WorldWideScience

Sample records for charge carrier solvation

  1. Ionic strength independence of charge distributions in solvation of biomolecules

    Energy Technology Data Exchange (ETDEWEB)

    Virtanen, J. J. [Department of Chemistry, University of Chicago, Chicago, Illinois 60637 (United States); James Franck Institute, University of Chicago, Chicago, Illinois 60637 (United States); Sosnick, T. R. [Department of Biochemistry and Molecular Biology, Institute for Biophysical Dynamics, University of Chicago, Chicago, Illinois 60637 (United States); Computation Institute, University of Chicago, Chicago, Illinois 60637 (United States); Freed, K. F. [Department of Chemistry, University of Chicago, Chicago, Illinois 60637 (United States); James Franck Institute, University of Chicago, Chicago, Illinois 60637 (United States); Computation Institute, University of Chicago, Chicago, Illinois 60637 (United States)

    2014-12-14

    Electrostatic forces enormously impact the structure, interactions, and function of biomolecules. We perform all-atom molecular dynamics simulations for 5 proteins and 5 RNAs to determine the dependence on ionic strength of the ion and water charge distributions surrounding the biomolecules, as well as the contributions of ions to the electrostatic free energy of interaction between the biomolecule and the surrounding salt solution (for a total of 40 different biomolecule/solvent combinations). Although water provides the dominant contribution to the charge density distribution and to the electrostatic potential even in 1M NaCl solutions, the contributions of water molecules and of ions to the total electrostatic interaction free energy with the solvated biomolecule are comparable. The electrostatic biomolecule/solvent interaction energies and the total charge distribution exhibit a remarkable insensitivity to salt concentrations over a huge range of salt concentrations (20 mM to 1M NaCl). The electrostatic potentials near the biomolecule's surface obtained from the MD simulations differ markedly, as expected, from the potentials predicted by continuum dielectric models, even though the total electrostatic interaction free energies are within 11% of each other.

  2. Ionic strength independence of charge distributions in solvation of biomolecules

    International Nuclear Information System (INIS)

    Virtanen, J. J.; Sosnick, T. R.; Freed, K. F.

    2014-01-01

    Electrostatic forces enormously impact the structure, interactions, and function of biomolecules. We perform all-atom molecular dynamics simulations for 5 proteins and 5 RNAs to determine the dependence on ionic strength of the ion and water charge distributions surrounding the biomolecules, as well as the contributions of ions to the electrostatic free energy of interaction between the biomolecule and the surrounding salt solution (for a total of 40 different biomolecule/solvent combinations). Although water provides the dominant contribution to the charge density distribution and to the electrostatic potential even in 1M NaCl solutions, the contributions of water molecules and of ions to the total electrostatic interaction free energy with the solvated biomolecule are comparable. The electrostatic biomolecule/solvent interaction energies and the total charge distribution exhibit a remarkable insensitivity to salt concentrations over a huge range of salt concentrations (20 mM to 1M NaCl). The electrostatic potentials near the biomolecule's surface obtained from the MD simulations differ markedly, as expected, from the potentials predicted by continuum dielectric models, even though the total electrostatic interaction free energies are within 11% of each other

  3. Solvation thermodynamics and heat capacity of polar and charged solutes in water

    Science.gov (United States)

    Sedlmeier, Felix; Netz, Roland R.

    2013-03-01

    The solvation thermodynamics and in particular the solvation heat capacity of polar and charged solutes in water is studied using atomistic molecular dynamics simulations. As ionic solutes we consider a F- and a Na+ ion, as an example for a polar molecule with vanishing net charge we take a SPC/E water molecule. The partial charges of all three solutes are varied in a wide range by a scaling factor. Using a recently introduced method for the accurate determination of the solvation free energy of polar solutes, we determine the free energy, entropy, enthalpy, and heat capacity of the three different solutes as a function of temperature and partial solute charge. We find that the sum of the solvation heat capacities of the Na+ and F- ions is negative, in agreement with experimental observations, but our results uncover a pronounced difference in the heat capacity between positively and negatively charged groups. While the solvation heat capacity ΔCp stays positive and even increases slightly upon charging the Na+ ion, it decreases upon charging the F- ion and becomes negative beyond an ion charge of q = -0.3e. On the other hand, the heat capacity of the overall charge-neutral polar solute derived from a SPC/E water molecule is positive for all charge scaling factors considered by us. This means that the heat capacity of a wide class of polar solutes with vanishing net charge is positive. The common ascription of negative heat capacities to polar chemical groups might arise from the neglect of non-additive interaction effects between polar and apolar groups. The reason behind this non-additivity is suggested to be related to the second solvation shell that significantly affects the solvation thermodynamics and due to its large spatial extent induces quite long-ranged interactions between solvated molecular parts and groups.

  4. Electrostatic solvation free energies of charged hard spheres using molecular dynamics with density functional theory interactions

    Science.gov (United States)

    Duignan, Timothy T.; Baer, Marcel D.; Schenter, Gregory K.; Mundy, Chistopher J.

    2017-10-01

    Determining the solvation free energies of single ions in water is one of the most fundamental problems in physical chemistry and yet many unresolved questions remain. In particular, the ability to decompose the solvation free energy into simple and intuitive contributions will have important implications for models of electrolyte solution. Here, we provide definitions of the various types of single ion solvation free energies based on different simulation protocols. We calculate solvation free energies of charged hard spheres using density functional theory interaction potentials with molecular dynamics simulation and isolate the effects of charge and cavitation, comparing to the Born (linear response) model. We show that using uncorrected Ewald summation leads to unphysical values for the single ion solvation free energy and that charging free energies for cations are approximately linear as a function of charge but that there is a small non-linearity for small anions. The charge hydration asymmetry for hard spheres, determined with quantum mechanics, is much larger than for the analogous real ions. This suggests that real ions, particularly anions, are significantly more complex than simple charged hard spheres, a commonly employed representation.

  5. Solid state cloaking for electrical charge carrier mobility control

    Science.gov (United States)

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

    2015-07-07

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

  6. Protonic and Electronic Charge Carriers in Solvated Biomacromolecules

    Science.gov (United States)

    1989-01-01

    was less than 1% of that expected from Couloub’s law]. When dryer samples (less than 5% water ), were electrolysed , the amount of oxygen could only be...2. The methodology involved the adsorption of water and other organic liquids on biomacromolecules and subsequent solid-state electrolysis. 3. The...in contrast, was not found in an electrolysis product even when water was the adsorbate., 6. -The conclusion is that protonic conductance in

  7. The charge-asymmetric nonlocally determined local-electric (CANDLE) solvation model

    Energy Technology Data Exchange (ETDEWEB)

    Sundararaman, Ravishankar; Goddard, William A. [Joint Center for Artificial Photosynthesis, Pasadena, California 91125 (United States)

    2015-02-14

    Many important applications of electronic structure methods involve molecules or solid surfaces in a solvent medium. Since explicit treatment of the solvent in such methods is usually not practical, calculations often employ continuum solvation models to approximate the effect of the solvent. Previous solvation models either involve a parametrization based on atomic radii, which limits the class of applicable solutes, or based on solute electron density, which is more general but less accurate, especially for charged systems. We develop an accurate and general solvation model that includes a cavity that is a nonlocal functional of both solute electron density and potential, local dielectric response on this nonlocally determined cavity, and nonlocal approximations to the cavity-formation and dispersion energies. The dependence of the cavity on the solute potential enables an explicit treatment of the solvent charge asymmetry. With four parameters per solvent, this “CANDLE” model simultaneously reproduces solvation energies of large datasets of neutral molecules, cations, and anions with a mean absolute error of 1.8 kcal/mol in water and 3.0 kcal/mol in acetonitrile.

  8. Solvation of excess electrons trapped in charge pockets on molecular surfaces

    Science.gov (United States)

    Jalbout, Abraham F.

    This work considers the ability of hydrogen fluoride (HF) to solvate excess electrons located on cyclic hydrocarbon surfaces. The principle applied involves the formation of systems in which excess electrons can be stabilized not only on concentrated molecular surface charge pockets but also by HF. Recent studies have shown that OH groups can form stable hydrogen-bonded networks on one side of a hydrocarbon surface (i.e. cyclohexane sheets), at the same time, the hydrogen atoms on the opposite side of this surface form a pocket of positive charge can attract the excess electron. This density can be further stabilized by the addition of an HF molecule that can form an 'anion with an internally solvated electron' (AISE) state. These systems are shown to be stable with respect to vertical electron detachment (VDE).

  9. Ultrafast dynamics of solvation and charge transfer in a DNA-based biomaterial.

    Science.gov (United States)

    Choudhury, Susobhan; Batabyal, Subrata; Mondol, Tanumoy; Sao, Dilip; Lemmens, Peter; Pal, Samir Kumar

    2014-05-01

    Charge migration along DNA molecules is a key factor for DNA-based devices in optoelectronics and biotechnology. The association of a significant amount of water molecules in DNA-based materials for the intactness of the DNA structure and their dynamic role in the charge-transfer (CT) dynamics is less documented in contemporary literature. In the present study, we have used a genomic DNA-cetyltrimethyl ammonium chloride (CTMA) complex, a technological important biomaterial, and Hoechest 33258 (H258), a well-known DNA minor groove binder, as fluorogenic probe for the dynamic solvation studies. The CT dynamics of CdSe/ZnS quantum dots (QDs; 5.2 nm) embedded in the as-prepared and swollen biomaterial have also been studied and correlated with that of the timescale of solvation. We have extended our studies on the temperature-dependent CT dynamics of QDs in a nanoenvironment of an anionic, sodium bis(2-ethylhexyl)sulfosuccinate reverse micelle (AOT RMs), whereby the number of water molecules and their dynamics can be tuned in a controlled manner. A direct correlation of the dynamics of solvation and that of the CT in the nanoenvironments clearly suggests that the hydration barrier within the Arrhenius framework essentially dictates the charge-transfer dynamics. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  10. Terahertz transport dynamics of graphene charge carriers

    DEFF Research Database (Denmark)

    Buron, Jonas Christian Due

    The electronic transport dynamics of graphene charge carriers at femtosecond (10-15 s) to picosecond (10-12 s) time scales are investigated using terahertz (1012 Hz) time-domain spectroscopy (THz-TDS). The technique uses sub-picosecond pulses of electromagnetic radiation to gauge the electrodynamic...... response of thin conducting films at up to multi-terahertz frequencies. In this thesis THz-TDS is applied towards two main goals; (1) investigation of the fundamental carrier transport dynamics in graphene at femtosecond to picosecond timescales and (2) application of terahertz time-domain spectroscopy...... to rapid and non-contact electrical characterization of large-area graphene, relevant for industrial integration. We show that THz-TDS is an accurate and reliable probe of graphene sheet conductance, and that the technique provides insight into fundamental aspects of the nanoscopic nature of conduction...

  11. Hot Charge Carrier Transmission from Plasmonic Nanostructures

    Science.gov (United States)

    Christopher, Phillip; Moskovits, Martin

    2017-05-01

    Surface plasmons have recently been harnessed to carry out processes such as photovoltaic current generation, redox photochemistry, photocatalysis, and photodetection, all of which are enabled by separating energetic (hot) electrons and holes—processes that, previously, were the domain of semiconductor junctions. Currently, the power conversion efficiencies of systems using plasmon excitation are low. However, the very large electron/hole per photon quantum efficiencies observed for plasmonic devices fan the hope of future improvements through a deeper understanding of the processes involved and through better device engineering, especially of critical interfaces such as those between metallic and semiconducting nanophases (or adsorbed molecules). In this review, we focus on the physics and dynamics governing plasmon-derived hot charge carrier transfer across, and the electronic structure at, metal-semiconductor (molecule) interfaces, where we feel the barriers contributing to low efficiencies reside. We suggest some areas of opportunity that deserve early attention in the still-evolving field of hot carrier transmission from plasmonic nanostructures to neighboring phases.

  12. Charge-carrier mobilities in disordered semiconducting polymers: effects of carrier density and electric field [refereed

    NARCIS (Netherlands)

    Meisel, K.D.; Pasveer, W.F.; Cottaar, J.; Tanase, C.; Coehoorn, R.; Bobbert, P.A.; Blom, P.W.M.; Leeuw, de D.M.; Michels, M.A.J.

    2006-01-01

    We model charge transport in disordered semiconducting polymers by hopping of charge carriers on a square lattice of sites with Gaussian on-site energy disorder, using Fermi-Dirac statistics. From numerically exact solns. of the Master equation, we study the dependence of the charge-carrier mobility

  13. Charge-carrier mobilities in disordered semiconducting polymers : effects of carrier density and electric field

    NARCIS (Netherlands)

    Meisel, K.D.; Pasveer, W.F.; Cottaar, J.; Tanase, C.; Coehoorn, R.; Bobbert, P.A.; Blom, P.W.M.; Leeuw, D.M. de; Michels, M.A.J.

    2006-01-01

    We model charge transport in disordered semiconducting polymers by hopping of charge carriers on a square lattice of sites with Gaussian on-site energy disorder, using Fermi-Dirac statistics. From numerically exact solutions of the Master equation, we study the dependence of the charge-carrier

  14. Affine-response model of molecular solvation of ions: Accurate predictions of asymmetric charging free energies.

    Science.gov (United States)

    Bardhan, Jaydeep P; Jungwirth, Pavel; Makowski, Lee

    2012-09-28

    Two mechanisms have been proposed to drive asymmetric solvent response to a solute charge: a static potential contribution similar to the liquid-vapor potential, and a steric contribution associated with a water molecule's structure and charge distribution. In this work, we use free-energy perturbation molecular-dynamics calculations in explicit water to show that these mechanisms act in complementary regimes; the large static potential (∼44 kJ/mol/e) dominates asymmetric response for deeply buried charges, and the steric contribution dominates for charges near the solute-solvent interface. Therefore, both mechanisms must be included in order to fully account for asymmetric solvation in general. Our calculations suggest that the steric contribution leads to a remarkable deviation from the popular "linear response" model in which the reaction potential changes linearly as a function of charge. In fact, the potential varies in a piecewise-linear fashion, i.e., with different proportionality constants depending on the sign of the charge. This discrepancy is significant even when the charge is completely buried, and holds for solutes larger than single atoms. Together, these mechanisms suggest that implicit-solvent models can be improved using a combination of affine response (an offset due to the static potential) and piecewise-linear response (due to the steric contribution).

  15. Affine-response model of molecular solvation of ions: Accurate predictions of asymmetric charging free energies

    Science.gov (United States)

    Bardhan, Jaydeep P.; Jungwirth, Pavel; Makowski, Lee

    2012-01-01

    Two mechanisms have been proposed to drive asymmetric solvent response to a solute charge: a static potential contribution similar to the liquid-vapor potential, and a steric contribution associated with a water molecule's structure and charge distribution. In this work, we use free-energy perturbation molecular-dynamics calculations in explicit water to show that these mechanisms act in complementary regimes; the large static potential (∼44 kJ/mol/e) dominates asymmetric response for deeply buried charges, and the steric contribution dominates for charges near the solute-solvent interface. Therefore, both mechanisms must be included in order to fully account for asymmetric solvation in general. Our calculations suggest that the steric contribution leads to a remarkable deviation from the popular “linear response” model in which the reaction potential changes linearly as a function of charge. In fact, the potential varies in a piecewise-linear fashion, i.e., with different proportionality constants depending on the sign of the charge. This discrepancy is significant even when the charge is completely buried, and holds for solutes larger than single atoms. Together, these mechanisms suggest that implicit-solvent models can be improved using a combination of affine response (an offset due to the static potential) and piecewise-linear response (due to the steric contribution). PMID:23020318

  16. Importance of polaron effects for charge carrier mobility above and ...

    Indian Academy of Sciences (India)

    It is shown that the scattering of polaronic charge carriers and bosonic Cooper pairs at acoustic and optical phonons are responsible for the charge carrier mobility above and below the PG temperature. We show that the energy scales of the binding energies of large polarons and polaronic Cooper pairs can be identified by ...

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

    International Nuclear Information System (INIS)

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

    2014-01-01

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

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

    Energy Technology Data Exchange (ETDEWEB)

    Ong, Zhun-Yong; Zhang, Gang; Zhang, Yong Wei [Institute of High Performance Computing, A*STAR, Singapore 138632 (Singapore)

    2014-12-07

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

  19. Magnetic Generation due to Mass Difference between Charge Carriers

    OpenAIRE

    Chen, Shi; Dan, JiaKun; Chen, ZiYu; Li, JianFeng

    2013-01-01

    The possibility of spontaneous magnetization due to the "asymmetry in mass" of charge carriers in a system is investigated. Analysis shows that when the masses of positive and negative charge carriers are identical, no magnetization is predicted. However, if the masses of two species are different, spontaneous magnetic field would appear, either due to the equipartition of magnetic energy or due to fluctuations together with a feedback mechanism. The conditions for magnetization to occur are ...

  20. Mobility of charge carriers in porous silicon layers

    International Nuclear Information System (INIS)

    Forsh, P. A.; Martyshov, M. N.; Latysheva, A. P.; Vorontsov, A. S.; Timoshenko, V. Yu.; Kashkarov, P. K.

    2008-01-01

    The (conduction) mobility of majority charge carriers in porous silicon layers of the n and p types is estimated by joint measurements of electrical conductivity and free charge carrier concentration, which is determined from IR absorption spectra. Adsorption of donor and acceptor molecules leading to a change in local electric fields in the structure is used to identify the processes controlling the mobility in porous silicon. It is found that adsorption of acceptor and donor molecules at porous silicon of the p and n types, respectively, leads to a strong increase in electrical conductivity, which is associated with an increase in the concentration of free carrier as well as in their mobility. The increase in the mobility of charge carriers as a result of adsorption indicates the key role of potential barriers at the boundaries of silicon nanocrystals and may be due to a decrease in the barrier height as a result of adsorption

  1. Infrared spectroscopic studies on the cluster size dependence of charge carrier structure in nitrous oxide cluster anions

    International Nuclear Information System (INIS)

    Thompson, Michael C.; Weber, J. Mathias

    2016-01-01

    We report infrared photodissociation spectra of nitrous oxide cluster anions of the form (N 2 O) n O − (n = 1–12) and (N 2 O) n − (n = 7–15) in the region 800–1600 cm −1 . The charge carriers in these ions are NNO 2 − and O − for (N 2 O) n O − clusters with a solvation induced core ion switch, and N 2 O − for (N 2 O) n − clusters. The N–N and N–O stretching vibrations of N 2 O − (solvated by N 2 O) are reported for the first time, and they are found at (1595 ± 3) cm −1 and (894 ± 5) cm −1 , respectively. We interpret our infrared spectra by comparison with the existing photoelectron spectroscopy data and with computational data in the framework of density functional theory.

  2. One-carrier free space charge motion under applied voltage

    Energy Technology Data Exchange (ETDEWEB)

    de ALMEIDA, L E.C.; FERREIRA, G F.L. [SAO PAULO UNIV., SAO CARLOS (BRAZIL). INSTITUTO DE FISICA E QUIMICA

    1975-12-01

    It is shown how to transform the system of partial differential equations, describing the free one-carrier space charge motion in solid dielectrics under a given applied voltage and while the charge distribution touches only one of the electrodes, into a first order ordinary differential equation from whose solution all the interesting quantities may be easily derived. It was found that some charge distributions can display current reversal.

  3. Study of Charge Carrier Transport in GaN Sensors

    Science.gov (United States)

    Gaubas, Eugenijus; Ceponis, Tomas; Kuokstis, Edmundas; Meskauskaite, Dovile; Pavlov, Jevgenij; Reklaitis, Ignas

    2016-01-01

    Capacitor and Schottky diode sensors were fabricated on GaN material grown by hydride vapor phase epitaxy and metal-organic chemical vapor deposition techniques using plasma etching and metal deposition. The operational characteristics of these devices have been investigated by profiling current transients and by comparing the experimental regimes of the perpendicular and parallel injection of excess carrier domains. Profiling of the carrier injection location allows for the separation of the bipolar and the monopolar charge drift components. Carrier mobility values attributed to the hydride vapor phase epitaxy (HVPE) GaN material have been estimated as μe = 1000 ± 200 cm2/Vs for electrons, and μh = 400 ± 80 cm2/Vs for holes, respectively. Current transients under injection of the localized and bulk packets of excess carriers have been examined in order to determine the surface charge formation and polarization effects. PMID:28773418

  4. Charge carrier coherence and Hall effect in organic semiconductors

    Science.gov (United States)

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

    2016-01-01

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

  5. Charge carrier coherence and Hall effect in organic semiconductors.

    Science.gov (United States)

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

    2016-03-30

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

  6. Charge carrier relaxation model in disordered organic semiconductors

    International Nuclear Information System (INIS)

    Lu, Nianduan; Li, Ling; Sun, Pengxiao; Liu, Ming

    2013-01-01

    The relaxation phenomena of charge carrier in disordered organic semiconductors have been demonstrated and investigated theoretically. An analytical model describing the charge carrier relaxation is proposed based on the pure hopping transport theory. The relation between the material disorder, electric field and temperature and the relaxation phenomena has been discussed in detail, respectively. The calculated results reveal that the increase of electric field and temperature can promote the relaxation effect in disordered organic semiconductors, while the increase of material disorder will weaken the relaxation. The proposed model can explain well the stretched-exponential law by adopting the appropriate parameters. The calculation shows a good agreement with the experimental data for organic semiconductors

  7. Dynamics of electron solvation in methanol: Excited state relaxation and generation by charge-transfer-to-solvent

    International Nuclear Information System (INIS)

    Elkins, Madeline H.; Williams, Holly L.; Neumark, Daniel M.

    2015-01-01

    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

  8. Dynamics of electron solvation in methanol: Excited state relaxation and generation by charge-transfer-to-solvent

    Science.gov (United States)

    Elkins, Madeline H.; Williams, Holly L.; Neumark, Daniel M.

    2015-06-01

    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.

