetic energy distributions are consistent with energy resonance in the initial electron transfer step. The branching ratio for CH3(+):CH2(+) is 85:15 over the full collision energy range, consistent with literature reports.

  2. Transient negative photoconductance in a charge transfer double quantum well under optical intersubband excitation

    NASA Astrophysics Data System (ADS)

    Rüfenacht, M.; Tsujino, S.; Sakaki, H.

    1998-06-01

    Recently, it was shown that an electron-hole radiative recombination is induced by a mid-infrared light exciting an intersubband transition in a charge transfer double quantum well (CTDQW). This recombination was attributed to an upstream transfer of electrons from an electron-rich well to a hole-rich well. In this study, we investigated the electrical response of a CTDQW under intersubband optical excitation, and found that a positive photocurrent, opposite in sign and proportional to the applied electric field, accompanies the intersubband-transition-induced luminescence (ITIL) signal. A negative photocurrent component was also observed and attributed to heating processes. This work brings a further evidence of the ITIL process and shows that an important proportion of the carriers are consumed by the transfer of electrons.

  3. Studies of Photosynthetic Energy and Charge Transfer by Two-dimensional Fourier transform electronic spectroscopy

    NASA Astrophysics Data System (ADS)

    Ogilvie, Jennifer

    2010-03-01

    Two-dimensional (2D) Fourier transform electronic spectroscopy has recently emerged as a powerful tool for the study of energy transfer in complex condensed-phase systems. Its experimental implementation is challenging but can be greatly simplified by implementing a pump-probe geometry, where the two phase-stable collinear pump pulses are created with an acousto-optic pulse-shaper. This approach also allows the use of a continuum probe pulse, expanding the available frequency range of the detection axis and allowing studies of energy transfer and electronic coupling over a broad range of frequencies. We discuss several benefits of 2D electronic spectroscopy and present 2D data on the D1-D2 reaction center complex of Photosystem II from spinach. We discuss the ability of 2D spectroscopy to distinguish between current models of energy and charge transfer in this system.

  4. Kapton charging characteristics: Effects of material thickness and electron-energy distribution

    NASA Technical Reports Server (NTRS)

    Williamson, W. S.; Dulgeroff, C. R.; Hymann, J.; Viswanathan, R.

    1985-01-01

    Charging characteristics of polyimide (Kapton) of varying thicknesses under irradiation by a very-low-curent-density electron beam, with the back surface of the sample grounded are reported. These charging characteristics are in good agreement with a simple analytical model which predicts that in thin samples at low current density, sample surface potential is limited by conduction leakage through the bulk material. The charging of Kapton in a low-current-density electron beam in which the beam energy was modulated to simulate Maxwellian and biMaxwellian distribution functions is measured.

  5. X-ray absorption structural study of a reversible, photoexcited charge-transfer state

    SciTech Connect

    Chen, L.X.; Bowman, M.K.; Norris, J.R. Univ. of Chicago, IL ); Montano, P.A. )

    1993-05-19

    Electron-transfer reactions can be accompanied by significant nuclear movements. Nuclear motion appears to be especially vital to the reversible, photoinduced charge-transfer chemistry of cyclopentadienylnickel nitrosyl (C[sub 5]H[sub 5]NiNO). Although extended X-ray absorption fine structure (EXAFS) spectroscopy has recorded photoinduced changes in the ligation of myoglobins, similar X-ray studies of electron-transfer chemistry have not been reported. Here we examine reversible, photoinduced structural changes in C[sub 5]H[sub 5]NiNO by EXAFS and propose a mechanism for the electron-transfer chemistry. This work demonstrates that EXAFS can measure distance changes accompanying photoinduced electron transfer to provide new details of the geometry of photoexcited state and suggests that electron transfer occurs in the transient, optically excited states of C[sub 5]H[sub 5]NiNO and C[sub 5]H[sub 5]NiNO[sup CT] as dictated by NO movement that produces either C[sub 5]H[sub 5]NiNO[sup CT] or C[sub 5]H[sub 5]NiNO[sup GS]. 14 refs., 2 figs.

  6. 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 π-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.

  7. Probing and Exploiting the Interplay between Nuclear and Electronic Motion in Charge Transfer Processes.

    PubMed

    Delor, Milan; Sazanovich, Igor V; Towrie, Michael; Weinstein, Julia A

    2015-04-21

    The Born-Oppenheimer approximation refers to the assumption that the nuclear and electronic wave functions describing a molecular system evolve and can be determined independently. It is now well-known that this approximation often breaks down and that nuclear-electronic (vibronic) coupling contributes greatly to the ultrafast photophysics and photochemistry observed in many systems ranging from simple molecules to biological organisms. In order to probe vibronic coupling in a time-dependent manner, one must use spectroscopic tools capable of correlating the motions of electrons and nuclei on an ultrafast time scale. Recent developments in nonlinear multidimensional electronic and vibrational spectroscopies allow monitoring both electronic and structural factors with unprecedented time and spatial resolution. In this Account, we present recent studies from our group that make use of different variants of frequency-domain transient two-dimensional infrared (T-2DIR) spectroscopy, a pulse sequence combining electronic and vibrational excitations in the form of a UV-visible pump, a narrowband (12 cm(-1)) IR pump, and a broadband (400 cm(-1)) IR probe. In the first example, T-2DIR is used to directly compare vibrational dynamics in the ground and relaxed electronic excited states of Re(Cl)(CO)3(4,4'-diethylester-2,2'-bipyridine) and Ru(4,4'-diethylester-2,2'-bipyridine)2(NCS)2, prototypical charge transfer complexes used in photocatalytic CO2 reduction and electron injection in dye-sensitized solar cells. The experiments show that intramolecular vibrational redistribution (IVR) and vibrational energy transfer (VET) are up to an order of magnitude faster in the triplet charge transfer excited state than in the ground state. These results show the influence of electronic arrangement on vibrational coupling patterns, with direct implications for vibronic coupling mechanisms in charge transfer excited states. In the second example, we show unambiguously that electronic and

  8. Molecular orbital (SCF-Xα-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 Xα-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.

  9. Ultrafast charge-transfer in organic photovoltaic interfaces: geometrical and functionalization effects.

    PubMed

    Santos, Elton J G; Wang, W L

    2016-09-21

    Understanding the microscopic mechanisms of electronic excitation in organic photovoltaic cells is a challenging problem in the design of efficient devices capable of performing sunlight harvesting. Here we develop and apply an ab initio approach based on time-dependent density functional theory and Ehrenfest dynamics to investigate photoinduced charge transfer in small organic molecules. Our calculations include mixed quantum-classical dynamics with ions moving classically and electrons quantum mechanically, where no experimental external parameter other than the material geometry is required. We show that the behavior of photocarriers in zinc phthalocyanine (ZnPc) and C60 systems, an effective prototype system for organic solar cells, is sensitive to the atomic orientation of the donor and the acceptor units as well as the functionalization of covalent molecules at the interface. In particular, configurations with the ZnPc molecules facing on C60 facilitate charge transfer between substrate and molecules that occurs within 200 fs. In contrast, configurations where ZnPc is tilted above C60 present extremely low carrier injection efficiency even at longer times as an effect of the larger interfacial potential level offset and higher energetic barrier between the donor and acceptor molecules. An enhancement of charge injection into C60 at shorter times is observed as binding groups connect ZnPc and C60 in a dyad system. Our results demonstrate a promising way of designing and controlling photoinduced charge transfer on the atomic level in organic devices that would lead to efficient carrier separation and maximize device performance.

  10. Melting of Pb Charge Glass and Simultaneous Pb-Cr Charge Transfer in PbCrO3 as the Origin of Volume Collapse

    DOE PAGES

    Yu, Runze; Hojo, Hajime; Watanuki, Tetsu; ...

    2015-09-15

    A metal to insulator transition in integer or half integer charge systems can be regarded as crystallization of charges. The insulating state tends to have a glassy nature when randomness or geometrical frustration exists. In this paper, we report that the charge glass state is realized in a perovskite compound PbCrO3, which has been known for almost 50 years, without any obvious inhomogeneity or triangular arrangement in the charge system. PbCrO3 has a valence state of Pb2+0.5Pb4+0.5Cr3+O3 with Pb2+–Pb4+ correlation length of three lattice-spacings at ambient condition. A pressure induced melting of charge glass and simultaneous Pb–Cr charge transfer causesmore » an insulator to metal transition and ~10% volume collapse.« less

  11. Transfer characteristics of rectangular phase gratings in interference microscopy.

    PubMed

    Lehmann, Peter; Xie, Weichang; Niehues, Jan

    2012-02-15

    In this Letter, the transfer characteristics of rectangular periodic phase objects are studied. It turns out that there are significant differences compared to amplitude objects. The imaging of an amplitude object can be understood as a linear process, whereas phase objects behave nonlinearly. It is shown that under certain conditions the correct shape of a rectangular phase grating can be obtained by an interference microscope as long as the first order diffraction component passes the optical imaging system. This result is in a good agreement with experimental observations and computer simulation results.

  12. An Electronic Structure Approach to Charge Transfer and Transport in Molecular Building Blocks for Organic Optoelectronics

    NASA Astrophysics Data System (ADS)

    Hendrickson, Heidi Phillips

    A fundamental understanding of charge separation in organic materials is necessary for the rational design of optoelectronic devices suited for renewable energy applications and requires a combination of theoretical, computational, and experimental methods. Density functional theory (DFT) and time-dependent (TD)DFT are cost effective ab-initio approaches for calculating fundamental properties of large molecular systems, however conventional DFT methods have been known to fail in accurately characterizing frontier orbital gaps and charge transfer states in molecular systems. In this dissertation, these shortcomings are addressed by implementing an optimally-tuned range-separated hybrid (OT-RSH) functional approach within DFT and TDDFT. The first part of this thesis presents the way in which RSH-DFT addresses the shortcomings in conventional DFT. Environmentally-corrected RSH-DFT frontier orbital energies are shown to correspond to thin film measurements for a set of organic semiconducting molecules. Likewise, the improved RSH-TDDFT description of charge transfer excitations is benchmarked using a model ethene dimer and silsesquioxane molecules. In the second part of this thesis, RSH-DFT is applied to chromophore-functionalized silsesquioxanes, which are currently investigated as candidates for building blocks in optoelectronic applications. RSH-DFT provides insight into the nature of absorptive and emissive states in silsesquioxanes. While absorption primarily involves transitions localized on one chromophore, charge transfer between chromophores and between chromophore and silsesquioxane cage have been identified. The RSH-DFT approach, including a protocol accounting for complex environmental effects on charge transfer energies, was tested and validated against experimental measurements. The third part of this thesis addresses quantum transport through nano-scale junctions. The ability to quantify a molecular junction via spectroscopic methods is crucial to their

  13. Complex and charge transfer between TiO2 and pyrroloquinoline quinone.

    PubMed

    Dimitrijevic, Nada M; Poluektov, Oleg G; Saponjic, Zoran V; Rajh, Tijana

    2006-12-21

    Pyrroloquinoline quinone (PQQ) forms a tridentate complex with coordinatively unsaturated titanium atoms on the surface of approximately 4.5 nm TiO2 particles; an association constant of K = 550 M-1 per Ti(IV)surf has been determined. Low-temperature electron paramagnetic resonance was employed in identification of localized charges and consequently produced radicals and in determination of charge-transfer processes. The photoexcitation of the PQQ-TiO2 complex results in the transfer of conduction band electrons from TiO2 to bound PQQ and the formation of the semiquinone radical. Attaching dopamine (DA) as an electron donor and PQQ as an electron acceptor on the surface of TiO2 results in spatial separation of photogenerated charges; the holes localize on dopamine and electrons on PQQ, with higher yields than for each component separately. In this triad-type assembly (PQQ-TiO2/DA) the PQQ that is bound to the particles acts as a sink for electrons allowing their almost complete scavenging even at temperature as low as 4 K.

  14. Nuclear Motion Driven Ultrafast Photodissociative Charge Transfer of the PENNA Cation: An Experimental and Computational Study.

    PubMed

    Sun, Shoutian; Mignolet, Benoit; Fan, Lin; Li, Wen; Levine, Raphael D; Remacle, Francoise

    2017-02-23

    Ultrafast nuclear driven charge transfer prior to dissociation is an important process in modular systems as was demonstrated experimentally in the bifunctional molecule 2-phenylethyl-N,N-dimethylamine (PENNA) in work by Lehr et al. ( J. Phys. Chem. A 2005 , 109 , 8074 ). The ultrafast dynamics of PENNA photoexcited to the three lowest electronic states of the cation (D0, D1, and D2) was studied using quantum chemistry and surface hoping. We show that a conical intersection, localized in the Franck-Condon region, between the D0 and the D1 states, leads to an ultrafast charge transfer, computed here to be on a time scale of 65 fs, between the phenyl and the amine charged subunits. On the D0 ground state, the dissociation proceeds on the 60 ps time scale through a 19 kcal/mol late barrier. The computed kinetic energy release is in good agreement with a new experimental measurement of PENNA ionization by an 800 nm 30 fs intense laser pulse.