  9. Dynamics of electron solvation in methanol: Excited state relaxation and generation by charge-transfer-to-solvent

    Energy Technology Data Exchange (ETDEWEB)

    Elkins, Madeline H.; Williams, Holly L. [Department of Chemistry, University of California, Berkeley, California 94720 (United States); Neumark, Daniel M. [Department of Chemistry, University of California, Berkeley, California 94720 (United States); Chemical Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720 (United States)

    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. Charge Carrier Dynamics at Silver Nanocluster-Molecular Acceptor Interfaces

    KAUST Repository

    Almansaf, Abdulkhaleq

    2017-07-01

    A fundamental understanding of interfacial charge transfer at donor-acceptor interfaces is very crucial as it is considered among the most important dynamical processes for optimizing performance in many light harvesting systems, including photovoltaics and photo-catalysis. In general, the photo-generated singlet excitons in photoactive materials exhibit very short lifetimes because of their dipole-allowed spin radiative decay and short diffusion lengths. In contrast, the radiative decay of triplet excitons is dipole forbidden; therefore, their lifetimes are considerably longer. The discussion in this thesis primarily focuses on the relevant parameters that are involved in charge separation (CS), charge transfer (CT), intersystem crossing (ISC) rate, triplet state lifetime, and carrier recombination (CR) at silver nanocluster (NCs) molecular-acceptors interfaces. A combination of steady-state and femto- and nanosecond broadband transient absorption spectroscopies were used to investigate the charge carrier dynamics in various donor-acceptor systems. Additionally, this thesis was prolonged to investigate some important factors that influence the charge carrier dynamics in Ag29 silver NCs donor-acceptor systems, such as the metal doping and chemical structure of the nanocluster and molecular acceptors. Interestingly, clear correlations between the steady-state measurements and timeresolved spectroscopy results are found. In the first study, we have investigated the interfacial charge transfer dynamics in positively charged meso units of 5, 10, 15, 20-tetra (1- methyl-4-pyridino)-porphyrin tetra (p-toluene sulfonate) (TMPyP) and neutral charged 5, 10, 15, 20-tetra (4-pyridyl)-porphyrin (TPyP), with negatively charged undoped and gold (Au)- doped silver Ag29 NCs. Moreover, this study showed the impact of Au doping on the charge carrier dynamics of the system. In the second study, we have investigated the interfacial charge transfer dynamics in [Pt2 Ag23 Cl7 (PPh3

  11. Photoinduced reversible switching of charge carrier mobility in conjugated polymers

    Czech Academy of Sciences Publication Activity Database

    Weiter, M.; Navrátil, J.; Vala, M.; Toman, Petr

    2009-01-01

    Roč. 48, č. 1 (2009), 10401_1-10401_6 ISSN 1286-0042 R&D Projects: GA ČR GA203/06/0285; GA AV ČR KAN401770651 Institutional research plan: CEZ:AV0Z40500505 Keywords : polymers * switch * charge carrier mobility Subject RIV: CF - Physical ; Theoretical Chemistry Impact factor: 0.756, year: 2009

  12. One-carrier free space charge motion under applied voltage

    International Nuclear Information System (INIS)

    Camargo, P.C.; Ferreira, G.F.L.

    1976-01-01

    The system of partial differential equations describing the one-carrier free space-charge motion under a given applied voltage is transformed into a system of two ordinary differential equations. The method is applied to find the external current injection [pt

  13. Charge carrier dynamics in thin film solar cells

    Energy Technology Data Exchange (ETDEWEB)

    Strothkaemper, Christian

    2013-06-24

    This work investigates the charge carrier dynamics in three different technological approaches within the class of thin film solar cells: radial heterojunctions, the dye solar cell, and microcrystalline CuInSe{sub 2}, focusing on charge transport and separation at the electrode, and the relaxation of photogenerated charge carriers due to recombination and energy dissipation to the phonon system. This work relies mostly on optical-pump terahertz-probe (OPTP) spectroscopy, followed by transient absorption (TA) and two-photon photoemission (2PPE). The charge separation in ZnO-electrode/In{sub 2}S{sub 3}-absorber core/shell nanorods, which represent a model system of a radial heterojunction, is analyzed by OPTP. It is concluded, that the dynamics in the absorber are determined by multiple trapping, which leads to a dispersive charge transport to the electrode that lasts over hundreds of picoseconds. The high trap density on the order of 10{sup 19}/cm{sup 3} is detrimental for the injection yield, which exhibits a decrease with increasing shell thickness. The heterogeneous electron transfer from a series of model dyes into ZnO proceeds on a time-scale of 200 fs. However, the photoconductivity builds up just on a 2-10 ps timescale, and 2PPE reveals that injected electrons are meanwhile localized spatially and energetically at the interface. It is concluded that the injection proceeds through adsorbate induced interface states. This is an important result because the back reaction from long lived interface states can be expected to be much faster than from bulk states. While the charge transport in stoichiometric CuInSe{sub 2} thin films is indicative of free charge carriers, CuInSe{sub 2} with a solar cell grade composition (Cu-poor) exhibits signs of carrier localization. This detrimental effect is attributed to a high density of charged defects and a high degree of compensation, which together create a spatially fluctuating potential that inhibits charge transport. On

  14. [Experimental and computation studies of polar solvation

    International Nuclear Information System (INIS)

    1990-01-01

    This report from the Pennsylvania State University contains seven sections: (1) radiative rate effects in solvatlvatochromic probes; (2) intramolecular charge transfer reactions; (3) Solvation dynamics in low temperature alcohols; (4) Ionic solvation dynamics; (5) solvation and proton-transfer dynamics in 7-azaindole; (6) computer simulations of solvation dynamics; (7) solvation in supercritical fluids. 20 refs., 11 figs

  15. A self-consistent phase-field approach to implicit solvation of charged molecules with Poisson–Boltzmann electrostatics

    Science.gov (United States)

    Sun, Hui; Wen, Jiayi; Zhao, Yanxiang; Li, Bo; McCammon, J. Andrew

    2015-01-01

    Dielectric boundary based implicit-solvent models provide efficient descriptions of coarse-grained effects, particularly the electrostatic effect, of aqueous solvent. Recent years have seen the initial success of a new such model, variational implicit-solvent model (VISM) [Dzubiella, Swanson, and McCammon Phys. Rev. Lett. 96, 087802 (2006) and J. Chem. Phys. 124, 084905 (2006)], in capturing multiple dry and wet hydration states, describing the subtle electrostatic effect in hydrophobic interactions, and providing qualitatively good estimates of solvation free energies. Here, we develop a phase-field VISM to the solvation of charged molecules in aqueous solvent to include more flexibility. In this approach, a stable equilibrium molecular system is described by a phase field that takes one constant value in the solute region and a different constant value in the solvent region, and smoothly changes its value on a thin transition layer representing a smeared solute-solvent interface or dielectric boundary. Such a phase field minimizes an effective solvation free-energy functional that consists of the solute-solvent interfacial energy, solute-solvent van der Waals interaction energy, and electrostatic free energy described by the Poisson–Boltzmann theory. We apply our model and methods to the solvation of single ions, two parallel plates, and protein complexes BphC and p53/MDM2 to demonstrate the capability and efficiency of our approach at different levels. With a diffuse dielectric boundary, our new approach can describe the dielectric asymmetry in the solute-solvent interfacial region. Our theory is developed based on rigorous mathematical studies and is also connected to the Lum–Chandler–Weeks theory (1999). We discuss these connections and possible extensions of our theory and methods. PMID:26723595

  16. A self-consistent phase-field approach to implicit solvation of charged molecules with Poisson-Boltzmann electrostatics.

    Science.gov (United States)

    Sun, Hui; Wen, Jiayi; Zhao, Yanxiang; Li, Bo; McCammon, J Andrew

    2015-12-28

    Dielectric boundary based implicit-solvent models provide efficient descriptions of coarse-grained effects, particularly the electrostatic effect, of aqueous solvent. Recent years have seen the initial success of a new such model, variational implicit-solvent model (VISM) [Dzubiella, Swanson, and McCammon Phys. Rev. Lett. 96, 087802 (2006) and J. Chem. Phys. 124, 084905 (2006)], in capturing multiple dry and wet hydration states, describing the subtle electrostatic effect in hydrophobic interactions, and providing qualitatively good estimates of solvation free energies. Here, we develop a phase-field VISM to the solvation of charged molecules in aqueous solvent to include more flexibility. In this approach, a stable equilibrium molecular system is described by a phase field that takes one constant value in the solute region and a different constant value in the solvent region, and smoothly changes its value on a thin transition layer representing a smeared solute-solvent interface or dielectric boundary. Such a phase field minimizes an effective solvation free-energy functional that consists of the solute-solvent interfacial energy, solute-solvent van der Waals interaction energy, and electrostatic free energy described by the Poisson-Boltzmann theory. We apply our model and methods to the solvation of single ions, two parallel plates, and protein complexes BphC and p53/MDM2 to demonstrate the capability and efficiency of our approach at different levels. With a diffuse dielectric boundary, our new approach can describe the dielectric asymmetry in the solute-solvent interfacial region. Our theory is developed based on rigorous mathematical studies and is also connected to the Lum-Chandler-Weeks theory (1999). We discuss these connections and possible extensions of our theory and methods.

  17. Charge carrier recombination dynamics in perovskite and polymer solar cells

    Energy Technology Data Exchange (ETDEWEB)

    Paulke, Andreas; Kniepert, Juliane; Kurpiers, Jona; Wolff, Christian M.; Schön, Natalie; Brenner, Thomas J. K.; Neher, Dieter [Institute of Physics and Astronomy, University of Potsdam, Karl-Liebknecht-Str. 24–25, 14476, Potsdam (Germany); Stranks, Samuel D. [Clarendon Laboratory, Department of Physics, University of Oxford, Parks Road, Oxford OX1 3PU (United Kingdom); Research Laboratory of Electronics, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, Massachusetts 02139 (United States); Cavendish Laboratory, JJ Thomson Avenue, Cambridge CB3 0HE (United Kingdom); Snaith, Henry J. [Clarendon Laboratory, Department of Physics, University of Oxford, Parks Road, Oxford OX1 3PU (United Kingdom)

    2016-03-14

    Time-delayed collection field experiments are applied to planar organometal halide perovskite (CH{sub 3}NH{sub 3}PbI{sub 3}) based solar cells to investigate charge carrier recombination in a fully working solar cell at the nanosecond to microsecond time scale. Recombination of mobile (extractable) charges is shown to follow second-order recombination dynamics for all fluences and time scales tested. Most importantly, the bimolecular recombination coefficient is found to be time-dependent, with an initial value of ca. 10{sup −9} cm{sup 3}/s and a progressive reduction within the first tens of nanoseconds. Comparison to the prototypical organic bulk heterojunction device PTB7:PC{sub 71}BM yields important differences with regard to the mechanism and time scale of free carrier recombination.

  18. Affine-response model of molecular solvation of ions: Accurate predictions of asymmetric charging free energies

    Czech Academy of Sciences Publication Activity Database

    Bardhan, J. P.; Jungwirth, Pavel; Makowski, L.

    Roč. 137, č. 12 ( 2012 ), 124101/1-124101/6 ISSN 0021-9606 R&D Projects: GA MŠk LH12001 Institutional research plan: CEZ:AV0Z40550506 Keywords : ion solvation * continuum models * linear response Subject RIV: CF - Physical ; Theoretical Chemistry Impact factor: 3.164, year: 2012

  19. Charge-carrier dynamics and Coulomb effects in semiconductor tetrapods

    International Nuclear Information System (INIS)

    Mauser, Christian

    2011-01-01

    In this thesis the Coulomb interaction and its influence on localization effects and dynamics of charge carriers in semiconductor nanocrystals were studied. In the studied nanostructures it deals with colloidal tetrapod heterostructures, which consist of a cadmium selenide (CdSe) core and four tetraedrical grown cadmium sulfide (CdS) respectively cadmium telluride (CdTe) legs, which exhibit a type-I respectively type-II band transition. The dynamics and interactions were studied by means of photoluminescence (PL) and absorption measurements both on the ensemble and on single nanoparticles, as well as time-resolved PL and transient absorption spectroscopy. Additionally theoretical simulations of the wave-function distributions were performed, which are based on the effective-mass approximation. The special band structure of the CdSe/CdS tetrapods offers a unique possibility to study the Coulomb interaction. The flat conduction band in these heterostructures makes the electron via the Coulomb interaction sensitive to the localization position of the hole within the structure. The valence band has instead a potential maximum in the CdSe, which leads to a directed localization of the hole and the photoluminescence of the core. Polarization-resolved measurements showed hereby an anisotropy of the photoluminescence, which could be explained by means of simulations of the wave-function distribution with an asymmetry at the branching point. Charge-carrier localization occur mainly both in longer structures and in trap states in the CdS leg and can be demonstrated in form of a dual emission from a nanocrystal. The charge-carrier dynamics of electron and hole in tetrapods is indeed coupled by the Coulomb interaction, however it cannot be completely described in an exciton picture. The coupled dynamics and the Coulomb interaction were studied concerning a possible influence of the geometry in CdSe/CdS nanorods and compared with those of the tetrapods. The interactions of the

  20. Charge Carrier Transport Properties of Vacuum Evaporated Anthrylvinylbenzene Thin Films

    Directory of Open Access Journals (Sweden)

    Haikel HRICHI

    2014-05-01

    Full Text Available The charge carrier conduction processes and dielectric properties of two new materials based on anthracene core structure, 1-(9 anthrylvinyl-4-benzyloxybenzene (AVB and 1,4- bis(9-anthrylvinylbenzene (AV2B diodes have been investigated using dc current density–voltage (J–V and AC impedance spectroscopy (100 Hz–10 MHz. The DC electrical properties of ITO/anthracene derivative /Al device showing an ohmic behavior at low voltages and switches to space charge limited current (SCLC conduction with exponential trap distribution at higher voltages. The best performance device was achieved from ITO/AVB/Al structure showing the high charge carrier mobility which has also been evaluated from SCLC as 6.55´10-6 cm/Vs. According to the impedance spectroscopy results the structures were modeled by equivalent circuit designed as a parallel resistor Rp and capacitor Cp network in series with resistor Rs. The evolution of the electrical parameters with frequency and bias voltage of these anthracene-based systems has been discussed. The conductivity s(w evolution with frequency and bias voltage was studied for ITO/anthracene derivatives/Al devices. The dc conductivity sdc for these devices has been determined. The ac conductivity sac showed a variation in angular frequency as A.ws with a critical exponent s< 1 suggesting a hopping conduction mechanism at high frequency.

  1. Charge-carrier transport in large-area epitaxial graphene

    Energy Technology Data Exchange (ETDEWEB)

    Kisslinger, Ferdinand; Popp, Matthias; Weber, Heiko B. [Lehrstuhl fuer Angewandte Physik, Friedrich-Alexander-Universitaet Erlangen-Nuernberg (FAU), Erlangen (Germany); Jobst, Johannes [Huygens-Kamerlingh Onnes Laboratorium, Leiden Institute of Physics, Leiden University (Netherlands); Shallcross, Sam [Lehrstuhl fuer theoretische Festkoerperphysik, Friedrich-Alexander-Universitaet Erlangen-Nuernberg (FAU), Erlangen (Germany)

    2017-11-15

    We present an overview of recent charge carrier transport experiments in both monolayer and bilayer graphene, with emphasis on the phenomena that appear in large-area samples. While many aspects of transport are based on quantum mechanical concepts, in the large-area limit classical corrections dominate and shape the magnetoresistance and the tunneling conductance. The discussed phenomena are very general and can, with little modification, be expected in any atomically thin 2D conductor. (copyright 2017 by WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

  2. Electronic structure of charge carriers in a polysilane quantum wire

    International Nuclear Information System (INIS)

    Kumagai, J.; Yoshida, H.; Ichikawa, T.

    1997-01-01

    The ESR, ESEEM and spectrophotometric studies on polysilane radical ions revealed that charge carriers, hole and conducting electrons, are not delocalized all over the Si-Si main chain but confined to a part of the chain composed of only six Si atoms, probably near the branch on the main chain. Comparison of the ESR spectra of the radical cations and anions revealed that the hole can migrate from the main chain to an adjacent polymer chain via the side chains, whereas the conducting electron can not migrate since the side chains act as good intermolecular insulators for the electron. (author)

  3. Protonic charge defect structures in floating water bridges observed as Zundel and Eigen solvation arrangements

    Science.gov (United States)

    Teschke, Omar; de Castro, Jose Roberto; Valente Filho, Juracyr Ferraz; Soares, David Mendez

    2017-10-01

    Protonic arrangements were detected in water bridge structures using confocal Raman microscopy, and the spectra show two formed structures. The measured Raman spectra were modified using the voltage applied to the bridge structure, which changed the proportion of these two species. Initially, for a 6.3 kV applied voltage, there was a measurable increase in the bridge current above the Ohmic contribution and the observed Raman spectrum of this new injected specie corresponded to the computed spectrum for the Zundel protonic arrangement. As the voltage further increases a contribution from the Eigen proton solvation specie is added to the measured spectrum.

  4. Detection of Intramolecular Charge Transfer and Dynamic Solvation in Eosin B by Femtosecond Two-Dimensional Electronic Spectroscopy

    Science.gov (United States)

    Ghosh, Soumen; Roscioli, Jerome D.; Beck, Warren F.

    2014-06-01

    We have employed 2D electronic photon echo spectroscopy to study intramolecular charge-transfer dynamics in eosin B. After preparation of the first excited singlet state (S_1) with 40-fs excitation pulses at 520 nm, the nitro group (--NO_2) in eosin B undergoes excited state torsional motion towards a twisted intramolecular charge transfer (TICT) state. As the viscosity of the surrounding solvent increases, the charge-transfer rate decreases because the twisting of the --NO_2 group is hindered. These conclusions are supported by the time evolution of the 2D spectrum, which provides a direct measure of the the ground-to-excited-state energy gap time-correlation function, M(t). In comparison to the inertial and diffusive solvation time scales exhibited by eosin Y, which lacks the nitro group, the M(t) function for eosin B exhibits under the same conditions an additional component on the 150-fs timescale that arises from quenching of the S_1 state by crossing to the TICT state. These results indicate that 2D electronic spectroscopy can be used as a sensitive probe of the rate of charge transfer in a molecular system and of the coupling to the motions of the surrounding solvent. (Supported by grant DE-SC0010847 from the Department of Energy, Office of Basic Energy Sciences, Photosynthetic Systems program.)

  5. Control of charge carrier dynamics in disordered conjugated polymers

    Energy Technology Data Exchange (ETDEWEB)

    Hertel, Dirk [Physical Chemistry, University of Cologne, Luxemburgerstr. 116, 50939 Cologne, Germany, (Germany)

    2011-07-01

    We developed a new method to probe charge carrier mobility on ultrafast time scale. It is based on electric field induced second harmonic generation. The method is applied to prototypical amorphous conjugated polymers of the polyphenylene- and polyfluorene-type. Typically the carrier mobility in these organic polymers decreases with time in a power law fashion from about 1 cm{sup 2}Vs{sup -1} at 1 ps to its stationary value of about 10{sup -6} cm{sup 2}Vs{sup -1} in hundreds of ns. The dynamics of the mobility is discussed. It is shown, that in nanoscale devices the macroscopic mobility is not adequate to describe charge transport. We study the influence of disorder, morphology and temperature on ultrafast transport. At early times the transport is dominated by tunneling and disorder plays already an essential role. Comparison of transient photocurrents with Monte-Carlo simulation reveals that on-chain transport has to be invoked to rationalize our results. The hopping rates for intrachain transport are much larger compared with interchain transport. The results give access to essential transport properties for the development of advanced theoretical models and may help to design improved solar cells.

  6. Measuring Charge Carrier Diffusion in Coupled Colloidal Quantum Dot Solids

    KAUST Repository

    Zhitomirsky, David

    2013-06-25

    Colloidal quantum dots (CQDs) are attractive materials for inexpensive, room-temperature-, and solution-processed optoelectronic devices. A high carrier diffusion length is desirable for many CQD device applications. In this work we develop two new experimental methods to investigate charge carrier diffusion in coupled CQD solids under charge-neutral, i.e., undepleted, conditions. The methods take advantage of the quantum-size-effect tunability of our materials, utilizing a smaller-bandgap population of quantum dots as a reporter system. We develop analytical models of diffusion in 1D and 3D structures that allow direct extraction of diffusion length from convenient parametric plots and purely optical measurements. We measure several CQD solids fabricated using a number of distinct methods and having significantly different doping and surface ligand treatments. We find that CQD materials recently reported to achieve a certified power conversion efficiency of 7% with hybrid organic-inorganic passivation have a diffusion length of 80 ± 10 nm. The model further allows us to extract the lifetime, trap density, mobility, and diffusion coefficient independently in each material system. This work will facilitate further progress in extending the diffusion length, ultimately leading to high-quality CQD solid semiconducting materials and improved CQD optoelectronic devices, including CQD solar cells. © 2013 American Chemical Society.

  7. Charge carrier transport mechanisms in nanocrystalline indium oxide

    International Nuclear Information System (INIS)

    Forsh, E.A.; Marikutsa, A.V.; Martyshov, M.N.; Forsh, P.A.; Rumyantseva, M.N.; Gaskov, A.M.; Kashkarov, P.K.

    2014-01-01

    The charge transport properties of nanocrystalline indium oxide (In 2 O 3 ) are studied. A number of nanostructured In 2 O 3 samples with various nanocrystal sizes are prepared by sol–gel method and characterized using various techniques. The mean nanocrystals size varies from 7–8 nm to 18–20 nm depending on the conditions of their preparation. Structural characterizations of the In 2 O 3 samples are performed by means of transmission electron microscopy and X-ray diffraction. The analysis of dc and ac conductivity in a wide temperature range (T = 50–300 K) shows that at high temperatures charge carrier transport takes place over conduction band and at low temperatures a variable range hopping transport mechanism can be observed. We find out that the temperature of transition from one mechanism to another depends on nanocrystal size: the transition temperature rises when nanocrystals are bigger in size. The average hopping distance between two sites and the activation energy are calculated basing on the analysis of dc conductivity at low temperature. Using random barrier model we show a uniform hopping mechanism taking place in our samples and conclude that nanocrystalline In 2 O 3 can be regarded as a disordered system. - Highlights: • In 2 O 3 samples with various nanocrystal sizes are prepared by sol–gel method. • The mean nanocrystal size varies from 7–8 nm to 18–20 nm. • At high temperatures charge carrier transport takes place over conduction band. • At low temperatures a variable range hopping transport mechanism can be observed. • We show a uniform hopping mechanism taking place in our samples

  8. Fragmentation study of isolated and nano-solvated biomolecules induced by collision with multiply charged ions and neutral particles

    International Nuclear Information System (INIS)

    Bernigaud, V.

    2009-01-01

    This thesis concerns a gas phase study of the fragmentation of bio-molecular systems induced by slow collisions with multiply charged ions (in the keV-region), alkali atoms and rare gases. The main objective was to study the physical processes involved in the dissociation of highly electronically excited systems. In order to elucidate the intrinsic properties of certain biomolecules (porphyrins and amino acids) we have performed experiments in the gas phase with isolated systems. The obtained results demonstrate the high stability of porphyrins after electron removal and attachment. Furthermore, a dependence of the fragmentation pattern produced by multiply charged ions on the isomeric structure of the alanine molecule has been shown. In a second part of the thesis, a strong influence of the environment of the biomolecule on the fragmentation channels, their modification and their new opening, has been clearly proven. This phenomenon occurs in the presence of other surrounding biomolecules (clusters of nucleobases) as well as for molecules of a solvent (molecules of water, methanol and acetonitrile) in which the biomolecule is embedded. In order to extend these studies to larger systems, a new experimental set-up, based on an electro-spray ion source combined with a quadrupole mass filter has been developed. Due to the successful tests and proposed improvements of the device future experiments will become available concerning the fragmentation of large charged and solvated bio-molecular systems induced by collision processes. (author) [fr

  9. Charge carrier density in Li-intercalated graphene

    KAUST Repository

    Kaloni, Thaneshwor P.

    2012-05-01

    The electronic structures of bulk C 6Li, Li-intercalated free-standing bilayer graphene, and Li-intercalated bilayer and trilayer graphene on SiC(0 0 0 1) are studied using density functional theory. Our estimate of Young\\'s modulus suggests that Li-intercalation increases the intrinsic stiffness. For decreasing Li-C interaction, the Dirac point shifts to the Fermi level and the associated band splitting vanishes. For Li-intercalated bilayer graphene on SiC(0 0 0 1) the splitting at the Dirac point is tiny. It is also very small at the two Dirac points of Li-intercalated trilayer graphene on SiC(0 0 0 1). For all the systems under study, a large enhancement of the charge carrier density is achieved by Li intercalation. © 2012 Elsevier B.V. All rights reserved.

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

    Science.gov (United States)

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

    2016-06-17

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

  11. Internal energy effects on the solvation and reactivity of multiply charged biomolecules for electrospray ionization mass spectroscopy. [Bovine ubiquitin

    Energy Technology Data Exchange (ETDEWEB)

    Light-Wahl, K.J.; Winger, B.E.; Rockwood, A.L.; Smith, R.D.

    1992-06-01

    Mild (capillary) interface conditions which do not completely desolvate the ions of proteins in electrospray ionization mass spectrometry (ESI-MS) may be required to probe the higher order structures and weak associations. For the small protein bovine ubiquitin, two ion distributions (unsolvated ions and unresolved solvated ions) were observed. The resolvable solvation for leucine-enkephalin with methanol and water shows that the use of countercurrent N{sub 2} flow at the capillary affects the solvation observed. 2 figs. (DLC)

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

    Directory of Open Access Journals (Sweden)

    T. C. Doan

    2014-10-01

    Full Text Available Due to its large in-plane thermal conductivity, high temperature and chemical stability, large energy band gap (˜ 6.4 eV, hexagonal boron nitride (hBN has emerged as an important material for applications in deep ultraviolet photonic devices. Among the members of the III-nitride material system, hBN is the least studied and understood. The study of the electrical transport properties of hBN is of utmost importance with a view to realizing practical device applications. Wafer-scale hBN epilayers have been successfully synthesized by metal organic chemical deposition and their electrical transport properties have been probed by variable temperature Hall effect measurements. The results demonstrate that undoped hBN is a semiconductor exhibiting weak p-type at high temperatures (> 700 °K. The measured acceptor energy level is about 0.68 eV above the valence band. In contrast to the electrical transport properties of traditional III-nitride wide bandgap semiconductors, the temperature dependence of the hole mobility in hBN can be described by the form of μ ∝ (T/T0−α with α = 3.02, satisfying the two-dimensional (2D carrier transport limit dominated by the polar optical phonon scattering. This behavior is a direct consequence of the fact that hBN is a layer structured material. The optical phonon energy deduced from the temperature dependence of the hole mobility is ħω = 192 meV (or 1546 cm-1, which is consistent with values previously obtained using other techniques. The present results extend our understanding of the charge carrier transport properties beyond the traditional III-nitride semiconductors.

  13. Communication: modeling charge-sign asymmetric solvation free energies with nonlinear boundary conditions.

    Science.gov (United States)

    Bardhan, Jaydeep P; Knepley, Matthew G

    2014-10-07

    We show that charge-sign-dependent asymmetric hydration can be modeled accurately using linear Poisson theory after replacing the standard electric-displacement boundary condition with a simple nonlinear boundary condition. Using a single multiplicative scaling factor to determine atomic radii from molecular dynamics Lennard-Jones parameters, the new model accurately reproduces MD free-energy calculations of hydration asymmetries for: (i) monatomic ions, (ii) titratable amino acids in both their protonated and unprotonated states, and (iii) the Mobley "bracelet" and "rod" test problems [D. L. Mobley, A. E. Barber II, C. J. Fennell, and K. A. Dill, "Charge asymmetries in hydration of polar solutes," J. Phys. Chem. B 112, 2405-2414 (2008)]. Remarkably, the model also justifies the use of linear response expressions for charging free energies. Our boundary-element method implementation demonstrates the ease with which other continuum-electrostatic solvers can be extended to include asymmetry.

  14. Communication: Modeling charge-sign asymmetric solvation free energies with nonlinear boundary conditions

    International Nuclear Information System (INIS)

    Bardhan, Jaydeep P.; Knepley, Matthew G.

    2014-01-01

    We show that charge-sign-dependent asymmetric hydration can be modeled accurately using linear Poisson theory after replacing the standard electric-displacement boundary condition with a simple nonlinear boundary condition. Using a single multiplicative scaling factor to determine atomic radii from molecular dynamics Lennard-Jones parameters, the new model accurately reproduces MD free-energy calculations of hydration asymmetries for: (i) monatomic ions, (ii) titratable amino acids in both their protonated and unprotonated states, and (iii) the Mobley “bracelet” and “rod” test problems [D. L. Mobley, A. E. Barber II, C. J. Fennell, and K. A. Dill, “Charge asymmetries in hydration of polar solutes,” J. Phys. Chem. B 112, 2405–2414 (2008)]. Remarkably, the model also justifies the use of linear response expressions for charging free energies. Our boundary-element method implementation demonstrates the ease with which other continuum-electrostatic solvers can be extended to include asymmetry

  15. Communication: Modeling charge-sign asymmetric solvation free energies with nonlinear boundary conditions

    Science.gov (United States)

    Bardhan, Jaydeep P.; Knepley, Matthew G.

    2014-01-01

    We show that charge-sign-dependent asymmetric hydration can be modeled accurately using linear Poisson theory after replacing the standard electric-displacement boundary condition with a simple nonlinear boundary condition. Using a single multiplicative scaling factor to determine atomic radii from molecular dynamics Lennard-Jones parameters, the new model accurately reproduces MD free-energy calculations of hydration asymmetries for: (i) monatomic ions, (ii) titratable amino acids in both their protonated and unprotonated states, and (iii) the Mobley “bracelet” and “rod” test problems [D. L. Mobley, A. E. Barber II, C. J. Fennell, and K. A. Dill, “Charge asymmetries in hydration of polar solutes,” J. Phys. Chem. B 112, 2405–2414 (2008)]. Remarkably, the model also justifies the use of linear response expressions for charging free energies. Our boundary-element method implementation demonstrates the ease with which other continuum-electrostatic solvers can be extended to include asymmetry. PMID:25296776

  16. Communication: Modeling charge-sign asymmetric solvation free energies with nonlinear boundary conditions

    Energy Technology Data Exchange (ETDEWEB)

    Bardhan, Jaydeep P. [Department of Mechanical and Industrial Engineering, Northeastern University, Boston, Massachusetts 02115 (United States); Knepley, Matthew G. [Computation Institute, The University of Chicago, Chicago, Illinois 60637 (United States)

    2014-10-07

    We show that charge-sign-dependent asymmetric hydration can be modeled accurately using linear Poisson theory after replacing the standard electric-displacement boundary condition with a simple nonlinear boundary condition. Using a single multiplicative scaling factor to determine atomic radii from molecular dynamics Lennard-Jones parameters, the new model accurately reproduces MD free-energy calculations of hydration asymmetries for: (i) monatomic ions, (ii) titratable amino acids in both their protonated and unprotonated states, and (iii) the Mobley “bracelet” and “rod” test problems [D. L. Mobley, A. E. Barber II, C. J. Fennell, and K. A. Dill, “Charge asymmetries in hydration of polar solutes,” J. Phys. Chem. B 112, 2405–2414 (2008)]. Remarkably, the model also justifies the use of linear response expressions for charging free energies. Our boundary-element method implementation demonstrates the ease with which other continuum-electrostatic solvers can be extended to include asymmetry.

  17. Enhancement of charge carrier recombination efficiency by utilizing a hole-blocking interlayer in white OLEDs

    International Nuclear Information System (INIS)

    Wang Qi; Yu Junsheng; Zhao Juan; Li Ming; Lu Zhiyun

    2013-01-01

    Charge carrier balance and recombination are essential factors relating to the performance of white organic light-emitting devices (WOLEDs). In this study, we discussed the contribution of charge carrier balance in the interlayer-based WOLEDs. By varying the interlayer thickness, the mechanisms of electroluminescent spectral alteration, energy transfer, and especially, charge carrier transport and balance in the devices were investigated and revealed in detail. With a 5 nm thick interlayer tailoring charge carrier transport and recombination, WOLEDs yielded a high power efficiency, current efficiency and external quantum efficiency of 36.1 lm W −1 , 47.1 cd A −1 and 18.3%, respectively. Additionally, single-carrier devices and quantitative analysis were subsequently carried out, demonstrating that the enhancement of carrier recombination efficiency corresponds to the optimization of device performance. (paper)

  18. On the role of local charge carrier mobility in the charge separation mechanism of organic photovoltaics.

    Science.gov (United States)

    Yoshikawa, Saya; Saeki, Akinori; Saito, Masahiko; Osaka, Itaru; Seki, Shu

    2015-07-21

    Although the charge separation (CS) and transport processes that compete with geminate and non-geminate recombination are commonly regarded as the governing factors of organic photovoltaic (OPV) efficiency, the details of the CS mechanism remain largely unexplored. Here we provide a systematic investigation on the role of local charge carrier mobility in bulk heterojunction films of ten different low-bandgap polymers and polythiophene analogues blended with methanofullerene (PCBM). By correlating with the OPV performances, we demonstrated that the local mobility of the blend measured by time-resolved microwave conductivity is more important for the OPV output than those of the pure polymers. Furthermore, the results revealed two separate trends for crystalline and semi-crystalline polymers. This work offers guidance in the design of high-performance organic solar cells.

  19. Drift of charge carriers in crystalline organic semiconductors

    Energy Technology Data Exchange (ETDEWEB)

    Dong, Jingjuan; Si, Wei [State Key Laboratory of Surface Physics and Department of Physics, Fudan University, Shanghai 200433 (China); Wu, Chang-Qin, E-mail: cqw@fudan.edu.cn [State Key Laboratory of Surface Physics and Department of Physics, Fudan University, Shanghai 200433 (China); Collaborative Innovation Center of Advanced Microstructures, Fudan University, Shanghai 200433 (China)

    2016-04-14

    We investigate the direct-current response of crystalline organic semiconductors in the presence of finite external electric fields by the quantum-classical Ehrenfest dynamics complemented with instantaneous decoherence corrections (IDC). The IDC is carried out in the real-space representation with the energy-dependent reweighing factors to account for both intermolecular decoherence and energy relaxation by which conduction occurs. In this way, both the diffusion and drift motion of charge carriers are described in a unified framework. Based on an off-diagonal electron-phonon coupling model for pentacene, we find that the drift velocity initially increases with the electric field and then decreases at higher fields due to the Wannier-Stark localization, and a negative electric-field dependence of mobility is observed. The Einstein relation, which is a manifestation of the fluctuation-dissipation theorem, is found to be restored in electric fields up to ∼10{sup 5} V/cm for a wide temperature region studied. Furthermore, we show that the incorporated decoherence and energy relaxation could explain the large discrepancy between the mobilities calculated by the Ehrenfest dynamics and the full quantum methods, which proves the effectiveness of our approach to take back these missing processes.

  20. Magnetoresistance based determination of basic parameters of minority charge carriers in solid matter

    Directory of Open Access Journals (Sweden)

    Y.O. Uhryn

    2017-12-01

    Full Text Available Magnetoresistance as a tool of basic parameters determination of minority charge carriers and the ratio of minority charge carriers conductivity to majority ones in solid matter has been considered within the framework of the phenomenological two-band model. The criterion of the application of this model has been found. As examples of these equations usage the conductor, semiconductor and superconductor have been introduced. From the obtained temperature dependences of the aforementioned values in superconductor, a supposition of a deciding role of minority charge carriers in the emergence of superconductivity state has been made.

  1. Large-scale atomistic and quantum-mechanical simulations of a Nafion membrane: Morphology, proton solvation and charge transport

    Directory of Open Access Journals (Sweden)

    Pavel V. Komarov

    2013-09-01

    Full Text Available Atomistic and first-principles molecular dynamics simulations are employed to investigate the structure formation in a hydrated Nafion membrane and the solvation and transport of protons in the water channel of the membrane. For the water/Nafion systems containing more than 4 million atoms, it is found that the observed microphase-segregated morphology can be classified as bicontinuous: both majority (hydrophobic and minority (hydrophilic subphases are 3D continuous and organized in an irregular ordered pattern, which is largely similar to that known for a bicontinuous double-diamond structure. The characteristic size of the connected hydrophilic channels is about 25–50 Å, depending on the water content. A thermodynamic decomposition of the potential of mean force and the calculated spectral densities of the hindered translational motions of cations reveal that ion association observed with decreasing temperature is largely an entropic effect related to the loss of low-frequency modes. Based on the results from the atomistic simulation of the morphology of Nafion, we developed a realistic model of ion-conducting hydrophilic channel within the Nafion membrane and studied it with quantum molecular dynamics. The extensive 120 ps-long density functional theory (DFT-based simulations of charge migration in the 1200-atom model of the nanochannel consisting of Nafion chains and water molecules allowed us to observe the bimodality of the van Hove autocorrelation function, which provides the direct evidence of the Grotthuss bond-exchange (hopping mechanism as a significant contributor to the proton conductivity.

  2. Terahertz radiation from accelerating charge carriers in graphene under ultrafast photoexcitation

    Science.gov (United States)

    Rustagi, Avinash; Stanton, C. J.

    2016-11-01

    We study the generation of terahertz (THz) radiation from the acceleration of ultrafast photoexcited charge carriers in graphene in the presence of a dc electric field. Our model is based on calculating the transient current density from the time-dependent distribution function which is determined using the Boltzmann transport equation (BTE) within a relaxation time approximation. We include the time-dependent generation of carriers by the pump pulse by solving for the carrier generation rate using the optical Bloch equations in the rotating wave approximation (RWA). The linearly polarized pump pulse generates an anisotropic distribution of photoexcited carriers in the kx-ky plane. The collision integral in the Boltzmann equation includes a term that leads to the thermalization of carriers via carrier-carrier scattering to an effective temperature above the lattice temperature, as well as a cooling term, which leads to energy relaxation via inelastic carrier-phonon scattering. The radiated signal is proportional to the time derivative of the transient current density. In spite of the fact that the magnitude of the velocity is the same for all the carriers in graphene, there is still emitted radiation from the photoexcited charge carriers with frequency components in the THz range due to a change in the direction of velocity of the photoexcited carriers in the external electric field as well as cooling of the photoexcited carriers on a subpicosecond time scale.

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

    Energy Technology Data Exchange (ETDEWEB)

    Zhu, Xiaoyang [Columbia Univ., New York, NY (United States); Frisbie, Daniel [Univ. of Minnesota, Minneapolis, MN (United States)

    2017-03-31

    The proposed research aims to achieve quantitative, molecular level understanding of charge carriers and traps in field-doped crystalline organic semiconductors via in situ linear and nonlinear optical spectroscopy, in conjunction with transport measurements and molecular/crystal engineering.

  4. Mobility of delocalized charge carriers in an ideal homopolar glass as a function of temperature

    International Nuclear Information System (INIS)

    Iskra, V.D.

    1986-01-01

    The relationship between temperature and the mobility of delocalized charge carriers for an intrinsic random field of a homopolar glass is investigated through application of a method of scattering amplitude calculation based on employing short-lived potential factorization

  5. Importance of polaron effects for charge carrier mobility above and ...

    Indian Academy of Sciences (India)

    Orifjon Ganiev

    2017-05-30

    May 30, 2017 ... sizes and effective masses are large polarons. According ... nating metallic and insulating domains with mobile ... The mobile polaronic carriers are con- ..... [51] T Kondo, Y Hamaya, A D Palczewski, T Takeuchi, J S Wen,.

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

    International Nuclear Information System (INIS)

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

    2014-01-01

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

  7. Charge transport in disordered organic host-guest systems: effects of carrier density and electric field

    NARCIS (Netherlands)

    Yimer, Y.Y.; Bobbert, P.A.; Coehoorn, R.

    2008-01-01

    We investigate charge transport in disordered organic host–guest systems with a bimodal Gaussian density of states (DOS). The energy difference between the two Gaussians defines the trap depth. By solving the Pauli master equation for the hopping of charge carriers on a regular lattice with site

  8. Charge transport in disordered organic host-guest systems: effects of carrier density and electric field

    NARCIS (Netherlands)

    Yimer, Y.Y.; Bobbert, P.A.; Coehoorn, R.

    2009-01-01

    We investigate charge transport in disordered organic host–guest systems with a bimodal Gaussian density of states. The energy difference between the peaks of the two Gaussians defines the trap depth. By solving the Pauli master equation for the hopping of charge carriers on a regular lattice we

  9. Study of charge-carrier relaxation in a disordered organic semiconductor by simulating impedance spectroscopy

    NARCIS (Netherlands)

    Mesta, M.; Cottaar, J.; Coehoorn, R.; Bobbert, P.A.

    2014-01-01

    Impedance spectroscopy is a very sensitive probe of nonstationary charge transport governed by charge-carrier relaxation in devices of disordered organic semiconductors. We simulate impedance spectroscopy measurements of hole-only devices of a polyfluorene-based disordered organic semiconductor by

  10. The state of itinerant charge carriers and thermoelectric effects in correlated oxide metals

    International Nuclear Information System (INIS)

    Kuzemsky, A.L.; Abdus Salam International Centre for Theoretical Physics, Trieste

    2000-10-01

    We analyzed the physics of transport processes and, in particular, the thermoelectric power in the mercurocuprates and other cuprates to get a better insight into the state of the carriers in these compounds. The actual problems related to the complicated mechanisms of carriers scattering above Tc are discussed. The experimental studies of thermoelectric power showed that the state of carriers in cuprates can be influenced by many complicated scattering processes, however the underlying mechanism for the linear decreasing of the TEP with increasing the temperature for most hole-doped HTSC cuprates is still not yet known. The actual problems related to the complicated mechanisms of carriers scattering above Tc are discussed for a few models of charge transport. A comparison between the analytical and experimental results is also made. It is concluded that the crucial factor for the understanding of the transport properties of correlated oxide metals is the nature of itinerant charge carriers, i.e. renormalized quasiparticles. (author)

  11. Drift of nonequilibrium charge carriers in GaAs-crystals with traps in ultrasonic fields

    International Nuclear Information System (INIS)

    Zaveryukhina, N.N.; Zaveryukhin, B.N.; Zaveryukhina, E.B.

    2007-01-01

    Full text: The drift of nonequilibrium charge carriers in a semiconductor is one of the basic processes determining the efficiency of semiconductor photodetectors. Gallium arsenide possesses certain advantages to other semiconductors in this respect, which allow GaAs-photodetectors to be obtained which possess the maximum efficiency in comparison with all other systems. The purpose of this study was to deepen and expand our knowledge about the acoustic-drift processes in GaAs- crystals. As is known, the drift of nonequilibrium charge carriers in a semiconductor is determined either by external electric fields and/or by internal (built-in) electrostatic fields related to an impurity concentration gradient in the semiconductor. Gallium arsenide is a piezoelectric semiconductor with a structure possessing no center of symmetry. An electric field applied to such a crystal produces deformation of the crystal, and vice versa, any deformation of the crystal leads to the appearance of an induced electric field. Therefore, investigation of the effect of deformation on the drift of nonequilibrium charge carriers is a very important task. One of the possible straining factors is ultrasonic wave. Interaction of the charge carriers with ultrasonic waves in piezo-semiconductors is mediated by piezo exertion. Straining a semiconductor by an ultrasonic wave field gives rise to a force acting upon the charge carriers, which is proportional to the wave vector and the piezoelectric constant of the crystal. The physics of interaction between an ultrasonic wave and nonequilibrium charge carriers in GaAs, as well as in non-polar semiconductors (Si, Ge), consists in the energy and momentum exchange between the wave and the carriers. Besides the ultrasonic waves interact with the traps of carriers and devastate them. These both acoustic effects lead to rise of amplitude of signal of GaAs-photodetectors. (authors)

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

    Science.gov (United States)

    Chen, Xinli; Liu, Lisha; Jiang, Chen

    2016-07-01

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

  13. Poly(silylene)s: Charge carrier photogeneration and transport

    Czech Academy of Sciences Publication Activity Database

    Nešpůrek, Stanislav; Eckhardt, A.

    2001-01-01

    Roč. 12, č. 7 (2001), s. 427-440 ISSN 1042-7147 R&D Projects: GA AV ČR IAA4050603; GA AV ČR IAA1050901; GA AV ČR KSK4050111 Institutional research plan: CEZ:AV0Z4050913 Keywords : charge photogeneration * charge-transfer * ion-pair Subject RIV: CC - Organic Chemistry Impact factor: 0.701, year: 2001

  14. Supermolecular structure and charge carriers mobilities of perylene diimides

    Energy Technology Data Exchange (ETDEWEB)

    Marcon, Valentina; Pisula, Wojtek; Andrienko, Denis [Max-Planck-Institut fuer Polymerforschung, Mainz (Germany); Kirkpatrick, James [Max-Planck-Institut fuer Polymerforschung, Mainz (Germany); Department of Physics, Imperial College London, London (United Kingdom)

    2008-07-01

    Perylene diimides form columnar phases, where the molecules stack on top of each other and the columns arrange in a regular lattice. The self-organization into well-ordered columns results in the one-dimensional charge transport along the stack of the aromatic cores of the molecules. Most of the discotic molecules which organize in columns are p-type semiconductors, while the class of rylene diimide molecules, to which perylene belongs, forms n-type organic semiconductors. Using atomistic molecular dynamics (MD) simulations we study the columnar phases of perylene diimides and establish correlations between the molecular structure, packing, and dynamical properties of these materials. By using a scheme which combines electronic structure calculations, MD and kinetic Monte Carlo simulations, a correlation is then established between the molecular structure and charge mobility of perylenes columnar mesophases.

  15. Charge carrier mobility in thin films of organic semiconductors by the gated van der Pauw method

    Science.gov (United States)

    Rolin, Cedric; Kang, Enpu; Lee, Jeong-Hwan; Borghs, Gustaaf; Heremans, Paul; Genoe, Jan

    2017-01-01

    Thin film transistors based on high-mobility organic semiconductors are prone to contact problems that complicate the interpretation of their electrical characteristics and the extraction of important material parameters such as the charge carrier mobility. Here we report on the gated van der Pauw method for the simple and accurate determination of the electrical characteristics of thin semiconducting films, independently from contact effects. We test our method on thin films of seven high-mobility organic semiconductors of both polarities: device fabrication is fully compatible with common transistor process flows and device measurements deliver consistent and precise values for the charge carrier mobility and threshold voltage in the high-charge carrier density regime that is representative of transistor operation. The gated van der Pauw method is broadly applicable to thin films of semiconductors and enables a simple and clean parameter extraction independent from contact effects. PMID:28397852

  16. Magnetic susceptibility of free charge carriers in bismuth tellurides (Bi2Te3)

    International Nuclear Information System (INIS)

    Guha Thakurta, S.R.; Dutta, A.K.