  15. Single-crystal charge transfer interfaces for efficient photonic devices (Conference Presentation)

    NASA Astrophysics Data System (ADS)

    Alves, Helena; Pinto, Rui M.; Maçôas, Ermelinda M. S.; Baleizão, Carlos; Santos, Isabel C.

    2016-09-01

    Organic semiconductors have unique optical, mechanical and electronic properties that can be combined with customized chemical functionality. In the crystalline form, determinant features for electronic applications such as molecular purity, the charge mobility or the exciton diffusion length, reveal a superior performance when compared with materials in a more disordered form. Combining crystals of two different conjugated materials as even enable a new 2D electronic system. However, the use of organic single crystals in devices is still limited to a few applications, such as field-effect transistors. In 2013, we presented the first system composed of single-crystal charge transfer interfaces presenting photoconductivity behaviour. The system composed of rubrene and TCNQ has a responsivity reaching 1 A/W, corresponding to an external quantum efficiency of nearly 100%. A similar approach, with a hybrid structure of a PCBM film and rubrene single crystal also presents high responsivity and the possibility to extract excitons generated in acceptor materials. This strategy led to an extended action towards the near IR. By adequate material design and structural organisation of perylediimides, we demonstrate that is possible to improve exciton diffusion efficiency. More recently, we have successfully used the concept of charge transfer interfaces in phototransistors. These results open the possibility of using organic single-crystal interfaces in photonic applications.

  16. Jahn-Teller effects in transition-metal compounds with small charge-transfer energy

    NASA Astrophysics Data System (ADS)

    Mizokawa, Takashi

    2013-04-01

    We have studied Jahn-Teller effects in Cs2Au2Br6, ACu3Co4O12(A=Ca or Y), and IrTe2 in which the ligand p-to-transition-metal d charge-transfer energy is small or negative. The Au+/Au3+ charge disproportionation of Cs2Au2Br6 manifests in Au 4f photoemission spectra. In Cs2Au2Br6 with negative Δ and intermediate U, the charge disproportionation can be described using effective d orbitals constructed from the Au 5d and Br 4p orbitals and is stabilized by the Jahn-Teller distortion of the Au3+ site with low-spin d8 configuration. In ACu3Co4O12, Δs for Cu3+ and Co4+ are negative and Us are very large. The Zhang-Rice picture is valid to describe the electronic state, and the valence change from Cu2+/Co4+ to Cu3+/Co3+ can be viewed as the O 2p hole transfer from Co to Cu or d9 + d6L → d9L + d6. In IrTe2, both Δ and U are small and the Ir 5d and Te 5p electrons are itinerant to form the multi-band Fermi surfaces. The ideas of band Jahn-Teller transition and Peierls transition are useful to describe the structural instabilities.

  17. 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).

  18. Theoretical investigation of charge transfer between N{sup 6+} and atomic hydrogen

    SciTech Connect

    Wu, Y.; Stancil, P. C.; Liebermann, H. P.; Funke, P.; Rai, S. N.; Buenker, R. J.; Schultz, D. R.; Hui, Y.; Draganic, I. N.; Havener, C. C.

    2011-08-15

    Charge transfer due to collisions of ground-state N{sup 6+}(1s {sup 2} S) with atomic hydrogen has been investigated theoretically using the quantum-mechanical molecular-orbital close-coupling (QMOCC) method, in which the adiabatic potentials and nonadiabatic couplings were obtained using the multireference single- and double-excitation configuration-interaction (MRDCI) approach. Total, n-, l-, and S-resolved cross sections have been obtained for energies between 10 meV/u and 10 keV/u. The QMOCC results were compared to available experimental and theoretical data as well as to merged-beams measurements and atomic-orbital close-coupling and classical trajectory Monte Carlo calculations. The accuracy of the QMOCC charge-transfer cross sections was found to be sensitive to the accuracy of the adiabatic potentials and couplings. Consequently, we developed a method to optimize the atomic basis sets used in the MRDCI calculations for highly charged ions. Since cross sections, especially those that are state selective, are necessary input for x-ray emission simulation of heliospheric and Martian exospheric spectra arising from solar wind ion-neutral gas collisions, a recommended set of state-selective cross sections, based on our evaluation of the calculations and measurements, is provided.

  19. Theoretical Investigation of Charge Transfer between N6+ and atomic Hydrogen

    SciTech Connect

    Wu, Y.; Stancil, P C; Liebermann, H. P.; Funke, P.; Rai, S. N.; Buenker, R. J.; Schultz, David Robert; Hui, Yawei; Draganic, Ilija N; Havener, Charles C

    2011-01-01

    Charge transfer due to collisions of ground-state N{sup 6+}(1s{sup 2} S) with atomic hydrogen has been investigated theoretically using the quantum-mechanical molecular-orbital close-coupling (QMOCC) method, in which the adiabatic potentials and nonadiabatic couplings were obtained using the multireference single- and double-excitation configuration-interaction (MRDCI) approach. Total, n-, l-, and S-resolved cross sections have been obtained for energies between 10 meV/u and 10 keV/u. The QMOCC results were compared to available experimental and theoretical data as well as to merged-beams measurements and atomic-orbital close-coupling and classical trajectory Monte Carlo calculations. The accuracy of the QMOCC charge-transfer cross sections was found to be sensitive to the accuracy of the adiabatic potentials and couplings. Consequently, we developed a method to optimize the atomic basis sets used in the MRDCI calculations for highly charged ions. Since cross sections, especially those that are state selective, are necessary input for x-ray emission simulation of heliospheric and Martian exospheric spectra arising from solar wind ion-neutral gas collisions, a recommended set of state-selective cross sections, based on our evaluation of the calculations and measurements, is provided.

  20. Atomic dipole polarization in charge-transfer complexes with halogen bonding.

    PubMed

    Bartashevich, E V; Tsirelson, V G

    2013-02-21

    The polarization effects associated with halogen bonding for the series of charge-transfer complexes D(m)···X-Y, where donor molecules D(m) = NH(3), H(2)O, H(2)S, C(2)H(4), CO and X-Y = Cl(2), ClF, Br(2), BrCl, ICl, I(2), are characterized in terms of the quantum theory of atoms in molecules using the B3LYP/6-311** Kohn-Sham wave functions. We study the electrostatic potential features of separate donor and acceptor molecules, the change in atomic charges as well as the atomic electric dipole moments and their components, and the intra-atomic electron density dipole polarization and the bonding dipole moments resulting from the electron density redistribution between the molecules in the charge-transfer complexes. The equation linking the most negative electrostatic potential values in the donor molecules and the most positive values in dihalogen molecules with the stretching force constants was found using two-factor regression. It is demonstrated that the dipole polarization of the acceptor atom mirrors the strength of halogen bonding in complexes in a series of different donors and acceptors. An exponential relationship between the magnitude of the total atomic electric dipole moment of the acceptor atom and the intermolecular stretching force constant is established for weakly bounded complexes.

  1. Surface Charge Transfer Doping of Low-Dimensional Nanostructures toward High-Performance Nanodevices.

    PubMed

    Zhang, Xiujuan; Shao, Zhibin; Zhang, Xiaohong; He, Yuanyuan; Jie, Jiansheng

    2016-12-01

    Device applications of low-dimensional semiconductor nanostructures rely on the ability to rationally tune their electronic properties. However, the conventional doping method by introducing impurities into the nanostructures suffers from the low efficiency, poor reliability, and damage to the host lattices. Alternatively, surface charge transfer doping (SCTD) is emerging as a simple yet efficient technique to achieve reliable doping in a nondestructive manner, which can modulate the carrier concentration by injecting or extracting the carrier charges between the surface dopant and semiconductor due to the work-function difference. SCTD is particularly useful for low-dimensional nanostructures that possess high surface area and single-crystalline structure. The high reproducibility, as well as the high spatial selectivity, makes SCTD a promising technique to construct high-performance nanodevices based on low-dimensional nanostructures. Here, recent advances of SCTD are summarized systematically and critically, focusing on its potential applications in one- and two-dimensional nanostructures. Mechanisms as well as characterization techniques for the surface charge transfer are analyzed. We also highlight the progress in the construction of novel nanoelectronic and nano-optoelectronic devices via SCTD. Finally, the challenges and future research opportunities of the SCTD method are prospected.

  2. Dynamic corona characteristics of water droplets on charged conductor surface

    NASA Astrophysics Data System (ADS)

    Xu, Pengfei; Zhang, Bo; Wang, Zezhong; Chen, Shuiming; He, Jinliang

    2017-03-01

    The formation of the Taylor cone of a water droplet on the surface of the conductor in a line-ground electrode system is captured using a high-speed camera, while the corona current is synchronously measured using a current measurement system. Repeated Taylor cone deformation is observed, yielding regular groupings of corona current pulses. The underlying mechanism of this deformation is studied and the correlation between corona discharge characteristics and cone deformation is investigated. Depending on the applied voltage and rate of water supply, the Taylor cone may be stable or unstable and has a significant influence on the characteristics of the corona currents. If the rate of water supply is large enough, the Taylor cone tends to be unstable and generates corona-current pulses of numerous induced current pulses with low amplitudes. In consequence, this difference suggests that large rainfall results in simultaneously lower radio interference and higher corona loss.

  3. Single Molecule Spectroelectrochemistry of Interfacial Charge Transfer Dynamics In Hybrid Organic Solar Cell

    SciTech Connect

    Pan, Shanlin

    2014-11-16

    Our research under support of this DOE grant is focused on applied and fundamental aspects of model organic solar cell systems. Major accomplishments are: 1) we developed a spectroelectorchemistry technique of single molecule single nanoparticle method to study charge transfer between conjugated polymers and semiconductor at the single molecule level. The fluorescence of individual fluorescent polymers at semiconductor surfaces was shown to exhibit blinking behavior compared to molecules on glass substrates. Single molecule fluorescence excitation anisotropy measurements showed the conformation of the polymer molecules did not differ appreciably between glass and semiconductor substrates. The similarities in molecular conformation suggest that the observed differences in blinking activity are due to charge transfer between fluorescent polymer and semiconductor, which provides additional pathways between states of high and low fluorescence quantum efficiency. Similar spectroelectrochemistry work has been done for small organic dyes for understand their charge transfer dynamics on various substrates and electrochemical environments; 2) We developed a method of transferring semiconductor nanoparticles (NPs) and graphene oxide (GO) nanosheets into organic solvent for a potential electron acceptor in bulk heterojunction organic solar cells which employed polymer semiconductor as the electron donor. Electron transfer from the polymer semiconductor to semiconductor and GO in solutions and thin films was established through fluorescence spectroscopy and electroluminescence measurements. Solar cells containing these materials were constructed and evaluated using transient absorption spectroscopy and dynamic fluorescence techniques to understand the charge carrier generation and recombination events; 3) We invented a spectroelectorchemistry technique using light scattering and electroluminescence for rapid size determination and studying electrochemistry of single NPs in an

  4. Tuning the role of charge-transfer states in intramolecular singlet exciton fission through side-group engineering.

    PubMed

    Lukman, Steven; Chen, Kai; Hodgkiss, Justin M; Turban, David H P; Hine, Nicholas D M; Dong, Shaoqiang; Wu, Jishan; Greenham, Neil C; Musser, Andrew J

    2016-12-07

    Understanding the mechanism of singlet exciton fission, in which a singlet exciton separates into a pair of triplet excitons, is crucial to the development of new chromophores for efficient fission-sensitized solar cells. The challenge of controlling molecular packing and energy levels in the solid state precludes clear determination of the singlet fission pathway. Here, we circumvent this difficulty by utilizing covalent dimers of pentacene with two types of side groups. We report rapid and efficient intramolecular singlet fission in both molecules, in one case via a virtual charge-transfer state and in the other via a distinct charge-transfer intermediate. The singlet fission pathway is governed by the energy gap between singlet and charge-transfer states, which change dynamically with molecular geometry but are primarily set by the side group. These results clearly establish the role of charge-transfer states in singlet fission and highlight the importance of solubilizing groups to optimize excited-state photophysics.

  5. Tuning the role of charge-transfer states in intramolecular singlet exciton fission through side-group engineering

    NASA Astrophysics Data System (ADS)

    Lukman, Steven; Chen, Kai; Hodgkiss, Justin M.; Turban, David H. P.; Hine, Nicholas D. M.; Dong, Shaoqiang; Wu, Jishan; Greenham, Neil C.; Musser, Andrew J.

    2016-12-01

    Understanding the mechanism of singlet exciton fission, in which a singlet exciton separates into a pair of triplet excitons, is crucial to the development of new chromophores for efficient fission-sensitized solar cells. The challenge of controlling molecular packing and energy levels in the solid state precludes clear determination of the singlet fission pathway. Here, we circumvent this difficulty by utilizing covalent dimers of pentacene with two types of side groups. We report rapid and efficient intramolecular singlet fission in both molecules, in one case via a virtual charge-transfer state and in the other via a distinct charge-transfer intermediate. The singlet fission pathway is governed by the energy gap between singlet and charge-transfer states, which change dynamically with molecular geometry but are primarily set by the side group. These results clearly establish the role of charge-transfer states in singlet fission and highlight the importance of solubilizing groups to optimize excited-state photophysics.

  6. Proton transfer assisted charge transfer phenomena in photochromic Schiff bases and effect of -NEt2 groups to the anil Schiff bases.

    PubMed

    Jana, Sankar; Dalapati, Sasanka; Guchhait, Nikhil

    2012-11-15

    Photochromic Schiff bases 5-diethylamino-2-[(4-diethylamino-benzylidene)-hydrazonomethyl]-phenol (DDBHP) and N,N'-bis(4-N,N-diethylaminosalisalidene) hydrazine (DEASH) with both the proton and charge transfer moieties have been synthesized, and their photophysical properties such as excited state intramolecular charge transfer (ICT) and proton transfer (ESIPT) processes have been reported on the basis of steady-state and time-resolved spectral measurement in various solvents. The ground-state six-membered intramolecular hydrogen bonding network at the proton transfer site accelerates the ESIPT process for these compounds. Both the compounds show large Stokes-shifted emission bands for proton transfer and charge transfer processes. The hydrogen bonding solvents play a crucial role in these photophysical processes. Excited-state dipole moment of DDBHP and DEASH calculated by the solvatochromic method supports the polar character of the charge transfer excited state. Introduction of -NEt(2) groups to the reported salicylaldehyde azine (SAA) Schiff base results an increase in fluorescence lifetime from femtosecond to picosecond time scale for the proton transfer process.

  7. Ultrafast charge transfer between MoTe2 and MoS2 monolayers

    NASA Astrophysics Data System (ADS)

    Pan, Shudi; Ceballos, Frank; Bellus, Matthew Z.; Zereshki, Peymon; Zhao, Hui

    2017-03-01

    High quality and stable electrical contact between metal and two-dimensional materials, such as transition metal dichalcogenides, is a necessary requirement that has yet to be achieved in order to successfully exploit the advantages that these materials offer to electronics and optoelectronics. MoTe2, owing to its phase changing property, can potentially offer a solution. A recent study demonstrated that metallic phase of MoTe2 connects its semiconducting phase with very low resistance. To utilize this property to connect other two-dimensional materials, it is important to achieve efficient charge transfer between MoTe2 and other semiconducting materials. Using MoS2 as an example, we report ultrafast and efficient charge transfer between MoTe2 and MoS2 monolayers. In the transient absorption measurements, an ultrashort pump pulse is used to selectively excite electrons in MoTe2. The appearance of the excited electrons in the conduction band of MoS2 is monitored by using a probe pulse that is tuned to the resonance of MoS2. We found that electrons transfer to MoS2 on a time scale of at most 0.3 ps. The transferred electrons give rise to a large transient absorption signal at both A-exciton and B-exciton resonances due to the screening effect. We also observed ultrafast transfer of holes from MoS2 to MoTe2. Our results suggest the feasibility of using MoTe2 as a bridge material to connect MoS2 and other transition metal dichalcogenides, and demonstrate a new transition metal dichalcogenide heterostructure involving MoTe2, which extends the spectral range of such structures to infrared.

  8. Ultrafast Charge Transfer of a Valence Double Hole in Glycine Driven Exclusively by Nuclear Motion

    NASA Astrophysics Data System (ADS)

    Li, Zheng; Vendrell, Oriol; Santra, Robin

    2015-10-01

    We explore theoretically the ultrafast transfer of a double electron hole between the functional groups of glycine after K -shell ionization and subsequent Auger decay. Although a large energy gap of about 15 eV initially exists between the two electronic states involved and coherent electronic dynamics play no role in the hole transfer, we find that the double hole is transferred within 3 to 4 fs between both functional ends of the glycine molecule driven solely by specific nuclear displacements and non-Born-Oppenheimer effects. The nuclear displacements along specific vibrational modes are of the order of 15% of a typical chemical bond between carbon, oxygen, and nitrogen atoms and about 30% for bonds involving hydrogen atoms. The time required for the hole transfer corresponds to less than half a vibrational period of the involved nuclear modes. This finding challenges the common wisdom that nuclear dynamics of the molecular skeleton are unimportant for charge transfer processes at the few-femtosecond time scale and shows that they can even play a prominent role. It also indicates that in x-ray imaging experiments, in which ionization is unavoidable, valence electron redistribution caused by nuclear dynamics might be much faster than previously anticipated. Thus, non-Born-Oppenheimer effects may affect the apparent electron densities extracted from such measurements.

  9. Dynamics of electron solvation in methanol: Excited state relaxation and generation by charge-transfer-to-solvent

    SciTech Connect

    Elkins, Madeline H.; Williams, Holly L.; Neumark, Daniel M.

    2015-06-21

    The charge-transfer-to-solvent dynamics (CTTS) and excited state relaxation mechanism of the solvated electron in methanol are studied by time-resolved photoelectron spectroscopy on a liquid methanol microjet by means of two-pulse and three-pulse experiments. In the two-pulse experiment, CTTS excitation is followed by a probe photoejection pulse. The resulting time-evolving photoelectron spectrum reveals multiple time scales characteristic of relaxation and geminate recombination of the initially generated electron which are consistent with prior results from transient absorption. In the three-pulse experiment, the relaxation dynamics of the solvated electron following electronic excitation are measured. The internal conversion lifetime of the excited electron is found to be 130 ± 40 fs, in agreement with extrapolated results from clusters and the non-adiabatic relaxation mechanism.

  10. Ambipolar Charge Photogeneration and Transfer at GaAs/P3HT Heterointerfaces.

    PubMed

    Panahandeh-Fard, Majid; Yin, Jun; Kurniawan, Michael; Wang, Zilong; Leung, Gle; Sum, Tze Chien; Soci, Cesare

    2014-04-03

    Recent work on hybrid photovoltaic systems based on conjugated polymers and III-V compound semiconductors with relatively high power conversion efficiency revived fundamental questions regarding the nature of charge separation and transfer at the interface between organic and inorganic semiconductors with different degrees of delocalization. In this work, we studied photoinduced charge generation and interfacial transfer dynamics in a prototypical photovoltaic n-type GaAs (111)B and poly(3-hexyl-thiophene) (P3HT) bilayer system. Ultrafast spectroscopy and density functional theory calculations indicate the coexistence of electron and hole transfer at the GaAs/P3HT interface, leading to the generation of long-lived species and photoinduced absorption upon creation of hybrid interfacial states. This opens up new avenues for the use of low-dimensional III-V compounds (e.g., nanowires or quantum dots) in hybrid organic/inorganic photovoltaics, where advanced bandgap and density of states engineering may also be exploited as design parameters.

  11. Non-Radiative Relaxation of Electronically Excited DNA Oligomers: Proton Coupled Charge Transfer

    NASA Astrophysics Data System (ADS)

    Lange, Adrian W.; Herbert, John M.

    2009-06-01

    We address possible relaxation mechanisms of electronically excited DNA oligomers with a combined quantum mechanics/molecular mechanics (QM/MM) approach. Using long-range corrected density functional theory (LRC-DFT), we show that charge transfer (CT) states between neighboring nucleobases appear at energies just above optically bright ^{1}ππ^{ast} excitonic states in aqueous solution. In double stranded DNA systems, both intrastrand and interstrand CT states are observed. It has been hypothesized that excitonic states may decay via a conical intersection into a CT state on a subpicosecond timescale. The proximity in energy of such states in out calculations appears consistent with this claim. Assuming that such a non-radiative mechanism occurs, we investigate subsequent relaxation of CT states by constructing and optimizing the geometry of model CT systems with constrained density functional theory (CDFT). We find that CT states relax in double stranded DNA through proton transfer across Watson-Crick base pairs with little to no energy barrier. Furthermore, the ground state energy shifts upwards along this reaction coordinate to nearly the same as that of the proton coupled charge transfer state, creating the possibility for a non-radiative pathway to the ground state. Q. Wu and T. Van Voorhis Phys. Rev. A (2005)

  12. Photochemical charge transfer excitation of trans-4-stilbazole at a silver electrode

    NASA Astrophysics Data System (ADS)

    McMahon, John J.; Gergel, Thomas J.; Otterson, David M.; McMahon, Caitlin R.; Kabbani, Raifah M.

    1999-10-01

    When adsorbed at the surface of a polycrystalline silver electrode, trans-4-stilbazole photoreacts, in the presence of dissolved oxygen, to form trans-4'-hydroxy-4-stilbazole. The structure of the photoproduct is confirmed by (1) a comparison of the surface Raman results with the normal Raman of trans-4'-hydroxy-4-stilbazole, and by (2) by ex-situ analysis of the irradiated electrode surface using high-resolution mass spectrometry. The surface photochemistry appears to be a one-photon process whose threshold wavelength lies in the middle of the visible range though neat trans-4-stilbazole absorbs only in the ultraviolet. The surface Raman intensity of the photoproduct increases synchronously with the Faradaic current of oxygen reduction. Attendant incorporation of oxygen exclusively at the 4' position of end-on trans-4-stilbazole evidences a photo-initiated electron transfer from the electrode to oxygen reducing at the other end of the molecule. Scattering from stilbazole adsorbed at two different surface sites is evident in the surface Raman spectrum: charged (Ag +) sites and more neutral surface sites. We assign excitation profile maxima for stilbazole at Ag + sites and the photochemical initiation to a silver-to-stilbazole charge transfer at those sites. Ab-initio molecular orbital calculations on a model composed of a ground state Li 0- trans-4-stilbazole and the anion radical excited state Li +- trans-4-stilbazole - reveal a low-energy transition that supports assignment of the visible excitation to a silver-to-stilbazole electron transfer.

  13. Coherence, Energy and Charge Transfers in De-Excitation Pathways of Electronic Excited State of Biomolecules in Photosynthesis

    NASA Astrophysics Data System (ADS)

    Bohr, Henrik G.; Malik, F. Bary

    2013-11-01

    The observed multiple de-excitation pathways of photo-absorbed electronic excited state in the peridinin-chlorophyll complex, involving both energy and charge transfers among its constituents, are analyzed using the bio-Auger (B-A) theory. It is also shown that the usually used Förster-Dexter theory, which does not allow for charge transfer, is a special case of B-A theory. The latter could, under appropriate circumstances, lead to excimers.

  14. Synthesis and electrochemical studies of charge-transfer complexes of thiazolidine-2,4-dione with σ and π acceptors

    NASA Astrophysics Data System (ADS)

    Singh, Prashant; Kumar, Pradeep; Katyal, Anju; Kalra, Rashmi; Dass, Sujata K.; Prakash, Satya; Chandra, Ramesh

    2010-03-01

    In the present work, we report the synthesis and characterization of novel charge-transfer complexes of thiazolidine-2,4-dione (TZD) with sigma acceptor (iodine) and pi acceptors (chloranil, dichlorodicyanoquinone, picric acid and duraquinone). We also evaluated their thermal and electrochemical properties and we conclude that these complexes are frequency dependent. Charge-transfer complex between thiazolidine-2,4-dione and iodine give best conductivity. In conclusion, complex with sigma acceptors are more conducting than with pi acceptors.

  15. Energy transfer through a multi-layer liner for shaped charges

    DOEpatents

    Skolnick, Saul; Goodman, Albert

    1985-01-01

    This invention relates to the determination of parameters for selecting materials for use as liners in shaped charges to transfer the greatest amount of energy to the explosive jet. Multi-layer liners constructed of metal in shaped charges for oil well perforators or other applications are selected in accordance with the invention to maximize the penetrating effect of the explosive jet by reference to four parameters: (1) Adjusting the explosive charge to liner mass ratio to achieve a balance between the amount of explosive used in a shaped charge and the areal density of the liner material; (2) Adjusting the ductility of each layer of a multi-layer liner to enhance the formation of a longer energy jet; (3) Buffering the intermediate layers of a multi-layer liner by varying the properties of each layer, e.g., composition, thickness, ductility, acoustic impedance and areal density, to protect the final inside layer of high density material from shattering upon impact of the explosive force and, instead, flow smoothly into a jet; and (4) Adjusting the impedance of the layers in a liner to enhance the transmission and reduce the reflection of explosive energy across the interface between layers.