    1977-01-01

    Principal magnetic susceptibilities of both p- and n-type Bi 2 Te 3 crystals have been measured over the range of temperature 90 deg K to 650 deg K. The observed susceptibilities are diamagnetic and temperature dependent. This temperature dependence has been attributed to the contribution of the free charge carriers to the susceptibilities. From the observed susceptibilities the carrier-susceptibilities have been separately obtained which are found to be paramagnetic. From the total carrier-susceptibilities, the susceptibilities of the carriers which are thermally liberated in the intrinsic region have been separated. From an analysis of the carrier-susceptibilities the band gap and its temperature coefficient have been found out and these compare favourably with those obtained from electrical measurements. (author)

  17. Semiconductor nanoparticles with spatial separation of charge carriers: synthesis and optical properties

    International Nuclear Information System (INIS)

    Vasiliev, Roman B; Dirin, Dmitry N; Gaskov, Alexander M

    2011-01-01

    The results of studies on core/shell semiconductor nanoparticles with spatial separation of photoexcited charge carriers are analyzed and generalized. Peculiarities of the electronic properties of semiconductor/semiconductor heterojunctions formed inside such particles are considered. Data on the effect of spatial separation of charge carriers on the optical properties of nanoparticles including spectral shifts of the exciton bands, absorption coefficients and electron–hole pair recombination times are presented. Methods of synthesis of core/shell semiconductor nanoparticles in solutions are discussed. Specific features of the optical properties of anisotropic semiconductor nanoparticles with the semiconductor/semiconductor junctions are noted. The bibliography includes 165 references.

  18. Hopping mobility of charge carriers in polymers in the earliest stages after their generation

    International Nuclear Information System (INIS)

    Tyutnev, A.P.; Subbotin, A.V.; Chekunaev, N.I.

    1989-01-01

    It has been found that both the photo- and the radiation conductivity of a number of polymers (primarily polyvinylcarbazole, polystyrene, and polyethylene terephthalate) are of a molecular nature, and movement of the generated charge carriers is by a hopping and not by a band mechanism. Analytical expressions for the instantaneous effective mobility and effective displacement of charge carriers in a unitary electric field were obtained in the approximation of isolated pairs of nearest neighbors for four species (monoenergetic, exponential, Gaussian, and bilevel) of energy application of hopping sites randomly distributed in space. Problems of the application of these expressions to real polymers are discussed on the example of polyvinylcarbazole

  19. Efficient photogeneration of charge carriers in silicon nanowires with a radial doping gradient

    International Nuclear Information System (INIS)

    Murthy, D H K; Houtepen, A J; Savenije, T J; Siebbeles, L D A; Xu, T; Nys, J P; Krzeminski, C; Grandidier, B; Stievenard, D; Chen, W H; Pareige, P; Jomard, F; Patriarche, G; Lebedev, O I

    2011-01-01

    by performing electrodeless time-resolved microwave conductivity measurements, the efficiency of charge carrier generation, their mobility, and the decay kinetics on photoexcitation were studied in arrays of Si nanowires grown by the vapor-liquid-solid mechanism. Large enhancements in the magnitude of the photoconductance and charge carrier lifetime are found depending on the incorporation of impurities during the growth. They are explained by the internal electric field that builds up, due to higher doped sidewalls, as revealed by detailed analysis of the nanowire morphology and chemical composition.

  20. Influence of packing motives on charge Carrier mobility in perylene tetracarboxdiimide derivatives

    Energy Technology Data Exchange (ETDEWEB)

    May, Falk; Andrienko, Denis [Max-Planck Institute for Polymer Research, Mainz (Germany); Marcon, Valentina [Center of Smart Interfaces, Darmstadt (Germany)

    2010-07-01

    Discotic mesophases are known for their ability to self-assemble into columnar structures and can serve as semiconducting molecular wires. Charge carrier mobility along these wires strongly depends on molecular packing which is controlled by intermolecular interactions. In this work we compare the influence of side chains on the packing motives of perylene tetracarboxdiimide (PDI) derivatives. Two different (alkyl and glycol) side chains are considered. We first establish how the packing of side chains affects the molecular orientation within the columns using molecular dynamics. Then, using the high temperature non-adiabatic limit of Marcus theory for hopping rates and solving the rate equation for charge transport, we analyze the link between the secondary structure and charge carrier mobility. This analysis eventually provides a pathway to rational design of columnar assemblies of PDI derivatives with high charge mobilities.

  1. Photogeneration of free charge carriers in .pi.-conjugated polymers with bulky side groups

    Czech Academy of Sciences Publication Activity Database

    Menšík, Miroslav; Jex, M.; Pfleger, Jiří; Jung, J.

    2012-01-01

    Roč. 404, 24 August (2012), s. 48-55 ISSN 0301-0104 R&D Projects: GA ČR(CZ) GAP205/10/2280; GA MŠk(CZ) OC10007 Institutional research plan: CEZ:AV0Z40500505 Institutional support: RVO:61389013 Keywords : photogeneration of free charge carriers * charge transfer states * localized excitation Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 1.957, year: 2012

  2. Modelling of the charge carrier mobility in disordered linear polymer materials

    Czech Academy of Sciences Publication Activity Database

    Toman, Petr; Menšík, Miroslav; Bartkowiak, W.; Pfleger, Jiří

    2017-01-01

    Roč. 19, č. 11 (2017), s. 7760-7771 ISSN 1463-9076 R&D Projects: GA ČR(CZ) GA15-05095S Grant - others:AV ČR(CZ) M200501204 Program:M Institutional support: RVO:61389013 Keywords : charge carrier mobility * conjugated polymer * charge transport modelling Subject RIV: BM - Solid Matter Physics ; Magnetism OBOR OECD: Condensed matter physics (including formerly solid state physics, supercond.) Impact factor: 4.123, year: 2016

  3. The Welsh Single-Use Carrier Bag Charge and behavioural spillover

    OpenAIRE

    Thomas, Gregory O.; Poortinga, Wouter; Sautkina, Elena

    2016-01-01

    A Single-Use Carrier Bag Charge (SUCBC) requires bags to be sold for a small fee, instead of free of charge. SUCBCs may produce ‘spillover’ effects, where other pro-environmental attitudes and behaviours could increase or decrease. We investigate the 2011 Welsh SUCBC, and whether spillover occurs in other behaviours and attitudes. Using the Understanding Society Survey (n = 17,636), results show that use of own shopping bags increased in Wales, compared to England and Scotland. Increased use ...

  4. Electronic properties of the charge carriers on oligofluorene backbone

    International Nuclear Information System (INIS)

    Koizumi, Yoshiko; Seki, Shu; Saeki, Akinori; Tagawa, Seiichi

    2007-01-01

    The transient absorption of radical anions and cations of 9,9'-di-n-hexyl-oligofluorene was measured using pulse radiolysis and low-temperature γ-radiolysis techniques. The infrared absorption maxima of both radical anions and cations exhibit red-shift continuously upon elongation of the chain length. The absorption bands are blue-shifted by 0.04-0.07 eV with increasing the temperature from 80 to 106 K. The extinction coefficients were determined by scavenging technique, demonstrating an increase with the elongation of the chain length. The optimized geometry of fluorene trimers, calculated using density functional theory, shows that the oligofluorene molecules are more planar in its charged state than in its neutral state

  5. Mechanism of the free charge carrier generation in the dielectric breakdown

    Science.gov (United States)

    Rahim, N. A. A.; Ranom, R.; Zainuddin, H.

    2017-12-01

    Many studies have been conducted to investigate the effect of environmental, mechanical and electrical stresses on insulator. However, studies on physical process of discharge phenomenon, leading to the breakdown of the insulator surface are lacking and difficult to comprehend. Therefore, this paper analysed charge carrier generation mechanism that can cause free charge carrier generation, leading toward surface discharge development. Besides, this paper developed a model of surface discharge based on the charge generation mechanism on the outdoor insulator. Nernst’s Planck theory was used in order to model the behaviour of the charge carriers while Poisson’s equation was used to determine the distribution of electric field on insulator surface. In the modelling of surface discharge on the outdoor insulator, electric field dependent molecular ionization was used as the charge generation mechanism. A mathematical model of the surface discharge was solved using method of line technique (MOL). The result from the mathematical model showed that the behaviour of net space charge density was correlated with the electric field distribution.

  6. Pressure dependence of excited-state charge-carrier dynamics in organolead tribromide perovskites

    Science.gov (United States)

    Liu, X. C.; Han, J. H.; Zhao, H. F.; Yan, H. C.; Shi, Y.; Jin, M. X.; Liu, C. L.; Ding, D. J.

    2018-05-01

    Excited-state charge-carrier dynamics governs the performance of organometal trihalide perovskites (OTPs) and is strongly influenced by the crystal structure. Characterizing the excited-state charge-carrier dynamics in OTPs under high pressure is imperative for providing crucial insights into structure-property relations. Here, we conduct in situ high-pressure femtosecond transient absorption spectroscopy experiments to study the excited-state carrier dynamics of CH3NH3PbBr3 (MAPbBr3) under hydrostatic pressure. The results indicate that compression is an effective approach to modulate the carrier dynamics of MAPbBr3. Across each pressure-induced phase, carrier relaxation, phonon scattering, and Auger recombination present different pressure-dependent properties under compression. Responsiveness is attributed to the pressure-induced variation in the lattice structure, which also changes the electronic band structure. Specifically, simultaneous prolongation of carrier relaxation and Auger recombination is achieved in the ambient phase, which is very valuable for excess energy harvesting. Our discussion provides clues for optimizing the photovoltaic performance of OTPs.

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

    Science.gov (United States)

    Johnston, Michael B; Herz, Laura M

    2016-01-19

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

  8. Theoretical modeling of influence of the structural disorder on the charge carrier mobility in triphenylene stacks

    Czech Academy of Sciences Publication Activity Database

    Mikolajczyk, M.; Toman, Petr; Bartkowiak, W.

    2010-01-01

    Roč. 485, 1-3 (2010), s. 253-257 ISSN 0009-2614 R&D Projects: GA MŠk MEB050815; GA AV ČR IAA401770601 Institutional research plan: CEZ:AV0Z40500505 Keywords : triphenylene * charge carrier mobility * tight-binding approximation Subject RIV: CD - Macromolecular Chemistry Impact factor: 2.282, year: 2010

  9. The generation of charge carriers in semi conductors – A theoretical study

    CSIR Research Space (South Africa)

    Kiarii, EM

    2017-04-01

    Full Text Available , vol. 678: 167-176 The generation of charge carriers in semi conductors – A theoretical study Kiarii EM Govender, Krishna K Ndungu PG Govender PG ABSTRACT: A systematic study of electronic and optical properties of titanium dioxide under...

  10. Free-carrier-compensated charged domain walls produced with super-bandgap illumination in insulating ferroelectrics

    Czech Academy of Sciences Publication Activity Database

    Bednyakov, Petr; Sluka, T.; Tagantsev, A.; Damjanovic, D.; Setter, N.

    2016-01-01

    Roč. 28, č. 43 (2016), s. 9498-9503 ISSN 0935-9648 R&D Projects: GA ČR GA15-04121S Institutional support: RVO:68378271 Keywords : super-bandgap illumination * charged domain walls * ferroelectric BaTiO 3 * free-carrier generation Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 19.791, year: 2016

  11. Ab initio theory of charge-carrier conduction in ultrapure organic crystals

    NARCIS (Netherlands)

    Hannewald, K.; Bobbert, P.A.

    2004-01-01

    We present an ab initio description of charge-carrier mobilities in organic molecular crystals of high purity. Our approach is based on Holstein's original concept of small-polaron bands but generalized with respect to the inclusion of nonlocal electron-phonon coupling. By means of an explicit

  12. Influence of injected charge carriers on photocurrents in polymer solar cells

    NARCIS (Netherlands)

    Wehenkel, D.J.; Koster, L.J.A.; Wienk, M.M.; Janssen, R.A.J.

    2012-01-01

    We determine and analyze the photocurrent Jph in polymer solar cells under conditions where, no, one, or two different charge carriers can be injected by choosing appropriate electrodes and compare the experimental results to simulations based on a drift-diffusion device model that accounts for

  13. Charge Carrier Trapping Processes in RE2O2S (RE = La, Gd, Y, and Lu)

    NARCIS (Netherlands)

    Luo, H.; Bos, A.J.J.; Dorenbos, P.

    2017-01-01

    Two different charge carrier trapping processes have been investigated in RE2O2S:Ln3+ (RE = La, Gd, Y, and Lu; Ln = Ce, Pr, and Tb) and RE2O2S:M (M = Ti4+ and Eu3+). Cerium, praseodymium and terbium act as recombination centers and hole trapping centers while host intrinsic defects provide the

  14. Determination of charge carrier mobility in doped low density polyethylene using DC transients

    DEFF Research Database (Denmark)

    Khalil, M.Salah; Henk, Peter O; Henriksen, Mogens

    1989-01-01

    Charge carrier mobility was determined for plain and doped low-density polyethylene (LDPE) using DC transient currents. Barium titanate was used as a strongly polar dopant and titanium dioxide as a semiconductor dopant. The values of the mobility obtained were on the order of 10-10 cm2 v-1 s-1...

  15. Hall mobility of free charge carriers in highly compensated p-Germanium

    International Nuclear Information System (INIS)

    Gavrilyuk, V.Yi.; Kirnas, Yi.G.; Balakyin, V.D.

    2000-01-01

    Hall mobility of free charge carriers in initial detectors Ge (Ga) is studied. It is established that an increase in the compensation factor results in the enlargement of Hall mobility in germanium highly compensated by introduction of Li ions during their drift in an electrical field

  16. Variation of minority charge carrier lifetime in high-resistance p-type silicon under irradiation

    International Nuclear Information System (INIS)

    Basheleishvili, Z.V.; Garnyk, V.S.; Gorin, S.N.; Pagava, T.A.

    1984-01-01

    The minority carrier lifetime (tau) variation was studied in the process of p-type silicon bombardment with fast 8 MeV electrons. The irradiation and all measurements were carried out at room temperature. The tau quantity was measured by the photoconductivity attenuation method at a low injection level 20% measurement error; the resistivity was measured by the four-probe method (10% error). The resistivity and minority charge carrier lifetime tau are shown to increase with the exposure dose. It is supposed that as radiation dose increases, the rearrangement of the centres responsible for reducing the lifetime occurs and results in a tau increase in the material being irradiated, however the tau value observed in the original samples is not attained. The restoration of the minority carrier lifetime in p-type high-resistance silicon with a growing exposure dose might proceed due to reduction in the free carrier concentration

  17. Large Modulation of Charge Carrier Mobility in Doped Nanoporous Organic Transistors

    Energy Technology Data Exchange (ETDEWEB)

    Zhang, Fengjiao [Department of Chemical and Biomolecular Engineering, University of Illinois Urbana-Champaign, 600 S. Mathews Ave. Urbana IL 61801 USA; Dai, Xiaojuan [Beijing National Laboratory for Molecular Sciences, Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190 P. R. China; Zhu, Weikun [Department of Chemical and Biomolecular Engineering, University of Illinois Urbana-Champaign, 600 S. Mathews Ave. Urbana IL 61801 USA; Chung, Hyunjoong [Department of Chemical and Biomolecular Engineering, University of Illinois Urbana-Champaign, 600 S. Mathews Ave. Urbana IL 61801 USA; Diao, Ying [Department of Chemical and Biomolecular Engineering, University of Illinois Urbana-Champaign, 600 S. Mathews Ave. Urbana IL 61801 USA

    2017-05-10

    Molecular doping of organic electronics has shown promise to sensitively modulate important device metrics. One critical challenge is the disruption of structure order upon doping of highly crystalline organic semiconductors, which significantly reduces the charge carrier mobility. This paper demonstrates a new method to achieve large modulation of charge carrier mobility via channel doping without disrupting the molecular ordering. Central to the method is the introduction of nanopores into the organic semiconductor thin films via a simple and robust templated meniscus-guided coating method. Using this method, the charge carrier mobility of C8-benzothieno[3,2-b]benzothiophene transistors is boosted by almost sevenfold. This paper further demonstrates enhanced electron transport by close to an order of magnitude in a diketopyrrolopyrrole-based donor–acceptor polymer. Combining spectroscopic measurements, density functional theory calculations, and electrical characterizations, the doping mechanism is identified as partial-charge-transfer induced trap filling. The nanopores serve to enhance the dopant/organic semiconductor charge transfer reaction by exposing the π-electrons to the pore wall.

  18. Studies of the mobility of charge carriers in low-dimensional systems in a transverse DC electric field

    Energy Technology Data Exchange (ETDEWEB)

    Sinyavskii, E. P., E-mail: sinyavskii@gmail.com [Academy of Sciences of Moldova, Institute of Applied Physics (Moldova, Republic of); Karapetyan, S. A., E-mail: karapetyan.sa@gmail.com [Shevchenko Pridnestrovskii State University (Moldova, Republic of)

    2011-08-15

    The mobility of charge carriers {mu} in a parabolic quantum well in an electric field E directed along the size-confinement axis is calculated. With consideration for scattering of charge carriers at a rough surface, the mobility {mu} is shown to decrease with increasing E. A physical interpretation of this effect is proposed.

  19. Solvation thermodynamics

    CERN Document Server

    Ben-Naim, Arieh

    1987-01-01

    This book deals with a subject that has been studied since the beginning of physical chemistry. Despite the thousands of articles and scores of books devoted to solvation thermodynamics, I feel that some fundamen­ tal and well-established concepts underlying the traditional approach to this subject are not satisfactory and need revision. The main reason for this need is that solvation thermodynamics has traditionally been treated in the context of classical (macroscopic) ther­ modynamics alone. However, solvation is inherently a molecular pro­ cess, dependent upon local rather than macroscopic properties of the system. Therefore, the starting point should be based on statistical mechanical methods. For many years it has been believed that certain thermodynamic quantities, such as the standard free energy (or enthalpy or entropy) of solution, may be used as measures of the corresponding functions of solvation of a given solute in a given solvent. I first challenged this notion in a paper published in 1978 b...

  20. Thermal generation and mobility of charge carriers in collective proton transport in hydrogen-bonded chains

    International Nuclear Information System (INIS)

    Peyrard, M.; Boesch, R.; Kourakis, I.

    1991-01-01

    The transport of protons in hydrogen-bonded systems is a long standing problem which has not yet obtained a satisfactorily theoretical description. Although this problem was examined first for ice, it is relevant in many systems and in particular in biology for the transport along proteins or for proton conductance across membranes, an essential process in cell life. The broad relevance makes the study of proton conduction very appealing. Since the original work of Bernal and Fowler on ice, the idea that the transport occurs through chains of hydrogen bonds has been well accepted. Such ''proton wires'' were invoked by Nagle and Morowitz for proton transport across membranes proteins and more recently across lipid bilayers. In this report, we assume the existence of such an hydrogen-bonded chain and discuss its consequences on the dynamics of the charge carriers. We show that this assumption leads naturally to the idea of soliton transport and we put a special emphasis on the role of the coupling between the protons and heavy ions motions. The model is presented. We show how the coupling affects strongly the dynamics of the charge carriers and we discuss the role it plays in the thermal generation of carriers. The work presented has been performed in 1986 and 87 with St. Pnevmatikos and N. Flyzanis and was then completed in collaboration with D. Hochstrasser and H. Buettner. Therefore the results presented in this part are not new but we think that they are appropriate in the context of this multidisciplinary workshop because they provide a rather complete example of the soliton picture for proton conduction. This paper discusses the thermal generation of the charge carriers when the coupling between the protons and heavy ions dynamics is taken into account. The results presented in this part are very recent and will deserve further analysis but they already show that the coupling can assist for the formation of the charge carriers

  1. Quantitative description of charge-carrier transport in a white organic light-emitting diode

    Science.gov (United States)

    Schober, M.; Anderson, M.; Thomschke, M.; Widmer, J.; Furno, M.; Scholz, R.; Lüssem, B.; Leo, K.

    2011-10-01

    We present a simulation model for the analysis of charge-carrier transport in organic thin-film devices, and apply it to a three-color white hybrid organic light-emitting diode (OLED) with fluorescent blue and phosphorescent red and green emission. We simulate a series of single-carrier devices, which reconstruct the OLED layer sequence step by step. Thereby, we determine the energy profiles for hole and electron transport, show how to discern bulk from interface limitation, and identify trap states.

  2. Measuring the lateral charge-carrier mobility in metal-insulator-semiconductor capacitors via Kelvin-probe.

    Science.gov (United States)

    Milotti, Valeria; Pietsch, Manuel; Strunk, Karl-Philipp; Melzer, Christian

    2018-01-01

    We report a Kelvin-probe method to investigate the lateral charge-transport properties of semiconductors, most notably the charge-carrier mobility. The method is based on successive charging and discharging of a pre-biased metal-insulator-semiconductor stack by an alternating voltage applied to one edge of a laterally confined semiconductor layer. The charge carriers spreading along the insulator-semiconductor interface are directly measured by a Kelvin-probe, following the time evolution of the surface potential. A model is presented, describing the device response for arbitrary applied biases allowing the extraction of the lateral charge-carrier mobility from experimentally measured surface potentials. The method is tested using the organic semiconductor poly(3-hexylthiophene), and the extracted mobilities are validated through current voltage measurements on respective field-effect transistors. Our widely applicable approach enables robust measurements of the lateral charge-carrier mobility in semiconductors with weak impact from the utilized contact materials.

  3. Measuring the lateral charge-carrier mobility in metal-insulator-semiconductor capacitors via Kelvin-probe

    Science.gov (United States)

    Milotti, Valeria; Pietsch, Manuel; Strunk, Karl-Philipp; Melzer, Christian

    2018-01-01

    We report a Kelvin-probe method to investigate the lateral charge-transport properties of semiconductors, most notably the charge-carrier mobility. The method is based on successive charging and discharging of a pre-biased metal-insulator-semiconductor stack by an alternating voltage applied to one edge of a laterally confined semiconductor layer. The charge carriers spreading along the insulator-semiconductor interface are directly measured by a Kelvin-probe, following the time evolution of the surface potential. A model is presented, describing the device response for arbitrary applied biases allowing the extraction of the lateral charge-carrier mobility from experimentally measured surface potentials. The method is tested using the organic semiconductor poly(3-hexylthiophene), and the extracted mobilities are validated through current voltage measurements on respective field-effect transistors. Our widely applicable approach enables robust measurements of the lateral charge-carrier mobility in semiconductors with weak impact from the utilized contact materials.

  4. Effects of compatibility of polymer binders with solvate ionic liquid electrolytes on discharge and charge reactions of lithium-sulfur batteries

    Science.gov (United States)

    Nakazawa, Toshitada; Ikoma, Ai; Kido, Ryosuke; Ueno, Kazuhide; Dokko, Kaoru; Watanabe, Masayoshi

    2016-03-01

    Electrochemical reactions in Li-S cells with a solvate ionic liquid (SIL) electrolyte composed of tetraglyme (G4) and Li[TFSA] (TFSA: bis(trifluoromethanesulfonyl)amide) are studied. The sulfur cathode (S cathode) comprises sulfur, carbon powder, and a polymer binder. Poly(ethylene oxide) (PEO) and poly(vinyl alcohol) (PVA-x) with different degrees of saponification (x%) are used as binders to prepare the composite cathodes. For the Li-S cell containing PEO binder, lithium polysulfides (Li2Sm, 2 ≤ m ≤ 8), reaction intermediates of the S cathode, dissolve into the electrolyte, and Li2Sm acts as a redox shuttle in the Li-S cell. In contrast, in the Li-S cell with PVA-x binder, the dissolution of Li2Sm is suppressed, leading to high columbic efficiencies during charge-discharge cycles. The compatibility of the PVA-x binder with the SIL electrolyte changes depending on the degree of saponification. Decreasing the degree of saponification leads to increased electrolyte uptake by the PVA-x binder, increasing the charge and discharge capacities of Li-S cell. The rate capability of Li-S cell is also enhanced by the partial swelling of the PVA-x binder. The enhanced performance of Li-S cell containing PVA-x is attributed to the lowering of resistance of Li+ ion transport in the composite cathode.