  16. 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

  17. Collisions of fast multicharged ions in gas targets: Charge transfer and ionization

    NASA Astrophysics Data System (ADS)

    Schlachter, A. S.

    1981-05-01

    Measurements of cross sections for charge transfer and ionization of H2 and rare-gas targets were made with fast, highly stripped projectiles in charge states as high as 59+. An empirical scaling rule for electron-capture cross section in H2 valid at energies above 275 keV/amu was found. Similar scaling might exist for other target gases. Cross sections are generally in good agreement with theory. A scaling rule was found for electron loss from H in collisions with a fast highly stripped projectile, based on Olson's classical-trajectory Monte-Carlo calculations, and confirmed by measurements in an H2 target. A similar scaling rule was for net ionization of rare-gas targets, based on Olson's CTMC calculations and the independent-electron model. Measurements are essentially consistent with the scaled cross sections. Calculations and measurements of recoil-ion charge-state spectra show large cross sections for the production of highly charged slow recoil ions.

  18. Ultrafast photoinduced charge transfer in pi-conjugated electron systems: Effects of structure, delocalization, and energetics (Conference Presentation)

    NASA Astrophysics Data System (ADS)

    Schanze, Kirk S.; Jones, Austin; Gish, Melissa; Zeman, Charles J.; Alsam, Amani A.; Aly, Shawkat M.; Papanikolas, John M.; Mohammed, Omar F.

    2016-09-01

    Photoinduced charge transfer is a key step in the mechanism of charge generation in organic solar cells. Charge transfer typically occurs from a photoexcited conjugated polymer donor to an electron acceptor. In an effort to better understand the primary events in solar cells, we have investigated photoinduced charge transfer in model donor-acceptor systems consisting of pi-conjugated oligomer donors that are covalently linked to diimide electron acceptors. These studies utilized oligo(thiophene), oligo(phenylene ethynylene) and oligo(fluorene) pi-conjugated systems with lengths varying from 4 to 12 repeat units linked to naphthalene diimide electron acceptors. Excitation with 100 femtosecond pulses at wavelengths correspoinding to the conjugated oligomer absorption band(s) leads to rapid photoinduced charge transfer to produce a charge separated state, (oligomer+)-(NDI-), which subsequently decays on timescales ranging from 100 ps to 5 ns. The dynamics of the forward and reverse electron transfer reactions depend strongly on the structure and length of the pi-conjugated oligomers, with the fastest rates occurring for oligo(thiophene)s, and considerably slower rates for oligo(phenylene ethynylene)s. The talk will discuss the structure-property relationships and energetic correlations that control the dynamics of charge separation and recombination.

  19. Clinical Characteristics of Diabetic Patients Transferred to Korean Referral Hospitals

    PubMed Central

    Oh, Min Young; Kim, Sang Soo; Lee, In Kyu; Baek, Hong Sun; Lee, Hyoung Woo; Chung, Min Young

    2014-01-01

    Background We evaluated the disease profile and clinical management, including the status of both glycemic control and complications, in patients with diabetes who were transferred to referral hospitals in Korea. Methods Patients referred to 20 referral hospitals in Gyeongsangnam/Gyeongsangbuk-do and Jeollanam/Jeollabuk-do with at least a 1-year history of diabetes between January and June 2011 were retrospectively reviewed using medical records, laboratory tests, and questionnaires. Results A total of 654 patients were enrolled in the study. In total, 437 patients (67%) were transferred from clinics and 197 (30%) patients were transferred from hospitals. A total of 279 patients (43%) visited higher medical institutions without a written medical request. The main reason for the referral was glycemic control in 433 patients (66%). Seventy-three patients (11%) had received more than one session of diabetic education. Only 177 patients (27%) had been routinely self-monitoring blood glucose, and 146 patients (22%) were monitoring hemoglobin A1c. In addition, proper evaluations for diabetic complications were performed for 74 patients (11%). The most common complication was neuropathy (32%) followed by nephropathy (31%). In total, 538 patients (82%) had been taking oral hypoglycemic agents. A relatively large number of patients (44%) had been taking antihypertensive medications. Conclusion We investigated the clinical characteristics of diabetic patients and identified specific problems in diabetic management prior to the transfer. We also found several problems in the medical system, which were divided into three medical institutions having different roles in Korea. Our findings suggested that the relationships among medical institutions have to be improved, particularly for diabetes. PMID:25349826

  20. 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.

    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.

  1. Charge Transfer in Collisions between Bare Ions and Hydrogenic Carbon Ions

    NASA Astrophysics Data System (ADS)

    Winter, T. G.

    1997-04-01

    Cross sections have been calculated for electron transfer, as well as ionization, in collisions between 125-1000 keV/amu protons, α particles, Li^2+ ions, etc. and C^5+(1s) ions. The dependence of cross sections on projectile charge has been determined and compared with results of first-order perturbation theory. This study parallels an earlier one in which the target nuclear charge was instead varied.(T. G. Winter, Phys. Rev. A 35), 3799 (1987). A coupled-Sturmian-pseudostate approach is again taken, yielding capture cross sections accurate to at least a few per cent. In the case of α-particle projectiles, the results are important for understanding α losses to the walls of the TFTR, (H. Herrmann (private communication, 1996).) and are much larger than existing published results.(M. Lal, M. K. Srivastava, and A. N. Tripathi, Phys. Rev. A 26), 305 (1982).

  2. Charge Transfer at Hybrid Interfaces: Plasmonics of Aromatic Thiol-Capped Gold Nanoparticles.

    PubMed

    Goldmann, Claire; Lazzari, Rémi; Paquez, Xavier; Boissière, Cédric; Ribot, François; Sanchez, Clément; Chanéac, Corinne; Portehault, David

    2015-07-28

    Although gold nanoparticles stabilized by organic thiols are the building blocks in a wide range of applications, the role of the ligands on the plasmon resonance of the metal core has been mostly ignored until now. Herein, a methodology based on the combination of spectroscopic ellipsometry and UV-vis spectroscopy is applied to extract dielectric functions of the different components. It is shown that aromatic thiols allow a significant charge transfer at the hybrid interface with the s and d bands of the gold core that yields "giant" red shifts of the plasmon band, up to 40 nm for spherical particles in the size range of 3-5 nm. These results suggest that hybrid nanoplasmonic devices may be designed through the suitable choice of metal core and organic components for optimized charge exchange.

  3. Doping Dependent Charge Transfer Gap and Realistic Electronic Model of n-type Cuprate Superconductors

    SciTech Connect

    Xiang, T.

    2010-05-03

    Based on the analysis of the measurement data of angle-resolved photoemission spectroscopy (ARPES) and optics, we show that the charge transfer gap is significantly smaller than the optical one and is reduced by doping in electron doped cuprate superconductors. This leads to a strong charge fluctuation between the Zhang-Rice singlet and the upper Hubbard bands. The basic model for describing this system is a hybridized two-band t-J model. In the symmetric limit where the corresponding intra- and inter-band hopping integrals are equal to each other, this two-band model is equivalent to the Hubbard model with an antiferromagnetic exchange interaction (i.e. the t-U-J model). The mean-field result of the t-U-J model gives a good account for the doping evolution of the Fermi surface and the staggered magnetization.

  4. Influence of an electrical potential on the charge transfer kinetics of bacteriorhodopsin

    PubMed Central

    Kleinschmidt, Christoph; Hess, Benno

    1990-01-01

    The adsorption of bacteriorhodopsin(bR)-containing purple membranes (PM) to black lipid membranes (BLM) was used to study the charge translocation kinetics of bR upon flash excitation. The discharge of the PM-BLM system after charging upon illumination is found to proceed quite slowly (discharge time up to several minutes) but is considerably accelerated by addition of the protonophore FCCP. Therefore, the dependence of the proton transfer kinetics in bR on electrical potentials generated by preceding flashes of varying repetition rate and intensity was investigated. The kinetics are slowed down with increasing flash intensity as well as repetition rate. This effect is partly abolished by small amounts of FCCP. A new model is introduced which takes into account the instantaneous feedback of the electrical potential on the kinetics of the pump current. It explains the observed deviations from first-order kinetics and renders an approach with “distributed kinetics” unnecessary. PMID:19431767

  5. Modeling of the charge transfer in a lateral drift field photo detector

    NASA Astrophysics Data System (ADS)

    Driewer, Adrian; Hosticka, Bedrich J.; Spickermann, Andreas; Vogt, Holger

    2016-12-01

    In this article a model is introduced that describes the charge transfer in pixels of an image sensor. The model is suitable for image sensors where lateral drift field photo detectors were implemented and considers the effects of thermal diffusion, drift due to the built-in potential gradient, and self-induced drift. The analytical result is compared with a numerical solution and confirmed by measurements. With this model it is possible to predict the amount of collected charge at the sense node for very short integration times in comparatively long pixel structures. This is particularly important for indirect time-of-flight applications with CMOS image sensors. This approach enables the optimization of the pixel layout as well as an advanced calibration that might possibly enhance the distance precision. The model can also be applied to image sensors featuring pinned photodiodes.

  6. Thermal and Quantum Peierls Transitions in Organic Charge-Transfer Salts

    NASA Astrophysics Data System (ADS)

    Bewick, Sharon; Soos, Zoltan

    2006-03-01

    The choice of donors (D) and acceptors (A) governs the charge-transfer ρ in organic CT salts with mixed one-dimensional DADA stacks. Strong D and A yield ρ ˜ 0.9 stacks of radical ions with thermally accessible spin and charge degrees of freedom whose Peierls transition can be described by a Hubbard model with site energies. The same microscopic model describes CT salts with smaller and variable ρ ˜ 0.5 in which neutral-ionic and/or Peierls transitions occur in the ground electronic state. Quantum transitions are driven by volume changes, with negligible thermal population of excite states. CT salts with thermal or quantum Peierls transitions are identified. Conflicting magnetic, vibrational and structural data in several CT salts are resolved in terms of mobile spin solitons, a dimerized ground state and a Peierls transition beyond the crystal's thermal stability.

  7. 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.

  8. Charge-transfer interactions in the inhibition of MAO-A by phenylisopropylamines - a QSAR study

    NASA Astrophysics Data System (ADS)

    Vallejos, Gabriel; Rezende, Marcos Caroli; Cassels, Bruce K.

    2002-02-01

    The HOMO energies and the charges on the aromatic carbons of two sets of MAO-A-inhibiting phenylisopropylamines, one containing 4-amino substituents, were calculated by the AM1 method, in order to evaluate the importance of charge-transfer interactions between drug and enzyme. Multiple-linear regressions of the pIC50values on the calculated descriptors were performed with 33 compounds from the two sets, and separately with each set. A poor correlation was obtained when the two sets were merged, as a result of opposing trends shown by the two separate sets. These opposing trends were reconciled by invoking a partial protonation of the basic 4-amino substituents by a hydrogen-bond-donor fragment of the enzyme. The resulting analysis indicated that electron-rich rings and higher HOMO levels tended to increase activity. This model received support from the evaluation of the IMAO activity of four new phenylisopropylamines.

  9. Charge-Transfer Effects in Ligand Exchange Reactions of Au25 Monolayer-Protected Clusters.

    PubMed

    Carducci, Tessa M; Blackwell, Raymond E; Murray, Royce W

    2015-04-16

    Reported here are second-order rate constants of associative ligand exchanges of Au25L18 nanoparticles (L = phenylethanethiolate) of various charge states, measured by proton nuclear magnetic resonance at room temperature and below. Differences in second-order rate constants (M(-1) s(-1)) of ligand exchange (positive clusters ∼1.9 × 10(-5) versus negative ones ∼1.2 × 10(-4)) show that electron depletion retards ligand exchange. The ordering of rate constants between the ligands benzeneselenol > 4-bromobenzene thiol > benzenethiol reveals that exchange is accelerated by higher acidity and/or electron donation capability of the incoming ligand. Together, these observations indicate that partial charge transfer occurs between the nanoparticle and ligand during the exchange and that this is a rate-determining effect in the process.

  10. Ribosome bypassing at serine codons as a test of the model of selective transfer RNA charging

    PubMed Central

    Lindsley, Dale; Bonthuis, Paul; Gallant, Jonathan; Tofoleanu, Teodora; Elf, Johan; Ehrenberg, Måns

    2005-01-01

    Recently, a model of the flux of amino acids through transfer RNAs (tRNAs) and into protein has been developed. The model predicts that the charging level of different isoacceptors carrying the same amino acid respond very differently to variation in supply of the amino acid or of the rate of charging. It has also been shown that ribosome bypassing is specifically stimulated at ‘hungry' codons calling for an aminoacyl-tRNA in short supply. We have constructed two reporters of bypassing, which differ only in the identity of the serine codon subjected to starvation. The stimulation of bypassing as a function of starvation differed greatly between the two serine codons, in good agreement with the quantitative predictions of the model. PMID:15678161

  11. Local equilibria and state transfer of charged classical particles on a helix in an electric field

    NASA Astrophysics Data System (ADS)

    Plettenberg, J.; Stockhofe, J.; Zampetaki, A. V.; Schmelcher, P.