  5. The thermoballistic transport model a novel approach to charge carrier transport in semiconductors

    CERN Document Server

    Lipperheide, Reinhard

    2014-01-01

    The book presents a comprehensive survey of the thermoballistic approach to charge carrier transport in semiconductors. This semi-classical approach, which the authors have developed over the past decade, bridges the gap between the opposing drift-diffusion and ballistic  models of carrier transport. While incorporating basic features of the latter two models, the physical concept underlying the thermoballistic approach constitutes a novel, unifying scheme. It is based on the introduction of "ballistic configurations" arising from a random partitioning of the length of a semiconducting sample into ballistic transport intervals. Stochastic averaging of the ballistic carrier currents over the ballistic configurations results in a position-dependent thermoballistic current, which is the key element of the thermoballistic concept and forms  the point of departure for the calculation of all relevant transport properties. In the book, the thermoballistic concept and its implementation are developed in great detai...

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

    Science.gov (United States)

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

    2015-06-01

    This article reviews the charge transport and photogeneration in bulk-heterojunction solar cells made from blend films of regioregular poly(3-hexylthiophene) (RR-P3HT) and methano-fullerene (PCBM). The charge transport, specifically the hole mobility in the RR-P3HT phase of the polymer:fullerene photovoltaic blend, is dramatically affected by thermal annealing. The hole mobility increases more than three orders of magnitude and reaches a value of up to 2 × 10(-4) cm(2) V(-1) s(-1) after the thermal annealing process as a result of an improved semi-crystallinity of the film. This significant increase of the hole mobility balances the electron and hole mobilities in a photovoltaic blend in turn reducing space-charge formation, and this is the most important factor for the strong enhancement of the photovoltaic efficiency compared to an as cast, that is, non-annealed device. In fact, the balanced charge carrier mobility in RR-P3HT:PCBM blends in combination with a field- and temperature-independent charge carrier generation and greatly reduced non-geminate recombination explains the large quantum efficiencies mea-sured in P3HT:PCBM photovoltaic devices. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  7. Charge Carrier Transport and Photogeneration in P3HT:PCBM Photovoltaic Blends

    KAUST Repository

    Laquai, Frederic

    2015-05-03

    This article reviews the charge transport and photogeneration in bulk-heterojunction solar cells made from blend films of regioregular poly(3-hexylthiophene) (RR-P3HT) and methano­fullerene (PCBM). The charge transport, specifically the hole mobility in the RR-P3HT phase of the polymer:fullerene photovoltaic blend, is dramatically affected by thermal annealing. The hole mobility increases more than three orders of magnitude and reaches a value of up to 2 × 10−4 cm2 V−1 s−1 after the thermal annealing process as a result of an improved semi-crystallinity of the film. This significant increase of the hole mobility balances the electron and hole mobilities in a photovoltaic blend in turn reducing space-charge formation, and this is the most important factor for the strong enhancement of the photovoltaic efficiency compared to an as cast, that is, non-annealed device. In fact, the balanced charge carrier mobility in RR-P3HT:PCBM blends in combination with a field- and temperature-independent charge carrier generation and greatly reduced non-geminate recombination explains the large quantum efficiencies mea­sured in P3HT:PCBM photovoltaic devices.

  8. Charge trapping and carrier transport mechanism in silicon-rich silicon oxynitride

    International Nuclear Information System (INIS)

    Yu Zhenrui; Aceves, Mariano; Carrillo, Jesus; Lopez-Estopier, Rosa

    2006-01-01

    The charge-trapping and carrier transport properties of silicon-rich silicon oxynitride (SRO:N) were studied. The SRO:N films were deposited by low pressure chemical vapor deposition. Infrared (IR) and transmission electron microscopic (TEM) measurements were performed to characterize their structural properties. Capacitance versus voltage and current versus voltage measurements (I-V) were used to study the charge-trapping and carrier transport mechanism. IR and TEM measurements revealed the existence of Si nanodots in SRO:N films. I-V measurements revealed that there are two conduction regimes divided by a threshold voltage V T . When the applied voltage is smaller than V T , the current is dominated by the charge transfer between the SRO:N and substrate; and in this regime only dynamic charging/discharging of the SRO:N layer is observed. When the voltage is larger than V T , the current increases rapidly and is dominated by the Poole-Frenkel mechanism; and in this regime, large permanent trapped charge density is obtained. Nitrogen incorporation significantly reduced the silicon nanodots or defects near the SRO:N/Si interface. However, a significant increase of the density of silicon nanodot in the bulk of the SRO:N layer is obtained

  9. Towards high charge carrier mobilities by rational design of organic semiconductors

    Energy Technology Data Exchange (ETDEWEB)

    Andrienko, Denis; Ruehle, Victor; Baumeier, Bjoern; Vehoff, Thorsten; Lukyanov, Alexander; Kremer, Kurt [Max Planck Institute for Polymer Research, Mainz (Germany); Marcon, Valentina [Technische Universitaet Darmstadt (Germany); Kirkpatrick, James; Nelson, Jenny [Imperial College London (United Kingdom); Lennartz, Christian [BASF AG, Ludwigshafen (Germany)

    2010-07-01

    The role of material morphology on charge carrier mobility in partially disordered organic semiconductors is discussed for several classes of materials: derivatives of hexabenzocoronenens, perylenediimides, triangularly-shaped polyaromatic hydrocarbons, and Alq{sub 3}. Simulations are performed using a package developed by Imperial College, London and Max Planck Institute for Polymer Research, Mainz (votca.org). This package combines several techniques into one scheme: quantum chemical methods for the calculation of molecular electronic structures and reorganization energies; molecular dynamics and systematic coarse-graining approaches for simulation of self-assembly and relative positions and orientations of molecules on large scales; kinetic Monte Carlo and master equation for studies of charge transport.

  10. Recombination of charge carriers on radiation-induced defects in silicon doped by transition metals impurities

    CERN Document Server

    Kazakevich, L A

    2003-01-01

    It has been studied the peculiarities of recombination of nonequilibrium charge carriers on radiation-induced defects in received according to Czochralski method p-silicon (p approx 3 - 20 Ohm centre dot cm), doped by one of the impurities of transition metals of the IV-th group of periodic table (titanium, zirconium, hafnium). Experimental results are obtained out of the analysis of temperature and injection dependence of the life time of charge carriers. The results are explained taking into consideration the influences of elastic stress fields created by the aggregates of transition metals atoms on space distribution over the crystal of oxygen and carbon background impurities as well as on the migration of movable radiation-induced defects during irradiation. (authors).

  11. Transient Zitterbewegung of charge carriers in mono- and bilayer graphene, and carbon nanotubes

    International Nuclear Information System (INIS)

    Rusin, Tomasz M.; Zawadzki, Wlodek

    2007-01-01

    Observable effects due to trembling motion [Zitterbewegung (ZB)] of charge carriers in bilayer graphene, monolayer graphene, and carbon nanotubes are calculated. It is shown that, when the charge carriers are prepared in the form of Gaussian wave packets, the ZB has a transient character with the decay time of femtoseconds in graphene and picoseconds in nanotubes. Analytical results for bilayer graphene allow us to investigate phenomena which accompany the trembling motion. In particular, it is shown that the transient character of ZB in graphene is due to the fact that wave subpackets related to positive and negative electron energies move in opposite directions, so their overlap diminishes with time. This behavior is analogous to that of the wave packets representing relativistic electrons in a vacuum

  12. Time-dependent mobility and recombination of the photoinduced charge carriers in conjugated polymer/fullerene bulk heterojunction solar cells

    Science.gov (United States)

    Mozer, A. J.; Dennler, G.; Sariciftci, N. S.; Westerling, M.; Pivrikas, A.; Österbacka, R.; Juška, G.

    2005-07-01

    Time-dependent mobility and recombination in the blend of poly[2-methoxy-5-(3,7-dimethyloctyloxy)-phenylene vinylene] (MDMO-PPV) and 1-(3-methoxycarbonyl)propyl-1-phenyl-(6,6)- C61 (PCBM) is studied simultaneously using the photoinduced charge carrier extraction by linearly increasing voltage technique. The charge carriers are photogenerated by a strongly absorbed, 3 ns laser flash, and extracted by the application of a reverse bias voltage pulse after an adjustable delay time (tdel) . It is found that the mobility of the extracted charge carriers decreases with increasing delay time, especially shortly after photoexcitation. The time-dependent mobility μ(t) is attributed to the energy relaxation of the charge carriers towards the tail states of the density of states distribution. A model based on a dispersive bimolecular recombination is formulated, which properly describes the concentration decay of the extracted charge carriers at all measured temperatures and concentrations. The calculated bimolecular recombination coefficient β(t) is also found to be time-dependent exhibiting a power law dependence as β(t)=β0t-(1-γ) with increasing slope (1-γ) with decreasing temperatures. The temperature dependence study reveals that both the mobility and recombination of the photogenerated charge carriers are thermally activated processes with activation energy in the range of 0.1 eV. Finally, the direct comparison of μ(t) and β(t) shows that the recombination of the long-lived charge carriers is controlled by diffusion.

  13. Grain Boundaries Act as Solid Walls for Charge Carrier Diffusion in Large Crystal MAPI Thin Films.

    Science.gov (United States)

    Ciesielski, Richard; Schäfer, Frank; Hartmann, Nicolai F; Giesbrecht, Nadja; Bein, Thomas; Docampo, Pablo; Hartschuh, Achim

    2018-03-07

    Micro- and nanocrystalline methylammonium lead iodide (MAPI)-based thin-film solar cells today reach power conversion efficiencies of over 20%. We investigate the impact of grain boundaries on charge carrier transport in large crystal MAPI thin films using time-resolved photoluminescence (PL) microscopy and numerical model calculations. Crystal sizes in the range of several tens of micrometers allow for the spatially and time resolved study of boundary effects. Whereas long-ranged diffusive charge carrier transport is observed within single crystals, no detectable diffusive transport occurs across grain boundaries. The observed PL transients are found to crucially depend on the microscopic geometry of the crystal and the point of observation. In particular, spatially restricted diffusion of charge carriers leads to slower PL decay near crystal edges as compared to the crystal center. In contrast to many reports in the literature, our experimental results show no quenching or additional loss channels due to grain boundaries for the studied material, which thus do not negatively affect the performance of the derived thin-film devices.

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

    Science.gov (United States)

    Ponseca, C. S., Jr.; Sundström, V.

    2016-03-01

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

  15. Excited state and charge-carrier dynamics in perovskite solar cell materials

    Science.gov (United States)

    Ponseca, Carlito S., Jr.; Tian, Yuxi; Sundström, Villy; Scheblykin, Ivan G.

    2016-02-01

    Organo-metal halide perovskites (OMHPs) have attracted enormous interest in recent years as materials for application in optoelectronics and solar energy conversion. These hybrid semiconductors seem to have the potential to challenge traditional silicon technology. In this review we will give an account of the recent development in the understanding of the fundamental light-induced processes in OMHPs from charge-photo generation, migration of charge carries through the materials and finally their recombination. Our and other literature reports on time-resolved conductivity, transient absorption and photoluminescence properties are used to paint a picture of how we currently see the fundamental excited state and charge-carrier dynamics. We will also show that there is still no fully coherent picture of the processes in OMHPs and we will indicate the problems to be solved by future research.

  16. Excited state and charge-carrier dynamics in perovskite solar cell materials

    International Nuclear Information System (INIS)

    Ponseca, Carlito S Jr; Tian, Yuxi; Sundström, Villy; Scheblykin, Ivan G

    2016-01-01

    Organo-metal halide perovskites (OMHPs) have attracted enormous interest in recent years as materials for application in optoelectronics and solar energy conversion. These hybrid semiconductors seem to have the potential to challenge traditional silicon technology. In this review we will give an account of the recent development in the understanding of the fundamental light-induced processes in OMHPs from charge-photo generation, migration of charge carries through the materials and finally their recombination. Our and other literature reports on time-resolved conductivity, transient absorption and photoluminescence properties are used to paint a picture of how we currently see the fundamental excited state and charge-carrier dynamics. We will also show that there is still no fully coherent picture of the processes in OMHPs and we will indicate the problems to be solved by future research. (topical review)

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

    Science.gov (United States)

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

    2016-07-20

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

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

    Energy Technology Data Exchange (ETDEWEB)

    Patidar, Manju Mishra, E-mail: manjumishra.iuc@gmail.com; Gorli, V. R.; Gangrade, Mohan; Nath, R.; Ganesan, V. [UGC-DAE CSR, University Campus, Khandwa Road, Indore (M.P.)-452001 (India); Panda, Richa [S.S. Jain Subodh Girls College, Airport Road Sanganer, Jaipur - 302029 (India)

    2016-05-23

    Kinetics of the photo-activated charge carriers has been investigated in Tin substituted Cadmium Sulphide, Cd{sub 1-x}Sn{sub x}S (x=0, 0.05, 0.10 and 0.15), thin films prepared by spray pyrolysis. X-Ray Diffraction shows an increase in strain that resulted in the decreased crystallite size upon Sn substitution. At the first sight, the photo current characteristics show a quenching effect on Sn substitution. However, survival of persistent photocurrents is seen even up to 15% of Sn substitution. Transient photo current decay could be explained with a 2τ relaxation model. CdS normally has an n-type character and the Sn doping expected to inject hole carriers. The two fold increase in τ{sub 1}, increase in activation energy and the decrease in photocurrents upon Sn substitution point towards a band gap cleaning scenario that include compensation and associated carrier injection dynamics. In addition Atomic Force Microscopy shows a drastic change in microstructure that modulates the carrier dynamics as a whole.

  19. Phase separation in strongly correlated electron systems with two types of charge carriers

    International Nuclear Information System (INIS)

    Kugel, K.I.; Rakhmanov, A.L.; Sboychakov, A.O.

    2007-01-01

    Full text: A competition between the localization of the charge carriers due to Jahn-Teller distortions and the energy gain due to their delocalization in doped manganite and related magnetic oxides is analyzed based on a Kondo-lattice type model. The resulting effective Hamiltonian is, in fact, a generalization of the Falicov-Kimball model. We find that the number of itinerant charge carriers can be significantly lower than that implied by the doping level x. The phase diagram of the model in the T plane is constructed. The system exhibits magnetic ordered (antiferromagnetic, ferromagnetic, or canted) states as well the paramagnetic states with zero and nonzero density of the itinerant electrons. It is shown that a phase-separation is favorable in energy for a wide doping range. The characteristic size of inhomogeneities in a phase-separated state is of the order of several lattice constants. We also analyzed the two-band Hubbard model in the limit of strong on-site Coulomb repulsion. It was shown that such a system has a tendency to phase separation into the regions with different charge densities even in the absence of magnetic or any other ordering, if the ratio of the bandwidths is large enough. The work was supported by the European project CoMePhS and by the Russian Foundation for Basic Research, project no. 05-02-17600. (authors)

  20. Electrical control of charged carriers and excitons in atomically thin materials

    Science.gov (United States)

    Wang, Ke; De Greve, Kristiaan; Jauregui, Luis A.; Sushko, Andrey; High, Alexander; Zhou, You; Scuri, Giovanni; Taniguchi, Takashi; Watanabe, Kenji; Lukin, Mikhail D.; Park, Hongkun; Kim, Philip

    2018-02-01

    Electrical confinement and manipulation of charge carriers in semiconducting nanostructures are essential for realizing functional quantum electronic devices1-3. The unique band structure4-7 of atomically thin transition metal dichalcogenides (TMDs) offers a new route towards realizing novel 2D quantum electronic devices, such as valleytronic devices and valley-spin qubits8. 2D TMDs also provide a platform for novel quantum optoelectronic devices9-11 due to their large exciton binding energy12,13. However, controlled confinement and manipulation of electronic and excitonic excitations in TMD nanostructures have been technically challenging due to the prevailing disorder in the material, preventing accurate experimental control of local confinement and tunnel couplings14-16. Here we demonstrate a novel method for creating high-quality heterostructures composed of atomically thin materials that allows for efficient electrical control of excitations. Specifically, we demonstrate quantum transport in the gate-defined, quantum-confined region, observing spin-valley locked quantized conductance in quantum point contacts. We also realize gate-controlled Coulomb blockade associated with confinement of electrons and demonstrate electrical control over charged excitons with tunable local confinement potentials and tunnel couplings. Our work provides a basis for novel quantum opto-electronic devices based on manipulation of charged carriers and excitons.

  1. Charge Carrier Transport Mechanism Based on Stable Low Voltage Organic Bistable Memory Device.

    Science.gov (United States)

    Ramana, V V; Moodley, M K; Kumar, A B V Kiran; Kannan, V

    2015-05-01

    A solution processed two terminal organic bistable memory device was fabricated utilizing films of polymethyl methacrylate PMMA/ZnO/PMMA on top of ITO coated glass. Electrical characterization of the device structure showed that the two terminal device exhibited favorable switching characteristics with an ON/OFF ratio greater than 1 x 10(4) when the voltage was swept between - 2 V and +3 V. The device maintained its state after removal of the bias voltage. The device did not show degradation after a 1-h retention test at 120 degrees C. The memory functionality was consistent even after fifty cycles of operation. The charge transport switching mechanism is discussed on the basis of carrier transport mechanism and our analysis of the data shows that the charge carrier trans- port mechanism of the device during the writing process can be explained by thermionic emission (TE) and space-charge-limited-current (SCLC) mechanism models while erasing process could be explained by the FN tunneling mechanism. This demonstration provides a class of memory devices with the potential for low-cost, low-power consumption applications, such as a digital memory cell.

  2. Observation of disorder effects on charged carrier mobility in triphenylene-based discotic materials

    International Nuclear Information System (INIS)

    Zhang Chunxiu; He, Zhiqun; Mao Huaxiang; Wang Junjie; Wang Dongdong; Wang Yongsheng; Li Zhongxiao; Pu Jialing

    2007-01-01

    A discotic 2,6,10-trihydroxy-3,7,11-tripentyloxytriphenylene material and a triphenylene-based hyperbranched macromolecule were synthesized, in which the latter was prepared from AB m molecules in a one-pot reaction. Adipic chloride and butyryl chloride were chosen as terminal groups to the 2,6,10-trihydroxy-3,7,11-tripentyloxytriphenylene. Mesophase and their structural orders were determined using a polarized optical microscope and a differential scanning calorimeter. Carrier mobilities of the pure and composite materials were measured via a time-of-flight method. A change in carrier mobility on the morphology of the materials was further discussed. It was found that degree of crystallization was the key for a discotic triphenylene material to possess charge-transporting properties, no matter it is ordered or disordered

  3. Positively Charged Nanostructured Lipid Carriers and Their Effect on the Dissolution of Poorly Soluble Drugs

    Directory of Open Access Journals (Sweden)

    Kyeong-Ok Choi

    2016-05-01

    Full Text Available The objective of this study is to develop suitable formulations to improve the dissolution rate of poorly water soluble drugs. We selected lipid-based formulation as a drug carrier and modified the surface using positively charged chitosan derivative (HTCC to increase its water solubility and bioavailability. Chitosan and HTCC-coated lipid particles had higher zeta-potential values than uncoated one over the whole pH ranges and improved encapsulation efficiency. In vitro drug release showed that all NLC formulations showed higher in vitro release efficiency than drug particle at pH 7.4. Furthermore, NLC formulation prepared with chitosan or HTCC represented good sustained release property. The results indicate that chitosan and HTCC can be excellent formulating excipients of lipid-based delivery carrier for improving poorly water soluble drug delivery.

  4. Positively Charged Nanostructured Lipid Carriers and Their Effect on the Dissolution of Poorly Soluble Drugs.

    Science.gov (United States)

    Choi, Kyeong-Ok; Choe, Jaehyeog; Suh, Seokjin; Ko, Sanghoon

    2016-05-20

    The objective of this study is to develop suitable formulations to improve the dissolution rate of poorly water soluble drugs. We selected lipid-based formulation as a drug carrier and modified the surface using positively charged chitosan derivative (HTCC) to increase its water solubility and bioavailability. Chitosan and HTCC-coated lipid particles had higher zeta-potential values than uncoated one over the whole pH ranges and improved encapsulation efficiency. In vitro drug release showed that all NLC formulations showed higher in vitro release efficiency than drug particle at pH 7.4. Furthermore, NLC formulation prepared with chitosan or HTCC represented good sustained release property. The results indicate that chitosan and HTCC can be excellent formulating excipients of lipid-based delivery carrier for improving poorly water soluble drug delivery.

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

    Science.gov (United States)

    Roller, John; Hamadani, Behrang; Dagenais, Mario

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

  6. Impact of Tortuosity on Charge-Carrier Transport in Organic Bulk Heterojunction Blends

    Science.gov (United States)

    Heiber, Michael C.; Kister, Klaus; Baumann, Andreas; Dyakonov, Vladimir; Deibel, Carsten; Nguyen, Thuc-Quyen

    2017-11-01

    The impact of the tortuosity of the charge-transport pathways through a bulk heterojunction film on the charge-carrier mobility is theoretically investigated using model morphologies and kinetic Monte Carlo simulations. The tortuosity descriptor provides a quantitative metric to characterize the quality of the charge-transport pathways, and model morphologies with controlled domain size and tortuosity are created using an anisotropic domain growth procedure. The tortuosity is found to be dependent on the anisotropy of the domain structure and is highly tunable. Time-of-flight charge-transport simulations on morphologies with a range of tortuosity values reveal that tortuosity can significantly reduce the magnitude of the mobility and the electric-field dependence relative to a neat material. These reductions are found to be further controlled by the energetic disorder and temperature. Most significantly, the sensitivity of the electric-field dependence to the tortuosity can explain the different experimental relationships previously reported, and exploiting this sensitivity could lead to simpler methods for characterizing and optimizing charge transport in organic solar cells.

  7. Theories of the solvated electron

    International Nuclear Information System (INIS)

    Kestner, N.R.

    1987-01-01

    In this chapter the authors address only the final state of the electron, that is, the solvated state, which, if no chemical reaction would occur, is a stable entity with well-defined characteristics. Except for some metal-ammonia solutions, and possible a few other cases, such stable species, in reality, exist but a short time (often as short as microseconds). Nevertheless, this chapter only deals with this final time-independent,'' completely solvated,'' equilibrium species. The last statement is added to indicate that the solvent around the electron has also come to thermal equilibrium with the field of the charge

  8. Behaviour of Charge Carriers in As-Deposited and Annealed Undoped TCO Films

    International Nuclear Information System (INIS)

    Zhou Yan-Wen; Wu Fa-Yu; Zheng Chun-Yan

    2011-01-01

    We examine the structures, cut-off points of transmittance spectra and electric properties of undoped ZnO, SnO 2 and CdO films by scanning electron microscopy, x-ray diffraction, spectrophotometer and Hall-effect measurements, respectively. The films are deposited by using an rf magnetron sputtering system from powder targets in argon and then annealed in vacuum. The structures and properties of the as-deposited films are compared with those of the annealed one. We try to explain the behaviour of charge carriers based on the semiconductor physics theory. (condensed matter: electronic structure, electrical, magnetic, and optical properties)

  9. Modelling of charge carrier transport in conjugated polymers doped by polar additives

    Czech Academy of Sciences Publication Activity Database

    Toman, Petr; Nešpůrek, Stanislav; Bartkowiak, W.

    2009-01-01

    Roč. 27, č. 3 (2009), s. 797-812 ISSN 0137-1339. [International Conference on Electrical and Related Properties of Organic Solids /11./. Piechowice, 13.07.2008-17.07.2008] R&D Projects: GA ČR GA203/06/0285; GA AV ČR KAN400720701; GA MŠk MEB050815 Institutional research plan: CEZ:AV0Z40500505 Keywords : conjugated polymers * charge carrier transport * molecular electronics Subject RIV: CD - Macromolecular Chemistry Impact factor: 0.384, year: 2009

  10. Top-gate dielectric induced doping and scattering of charge carriers in epitaxial graphene

    Science.gov (United States)

    Puls, Conor P.; Staley, Neal E.; Moon, Jeong-Sun; Robinson, Joshua A.; Campbell, Paul M.; Tedesco, Joseph L.; Myers-Ward, Rachael L.; Eddy, Charles R.; Gaskill, D. Kurt; Liu, Ying

    2011-07-01

    We show that an e-gun deposited dielectric impose severe limits on epitaxial graphene-based device performance based on Raman spectroscopy and low-temperature transport measurements. Specifically, we show from studies of epitaxial graphene Hall bars covered by SiO2 that the measured carrier density is strongly inhomogenous and predominantly induced by charged impurities at the grapheme/dielectric interface that limit mobility via Coulomb interactions. Our work emphasizes that material integration of epitaxial graphene and a gate dielectric is the next major road block towards the realization of graphene-based electronics.

  11. Ballistic charge carrier transmission through graphene multi-barrier structures in uniform magnetic field

    International Nuclear Information System (INIS)

    Zubarev, A; Dragoman, D

    2014-01-01

    We investigate charge carrier transport in graphene multi-barrier structures placed in a uniform magnetic field. The transmission coefficient is found analytically by generalizing the transfer matrix method for the case of graphene regions subjected to a uniform magnetic field. The transmission coefficient through the structure can be modulated by varying the gate voltages, the magnetic field and/or the width of the gated regions. Such a configuration could be used in multiple-valued logic circuits, since it has several output states with discrete and easily selectable transmission/current values. (paper)

  12. Recombination of charge carriers in the GaAs-based p-i-n diode

    International Nuclear Information System (INIS)

    Ayzenshtat, G. I.; Yushenko, A. Y.; Gushchin, S. M.; Dmitriev, D. V.; Zhuravlev, K. S.; Toropov, A. I.

    2010-01-01

    It is established that the radiative recombination of charge carriers plays a substantial role in the GaAs-based p-i-n diodes at high densities of the forward current. It is shown experimentally that the diodes operating in microwave integrated circuits intensely emit light in the IR range with wavelengths from 890 to 910 nm. The obtained results indicate the necessity of taking into account the features of recombination processes in the GaAs-based microwave p-i-n diodes.

  13. Designing thiophene-based azomethine oligomers with tailored properties: Self-assembly and charge carrier mobility

    DEFF Research Database (Denmark)

    Kiriy, N.; Bocharova, V.; Kiriy, A.

    2004-01-01

    This paper describes synthesis and characterization of two thiophene-based azomethines designed to optimize solubility, self-assembly, and charge carrier mobility. We found that incorporation of azomethine and amide moieties in the alpha,omega-position, and hexyl chains in the beta-position of th...... with the mobilities of the best organic semiconductors. All these significant differences in properties of related compounds can be attributed to the hydrogen bonding between QT-amide molecules responsible for the observed self-assembly....

  14. Modelling of charge carrier mobility for transport between elastic polyacetylene-like polymer nanorods

    Czech Academy of Sciences Publication Activity Database

    Menšík, Miroslav; Sun, S. J.; Toman, Petr; Král, Karel

    2017-01-01

    Roč. 61, č. 2 (2017), s. 127-135 ISSN 0862-5468 R&D Projects: GA MŠk(CZ) LD14011; GA ČR(CZ) GA15-05095S Grant - others:European Commission(XE) COST Action MP1202 HINT; AV ČR(CZ) KONNECT-007 Program:Bilaterální spolupráce Institutional support: RVO:61389013 ; RVO:68378271 Keywords : charge carrier mobility * polymers * electron-phonon coupling Subject RIV: CF - Physical ; Theoretical Chemistry; CF - Physical ; Theoretical Chemistry (FZU-D) OBOR OECD: Physical chemistry; Physical chemistry (FZU-D) Impact factor: 0.439, year: 2016

  15. Sensitized charge carrier injection into organic crystals studied by isotope effects in weak magnetic fields

    International Nuclear Information System (INIS)

    Bube, W.; Michel-Beyerle, M.E.; Haberkorn, R.; Steffens, E.

    1977-01-01

    The magnetic field (H approximately 50 Oe) dependence of the rhodamine sensitized triplet exciton density in anthracene crystals is influenced by isotopic substitution. This confirms the hyperfine interaction as mechanism explaining the change of the spin multiplicity in the initially formed singlet state of the radical pair. The isotope effect occurs in the sensitizing dye ( 14 N/ 15 N) rather than at the molecular site of the injected charge within the crystal. This can be understood in terms of the high hopping frequency of the charge carriers as compared to the time constant of the hyperfine induced singlet-triplet transition. Since the dye molecules adsorb in an oriented fashion, the angular dependence of the magnetic field modulation of the triplet exciton density can be interpreted without assuming any additional interactions. (Auth.)

  16. Dynamics of charge carrier trapping in NO 2 sensors based on ZnO field-effect transistors

    NARCIS (Netherlands)

    Andringa, A.-M.; Vlietstra, N.; Smits, E.C.P.; Spijkman, M.-J.; Gomes, H.L.; Klootwijk, J.H.; Blom, P.W.M.; Leeuw, D.M. de

    2012-01-01

    Nitrogen dioxide (NO 2) detection with ZnO field-effect transistors is based on charge carrier trapping. Here we investigate the dynamics of charge trapping and recovery as a function of temperature by monitoring the threshold voltage shift. The threshold voltage shifts follow a

  17. Charge Carrier Generation Followed by Triplet State Formation, Annihilation, and Carrier Recreation in PBDTTT-C:PC 60 BM Photovoltaic Blends

    KAUST Repository

    Gehrig, Dominik W.

    2015-05-22

    Triplet state formation after photoexcitation of low-bandgap polymer:fullerene blends has recently been demonstrated, however, the precise mechanism and its impact on solar cell performance is still under debate. Here, we study exciton dissociation, charge carrier generation and triplet state formation in low-bandgap polymer PBDTTT-C:PC60BM bulk heterojunction photovoltaic blends by a combination of fs-µs broadband Vis-NIR transient absorption (TA) pump-probe spectroscopy and multivariate curve resolution (MCR) data analysis. We found sub-ps exciton dissociation and charge generation followed by sub-ns triplet state creation. The carrier dynamics and triplet state dynamics exhibited a very pronounced intensity dependence indicating non-geminate recombination of free carriers is the origin of triplet formation in these blends. Triplets were found to be the dominant state present on the nanosecond timescale. Surprisingly, the carrier population increased again on the ns-µs timescale. We attribute this to triplet-triplet annihilation and the formation of higher energy excited states that subsequently underwent charge transfer. This unique dip and recovery of the charge population is a clear indication that triplets are formed by non-geminate recombination, as such a kinetic is incompatible with a monomolecular triplet state formation process.

  18. Charge Carrier Generation Followed by Triplet State Formation, Annihilation, and Carrier Recreation in PBDTTT-C:PC 60 BM Photovoltaic Blends

    KAUST Repository

    Gehrig, Dominik W.; Howard, Ian A.; Laquai, Fré dé ric

    2015-01-01

    Triplet state formation after photoexcitation of low-bandgap polymer:fullerene blends has recently been demonstrated, however, the precise mechanism and its impact on solar cell performance is still under debate. Here, we study exciton dissociation, charge carrier generation and triplet state formation in low-bandgap polymer PBDTTT-C:PC60BM bulk heterojunction photovoltaic blends by a combination of fs-µs broadband Vis-NIR transient absorption (TA) pump-probe spectroscopy and multivariate curve resolution (MCR) data analysis. We found sub-ps exciton dissociation and charge generation followed by sub-ns triplet state creation. The carrier dynamics and triplet state dynamics exhibited a very pronounced intensity dependence indicating non-geminate recombination of free carriers is the origin of triplet formation in these blends. Triplets were found to be the dominant state present on the nanosecond timescale. Surprisingly, the carrier population increased again on the ns-µs timescale. We attribute this to triplet-triplet annihilation and the formation of higher energy excited states that subsequently underwent charge transfer. This unique dip and recovery of the charge population is a clear indication that triplets are formed by non-geminate recombination, as such a kinetic is incompatible with a monomolecular triplet state formation process.

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

    International Nuclear Information System (INIS)

    Song, Linze; Shi, Qiang

    2015-01-01

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

  20. Investigating Recombination and Charge Carrier Dynamics in a One-Dimensional Nanopillared Perovskite Absorber.

    Science.gov (United States)

    Kwon, Hyeok-Chan; Yang, Wooseok; Lee, Daehee; Ahn, Jihoon; Lee, Eunsong; Ma, Sunihl; Kim, Kyungmi; Yun, Seong-Cheol; Moon, Jooho

    2018-05-22

    Organometal halide perovskite materials have become an exciting research topic as manifested by intense development of thin film solar cells. Although high-performance solar-cell-based planar and mesoscopic configurations have been reported, one-dimensional (1-D) nanostructured perovskite solar cells are rarely investigated despite their expected promising optoelectrical properties, such as enhanced charge transport/extraction. Herein, we have analyzed the 1-D nanostructure effects of organometal halide perovskite (CH 3 NH 3 PbI 3- x Cl x ) on recombination and charge carrier dynamics by utilizing a nanoporous anodized alumina oxide scaffold to fabricate a vertically aligned 1-D nanopillared array with controllable diameters. It was observed that the 1-D perovskite exhibits faster charge transport/extraction characteristics, lower defect density, and lower bulk resistance than the planar counterpart. As the aspect ratio increases in the 1-D structures, in addition, the charge transport/extraction rate is enhanced and the resistance further decreases. However, when the aspect ratio reaches 6.67 (diameter ∼30 nm), the recombination rate is aggravated due to high interface-to-volume ratio-induced defect generation. To obtain the full benefits of 1-D perovskite nanostructuring, our study provides a design rule to choose the appropriate aspect ratio of 1-D perovskite structures for improved photovoltaic and other optoelectrical applications.

  1. Mapping Charge Carrier Density in Organic Thin-Film Transistors by Time-Resolved Photoluminescence Lifetime Studies

    DEFF Research Database (Denmark)

    Leißner, Till; Jensen, Per Baunegaard With; Liu, Yiming

    2017-01-01

    The device performance of organic transistors is strongly influenced by the charge carrier distribution. A range of factors effect this distribution, including injection barriers at the metal-semiconductor interface, the morphology of the organic film, and charge traps at the dielectric/organic...... interface or at grain boundaries. In our comprehensive experimental and analytical work we demonstrate a method to characterize the charge carrier density in organic thin-film transistors using time-resolved photoluminescence spectroscopy. We developed a numerical model that describes the electrical...... and optical responses consistently. We determined the densities of free and trapped holes at the interface between the organic layer and the SiO2 gate dielectric by comparison to electrical measurements. Furthermore by applying fluorescence lifetime imaging microscopy we determine the local charge carrier...

  2. Triphenylene columnar liquid crystals: spectroscopic study of triplets states and charge carriers

    International Nuclear Information System (INIS)

    Bondkowski, Jens

    2000-01-01

    This research thesis reports the study of three oxygenated derivatives of triphenylene (two monomers, a symmetric one and an asymmetric one, and a tetramer) by using different experimental techniques: absorption spectroscopy and fluorescence spectroscopy in stationary regime, and time-resolved fluorescence spectroscopy (also said single photon counting). Moreover, the author adapted an existing experiment of transient absorption spectroscopy time-resolved at the microsecond level to obtain spectra of thin layers under electric field. A cyclic voltammetry experiment and a spectro-electrochemistry experiment have also been performed. The report first presents the studied materials, the characterisation of singlet states, and the study of the effect molecular symmetry decreasing have on molecular transitions. Then, the author reports the study of cationic species of the triphenylene derivatives. The next chapters address the characterisation of derivative triplet states, and the study of energy transfer within the meso phase of one of these derivatives. The last chapters address charge carriers of columnar liquid crystals, and the molecular nature of these charge carriers

  3. Control of polythiophene film microstructure and charge carrier dynamics through crystallization temperature

    KAUST Repository

    Marsh, Hilary S.; Reid, Obadiah G.; Barnes, George; Heeney, Martin; Stingelin, Natalie; Rumbles, Garry

    2014-01-01

    The microstructure of neat conjugated polymers is crucial in determining the ultimate morphology and photovoltaic performance of polymer/fullerene blends, yet until recently, little work has focused on controlling the former. Here, we demonstrate that both the long-range order along the (100)-direction and the lamellar crystal thickness along the (001)-direction in neat poly(3-hexylthiophene) (P3HT) and poly[(3,3″-didecyl[2,2′:5′, 2″-terthiophene]-5,5″-diyl)] (PTTT-10) thin films can be manipulated by varying crystallization temperature. Changes in crystalline domain size impact the yield and dynamics of photogenerated charge carriers. Time-resolved microwave conductivity measurements show that neat polymer films composed of larger crystalline domains have longer photoconductance lifetimes and charge carrier yield decreases with increasing crystallite size for P3HT. Our results suggest that the classical polymer science description of temperature-dependent crystallization of polymers from solution can be used to understand thin-film formation in neat conjugated polymers, and hence, should be considered when discussing the structural evolution of organic bulk heterojunctions. © 2014 Wiley Periodicals, Inc.

  4. Control of polythiophene film microstructure and charge carrier dynamics through crystallization temperature

    KAUST Repository

    Marsh, Hilary S.

    2014-03-22

    The microstructure of neat conjugated polymers is crucial in determining the ultimate morphology and photovoltaic performance of polymer/fullerene blends, yet until recently, little work has focused on controlling the former. Here, we demonstrate that both the long-range order along the (100)-direction and the lamellar crystal thickness along the (001)-direction in neat poly(3-hexylthiophene) (P3HT) and poly[(3,3″-didecyl[2,2′:5′, 2″-terthiophene]-5,5″-diyl)] (PTTT-10) thin films can be manipulated by varying crystallization temperature. Changes in crystalline domain size impact the yield and dynamics of photogenerated charge carriers. Time-resolved microwave conductivity measurements show that neat polymer films composed of larger crystalline domains have longer photoconductance lifetimes and charge carrier yield decreases with increasing crystallite size for P3HT. Our results suggest that the classical polymer science description of temperature-dependent crystallization of polymers from solution can be used to understand thin-film formation in neat conjugated polymers, and hence, should be considered when discussing the structural evolution of organic bulk heterojunctions. © 2014 Wiley Periodicals, Inc.

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

    Science.gov (United States)

    Freund, Friedemann T.; Freund, Minoru M.

    2012-01-01

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

  6. Effects of Te inclusions on charge-carrier transport properties in CdZnTe radiation detectors

    International Nuclear Information System (INIS)

    Gu, Yaxu; Rong, Caicai; Xu, Yadong; Shen, Hao; Zha, Gangqiang; Wang, Ning; Lv, Haoyan; Li, Xinyi; Wei, Dengke; Jie, Wanqi

    2015-01-01

    Highlights: • This work reveals the behaviors of Te inclusion in affecting charge-carrier transport properties in CdZnTe detectors for the first time and analysis the mechanism therein. • The results show that charge collection efficiencies in Te inclusion degraded regions experience fast ascent under low biases and slow descent at high applied biases, which deviates from the Hecht rule. • This phenomenon is attributed to the competitive influence of two mechanisms under different biases, namely charge carrier trapping due to uniformly distributed point defects and Te inclusion induced transient charge loss. • A modified Hecht equation is further proposed to explain the effects of high-density localized defects, say Te inclusions, on the charge collection efficiency. • We believe that this research has wide appeal to analyze the macroscopic defects and their influence on charge transport properties in semiconductor radiation detectors. - Abstract: The influence of tellurium (Te) inclusions on the charge collection efficiency in cadmium zinc telluride (CdZnTe or CZT) detectors has been investigated using ion beam induced charge (IBIC) technique. Combining the analysis of infrared transmittance image, most of the low charge collection areas in the IBIC images prove the existence of Te inclusions. To further clarify the role of Te inclusions on charge transport properties, bias dependent local IBIC scan was performed on Te inclusion related regions from 20 V to 500 V. The result shows that charge collection efficiencies in Te inclusion degraded regions experience fast ascent under low biases and slow descent at high applied biases, which deviates from Hecht rule. This behavior is attributed to the competitive influence of two mechanisms under different biases, namely charge carrier trapping due to uniformly distributed point defects and Te inclusion induced transient charge loss. A modified Hecht equation is further proposed to explain the effects of high

  7. Effect of trap states and microstructure on charge carrier conduction mechanism through semicrystalline poly(vinyl alcohol) granular film

    Science.gov (United States)

    Das, A. K.; Bhowmik, R. N.; Meikap, A. K.

    2018-05-01

    We report a comprehensive study on hysteresis behaviour of current-voltage characteristic and impedance spectroscopy of granular semicrystalline poly(vinyl alcohol) (PVA) film. The charge carrier conduction mechanism and charge traps of granular PVA film by measuring and analyzing the temperature dependent current-voltage characteristic indicate a bi-stable electronic state in the film. A sharp transformation of charge carrier conduction mechanism from Poole-Frenkel emission to space charge limited current mechanism has been observed. An anomalous oscillatory behaviour of current has been observed due to electric pulse effect on the molecular chain of the polymer. Effect of microstructure on charge transport mechanism has been investigated from impedance spectroscopy analysis. An equivalent circuit model has been proposed to explain the result.

  8. Determination of Charge-Carrier Mobility in Disordered Thin-Film Solar Cells as a Function of Current Density

    Science.gov (United States)

    Mäckel, Helmut; MacKenzie, Roderick C. I.

    2018-03-01

    Charge-carrier mobility is a fundamental material parameter, which plays an important role in determining solar-cell efficiency. The higher the mobility, the less time a charge carrier will spend in a device and the less likely it is that it will be lost to recombination. Despite the importance of this physical property, it is notoriously difficult to measure accurately in disordered thin-film solar cells under operating conditions. We, therefore, investigate a method previously proposed in the literature for the determination of mobility as a function of current density. The method is based on a simple analytical model that relates the mobility to carrier density and transport resistance. By revising the theoretical background of the method, we clearly demonstrate what type of mobility can be extracted (constant mobility or effective mobility of electrons and holes). We generalize the method to any combination of measurements that is able to determine the mean electron and hole carrier density, and the transport resistance at a given current density. We explore the robustness of the method by simulating typical organic solar-cell structures with a variety of physical properties, including unbalanced mobilities, unbalanced carrier densities, and for high or low carrier trapping rates. The simulations reveal that near VOC and JSC , the method fails due to the limitation of determining the transport resistance. However, away from these regions (and, importantly, around the maximum power point), the method can accurately determine charge-carrier mobility. In the presence of strong carrier trapping, the method overestimates the effective mobility due to an underestimation of the carrier density.

  9. Internal transmission coefficient in charges carrier generation layer of graphene/Si based solar cell device

    International Nuclear Information System (INIS)

    Rosikhin, Ahmad; Winata, Toto

    2016-01-01

    Internal transmission profile in charges carrier generation layer of graphene/Si based solar cell has been explored theoretically. Photovoltaic device was constructed from graphene/Si heterojunction forming a multilayer stuck with Si as generation layer. The graphene/Si sheet was layered on ITO/glass wafer then coated by Al forming Ohmic contact with Si. Photon incident propagate from glass substrate to metal electrode and assumed that there is no transmission in Al layer. The wavelength range spectra used in this calculation was 200 – 1000 nm. It found that transmission intensity in the generation layer show non-linear behavior and partitioned by few areas which related with excitation process. According to this information, it may to optimize the photons absorption to create more excitation process by inserting appropriate material to enhance optical properties in certain wavelength spectra because of the exciton generation is strongly influenced by photon absorption.

  10. Charge carriers at organic heterojunction interface: Exciplex emission or electroplex emission?

    Science.gov (United States)

    Yang, Shengyi; Zhang, Xiulong; Hou, Yanbing; Deng, Zhenbo; Xu, Xurong

    2007-05-01

    We report the electroluminescence (EL) of organic heterojunction devices based on N ,N'-diphenyl-N ,N'-bis(3-methylphenyl)-(1,1'-biphenyl)-4,4',-diamine (TPD) and 2-(4'-biphenyl)-5-(4″-tert-butylphenyl)-1,3,4-oxadiazole (PBD). Besides monomolecular emissions from TPD, there are two additional EL peaks at around 460 and 480nm from the bilayer device indium tin oxide (ITO)/TPD(100nm )/PBD(45nm)/Al. Our experimental data confirmed that the EL emission maximized at around 460nm is from electroplex as the result of charge carriers cross recombination at the TPD/PBD interface and the EL emission maximized at around 480nm originates from (TPD*PBD)-type exciplex.

  11. MODELLING OF CHARGE CARRIER MOBILITY FOR TRANSPORT BETWEEN ELASTIC POLYACETYLENE-LIKE POLYMER NANORODS

    Directory of Open Access Journals (Sweden)

    M. Mensik

    2017-03-01

    Full Text Available A quantum model solving the charge carrier mobility between polyacetylene-like polymer nanorods is presented. The model assumes: a Quantum mechanical calculation of hole on-chain delocalization involving electron-phonon coupling leading to the Peierls instability, b Hybridization coupling between the polymer backbone and side-groups (or environmental states, which act as hole traps, and c Semiclassical description of the inter-chain hole transfer in an applied voltage based on Marcus theory. We have found that mobility resonantly depends on the hybridization coupling between polymer and linked groups. We observed also non-trivial mobility dependences on the difference of energies of the highest occupied molecular orbitals localized on the polymer backbone and side-groups, respectively, and hole concentration. Those findings are important for optimization of hybrid opto-electronic devices.