    2017-01-01

    We explore the effects of a homogeneous external electric field on the static properties and dynamical behavior of two charged particles confined to a helix. In contrast to the field-free setup which provides a separation of the center-of-mass and relative motion, the existence of an external force perpendicular to the helix axis couples the center-of-mass to the relative degree of freedom leading to equilibria with a localized center of mass. By tuning the external field various fixed points are created and/or annihilated through different bifurcation scenarios. We provide a detailed analysis of these bifurcations based on which we demonstrate a robust state transfer between essentially arbitrary equilibrium configurations of the two charges that can be induced by making the external force time dependent.

  12. Charge separation distance for flexible donor-bridge-acceptor systems after electron-transfer quenching.

    PubMed

    Zhou, Jinwei; Lukin, Leonid V; Braun, Charles L

    2008-08-21

    Photoinduced transient dipole experiments are used to measure the effective charge separation distance, which is equivalent to the photoinduced change in dipole moment divided by the electron charge of flexible electron-donor/acceptor systems, D-(CH2)n-A, where D is 4- N,N-dimethylaniline, A is 9-anthryl, and n = 3, 4. We find that the dipole moments increase strongly with solvent polarity. For the compound with n = 4 (DBA4), analysis of dipole signals indicates that the effective charge separation distances in toluene, 1,4-dioxane, ethyl acetate, tetrahydrofuran, dichloromethane, 1,2-dichloroethane, 2-methylpentanone-3, 3-pentanone, and benzonitrile are 2.2, 2.5, 4.5, 4.7, 5.5, 5.5, 4.8, and 6.3 A, respectively. These values can be understood as the root-mean-square charge separation distance in the solutions of different solvents. We assume that the folded contact configuration has a separation distance of 3.5 A, the extended, solvent-separated configuration has a separation distance of 8.0 A, and that they are the only two stable species after electron-transfer quenching. The formation efficiencies of contact radical ion pairs (CRIPs) and solvent-separated radical ion pairs (SSRIPs) are estimated in different solvents. The results indicate that a significant fraction of the ion pairs exist as solvent-separated ion pairs when the dielectric constant of the solvent is larger than 10. These results indicate that electron-transfer quenching can indeed happen at large separations in polar solvents. They also reveal that there is a barrier for ion pairs formed at large separations, hindering collapse to a contact separation of around 3.5 A.

  13. Study of charge transfer complexes of [70]fullerene with phenol and substituted phenols.

    PubMed

    Bhattacharya, Sumanta; Banerjee, Shrabanti; Banerjee, Manas

    2005-07-01

    To improve the understanding of the charge transfer (CT) interaction of [70]fullerene with electron donors, interaction of [70]fullerene with a series of phenols, e.g., phenol, resorcinol and p-quinol were studied in 1,4-dioxan medium using absorption spectroscopy. An absorption band due to CT transition was observed in the visible region. The experimental CT transition energies (h nuCT) are well correlated (through Mulliken's equation) with the vertical ionisation potentials (I(D)v) of the series of phenols studied. From an analysis of this correlation degrees of charge transfer for the [70]fullerene-phenol complexes were estimated. The degrees of charge transfer in the ground state of the complexes have been found to be very low (<2%). The h nuCT values change systematically as the number and position of the -OH groups change on the aromatic ring of the phenol moiety. From the trends in the h nuCT values, the Hückel parameters (h(O) and k(C-O)) for the -OH group were obtained in a straightforward way and the values so obtained, viz., 1.91 and 1.0, respectively, are close to the ones (1.8 and 0.8) recommended by Streitwieser on the basis of other evidence. Oscillator strengths, transition dipole strengths and resonance energies of the [70]fullerene-phenol complexes were determined. Formation constants of the CT complexes were determined at four different temperatures from which enthalpies and entropies of formation of the complexes were estimated.

  14. Structure and Bonding in Nickel-Thiolate-Iodine Charge-Transfer Complexes.

    PubMed

    Beyer, Norman; Steinfeld, Gunther; Lozan, Vasile; Naumov, Sergej; Flyunt, Roman; Abel, Bernd; Kersting, Berthold

    2017-02-16

    The dinuclear nickel complexes [Ni2 L(μ-O2 CR)](ClO4 ) [R=Me (4), R=OMe (6)], where L(2-) is a 24-membered macrocyclic N6 S2 ligand, react readily with excess I2 in MeCN solution at 4 °C to form stable mono-(I2 ) and bis-(I2 ) charge-transfer (CT) adducts of the type [Ni2 L(μ-O2 CR)(I2 )n ](+) (n=1 or 2) containing linear RS-I-I linkages. Three new CT compounds, namely, [Ni2 L(OAc)(I2 )](I2 )(I3 ) (5), [Ni2 L(O2 COMe)(I2 )](I5 )⋅MeCN (7⋅MeCN), and [Ni2 L(O2 COMe)(I2 )2 ](I5 )⋅MeCN (8⋅MeCN) as well as the triiodide salt [Ni2 L(OAc)](I3 ) (9) were synthesized and fully characterized. A common feature of the CT adducts is a polyiodide matrix, which surrounds the individual complex molecules, stabilized by secondary I⋅⋅⋅I interactions with the CT linkages. The scatter in both the RS-I (2.6 to 3.0 Å) and the I-I bond lengths (2.7 to 3.0 Å) is indicative of both a variable strength of the RS(-) →I2 bond and a varying degree of charge transfer. An analysis of the structural parameters was undertaken accompanied by DFT calculations to quantify the donating ability of the bridging thiolate functions and to shed more light on the bonding in this rare sort of charge-transfer complexes. The stability of the CT complexes and the results of preliminary transport measurements are also reported.

  15. 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.

  16. 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.

  17. Charge transfer fluorescence and 34 nm exciton diffusion length in polymers with electron acceptor end traps

    SciTech Connect

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

    2014-12-22

    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 to 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 LD =34 nm, which is much larger than diffusion lengths reported in polymer films or than previously known for diffusion along isolated chains. As a result, the efficiency of exciton capture depends on chain length, but not on trap depth, solvent polarity or which trap group is present.

  18. Charge transfer fluorescence and 34 nm exciton diffusion length in polymers with electron acceptor end traps

    DOE PAGES

    Zaikowski, Lori; Mauro, Gina; Bird, Matthew; ...

    2014-12-22

    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 to 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 asmore » 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 LD =34 nm, which is much larger than diffusion lengths reported in polymer films or than previously known for diffusion along isolated chains. As a result, the efficiency of exciton capture depends on chain length, but not on trap depth, solvent polarity or which trap group is present.« less

  19. Probing the charge transfer reaction coordinate of 4-(dimethylamino)benzonitrile with femtosecond stimulated Raman spectroscopy.

    PubMed

    Rhinehart, Justin M; Mehlenbacher, Randy D; McCamant, David

    2010-11-18

    Femtosecond stimulated Raman spectroscopy (FSRS) and femtosecond transient absorption have been used to probe the photoinduced charge transfer (CT) dynamics of 4-(dimethylamino)benzonitrile in methanol and n-hexane. Through a combined analysis of temporal changes in the Raman modes and transient absorption kinetics, a more complete picture of the reaction coordinate of the intramolecular charge transfer process has been established. FSRS spectra of the phenyl C═C stretching mode (Wilson mode 8a) at 1607 cm(-1), which shifts to 1581 cm(-1) in the CT state, and transient absorption measurements ranging from 360 to 700 nm support internal conversion from the locally excited to the charge transfer state in 4-5 ps and then a subsequent vibrational relaxation within the CT state manifold on a 6-8 ps time scale. Dramatic shifting and narrowing of the 1581 cm(-1) quinoidal C═C stretch (ν(8a)) on the ∼7 ps time scale indicates that the quinoidal distortion is an important probe of the CT reaction dynamics. The cause of the spectral shifts is determined by comparing the observed shifts in the vibrational spectrum to anharmonic couplings computed for the benzonitrile radical anion by density functional theory (DFT) and with quantitative theoretical models of the solvent induced vibrational peak shifts. The DFT calculations indicate that the 10 cm(-1) downshift of the C═C stretch is most likely attributable to significant vibrational excitation in nontotally symmetric modes that are strongly anharmonically coupled to the C═C stretch.

  20. Interface charge transfer process in ZnO:Mn/ZnS nanocomposites

    NASA Astrophysics Data System (ADS)

    Stefan, M.; Toloman, D.; Popa, A.; Mesaros, A.; Vasile, O. R.; Leostean, C.; Pana, O.

    2016-03-01

    ZnO:Mn/ZnS nanocomposites were prepared by seed-mediated growth of ZnS QDs onto the preformed ZnO:Mn nanoparticles. The formation of the nanocomposite structure has been evidenced by XRD, HRTEM, and XPS. The architecture of the nanocomposite with outer ZnS QDs around ZnO:Mn cores is sustained by the sulfur and oxygen depth profiles resulted from XPS. When the two components are brought together, the band gap of ZnS component decreases while that of ZnO:Mn increases. It is the result of interface charge transfer from ZnO:Mn to ZnS QDs. Here ZnO:Mn valence states are extended through the interface into unoccupied gap states of ZnS. The energy band setup is modified from a type II into a type I band alignment. The process is accompanied by enhancement of composite UV emission of PL spectra as compared to its counterparts. The charge transfer from valence band also determines the increase of the core-polarization effect of s shell electrons at Mn2+ nucleus, thus determining the increase of the hyperfine field through the reduction of the covalency degree of Zn(Mn)-O bonds. The quantum confinement in ZnS QDs promotes the ferromagnetic coupling of singly occupied states due to Zn vacancies determining a superparamagnetic behavior of the ensemble. When the nanocomposites are formed, due to interface charge transfer effects, an increased number of filled cation vacancies in ZnS QDs develop, thus disrupting the pre-existing ferromagnetic coupling between spins resulting in a significant reduction of the overall saturation magnetization. The possibility to modulate nanocomposite properties by controlling the interface interactions may be foreseen in these types of materials.

  1. EV Charging Through Wireless Power Transfer: Analysis of Efficiency Optimization and Technology Trends

    SciTech Connect

    Miller, John M; Rakouth, Heri; Suh, In-Soo

    2012-01-01

    This paper is aimed at reviewing the technology trends for wireless power transfer (WPT) for electric vehicles (EV). It also analyzes the factors affecting its efficiency and describes the techniques currently used for its optimization. The review of the technology trends encompasses both stationary and moving vehicle charging systems. The study of the stationary vehicle charging technology is based on current implementations and on-going developments at WiTricity and Oak Ridge National Lab (ORNL). The moving vehicle charging technology is primarily described through the results achieved by the Korean Advanced Institute of Technology (KAIST) along with on-going efforts at Stanford University. The factors affecting the efficiency are determined through the analysis of the equivalent circuit of magnetic resonant coupling. The air gap between both transmitting and receiving coils along with the magnetic field distribution and the relative impedance mismatch between the related circuits are the primary factors affecting the WPT efficiency. Currently the industry is looking at an air gap of 25 cm or below. To control the magnetic field distribution, Kaist has recently developed the Shaped Magnetic Field In Resonance (SMFIR) technology that uses conveniently shaped ferrite material to provide low reluctance path. The efficiency can be further increased by means of impedance matching. As a result, Delphi's implementation of the WiTricity's technology exhibits a WPT efficiency above 90% for stationary charging while KAIST has demonstrated a maximum efficiency of 83% for moving vehicle with its On Line Vehicle (OLEV) project. This study is restricted to near-field applications (short and mid-range) and does not address long-range technology such as microwave power transfer that has low efficiency as it is based on radiating electromagnetic waves. This paper exemplifies Delphi's work in powertrain electrification as part of its innovation for the real world program geared

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

    SciTech Connect

    Baltrus, John P.; Ohodnicki, Paul R.

    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.

  3. Topological charge transfer in frequency doubling of fractional orbital angular momentum state

    NASA Astrophysics Data System (ADS)

    Ni, R.; Niu, Y. F.; Du, L.; Hu, X. P.; Zhang, Y.; Zhu, S. N.