  12. i-CELIV technique for investigation of charge carriers transport properties

    Energy Technology Data Exchange (ETDEWEB)

    Važgėla, J., E-mail: julius.vazgela@ff.vu.lt; Genevičius, K.; Juška, G.

    2016-10-20

    The extraction of the injected charge carriers by linearly increasing voltage (i-CELIV) is a promising method for separate analysis of the holes and electrons transport properties in the bulk heterojunction layers. We are demonstrating how to establish the mobility dependence on the electric field and obtain more precise results by performing corrections in transit time by this technique. [6,6]-Phenyl C61 butyric acid methyl ester (PCBM) and poly[2,6-(4,4-bis-(2-ethylhexyl)-4H-cyclopenta [2,1-b;3,4-b′]dithiophene)-alt-4,7(2,1,3-benzothiadiazole)] (PCPDTBT) bulk heterojunctions with different blend ratios were experimentally tested with i-CELIV method. The hole and electron mobilities were found to be heavily imbalanced in the optimised 3:1 PCBM:PCPDTBT bulk heterojunction.

  13. Charge-carrier transport in epitactical strontium titanate layers for the application in superconducting components

    International Nuclear Information System (INIS)

    Grosse, Veit

    2011-01-01

    In this thesis thin STO layers were epitactically deposited on YBCO for a subsequent electrical characterization. YBCO layers with a roughness of less than 2 nm (RMS), good out-of-plane orientation with a half-width in the rocking curve in the range (0.2..0.3) at only slightly diminished critical temperature could be reached. The STO layers exhibited also very good crystallographic properties. The charge-carrier transport in STO is mainly dominated by interface-limited processes. By means of an in thesis newly developed barrier model thereby the measured dependencies j(U,T) respectively σ(U,T) could be described very far-reachingly. At larger layer thicknesses and low temperatures the charge-carrier transport succeeds by hopping processes. So in the YBCO/STO/YBCO system the variable-range hopping could be identified as dominating transport process. Just above U>10 V a new behaviour is observed, which concerning its temperature dependence however is also tunnel-like. The STO layers exhibit here very large resistances, so that fields up to 10 7 ..10 8 V/m can be reached without flowing of significant leakage currents through the barrier. In the system YBCO/STO/Au the current transport can be principally in the same way as in the YBCO/STO/YBCO system. The special shape and above all the asymmetry of the barrier however work out very distinctly. It could be shown that at high temperatures according to the current direction a second barrier on the opposite electrode must be passed. So often observed breakdown effects can be well described. For STO layer-thicknesses in the range around 25 nm in the whole temperature range studied inelastic tunneling over chains of localized states was identified as dominating transport process. It could however for the first time be shown that at very low temperatures in the STO layers Coulomb blockades can be formed.

  14. Origin of long lifetime of band-edge charge carriers in organic-inorganic lead iodide perovskites.

    Science.gov (United States)

    Chen, Tianran; Chen, Wei-Liang; Foley, Benjamin J; Lee, Jooseop; Ruff, Jacob P C; Ko, J Y Peter; Brown, Craig M; Harriger, Leland W; Zhang, Depei; Park, Changwon; Yoon, Mina; Chang, Yu-Ming; Choi, Joshua J; Lee, Seung-Hun

    2017-07-18

    Long carrier lifetime is what makes hybrid organic-inorganic perovskites high-performance photovoltaic materials. Several microscopic mechanisms behind the unusually long carrier lifetime have been proposed, such as formation of large polarons, Rashba effect, ferroelectric domains, and photon recycling. Here, we show that the screening of band-edge charge carriers by rotation of organic cation molecules can be a major contribution to the prolonged carrier lifetime. Our results reveal that the band-edge carrier lifetime increases when the system enters from a phase with lower rotational entropy to another phase with higher entropy. These results imply that the recombination of the photoexcited electrons and holes is suppressed by the screening, leading to the formation of polarons and thereby extending the lifetime. Thus, searching for organic-inorganic perovskites with high rotational entropy over a wide range of temperature may be a key to achieve superior solar cell performance.

  15. Where do ions solvate?

    Indian Academy of Sciences (India)

    We study a simple model of ionic solvation inside a water cluster. The cluster is modeled as a spherical dielectric continuum. It is found that unpolarizable ions always prefer the bulk solvation. On the other hand, for polarizable ions, there exists a critical value of polarization above which surface solvation becomes ...

  16. Charge separation and carrier dynamics in donor-acceptor heterojunction photovoltaic systems.

    Science.gov (United States)

    Teuscher, Joël; Brauer, Jan C; Stepanov, Andrey; Solano, Alicia; Boziki, Ariadni; Chergui, Majed; Wolf, Jean-Pierre; Rothlisberger, Ursula; Banerji, Natalie; Moser, Jacques-E

    2017-11-01

    Electron transfer and subsequent charge separation across donor-acceptor heterojunctions remain the most important areas of study in the field of third-generation photovoltaics. In this context, it is particularly important to unravel the dynamics of individual ultrafast processes (such as photoinduced electron transfer, carrier trapping and association, and energy transfer and relaxation), which prevail in materials and at their interfaces. In the frame of the National Center of Competence in Research "Molecular Ultrafast Science and Technology," a research instrument of the Swiss National Science Foundation, several groups active in the field of ultrafast science in Switzerland have applied a number of complementary experimental techniques and computational simulation tools to scrutinize these critical photophysical phenomena. Structural, electronic, and transport properties of the materials and the detailed mechanisms of photoinduced charge separation in dye-sensitized solar cells, conjugated polymer- and small molecule-based organic photovoltaics, and high-efficiency lead halide perovskite solar energy converters have been scrutinized. Results yielded more than thirty research articles, an overview of which is provided here.

  17. Charge separation and carrier dynamics in donor-acceptor heterojunction photovoltaic systems

    Directory of Open Access Journals (Sweden)

    Joël Teuscher

    2017-11-01

    Full Text Available Electron transfer and subsequent charge separation across donor-acceptor heterojunctions remain the most important areas of study in the field of third-generation photovoltaics. In this context, it is particularly important to unravel the dynamics of individual ultrafast processes (such as photoinduced electron transfer, carrier trapping and association, and energy transfer and relaxation, which prevail in materials and at their interfaces. In the frame of the National Center of Competence in Research “Molecular Ultrafast Science and Technology,” a research instrument of the Swiss National Science Foundation, several groups active in the field of ultrafast science in Switzerland have applied a number of complementary experimental techniques and computational simulation tools to scrutinize these critical photophysical phenomena. Structural, electronic, and transport properties of the materials and the detailed mechanisms of photoinduced charge separation in dye-sensitized solar cells, conjugated polymer- and small molecule-based organic photovoltaics, and high-efficiency lead halide perovskite solar energy converters have been scrutinized. Results yielded more than thirty research articles, an overview of which is provided here.

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

    KAUST Repository

    Shi, Dong

    2016-04-15

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

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

    International Nuclear Information System (INIS)

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

    2016-01-01

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

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

    Science.gov (United States)

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

    2016-08-01

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

  1. Charge carrier mobility and electronic properties of Al(Op3: impact of excimer formation

    Directory of Open Access Journals (Sweden)

    Andrea Magri

    2015-05-01

    Full Text Available We have studied the electronic properties and the charge carrier mobility of the organic semiconductor tris(1-oxo-1H-phenalen-9-olatealuminium(III (Al(Op3 both experimentally and theoretically. We experimentally estimated the HOMO and LUMO energy levels to be −5.93 and −3.26 eV, respectively, which were close to the corresponding calculated values. Al(Op3 was successfully evaporated onto quartz substrates and was clearly identified in the absorption spectra of both the solution and the thin film. A structured steady state fluorescence emission was detected in solution, whereas a broad, red-shifted emission was observed in the thin film. This indicates the formation of excimers in the solid state, which is crucial for the transport properties. The incorporation of Al(Op3 into organic thin film transistors (TFTs was performed in order to measure the charge carrier mobility. The experimental setup detected no electron mobility, while a hole mobility between 0.6 × 10−6 and 2.1 × 10−6 cm2·V−1·s−1 was measured. Theoretical simulations, on the other hand, predicted an electron mobility of 9.5 × 10−6 cm2·V−1·s−1 and a hole mobility of 1.4 × 10−4 cm2·V−1·s−1. The theoretical simulation for the hole mobility predicted an approximately one order of magnitude higher hole mobility than was observed in the experiment, which is considered to be in good agreement. The result for the electron mobility was, on the other hand, unexpected, as both the calculated electron mobility and chemical common sense (based on the capability of extended aromatic structures to efficiently accept and delocalize additional electrons suggest more robust electron charge transport properties. This discrepancy is explained by the excimer formation, whose inclusion in the multiscale simulation workflow is expected to bring the theoretical simulation and experiment into agreement.

  2. How High Local Charge Carrier Mobility and an Energy Cascade in a Three-Phase Bulk Heterojunction Enable >90% Quantum Efficiency

    KAUST Repository

    Burke, Timothy M.

    2013-12-27

    Charge generation in champion organic solar cells is highly efficient in spite of low bulk charge-carrier mobilities and short geminate-pair lifetimes. In this work, kinetic Monte Carlo simulations are used to understand efficient charge generation in terms of experimentally measured high local charge-carrier mobilities and energy cascades due to molecular mixing. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  3. How High Local Charge Carrier Mobility and an Energy Cascade in a Three-Phase Bulk Heterojunction Enable >90% Quantum Efficiency

    KAUST Repository

    Burke, Timothy M.; McGehee, Michael D.

    2013-01-01

    Charge generation in champion organic solar cells is highly efficient in spite of low bulk charge-carrier mobilities and short geminate-pair lifetimes. In this work, kinetic Monte Carlo simulations are used to understand efficient charge generation in terms of experimentally measured high local charge-carrier mobilities and energy cascades due to molecular mixing. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  4. Photogeneration and decay of charge carriers in hybrid bulk heterojunctions of ZnO nanoparticles and conjugated polymers

    NARCIS (Netherlands)

    Quist, P.A.C.; Beek, W.J.E.; Wienk, M.M.; Janssen, R.A.J.; Savenije, T.J.; Siebbeles, L.D.A.

    2006-01-01

    The photogeneration and decay of charge carriers in blend films of ZnO nanoparticles (diam. 5 nm) and poly[2-methoxy-5-(3',7'-dimethyloctyloxy)-1,4-phenylenevinylene] (MDMO-PPV) or poly(3-hexylthiophene) (P3HT) were studied by means of microwave-photoconductance measurements. Excitation of the

  5. Manipulation of charge carrier injection into organic field-effect transistors by self-assembled monolayers of alkanethiols

    NARCIS (Netherlands)

    Asadi, Kamal; Gholamrezaie, Fatemeh; Smits, Edsger C. P.; Blom, Paul W. M.; de Boer, Bert

    2007-01-01

    Charge carrier injection into two semiconducting polymers is investigated in field-effect transistors using gold source and drain electrodes that are modified by self-assembled monolayers of alkanethiols and perfluorinated alkanethiols. The presence of an interfacial dipole associated with the

  6. Interfacial Engineering and Charge Carrier Dynamics in Extremely Thin Absorber Solar Cells

    Science.gov (United States)

    Edley, Michael

    Photovoltaic energy is a clean and renewable source of electricity; however, it faces resistance to widespread use due to cost. Nanostructuring decouples constraints related to light absorption and charge separation, potentially reducing cost by allowing a wider variety of processing techniques and materials to be used. However, the large interfacial areas also cause an increased dark current which negatively affects cell efficiency. This work focuses on extremely thin absorber (ETA) solar cells that used a ZnO nanowire array as a scaffold for an extremely thin CdSe absorber layer. Photoexcited electrons generated in the CdSe absorber are transferred to the ZnO layer, while photogenerated holes are transferred to the liquid electrolyte. The transfer of photoexcited carriers to their transport layer competes with bulk recombination in the absorber layer. After charge separation, transport of charge carriers to their respective contacts must occur faster than interfacial recombination for efficient collection. Charge separation and collection depend sensitively on the dimensions of the materials as well as their interfaces. We demonstrated that an optimal absorber thickness can balance light absorption and charge separation. By treating the ZnO/CdSe interface with a CdS buffer layer, we were able to improve the Voc and fill factor, increasing the ETA cell's efficiency from 0.53% to 1.34%, which is higher than that achievable using planar films of the same material. We have gained additional insight into designing ETA cells through the use of dynamic measurements. Ultrafast transient absorption spectroscopy revealed that characteristic times for electron injection from CdSe to ZnO are less than 1 ps. Electron injection is rapid compared to the 2 ns bulk lifetime in CdSe. Optoelectronic measurements such as transient photocurrent/photovoltage and electrochemical impedance spectroscopy were applied to study the processes of charge transport and interfacial recombination

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

    International Nuclear Information System (INIS)

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

    2009-01-01

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

  8. The effects of free volumes on charge carrier transport in polysilanes probed by positron annihilation

    International Nuclear Information System (INIS)

    Seki, Shu; Terashima, Y.; Kunimi, Y.; Kawamori, T.; Tashiro, M.; Honda, Y.; Tagawa, S.

    2003-01-01

    Free volume characteristics were investigated by positron annihilation technique in poly(n-alkylphenylsilane)s with a variety length of n-alkyl chains from methyl (C1) to n-dodecyl (C12). The average radius of free volume: R changes in two steps. An increase in R is observed with an elongation of n-alkyl side-groups from C1 to n-pentyl (C5), followed by an abrupt decrease in R between C5 and n-hexyl (C6), and a gradual increase by further elongation from C6 to C12. The sudden decrease in R at C5 and C6 gives a good interpretation to the reduction of inter-site hopping distances and their fluctuation for the charge carrier (hole) transport estimated by time-of-flight measurements. The values of free volume fraction in the polymers mainly reflect the density of the polymers; however, differences in the microscopic inter-molecular structure are also observed for poly(n-hexylphenylsilane) in the present study

  9. Field effect measurements on charge carrier mobilities in various polymer-fullerene blend compositions

    International Nuclear Information System (INIS)

    Hauff, Elizabeth von; Parisi, Juergen; Dyakonov, Vladimir

    2006-01-01

    In this study we investigated materials typically used in polymer photovoltaics. Field effect measurements were performed in order to determine the hole mobilities in the conjugated polymer poly(3-hexylthiophene) (P3HT) and the electron mobilities in the methanofullerene[6,6]-phenyl C 61 -butyric acid methyl ester (PCBM), and, particularly, in the polymer-fullerene composite blends. Regarding the pure films, electron mobilities in PCBM were found to be in the 10 -2 cm 2 /Vs range, and hole mobilities in P3HT were found to be in the 10 -3 cm2/Vs range. In the PCBM:P3HT blends, it was found that varying the PCBM content in PCBM:P3HT blends led to a steep increase in electron mobility with increasing PCBM content, while the hole mobility was found to slightly decrease with the increasing PCBM concentration. In 2:1 PCBM:P3HT tempered blends, the charge carrier mobilities were found to be roughly balanced, at 10 -3 cm 2 /Vs. For improved electron transport in the blends, tempering was found to be crucial

  10. Accurate Extraction of Charge Carrier Mobility in 4-Probe Field-Effect Transistors

    KAUST Repository

    Choi, Hyun Ho; Rodionov, Yaroslav I.; Paterson, Alexandra F.; Panidi, Julianna; Saranin, Danila; Kharlamov, Nikolai; Didenko, Sergei I.; Anthopoulos, Thomas D.; Cho, Kilwon; Podzorov, Vitaly

    2018-01-01

    Charge carrier mobility is an important characteristic of organic field-effect transistors (OFETs) and other semiconductor devices. However, accurate mobility determination in FETs is frequently compromised by issues related to Schottky-barrier contact resistance, that can be efficiently addressed by measurements in 4-probe/Hall-bar contact geometry. Here, it is shown that this technique, widely used in materials science, can still lead to significant mobility overestimation due to longitudinal channel shunting caused by voltage probes in 4-probe structures. This effect is investigated numerically and experimentally in specially designed multiterminal OFETs based on optimized novel organic-semiconductor blends and bulk single crystals. Numerical simulations reveal that 4-probe FETs with long but narrow channels and wide voltage probes are especially prone to channel shunting, that can lead to mobilities overestimated by as much as 350%. In addition, the first Hall effect measurements in blended OFETs are reported and how Hall mobility can be affected by channel shunting is shown. As a solution to this problem, a numerical correction factor is introduced that can be used to obtain much more accurate experimental mobilities. This methodology is relevant to characterization of a variety of materials, including organic semiconductors, inorganic oxides, monolayer materials, as well as carbon nanotube and semiconductor nanocrystal arrays.

  11. Functionalized organic semiconductor molecules to enhance charge carrier injection in electroluminescent cell

    Science.gov (United States)

    Yalcin, Eyyup; Kara, Duygu Akin; Karakaya, Caner; Yigit, Mesude Zeliha; Havare, Ali Kemal; Can, Mustafa; Tozlu, Cem; Demic, Serafettin; Kus, Mahmut; Aboulouard, Abdelkhalk

    2017-07-01

    Organic semiconductor (OSC) materials as a charge carrier interface play an important role to improve the device performance of organic electroluminescent cells. In this study, 4,4″-bis(diphenyl amino)-1,1':3‧,1″-terphenyl-5'-carboxylic acid (TPA) and 4,4″-di-9H-carbazol-9-yl-1,1':3‧,1″-terphenyl-5'-carboxylic acid (CAR) has been designed and synthesized to modify indium tin oxide (ITO) layer as interface. Bare ITO and PEDOT:PSS coated on ITO was used as reference anode electrodes for comparison. Furthermore, PEDOT:PSS coated over CAR/ITO and TPA/ITO to observe stability of OSC molecules and to completely cover the ITO surface. Electrical, optical and surface characterizations were performed for each device. Almost all modified devices showed around 36% decrease at the turn on voltage with respect to bare ITO. The current density of bare ITO, ITO/CAR and ITO/TPA were measured as 288, 1525 and 1869 A/m2, respectively. By increasing current density, luminance of modified devices showed much better performance with respect to unmodified devices.

  12. Carrier mobility in mesoscale heterogeneous organic materials: Effects of crystallinity and anisotropy on efficient charge transport

    Science.gov (United States)

    Kobayashi, Hajime; Shirasawa, Raku; Nakamoto, Mitsunori; Hattori, Shinnosuke; Tomiya, Shigetaka

    2017-07-01

    Charge transport in the mesoscale bulk heterojunctions (BHJs) of organic photovoltaic devices (OPVs) is studied using multiscale simulations in combination with molecular dynamics, the density functional theory, the molecular-level kinetic Monte Carlo (kMC) method, and the coarse-grained kMC method, which was developed to estimate mesoscale carrier mobility. The effects of the degree of crystallinity and the anisotropy of the conductivity of donors on hole mobility are studied for BHJ structures that consist of crystalline and amorphous pentacene grains that act as donors and amorphous C60 grains that act as acceptors. We find that the hole mobility varies dramatically with the degree of crystallinity of pentacene because it is largely restricted by a low-mobility amorphous region that occurs in the hole transport network. It was also found that the percolation threshold of crystalline pentacene is relatively high at approximately 0.6. This high percolation threshold is attributed to the 2D-like conductivity of crystalline pentacene, and the threshold is greatly improved to a value of approximately 0.3 using 3D-like conductive donors. We propose essential guidelines to show that it is critical to increase the degree of crystallinity and develop 3D conductive donors for efficient hole transport through percolative networks in the BHJs of OPVs.

  13. Charge-carrier transport and recombination in heteroepitaxial CdTe

    International Nuclear Information System (INIS)

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

    2014-01-01

    We analyze charge-carrier dynamics using time-resolved spectroscopy and varying epitaxial CdTe thickness in undoped heteroepitaxial CdTe/ZnTe/Si. By employing one-photon and nonlinear two-photon excitation, we assess surface, interface, and bulk recombination. Two-photon excitation with a focused laser beam enables characterization of recombination velocity at the buried epilayer/substrate interface, 17.5 μm from the sample surface. Measurements with a focused two-photon excitation beam also indicate a fast diffusion component, from which we estimate an electron mobility of 650 cm 2 (Vs) −1 and diffusion coefficient D of 17 cm 2  s −1 . We find limiting recombination at the epitaxial film surface (surface recombination velocity S surface  = (2.8 ± 0.3) × 10 5  cm s −1 ) and at the heteroepitaxial interface (interface recombination velocity S interface  = (4.8 ± 0.5) × 10 5  cm s −1 ). The results demonstrate that reducing surface and interface recombination velocity is critical for photovoltaic solar cells and electronic devices that employ epitaxial CdTe.

  14. Corneal permeation properties of a charged lipid nanoparticle carrier containing dexamethasone

    Science.gov (United States)

    Ban, Junfeng; Zhang, Yan; Huang, Xin; Deng, Guanghan; Hou, Dongzhi; Chen, Yanzhong; Lu, Zhufen

    2017-01-01

    Drug delivery carriers can maintain effective therapeutic concentrations in the eye. To this end, we developed lipid nanoparticles (L/NPs) in which the surface was modified with positively charged chitosan, which engaged in hydrogen bonding with the phospholipid membrane. We evaluated in vitro corneal permeability and release characteristics, ocular irritation, and drug dynamics of modified and unmodified L/NPs in aqueous humor. The size of L/NPs was uniform and showed a narrow distribution. Corneal permeation was altered by the presence of chitosan and was dependent on particle size; the apparent permeability coefficient of dexamethasone increased by 2.7 and 1.8 times for chitosan-modified and unmodified L/NPs, respectively. In conclusion, a chitosan-modified system could be a promising method for increasing the ocular bioavailability of unmodified L/NPs by enhancing their retention time and permeation into the cornea. These findings provide a theoretical basis for the development of effective drug delivery systems in the treatment of ocular disease. PMID:28243093

  15. InN/GaN quantum dot superlattices: Charge-carrier states and surface electronic structure

    Science.gov (United States)

    Kanouni, F.; Brezini, A.; Djenane, M.; Zou, Q.

    2018-03-01

    We have theoretically investigated the electron energy spectra and surface states energy in the three dimensionally ordered quantum dot superlattices (QDSLs) made of InN and GaN semiconductors. The QDSL is assumed in this model to be a matrix of GaN containing cubic dots of InN of the same size and uniformly distributed. For the miniband’s structure calculation, the resolution of the effective mass Schrödinger equation is done by decoupling it in the three directions within the framework of Kronig-Penney model. We found that the electrons minibands in infinite ODSLs are clearly different from those in the conventional quantum-well superlattices. The electrons localization and charge-carrier states are very dependent on the quasicrystallographic directions, the size and the shape of the dots which play a role of the artificial atoms in such QD supracrystal. The energy spectrum of the electron states localized at the surface of InN/GaN QDSL is represented by Kronig-Penney like-model, calculated via direct matching procedure. The calculation results show that the substrate breaks symmetrical shape of QDSL on which some localized electronic surface states can be produced in minigap regions. Furthermore, we have noticed that the surface states degeneracy is achieved in like very thin bands located in the minigaps, identified by different quantum numbers nx, ny, nz. Moreover, the surface energy bands split due to the reduction of the symmetry of the QDSL in z-direction.