    2016-10-01

    Nonlinear frequency conversion is promising for manipulating photons with orbital angular momentum (OAM). In this letter, we investigate the second harmonic generation (SHG) of light beams carrying fractional OAM. By measuring the OAM components of the generated second harmonic (SH) waves, we find that the integer components of the fundamental beam will interact with each other during the nonlinear optical process; thus, we figure out the law for topological charge transfer in frequency doubling of the fractional OAM state. Theoretical predictions by solving the nonlinear coupled wave equations are consistent with the experimental results.

  4. Formation of charge-transfer-complex in organic:metal oxides systems

    NASA Astrophysics Data System (ADS)

    Wu, S. P.; Kang, Y.; Liu, T. L.; Jin, Z. H.; Jiang, N.; Lu, Z. H.

    2013-04-01

    It is found that composite systems consisting of 4,4'-bis(carbazol-9-yl)biphenyl (CBP) and molybdenum trioxide (MoO3) form an IR absorption band around 847 nm. It is also found that the vibrational modes of the CBP, as measured by Fourier Transform Infrared Spectroscopy, are quenched upon the formation of charge-transfer-complex (CTC) between CBP and MoO3. By examining several sets of organic:metal oxides systems, we discovered that the IR absorption band of the CTCs follow two distinct mechanisms depending on the nature and location of the HOMOs in the organic molecules.

  5. 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).

  6. Potential Energy Surfaces and Charge Transfer of PAH-Sodium-PAH Complexes.

    PubMed

    Hjertenaes, Eirik; Andersson, Stefan; Koch, Henrik

    2016-09-19

    To further understanding of the role of sodium in carbon cathode degradation in Hall-Héroult cells, potential-energy surfaces and charge-transfer curves are presented for finite-size complexes of sodium intercalated between various polycyclic aromatic hydrocarbons. Calculations for lithium and potassium are included to highlight the disparate intercalation behaviour of the alkali metals in graphite intercalation compounds. Static energy barriers from DFT are used to compute macroscopic diffusion coefficients according to transition-state theory. Comparing the calculated diffusion coefficient to experimental values from the literature sheds light on the role of lattice diffusion of sodium-graphite intercalation compounds in sodium intrusion in graphitic carbon cathodes.

  7. Charge transfer in time-dependent density-functional theory via spin-symmetry breaking

    SciTech Connect

    Fuks, Johanna I.; Maitra, Neepa T.

    2011-04-15

    Long-range charge-transfer excitations pose a major challenge for time-dependent density-functional approximations. We show that spin-symmetry breaking offers a simple solution for molecules composed of open-shell fragments, yielding accurate excitations at large separations when the acceptor effectively contains one active electron. Unrestricted exact-exchange and self-interaction-corrected functionals are performed on one-dimensional models and on the real LiH molecule within the pseudopotential approximation to demonstrate our results.

  8. Metallization and charge-transfer gap closure of transition-metal iodides under pressure

    SciTech Connect

    Chen, A. Li-Chung

    1993-05-01

    It is shown with resistivity and near-IR absorption measurements that NiI{sub 2}, CoI{sub 2}, and FeI{sub 2} metallize under pressure by closure of the charge-transfer energy gap at pressures of 17, 10, and 23 GPa, respectively, which is close to the antiferromagnetic-diamagnetic transition in NiI{sub 2} and CoI{sub 2}. Thus, the magnetic transitions probably are caused by the metallization; in NiI{sub 2} and CoI{sub 2}, the insulator-metal transitions are first order. Moessbauer and XRD data were also collected. Figs, 46 refs.

  9. Strong charge-transfer excitonic effects and the Bose-Einstein exciton condensate in graphane.

    PubMed

    Cudazzo, Pierluigi; Attaccalite, Claudio; Tokatly, Ilya V; Rubio, Angel

    2010-06-04

    Using first principles many-body theory methods (GW+Bethe-Salpeter equation) we demonstrate that the optical properties of graphane are dominated by localized charge-transfer excitations governed by enhanced electron correlations in a two-dimensional dielectric medium. Strong electron-hole interaction leads to the appearance of small radius bound excitons with spatially separated electron and hole, which are localized out of plane and in plane, respectively. The presence of such bound excitons opens the path towards an excitonic Bose-Einstein condensate in graphane that can be observed experimentally.

  10. Modelling flavoenzymatic charge transfer events: development of catalytic indole deuteration strategies.

    PubMed

    Murray, Alexander T; Challinor, Jonathan D; Gulácsy, Christina E; Lujan, Cristina; Hatcher, Lauren E; Pudney, Christopher R; Raithby, Paul R; John, Matthew P; Carbery, David R

    2016-04-12

    The formation and chemistry of flavin-indole charge transfer (CT) complexes has been studied using a model cationic flavin. The ability to form a CT complex is sensitive to indole structure as gauged by spectroscopic, kinetics and crystallographic studies. Single crystals of sufficient quality of a flavin-indole CT complex, suitable for X-ray diffraction, have been grown, allowing solid-state structural analysis. When CT complex formation is conducted in d4-methanol, an efficient and synthetically useful C-3 indole deuteration is observed.

  11. Coloration of tyrosine by organic-semiconductor interfacial charge-transfer transitions

    NASA Astrophysics Data System (ADS)

    Fujisawa, Jun-ichi; Kikuchi, Natsumi; Hanaya, Minoru

    2016-11-01

    L-tyrosine (Tyr) plays a crucial role as a proteinogenic amino acid and also as a precursor to several neurotransmitters and hormones. Here we demonstrate coloration of Tyr based on organic-semiconductor interfacial charge-transfer (ICT) transitions. The ICT transitions from Tyr to TiO2 are induced by the chemisorption of Tyr on TiO2 surfaces via the hydroxy group of the phenol moiety. Because other amino acids possess no chemical group to induce ICT transitions, this coloration method enables to detect Tyr selectively without drastic structural change in contrast to the conventional coloration methods.

  12. Charge-transfer complexation as a general phenomenon in the copigmentation of anthocyanins.

    PubMed

    Ferreira da Silva, Palmira; Lima, João C; Freitas, Adilson A; Shimizu, Karina; Maçanita, Antonio L; Quina, Frank H

    2005-08-18

    Color intensification of anthocyanin solutions in the presence of natural polyphenols (copigmentation) is re-interpreted in terms of charge transfer from the copigment to the anthocyanin. Flavylium cations are shown to be excellent electron acceptors (E(red) approximately -0.3 V vs SCE). It is also demonstrated, for a large series of anthocyanin-copigment pairs, that the standard Gibbs free energy of complex formation decreases linearly with EA(Anthoc) - IP(Cop), the difference between the electron affinity of the anthocyanin, EA(Anthoc), and the ionization potential of the copigment, IP(Cop). Based on this correlation, copigmentation strengths of potential candidates for copigments can be predicted.

  13. On the charge transfer between single-walled carbon nanotubes and graphene

    SciTech Connect

    Rao, Rahul Pierce, Neal; Dasgupta, Archi

    2014-08-18

    It is important to understand the electronic interaction between single-walled carbon nanotubes (SWNTs) and graphene in order to use them efficiently in multifunctional hybrid devices. Here, we deposited SWNT bundles on graphene-covered copper and SiO{sub 2} substrates by chemical vapor deposition and investigated the charge transfer between them by Raman spectroscopy. Our results revealed that, on both copper and SiO{sub 2} substrates, graphene donates electrons to the SWNTs, resulting in p-type doped graphene and n-type doped SWNTs.

  14. Environmental Effects on Hysteresis of Transfer Characteristics in Molybdenum Disulfide Field-Effect Transistors

    NASA Astrophysics Data System (ADS)

    Shimazu, Yoshihiro; Tashiro, Mitsuki; Sonobe, Satoshi; Takahashi, Masaki

    2016-07-01

    Molybdenum disulfide (MoS2) has recently received much attention for nanoscale electronic and photonic applications. To explore the intrinsic properties and enhance the performance of MoS2-based field-effect transistors, thorough understanding of extrinsic effects such as environmental gas and contact resistance of the electrodes is required. Here, we report the effects of environmental gases on the transport properties of back-gated multilayered MoS2 field-effect transistors. Comparisons between different gases (oxygen, nitrogen, and air and nitrogen with varying relative humidities) revealed that water molecules acting as charge-trapping centers are the main cause of hysteresis in the transfer characteristics. While the hysteresis persisted even after pumping out the environmental gas for longer than 10 h at room temperature, it disappeared when the device was cooled to 240 K, suggesting a considerable increase in the time constant of the charge trapping/detrapping at these modestly low temperatures. The suppression of the hysteresis or instability in the easily attainable temperature range without surface passivation is highly advantageous for the device application of this system. The humidity dependence of the threshold voltages in the transfer curves indicates that the water molecules dominantly act as hole-trapping centers. A strong dependence of the on-state current on oxygen pressure was also observed.

  15. [Effect of the mobility of gate charges on volt-ampere characteristics of excitable membranes].

    PubMed

    Radchenko, A N

    1996-01-01

    An assumption on nature of the gate charges and known data on gate changes mobility allow to deduce the volt-ampere characteristics of ionic channels and the same for membrane. Model research shows that the volt-ampere curve shape depends on gate charges mobility. Its reduction and the followed gate charges immobilization during membrane excitation process are expressed as the changes of volt-ampere curves. These changes might be to specify as the fast components of the inactivation process. A number critical values of the gate charges mobility are calculated which are important for the functions of memory (hysteresis) and excitation (negative resistance). The coincidence of values of biased charge in model and experiment is noted. The formulae that are drown are compared with Hodgkin-Huxley approximations.

  16. Effect of Surface Defect States on Valence Band and Charge Separation and Transfer Efficiency

    PubMed Central

    Xu, Juan; Teng, Yiran; Teng, Fei

    2016-01-01

    Both energy band and charge separation and transfer are the crucial affecting factor for a photochemical reaction. Herein, the BiOCl nanosheets without and with surface bismuth vacancy (BOC, V-BOC) are prepared by a simple hydrothermal method. It is found that the new surface defect states caused by bismuth vacancy have greatly up-shifted the valence band and efficiently enhanced the separation and transfer rates of photogenerated electron and hole. It is amazing that the photocatalytic activity of V-BOC is 13.6 times higher than that of BOC for the degradation methyl orange (MO). We can develop an efficient photocatalyst by the introduction of defects. PMID:27586149

  17. Measurement of charge transfer potential barrier in pinned photodiode CMOS image sensors

    NASA Astrophysics Data System (ADS)

    Chen, Cao; Bing, Zhang; Junfeng, Wang; Longsheng, Wu

    2016-05-01

    The charge transfer potential barrier (CTPB) formed beneath the transfer gate causes a noticeable image lag issue in pinned photodiode (PPD) CMOS image sensors (CIS), and is difficult to measure straightforwardly since it is embedded inside the device. From an understanding of the CTPB formation mechanism, we report on an alternative method to feasibly measure the CTPB height by performing a linear extrapolation coupled with a horizontal left-shift on the sensor photoresponse curve under the steady-state illumination. The theoretical study was performed in detail on the principle of the proposed method. Application of the measurements on a prototype PPD-CIS chip with an array of 160 × 160 pixels is demonstrated. Such a method intends to shine new light on the guidance for the lag-free and high-speed sensors optimization based on PPD devices. Project supported by the National Defense Pre-Research Foundation of China (No. 51311050301095).

  18. 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.

  19. Charge and discharge characteristics of a commercial LiCoO 2-based 18650 Li-ion battery

    NASA Astrophysics Data System (ADS)

    Zhang, S. S.; Xu, K.; Jow, T. R.

    We studied the charge and discharge characteristics of commercial LiCoO 2-based 18650 cells by using various electrochemical methods, including discharging at constant power, ac impedance spectroscopy, and dc-voltage pulse. At 20 °C, these cells deliver 8.7-6.8 Wh of energy when discharged at a power range of 1-12 W between 2.5 and 4.2 V. Ragone plots show that the effect of discharge power on the energy is significantly increased with decreasing of the temperature. For example, energy of the cell is entirely lost when the temperature downs to -10 °C and the discharge rate still remains at 10 W. Impedance analyses indicate that the total cell resistance (R cell) is mainly contributed by the bulk resistance (R b, including electric contact resistance and electrolytic ionic conductivity), solid electrolyte interface resistance (R sei), and charge-transfer resistance (R ct). Individual contribution of these three resistances to the cell resistance is greatly varied with the temperature. Near room temperature, the R b occupies up to half of the cell resistance, which means that the rate performance of the cell could be improved by modifying cell design such as employing electrolyte with higher ionic conductivity and enhancing electric contact of the active material particles. At low temperature, the R ct, which is believed to reflect cell reaction kinetics, dominates the cell resistance. In addition, galvanosatic cycling tests indicate that the charge and discharge processes have nearly same kinetics. The performance discrepancy observed during charging and discharging, especially at low temperatures, can be attributed to these two factors of: (1) substantially higher R ct at the discharged state than at the charged state; (2) asymmetric voltage limits pre-determined for the charge and discharge processes.

  20. Electron Transfer Dissociation: Effects of Cation Charge State on Product Partitioning in Ion/Ion Electron Transfer to Multiply Protonated Polypeptides

    PubMed Central

    Liu, Jian; McLuckey, Scott A.

    2012-01-01

    The effect of cation charge state on product partitioning in the gas-phase ion/ion electron transfer reactions of multiply protonated tryptic peptides, model peptides, and relatively large peptides with singly charged radical anions has been examined. In particular, partitioning into various competing channels, such as proton transfer (PT) versus electron transfer (ET), electron transfer with subsequent dissociation (ETD) versus electron transfer with no dissociation (ET,noD), and fragmentation of backbone bonds versus fragmentation of side chains, was measured quantitatively as a function of peptide charge state to allow insights to be drawn about the fundamental aspects of ion/ion reactions that lead to ETD. The ET channel increases relative to the PT channel, ETD increases relative to ET,noD, and fragmentation at backbone bonds increases relative to side-chain cleavages as cation charge state increases. The increase in ET versus PT with charge state is consistent with a Landau-Zener based curve-crossing model. An optimum charge state for ET is predicted by the model for the ground state-to-ground state reaction. However, when the population of excited product ion states is considered, it is possible that a decrease in ET efficiency as charge state increases will not be observed due to the possibility of the population of excited electronic states of the products. Several factors can contribute to the increase in ETD versus ET,noD and backbone cleavage versus side-chain losses. These factors include an increase in reaction exothermicity and charge state dependent differences in precursor and product ion structures, stabilities, and sites of protonation. PMID:23264749

  1. Charge-Transfer Supra-Amphiphiles Built by Water-Soluble Tetrathiafulvalenes and Viologen-Containing Amphiphiles: Supramolecular Nanoassemblies with Modifiable Dimensions.

    PubMed

    Lv, Zhong-Peng; Chen, Bin; Wang, Hai-Ying; Wu, Yue; Zuo, Jing-Lin

    2015-08-05

    In this study, multidimensional nanoassemblies with various morphologies such as nanosheets, nanorods, and nanofibers are developed via charge-transfer interaction and supra-amphiphile self-assembling in aqueous phase. The charge-transfer interactions between tetrathiafulvalene derivatives (TTFs) and methyl viologen derivatives (MVs) have been confirmed by the characteristic charger-transfer absorption. (1) H NMR and electrospray ionizsation mass spectrometry (ESI-MS) analyses also indicate supra-amphiphiles are formed by the combination of TTFs and MVs head group through charge-transfer interaction and Coulombic force. X-ray single crystal structural studies, transmission electron microscopy (TEM), and scanning electron microscopy (SEM) reveal that both linkage pattern of TTFs in hydrophilic part and alkane chain structure in hydrophobic part have significant influence on nanoassemblies morphology and microstructure. Moreover, gold nanoparticles (AuNPs) are introduced in the above supramolecular nanoassemblies to construct a supra-amphiphile-driven organic-AuNPs assembly system. AuNPs could be assembled into 1D-3D structures by adding different amount of MVs.

  2. Charge transfer mechanism in titanium-doped microporous silica for photocatalytic water-splitting applications

    DOE PAGES

    Sapp, Wendi; Koodali, Ranjit; Kilin, Dmitri

    2016-02-29

    Solar energy conversion into chemical form is possible using artificial means. One example of a highly-efficient fuel is solar energy used to split water into oxygen and hydrogen. Efficient photocatalytic water-splitting remains an open challenge for researchers across the globe. Despite significant progress, several aspects of the reaction, including the charge transfer mechanism, are not fully clear. Density functional theory combined with density matrix equations of motion were used to identify and characterize the charge transfer mechanism involved in the dissociation of water. A simulated porous silica substrate, using periodic boundary conditions, with Ti4+ ions embedded on the inner poremore » wall was found to contain electron and hole trap states that could facilitate a chemical reaction. A trap state was located within the silica substrate that lengthened relaxation time, which may favor a chemical reaction. A chemical reaction would have to occur within the window of photoexcitation; therefore, the existence of a trapping state may encourage a chemical reaction. Furthermore, this provides evidence that the silica substrate plays an integral part in the electron/hole dynamics of the system, leading to the conclusion that both components (photoactive materials and support) of heterogeneous catalytic systems are important in optimization of catalytic efficiency.« less

  3. Charge transfer and mixed-valence behavior in phtalocyanine-dimer cations.

    PubMed

    Monari, Antonio; Evangelisti, Stefano; Leininger, Thierry

    2010-09-28

    Phtalocyanine compounds deserved a considerable interest in recent times, particularly because of their possible use in the field of nanoelectronics. In particular, the charge mobility (of both electrons and holes) in phtalocyanine stacked arrangements has been recently extensively investigated. The present work focuses on the study of the hole-transfer mechanism between two phtalocyanine monomers. For an interdisk distance larger than 4.5 bohrs, the eclipsed dimer exhibits a mixed-valence behavior, with a saddle point transition state separating two equivalent minima. This behavior, however, is strongly dependent on the relative angle between the disks. In particular, the mixed-valence character of the compound is strongly enhanced for arrangements that are far from the eclipsed geometry. Moreover, for values of the angle close to π/8 and 3π/8, the ground and excited transition states have exactly the same energy, thus implying the presence of a conical intersection. These results can have deep implication in the charge transfer along phtalocyanine chains.

  4. Multivalence Charge Transfer in Doped and Codoped Photocatalytic TiO2.

    PubMed

    Ren, Hangjuan; Koshy, Pramod; Cao, Fuyang; Sorrell, Charles Christopher

    2016-08-15

    The present work reports data for the mineralogical and chemical properties of anatase thin films individually doped or codoped with chromium and vanadium, fabricated by sol-gel spin coating on glass substrates and annealing at 450 °C for 2 h. X-ray photoelectron spectroscopy data indicated the presence of Ti(4+), Ti(3+), Cr(3+), and possibly Cr(4+) in the Cr-doped thin films; Ti(4+), Ti(3+), V(3+), V(4+), and possibly V(5+) in the V-doped thin films; and Ti(4+), Ti(3+), Cr(3+), Cr(4+), V(3+), V(4+), and possibly V(5+) in the codoped thin films. While the thermodynamically stable valences Ti(4+), Cr(3+), and V(5+) would be expected to have formed, the presence of the nonequilibrium valences Ti(3+), Cr(4+), V(3+), and V(4+) is considered to have resulted from intervalence charge transfer for the Cr-doped and V-doped systems but from multivalence charge transfer (MVCT) for the codoped system. The latter phenomenon, which is introduced as a new conceptual term, describes the nature of the mutual exchange of electrons during valence changes of both dopant (Cr, V) and matrix (Ti) ions during annealing. In the present case, MVCT appears to be a transient metastable condition that acts during annealing, but subsequent UV irradiation can alter its effects.

  5. Time-dependent quantum wave packet dynamics to study charge transfer in heavy particle collisions

    NASA Astrophysics Data System (ADS)

    Zhang, Song Bin; Wu, Yong; Wang, Jian Guo

    2016-12-01

    The method of time-dependent quantum wave packet dynamics has been successfully extended to study the charge transfer/exchange process in low energy two-body heavy particle collisions. The collision process is described by coupled-channel equations with diabatic potentials and (radial and rotational) couplings. The time-dependent coupled equations are propagated with the multiconfiguration time-dependent Hartree method and the modulo squares of S-matrix is extracted from the wave packet by the flux operator with complex absorbing potential (FCAP) method. The calculations of the charge transfer process 12Σ+ H-(1s2) +Li(1 s22 s ) →22Σ+ /32 Σ+ /12 Π H(1 s ) +Li-(1s 22 s 2 l ) (l =s ,p ) at the incident energy of about [0.3, 1.3] eV are illustrated as an example. It shows that the calculated reaction probabilities by the present FCAP reproduce that of quantum-mechanical molecular-orbital close-coupling very well, including the peak structures contributed by the resonances. Since time-dependent external interactions can be directly included in the present FCAP calculations, the successful implementation of FCAP provides us a powerful potential tool to study the quantum control of heavy particle collisions by lasers in the near future.

  6. Charge transfer at carbon nanotube-graphene van der Waals heterojunctions

    NASA Astrophysics Data System (ADS)

    Liu, Yuanda; Wang, Fengqiu; Liu, Yujie; Wang, Xizhang; Xu, Yongbing; Zhang, Rong

    2016-06-01

    Carbon nanotubes and graphene are two most widely investigated low-dimensional materials for photonic and optoelectronic devices. Combining these two materials into all-carbon hybrid nanostructures has shown enhanced properties in a range of devices, such as photodetectors and flexible electrodes. Interfacial charge transfer is the most fundamental physical process that directly impacts device design and performance, but remains a subject less well studied. Here, we complemented Raman spectroscopy with photocurrent probing, a robust way of illustrating the interfacial built-in fields, and unambiguously revealed both static and dynamic (photo-induced) charge transfer processes at the nanotube-graphene interfaces. Significantly, the effects of nanotube species, i.e. metallic as opposed to semiconducting, are for the first time compared. Of all the devices examined, the graphene sheet was found to be p-type doped with (6, 5) chirality-enriched semiconducting SWNTs (s-SWNTs), while n-type doped with highly pure (>99%) metallic SWNTs (m-SWNTs). Our results provide important design guidelines for all-carbon hybrid based devices.

  7. Charge transfer at carbon nanotube-graphene van der Waals heterojunctions.

    PubMed

    Liu, Yuanda; Wang, Fengqiu; Liu, Yujie; Wang, Xizhang; Xu, Yongbing; Zhang, Rong

    2016-07-14

    Carbon nanotubes and graphene are two most widely investigated low-dimensional materials for photonic and optoelectronic devices. Combining these two materials into all-carbon hybrid nanostructures has shown enhanced properties in a range of devices, such as photodetectors and flexible electrodes. Interfacial charge transfer is the most fundamental physical process that directly impacts device design and performance, but remains a subject less well studied. Here, we complemented Raman spectroscopy with photocurrent probing, a robust way of illustrating the interfacial built-in fields, and unambiguously revealed both static and dynamic (photo-induced) charge transfer processes at the nanotube-graphene interfaces. Significantly, the effects of nanotube species, i.e. metallic as opposed to semiconducting, are for the first time compared. Of all the devices examined, the graphene sheet was found to be p-type doped with (6, 5) chirality-enriched semiconducting SWNTs (s-SWNTs), while n-type doped with highly pure (>99%) metallic SWNTs (m-SWNTs). Our results provide important design guidelines for all-carbon hybrid based devices.

  8. Ultrafast spin exchange-coupling torque via photo-excited charge-transfer processes

    SciTech Connect

    Ma, X.; Fang, F.; Li, Q.; Zhu, J.; Yang, Y.; Wu, Y. Z.; Zhao, H. B.; Lüpke, G.

    2015-10-28

    In this study, optical control of spin is of central importance in the research of ultrafast spintronic devices utilizing spin dynamics at short time scales. Recently developed optical approaches such as ultrafast demagnetization, spin-transfer and spin-orbit torques open new pathways to manipulate spin through its interaction with photon, orbit, charge or phonon. However, these processes are limited by either the long thermal recovery time or the low-temperature requirement. Here we experimentally demonstrate ultrafast coherent spin precession via optical charge-transfer processes in the exchange-coupled Fe/CoO system at room temperature. The efficiency of spin precession excitation is significantly higher and the recovery time of the exchange-coupling torque is much shorter than for the demagnetization procedure, which is desirable for fast switching. The exchange coupling is a key issue in spin valves and tunnelling junctions, and hence our findings will help promote the development of exchange-coupled device concepts for ultrafast coherent spin manipulation.

  9. Ultrafast spin exchange-coupling torque via photo-excited charge-transfer processes

    DOE PAGES

    Ma, X.; Fang, F.; Li, Q.; ...

    2015-10-28

    In this study, optical control of spin is of central importance in the research of ultrafast spintronic devices utilizing spin dynamics at short time scales. Recently developed optical approaches such as ultrafast demagnetization, spin-transfer and spin-orbit torques open new pathways to manipulate spin through its interaction with photon, orbit, charge or phonon. However, these processes are limited by either the long thermal recovery time or the low-temperature requirement. Here we experimentally demonstrate ultrafast coherent spin precession via optical charge-transfer processes in the exchange-coupled Fe/CoO system at room temperature. The efficiency of spin precession excitation is significantly higher and the recoverymore » time of the exchange-coupling torque is much shorter than for the demagnetization procedure, which is desirable for fast switching. The exchange coupling is a key issue in spin valves and tunnelling junctions, and hence our findings will help promote the development of exchange-coupled device concepts for ultrafast coherent spin manipulation.« less

  10. Spectrophotometric and electrical studies of charge-transfer complexes of sodium flucloxacillin with π-acceptors

    NASA Astrophysics Data System (ADS)

    Refat, Moamen S.; El-Didamony, Akram M.

    2006-11-01

    The present study is interested to develop a simple, rapid and accurate spectrophotometric method for determination of sodium flucloxacillin (fluc) in pure form and pharmaceutical formulations. The charge-transfer (CT) interactions between sodium flucloxacillin as electron donor and chloranilic acid (CLA), dichloroquinone 4-chloroimide (DCQ), 2,3-dichloro-5,6-dicyano- p-benzoquinone (DDQ) and 7,7,8,8 tetracyano- p-quinodimethane (TCNQ), as π-electron acceptors have been investigated spectrophotometrically. Different variables affecting the reaction were studied and optimized. Under the optimum conditions, linear relationships with good correlation coefficients (0.9979-0.9995) were found between the absorbance and the concentration of the drug in the range 16-880 μg ml -1. The proposed methods were applied successfully to the determination of the examined drug either in pure or pharmaceutical dosage forms with good accuracy and precision. The formation of the CT-complexes and the sites of interaction were confirmed by elemental analysis CHN, UV-vis, IR, 1H NMR and mass spectra techniques. Based on Job's method of continuous variation plots, the obtained results indicate the formation of 1:1 charge-transfer complexes with the general formula [(fluc)(acceptor)]. Statistical analysis of the obtained results showed no significant difference between the proposed method and official method.

  11. Ultrafast spin exchange-coupling torque via photo-excited charge-transfer processes

    PubMed Central

    Ma, X.; Fang, F.; Li, Q.; Zhu, J.; Yang, Y.; Wu, Y. Z.; Zhao, H. B.; Lüpke, G.

    2015-01-01

    Optical control of spin is of central importance in the research of ultrafast spintronic devices utilizing spin dynamics at short time scales. Recently developed optical approaches such as ultrafast demagnetization, spin-transfer and spin-orbit torques open new pathways to manipulate spin through its interaction with photon, orbit, charge or phonon. However, these processes are limited by either the long thermal recovery time or the low-temperature requirement. Here we experimentally demonstrate ultrafast coherent spin precession via optical charge-transfer processes in the exchange-coupled Fe/CoO system at room temperature. The efficiency of spin precession excitation is significantly higher and the recovery time of the exchange-coupling torque is much shorter than for the demagnetization procedure, which is desirable for fast switching. The exchange coupling is a key issue in spin valves and tunnelling junctions, and hence our findings will help promote the development of exchange-coupled device concepts for ultrafast coherent spin manipulation. PMID:26508587

  12. Theory of the J-band: From the Frenkel exciton to charge transfer

    NASA Astrophysics Data System (ADS)

    Egorov, Vladimir V.

    2009-08-01

    This review concerns the current status of the theory of formation of the so-called J-band (Jelley, Scheibe, 1936), an abnormally narrow, high-intensity, red-shifted optical absorption band arising from the aggregation of polymethine dyes. Two opposite approaches to explaining the physical nature of the J-band are given special attention. In the first of these, the old one based on Frenkel's statistical exciton model, the specific structure of the dye is considered irrelevant, and the J-band is explained by assuming that the quickly moving Frenkel exciton acts to average out the quasistatic disorder in electronic transition energies of molecules in the linear J-aggregate (Knapp, 1984). In the second approach, on the contrary, the specific structure of the dye (the existence of a quasilinear polymethine chain) is supposed to be very important. This new approach is based on a new theory of charge transfer. The explanation of the J-band here is that an elementary charge transfer along the J-aggregate's chromophore is dynamically pumped by the chaotic reorganization of nuclei in the nearby environment at a resonance between electronic and nuclear movements-when the motion of nuclei being reorganized is only weakly chaotic (Egorov, 2001).

  13. Charge transfer mechanism in titanium-doped microporous silica for photocatalytic water-splitting applications

    SciTech Connect

    Sapp, Wendi; Koodali, Ranjit; Kilin, Dmitri

    2016-02-29

    Solar energy conversion into chemical form is possible using artificial means. One example of a highly-efficient fuel is solar energy used to split water into oxygen and hydrogen. Efficient photocatalytic water-splitting remains an open challenge for researchers across the globe. Despite significant progress, several aspects of the reaction, including the charge transfer mechanism, are not fully clear. Density functional theory combined with density matrix equations of motion were used to identify and characterize the charge transfer mechanism involved in the dissociation of water. A simulated porous silica substrate, using periodic boundary conditions, with Ti4+ ions embedded on the inner pore wall was found to contain electron and hole trap states that could facilitate a chemical reaction. A trap state was located within the silica substrate that lengthened relaxation time, which may favor a chemical reaction. A chemical reaction would have to occur within the window of photoexcitation; therefore, the existence of a trapping state may encourage a chemical reaction. Furthermore, this provides evidence that the silica substrate plays an integral part in the electron/hole dynamics of the system, leading to the conclusion that both components (photoactive materials and support) of heterogeneous catalytic systems are important in optimization of catalytic efficiency.

  14. Oscillatory Noncollinear Magnetism Induced by Interfacial Charge Transfer in Superlattices Composed of Metallic Oxides

    NASA Astrophysics Data System (ADS)

    Hoffman, Jason D.; Kirby, Brian J.; Kwon, Jihwan; Fabbris, Gilberto; Meyers, D.; Freeland, John W.; Martin, Ivar; Heinonen, Olle G.; Steadman, Paul; Zhou, Hua; Schlepütz, Christian M.; Dean, Mark P. M.; te Velthuis, Suzanne G. E.; Zuo, Jian-Min; Bhattacharya, Anand

    2016-10-01

    Interfaces between correlated complex oxides are promising avenues to realize new forms of magnetism that arise as a result of charge transfer, proximity effects, and locally broken symmetries. We report on the discovery of a noncollinear magnetic structure in superlattices of the ferromagnetic metallic oxide La2 /3Sr1 /3MnO3 (LSMO) and the correlated metal LaNiO3 (LNO). The exchange interaction between LSMO layers is mediated by the intervening LNO, such that the angle between the magnetization of neighboring LSMO layers varies in an oscillatory manner with the thickness of the LNO layer. The magnetic field, temperature, and spacer thickness dependence of the noncollinear structure are inconsistent with the bilinear and biquadratic interactions that are used to model the magnetic structure in conventional metallic multilayers. A model that couples the LSMO layers to a helical spin state within the LNO fits the observed behavior. We propose that the spin-helix results from the interaction between a spatially varying spin susceptibility within the LNO and interfacial charge transfer that creates localized Ni2 + states. Our work suggests a new approach to engineering noncollinear spin textures in metallic oxide heterostructures.

  15. Charge-transfer interactions induce surface dependent conformational changes in apolipoprotein biocorona.

    PubMed

    Raghavendra, Achyut J; Alsaleh, Nasser; Brown, Jared M; Podila, Ramakrishna

    2017-03-07

    Upon introduction into a biological system, engineered nanomaterials (ENMs) rapidly associate with a variety of biomolecules such as proteins and lipids to form a biocorona. The presence of "biocorona" influences nano-bio interactions considerably, and could ultimately result in altered biological responses. Apolipoprotein A-I (ApoA-I), the major constituent of high-density lipoprotein (HDL), is one of the most prevalent proteins found in ENM-biocorona irrespective of ENM nature, size, and shape. Given the importance of ApoA-I in HDL and cholesterol transport, it is necessary to understand the mechanisms of ApoA-I adsorption and the associated structural changes for assessing consequences of ENM exposure. Here, the authors used a comprehensive array of microscopic and spectroscopic tools to elucidate the interactions between ApoA-I and 100 nm Ag nanoparticles (AgNPs) with four different surface functional groups. The authors found that the protein adsorption and secondary structural changes are highly dependent on the surface functionality. Our electrochemical studies provided new evidence for charge transfer interactions that influence ApoA-I unfolding. While the unfolding of ApoA-I on AgNPs did not significantly change their uptake and short-term cytotoxicity, the authors observed that it strongly altered the ability of only some AgNPs to generate of reactive oxygen species. Our results shed new light on the importance of surface functionality and charge transfer interactions in biocorona formation.

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

    DOE PAGES

    Miller, John M.; Onar, Omer C.; Chinthavali, Madhu

    2014-12-22

    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 resemblancemore » 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. Lastly, this paper also provides an experimental evidence for frequency selection, fringe field assessment, and the need for low-latency communications in the feedback path.« less

  17. Excited State Structural Dynamics of Carotenoids and ChargeTransfer Systems

    SciTech Connect

    Van Tassle, Aaron Justin

    2006-01-01

    This dissertation describes the development andimplementation of a visible/near infrared pump/mid-infrared probeapparatus. Chapter 1 describes the background and motivation ofinvestigating optically induced structural dynamics, paying specificattention to solvation and the excitation selection rules of highlysymmetric molecules such as carotenoids. Chapter 2 describes thedevelopment and construction of the experimental apparatus usedthroughout the remainder of this dissertation. Chapter 3 will discuss theinvestigation of DCM, a laser dye with a fluorescence signal resultingfrom a charge transfer state. By studying the dynamics of DCM and of itsmethyl deuterated isotopomer (an otherwise identical molecule), we areable to investigate the origins of the charge transfer state and provideevidence that it is of the controversial twisted intramolecular (TICT)type. Chapter 4 introduces the use of two-photon excitation to the S1state, combined with one-photon excitation to the S2 state of thecarotenoid beta-apo-8'-carotenal. These 2 investigations show evidencefor the formation of solitons, previously unobserved in molecular systemsand found only in conducting polymers Chapter 5 presents an investigationof the excited state dynamics of peridinin, the carotenoid responsiblefor the light harvesting of dinoflagellates. This investigation allowsfor a more detailed understanding of the importance of structuraldynamics of carotenoids in light harvesting.

  18. Relation between Nonlinear Optical Properties of Push-Pull Molecules and Metric of Charge Transfer Excitations.

    PubMed

    List, Nanna Holmgaard; Zaleśny, Robert; Murugan, N Arul; Kongsted, Jacob; Bartkowiak, Wojciech; Ågren, Hans

    2015-09-08

    We establish the relationships between the metric of charge transfer excitation (Δr) for the bright ππ* state and the two-photon absorption probability as well as the first hyperpolarizability for two families of push-pull π-conjugated systems. As previously demonstrated by Guido et al. (J. Chem. Theory Comput. 2013, 9, 3118-3126), Δr is a measure for the average hole-electron distance upon excitation and can be used to discriminate between short- and long-range electronic excitations. We indicate two new benefits from using this metric for the analyses of nonlinear optical properties of push-pull systems. First, the two-photon absorption probability and the first hyperpolarizability are found to be interrelated through Δr; if β ∼ (Δr)(k), then roughly, δ(TPA) ∼ (Δr)(k+1). Second, a simple power relation between Δr and the molecular hyperpolarizabilities of push-pull systems offers the possibility of estimating properties for longer molecular chains without performing calculations of high-order response functions explicitly. We further demonstrate how to link the hyperpolarizabilities with the chain length of the push-pull π-conjugated systems through the metric of charge transfer.

  19. Observation of excited state charge transfer with fs/ps-CARS

    SciTech Connect

    Blom, Alex Jason

    2009-01-01

    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'-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.

  20. Experimental and modeling study on charge storage/transfer mechanism of graphene-based supercapacitors

    NASA Astrophysics Data System (ADS)

    Ban, Shuai; Jing, Xie; Zhou, Hongjun; Zhang, Lei; Zhang, Jiujun

    2014-12-01

    A symmetrical graphene-based supercapacitor is constructed for studying the charge-transfer mechanism within the graphene-based electrodes using both experiment measurements and molecular simulation. The in-house synthesized graphene is characterized by XRD, SEM and BET measurements for morphology and surface area. It is observed that the electric capacity of graphene electrode can be reduced by both high internal resistance and limited mass transfer. Computer modeling is conducted at the molecular level to characterize the diffusion behavior of electrolyte ions to the interior of electrode with emphasis on the unique 2D confinement imposed by graphene layers. Although graphene powder poses a moderate internal surface of 400 m2 g-1, the capacitance performance of graphene electrode can be as good as that of commercial activated carbon which has an overwhelming surface area of 1700 m2 g-1. An explanation to this abnormal correlation is that graphene material has an intrinsic capability of adaptively reorganizing its microporous structure in response to intercalation of ions and immergence of electrolyte solvent. The accessible surface of graphene is believed to be dramatically enlarged for ion adsorption during the charging process of capacitor.