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

    Science.gov (United States)

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

    2012-08-01

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

  17. Optimization of white organic light emitting diodes based on emitting layer charge carrier conduction properties

    International Nuclear Information System (INIS)

    Baek, H I; Lee, C H

    2008-01-01

    We have fabricated white organic light emitting diodes (OLEDs) with multi-emitting layer (EML) structures in which 4,4'-N,N'-dicarbazole-biphenyl (CBP) layers doped with the phosphorescent dopants fac-tris(2-phenylpyridine) iridium (Ir(ppy) 3 ) and bis(2-(2'-benzo[4,5-a]thienyl)pyridinato-N,C3')iridium(acetylacetonate) (btp 2 Ir(acac)) and the fluorescent dopant 4,4'-bis[2-{4-(N,N-diphenylamino) phenyl}vinyl]biphenyl (DPAVBi) were used as green (G), red (R) and blue (B) EMLs, respectively. A higher efficiency was expected with the R/G/B EML sequence from the hole transport layer interface than with the G/R/B sequence because of the differences in the charge carrier conduction properties of the EMLs doped with phosphorescent dopants and the luminance balance between the phosphorescent and fluorescent emissions. A high efficiency of 18.3 cd A -1 (an external quantum efficiency of 8.5%) at 100 cd m -2 and good colour stability were achieved with the R/G/B EML sequence as expected, with an additional non-doped CBP interlayer used between the G and B EMLs. In addition, the OLED with this sequence was found to have the longest lifetime of the white devices we tested

  18. Optimization of white organic light emitting diodes based on emitting layer charge carrier conduction properties

    Energy Technology Data Exchange (ETDEWEB)

    Baek, H I; Lee, C H [School of Electrical Engineering and Computer Science and Inter-University Semiconductor Research Center, Seoul National University, Seoul 151-744 (Korea, Republic of)], E-mail: hibaek75@snu.ac.kr

    2008-05-21

    We have fabricated white organic light emitting diodes (OLEDs) with multi-emitting layer (EML) structures in which 4,4'-N,N'-dicarbazole-biphenyl (CBP) layers doped with the phosphorescent dopants fac-tris(2-phenylpyridine) iridium (Ir(ppy){sub 3}) and bis(2-(2'-benzo[4,5-a]thienyl)pyridinato-N,C3')iridium(acetylacetonate) (btp{sub 2}Ir(acac)) and the fluorescent dopant 4,4'-bis[2-{l_brace}4-(N,N-diphenylamino) phenyl{r_brace}vinyl]biphenyl (DPAVBi) were used as green (G), red (R) and blue (B) EMLs, respectively. A higher efficiency was expected with the R/G/B EML sequence from the hole transport layer interface than with the G/R/B sequence because of the differences in the charge carrier conduction properties of the EMLs doped with phosphorescent dopants and the luminance balance between the phosphorescent and fluorescent emissions. A high efficiency of 18.3 cd A{sup -1} (an external quantum efficiency of 8.5%) at 100 cd m{sup -2} and good colour stability were achieved with the R/G/B EML sequence as expected, with an additional non-doped CBP interlayer used between the G and B EMLs. In addition, the OLED with this sequence was found to have the longest lifetime of the white devices we tested.

  19. Accurate Extraction of Charge Carrier Mobility in 4-Probe Field-Effect Transistors

    KAUST Repository

    Choi, Hyun Ho

    2018-04-30

    Charge carrier mobility is an important characteristic of organic field-effect transistors (OFETs) and other semiconductor devices. However, accurate mobility determination in FETs is frequently compromised by issues related to Schottky-barrier contact resistance, that can be efficiently addressed by measurements in 4-probe/Hall-bar contact geometry. Here, it is shown that this technique, widely used in materials science, can still lead to significant mobility overestimation due to longitudinal channel shunting caused by voltage probes in 4-probe structures. This effect is investigated numerically and experimentally in specially designed multiterminal OFETs based on optimized novel organic-semiconductor blends and bulk single crystals. Numerical simulations reveal that 4-probe FETs with long but narrow channels and wide voltage probes are especially prone to channel shunting, that can lead to mobilities overestimated by as much as 350%. In addition, the first Hall effect measurements in blended OFETs are reported and how Hall mobility can be affected by channel shunting is shown. As a solution to this problem, a numerical correction factor is introduced that can be used to obtain much more accurate experimental mobilities. This methodology is relevant to characterization of a variety of materials, including organic semiconductors, inorganic oxides, monolayer materials, as well as carbon nanotube and semiconductor nanocrystal arrays.

  20. Direct femtosecond observation of charge carrier recombination in ternary semiconductor nanocrystals: The effect of composition and shelling

    KAUST Repository

    Bose, Riya

    2015-02-12

    Heavy-metal free ternary semiconductor nanocrystals are emerging as key materials in photoactive applications. However, the relative abundance of intra-bandgap defect states and lack of understanding of their origins within this class of nanocrystals are major factors limiting their applicability. To remove these undesirable defect states which considerably shorten the lifetimes of photogenerated excited carriers, a detailed understanding about their origin and nature is required. In this report, we monitor the ultrafast charge carrier dynamics of CuInS2 (CIS), CuInSSe (CISSe), and CuInSe2 (CISe) nanocrystals, before and after ZnS shelling, using state-of-the-art time-resolved laser spectroscopy with broadband capabilities. The experimental results demonstrate the presence of both electron and hole trapping intra-bandgap states in the nanocrystals which can be removed significantly by ZnS shelling, and the carrier dynamics is slowed down. Another important observation remains the reduction of carrier lifetime in the presence of Se, and the shelling strategy is observed to be less effective at suppressing trap states. This study provides quantitative physical insights into the role of anion composition and shelling on the charge carrier dynamics in ternary CIS, CISSe, and CISe nanocrystals which are essential to improve their applicability for photovoltaics and optoelectronics.

  1. Side chain engineering of fused aromatic thienopyrazine based low band-gap polymers for enhanced charge carrier mobility

    KAUST Repository

    Mondal, Rajib

    2011-01-01

    A strategic side-chain engineering approach leads to the two orders of magnitude enhancement of charge carrier mobility in phenanthrene based fused aromatic thienopyrazine polymers. Hole carrier mobility up to 0.012 cm 2/Vs can be obtained in thin film transistor devices. Polymers were also utilized to fabricate bulk heterojunction photovoltaic devices and the maximum PCE obtained in these OPV\\'s was 1.15%. Most importantly, performances of the devices were correlated with thin morphological analysis performed by atomic force microscopy and grazing incidence X-ray scattering. © 2011 The Royal Society of Chemistry.

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

    Science.gov (United States)

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

    2016-08-01

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

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

    Energy Technology Data Exchange (ETDEWEB)

    Spencer, J.; Gajdos, F.; Blumberger, J., E-mail: j.blumberger@ucl.ac.uk [Department of Physics and Astronomy, University College London, Gower Street, London WC1E 6BT (United Kingdom)

    2016-08-14

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

  4. Semiconducting lithium indium diselenide: Charge-carrier properties and the impacts of high flux thermal neutron irradiation

    Science.gov (United States)

    Hamm, Daniel S.; Rust, Mikah; Herrera, Elan H.; Matei, Liviu; Buliga, Vladimir; Groza, Michael; Burger, Arnold; Stowe, Ashley; Preston, Jeff; Lukosi, Eric D.

    2018-06-01

    This paper reports on the charge carrier properties of several lithium indium diselenide (LISe) semiconductors. It was found that the charge collection efficiency of LISe was improved after high flux thermal neutron irradiation including the presence of a typically unobservable alpha peak from hole-only collection. Charge carrier trap energies of the irradiated sample were measured using photo-induced current transient spectroscopy. Compared to previous studies of this material, no significant differences in trap energies were observed. Through trap-filled limited voltage measurements, neutron irradiation was found to increase the density of trap states within the bulk of the semiconductor, which created a polarization effect under alpha exposure but not neutron exposure. Further, the charge collection efficiency of the irradiated sample was higher (14-15 fC) than that of alpha particles (3-5 fC), indicating that an increase in hole signal contribution resulted from the neutron irradiation. Finally, it was observed that significant charge loss takes place near the point of generation, producing a significant scintillation response and artificially inflating the W-value of all semiconducting LISe crystals.

  5. On the definition of dielectric permittivity for media with temporal dispersion in the presence of free charge carriers

    International Nuclear Information System (INIS)

    Bordag, M; Geyer, B; Klimchitskaya, G L; Mostepanenko, V M

    2010-01-01

    We show that in the presence of free charge carriers the definition of the frequency-dependent dielectric permittivity requires additional regularization. As an example, the dielectric permittivity of the Drude model is considered and its time-dependent counterpart is derived and analyzed. The respective electric displacement cannot be represented in terms of the standard Fourier integral. The regularization procedure allowing the circumvention of these difficulties is suggested. For the purpose of comparison it is shown that the frequency-dependent dielectric permittivity of insulators satisfies all rigorous mathematical criteria. This permits us to conclude that in the presence of free charge carriers the concept of dielectric permittivity is not as well defined as for insulators and we make a link to widely discussed puzzles in the theory of thermal Casimir force which might be caused by the use of this kind of permittivities.

  6. On the definition of dielectric permittivity for media with temporal dispersion in the presence of free charge carriers

    Energy Technology Data Exchange (ETDEWEB)

    Bordag, M; Geyer, B; Klimchitskaya, G L; Mostepanenko, V M [Institute for Theoretical Physics, Leipzig University, Postfach 100920, D-04009, Leipzig (Germany)

    2010-01-08

    We show that in the presence of free charge carriers the definition of the frequency-dependent dielectric permittivity requires additional regularization. As an example, the dielectric permittivity of the Drude model is considered and its time-dependent counterpart is derived and analyzed. The respective electric displacement cannot be represented in terms of the standard Fourier integral. The regularization procedure allowing the circumvention of these difficulties is suggested. For the purpose of comparison it is shown that the frequency-dependent dielectric permittivity of insulators satisfies all rigorous mathematical criteria. This permits us to conclude that in the presence of free charge carriers the concept of dielectric permittivity is not as well defined as for insulators and we make a link to widely discussed puzzles in the theory of thermal Casimir force which might be caused by the use of this kind of permittivities.

  7. The Role of Polymer Fractionation in Energetic Losses and Charge Carrier Lifetimes of Polymer: Fullerene Solar Cells

    KAUST Repository

    Baran, Derya

    2015-08-10

    Non-radiative recombination reduces the open-circuit voltage relative to its theoretical limit and leads to reduced luminescence emission at a given excitation. Therefore it is possible to correlate changes in luminescence emission with changes in open-circuit voltage and in the charge carrier lifetime. Here we use luminescence studies combined with transient photovoltage and differential charging analyses to study the effect of polymer fractionation in indacenoedithiophene-co-benzothiadiazole (IDTBT):fullerene solar cells. In this system, polymer fractionation increases electroluminescence and reduces non-radiative recombination. High molecular weight and fractionated IDTBT polymers exhibit higher carrier lifetime-mobility product compared to their non-fractionated analogues, resulting in improved solar cell performance.

  8. Charge carriers bulk recombination instead of electroplex emission after their tunneling through hole-blocking layer in OLEDs

    Science.gov (United States)

    Yang, S. Y.; Liu, D.; Jiang, Y.; Teng, F.; Xu, Z.; Hou, Y.; Xu, X. R.

    2006-08-01

    Charge carriers bulk recombination instead of forming electroplex after their tunneling through a hole-blocking layer, i.e. 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline (BCP), in organic electroluminescence (EL) device ITO/poly-(N-vinyl-carbazole)(PVK)/BCP/tris(8-hydroxyquinoline) aluminum (Alq3)/Al is reported. By changing the thickness of BCP layer, one can find that high electric fields enhance the tunneling process of holes accumulated at the PVK/BCP interface into BCP layer instead of forming “electroplex emission” as reported earlier in literatures. Our experimental data show that charge carriers bulk recombination takes place in both PVK layer and BCP layer, and even in Alq3 layer when BCP layer is thin enough. Further, it is suggested that PVK is the origin of the emission shoulder at 595 nm in the EL spectra of trilayer device ITO/PVK/BCP/Alq3/Al.

  9. The Role of Polymer Fractionation in Energetic Losses and Charge Carrier Lifetimes of Polymer: Fullerene Solar Cells

    KAUST Repository

    Baran, Derya; Vezie, Michelle S; Gasparini, Nicola; Deledalle, Florent; Yao, Jizhong; Schroeder, Bob C.; Bronstein, Hugo; Ameri, Tayebeh; Kirchartz, Thomas; McCulloch, Iain; Nelson, Jenny; Brabec, Christoph J

    2015-01-01

    Non-radiative recombination reduces the open-circuit voltage relative to its theoretical limit and leads to reduced luminescence emission at a given excitation. Therefore it is possible to correlate changes in luminescence emission with changes in open-circuit voltage and in the charge carrier lifetime. Here we use luminescence studies combined with transient photovoltage and differential charging analyses to study the effect of polymer fractionation in indacenoedithiophene-co-benzothiadiazole (IDTBT):fullerene solar cells. In this system, polymer fractionation increases electroluminescence and reduces non-radiative recombination. High molecular weight and fractionated IDTBT polymers exhibit higher carrier lifetime-mobility product compared to their non-fractionated analogues, resulting in improved solar cell performance.

  10. Charge and excitation dynamics in semiconducting polymer layers doped with emitters and charge carrier traps; Ladungstraeger- und Anregungsdynamik in halbleitenden Polymerschichten mit eingemischten Emittern und Ladungstraegerfallen

    Energy Technology Data Exchange (ETDEWEB)

    Jaiser, F

    2006-06-15

    Light-emitting diodes generate light from the recombination of injected charge carriers. This can be obtained in inorganic materials. Here, it is necessary to produce highly ordered crystalline structures that determine the properties of the device. Another possibility is the utilization of organic molecules and polymers. Based on the versatile organic chemistry, it is possible to tune the properties of the semiconducting polymers already during synthesis. In addition, semiconducting polymers are mechanically flexible. Thus, it is possible to construct flexible, large-area light sources and displays. The first light-emitting diode using a polymer emitter was presented in 1990. Since then, this field of research has grown rapidly up to the point where first products are commercially available. It has become clear that the properties of polymer light-emitting diodes such as color and efficiency can be improved by incorporating multiple components inside the active layer. At the same time, this gives rise to new interactions between these components. While components are often added either to improve the charge transport or to change the emission, it has to made sure that other processes are not influenced in a negative manner. This work investigates some of these interactions and describes them with simple physical models. First, blue light-emitting diodes based on polyfluorene are analyzed. This polymer is an efficient emitter, but it is susceptible to the formation of chemical defects that can not be suppressed completely. These defects form electron traps, but their effect can be compensated by the addition of hole traps. The underlying process, namely the changed charge carrier balance, is explained. In the following, blend systems with dendronized emitters that form electron traps are investigated. The different influence of the insulating shell on the charge and energy transfer between polymer host and the emissive core of the dendrimers is examined. In the

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

    Energy Technology Data Exchange (ETDEWEB)

    Nian, Qiong; Cheng, Gary J., E-mail: gjcheng@purdue.edu [Birck Nanotechnology Center, Purdue University, West Lafayette, Indiana 47906 (United States); School of Industrial Engineering, Purdue University, West Lafayette, Indiana 47906 (United States); Zhang, Martin Y. [School of Industrial Engineering, Purdue University, West Lafayette, Indiana 47906 (United States); Wang, Yuefeng [Birck Nanotechnology Center, Purdue University, West Lafayette, Indiana 47906 (United States); School of Materials Engineering, Purdue University, West Lafayette, Indiana 47906 (United States); Das, Suprem R.; Bhat, Venkataprasad S. [Birck Nanotechnology Center, Purdue University, West Lafayette, Indiana 47906 (United States); Huang, Fuqiang [Shanghai Institute of Ceramics, Chinese Academy of Science, Shanghai 200050 (China)

    2014-09-15

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

  12. The Impact of Donor-Acceptor Phase Separation on the Charge Carrier Dynamics in pBTTT:PCBM Photovoltaic Blends

    KAUST Repository

    Gehrig, Dominik W.

    2015-04-07

    The effect of donor–acceptor phase separation, controlled by the donor–acceptor mixing ratio, on the charge generation and recombination dynamics in pBTTT-C14:PC70BM bulk heterojunction photovoltaic blends is presented. Transient absorption (TA) spectroscopy spanning the dynamic range from pico- to microseconds in the visible and near-infrared spectral regions reveals that in a 1:1 blend exciton dissociation is ultrafast; however, charges cannot entirely escape their mutual Coulomb attraction and thus predominantly recombine geminately on a sub-ns timescale. In contrast, a polymer:fullerene mixing ratio of 1:4 facilitates the formation of spatially separated, that is free, charges and reduces substantially the fraction of geminate charge recombination, in turn leading to much more efficient photovoltaic devices. This illustrates that spatially extended donor or acceptor domains are required for the separation of charges on an ultrafast timescale (<100 fs), indicating that they are not only important for efficient charge transport and extraction, but also critically influence the initial stages of free charge carrier formation.

  13. The Impact of Donor-Acceptor Phase Separation on the Charge Carrier Dynamics in pBTTT:PCBM Photovoltaic Blends

    KAUST Repository

    Gehrig, Dominik W.; Howard, Ian A.; Sweetnam, Sean; Burke, Timothy M.; McGehee, Michael D.; Laquai, Fré dé ric

    2015-01-01

    The effect of donor–acceptor phase separation, controlled by the donor–acceptor mixing ratio, on the charge generation and recombination dynamics in pBTTT-C14:PC70BM bulk heterojunction photovoltaic blends is presented. Transient absorption (TA) spectroscopy spanning the dynamic range from pico- to microseconds in the visible and near-infrared spectral regions reveals that in a 1:1 blend exciton dissociation is ultrafast; however, charges cannot entirely escape their mutual Coulomb attraction and thus predominantly recombine geminately on a sub-ns timescale. In contrast, a polymer:fullerene mixing ratio of 1:4 facilitates the formation of spatially separated, that is free, charges and reduces substantially the fraction of geminate charge recombination, in turn leading to much more efficient photovoltaic devices. This illustrates that spatially extended donor or acceptor domains are required for the separation of charges on an ultrafast timescale (<100 fs), indicating that they are not only important for efficient charge transport and extraction, but also critically influence the initial stages of free charge carrier formation.

  14. Characterization of Charge-Carrier Transport in Semicrystalline Polymers: Electronic Couplings, Site Energies, and Charge-Carrier Dynamics in Poly(bithiophene- alt -thienothiophene) [PBTTT

    KAUST Repository

    Poelking, Carl

    2013-01-31

    We establish a link between the microscopic ordering and the charge-transport parameters for a highly crystalline polymeric organic semiconductor, poly(2,5-bis(3-tetradecylthiophen-2-yl)thieno[3,2-b]thiophene) (PBTTT). We find that the nematic and dynamic order parameters of the conjugated backbones, as well as their separation, evolve linearly with temperature, while the side-chain dynamic order parameter and backbone paracrystallinity change abruptly upon the (also experimentally observed) melting of the side chains around 400 K. The distribution of site energies follows the behavior of the backbone paracrystallinity and can be treated as static on the time scale of a single-charge transfer reaction. On the contrary, the electronic couplings between adjacent backbones are insensitive to side-chain melting and vary on a much faster time scale. The hole mobility, calculated after time-averaging of the electronic couplings, reproduces well the value measured in a short-channel thin-film transistor. The results underline that to secure efficient charge transport in lamellar arrangements of conjugated polymers: (i) the electronic couplings should present high average values and fast dynamics, and (ii) the energetic disorder (paracrystallinity) should be small. © 2013 American Chemical Society.

  15. Characterization of Charge-Carrier Transport in Semicrystalline Polymers: Electronic Couplings, Site Energies, and Charge-Carrier Dynamics in Poly(bithiophene- alt -thienothiophene) [PBTTT

    KAUST Repository

    Poelking, Carl; Cho, Eunkyung; Malafeev, Alexander; Ivanov, Viktor; Kremer, Kurt; Risko, Chad; Bré das, Jean-Luc; Andrienko, Denis

    2013-01-01

    We establish a link between the microscopic ordering and the charge-transport parameters for a highly crystalline polymeric organic semiconductor, poly(2,5-bis(3-tetradecylthiophen-2-yl)thieno[3,2-b]thiophene) (PBTTT). We find that the nematic and dynamic order parameters of the conjugated backbones, as well as their separation, evolve linearly with temperature, while the side-chain dynamic order parameter and backbone paracrystallinity change abruptly upon the (also experimentally observed) melting of the side chains around 400 K. The distribution of site energies follows the behavior of the backbone paracrystallinity and can be treated as static on the time scale of a single-charge transfer reaction. On the contrary, the electronic couplings between adjacent backbones are insensitive to side-chain melting and vary on a much faster time scale. The hole mobility, calculated after time-averaging of the electronic couplings, reproduces well the value measured in a short-channel thin-film transistor. The results underline that to secure efficient charge transport in lamellar arrangements of conjugated polymers: (i) the electronic couplings should present high average values and fast dynamics, and (ii) the energetic disorder (paracrystallinity) should be small. © 2013 American Chemical Society.

  16. Enhancing Charge Carrier Lifetime in Metal Oxide Photoelectrodes through Mild Hydrogen Treatment

    KAUST Repository

    Jang, Ji-Wook; Friedrich, Dennis; Mü ller, Sö nke; Lamers, Marlene; Hempel, Hannes; Lardhi, Sheikha F.; Cao, Zhen; Harb, Moussab; Cavallo, Luigi; Heller, René ; Eichberger, Rainer; van de Krol, Roel; Abdi, Fatwa F.

    2017-01-01

    and are relatively cheap, are particularly interesting, but high efficiency is still hindered by the poor carrier transport properties (i.e., carrier mobility and lifetime). Here, a mild hydrogen treatment is introduced to bismuth vanadate (BiVO4), which is one

  17. Solvation in supercritical water

    International Nuclear Information System (INIS)

    Cochran, H.D.; Cummings, P.T.; Karaborni, S.

    1991-01-01

    The aim of this work is to determine the solvation structure in supercritical water composed with that in ambient water and in simple supercritical solvents. Molecular dynamics studies have been undertaken of systems that model ionic sodium and chloride, atomic argon, and molecular methanol in supercritical aqueous solutions using the simple point charge model of Berendsen for water. Because of the strong interactions between water and ions, ionic solutes are strongly attractive in supercritical water, forming large clusters of water molecules around each ion. Methanol is found to be a weakly-attractive solute in supercritical water. The cluster of excess water molecules surrounding a dissolved ion or polar molecule in supercritical aqueous solutions is comparable to the solvent clusters surrounding attractive solutes in simple supercritical fluids. Likewise, the deficit of water molecules surrounding a dissolved argon atom in supercritical aqueous solutions is comparable to that surrounding repulsive solutes in simple supercritical fluids. The number of hydrogen bonds per water molecule in supercritical water was found to be about one third the number in ambient water. The number of hydrogen bonds per water molecule surrounding a central particle in supercritical water was only mildly affected by the identify of the central particle--atom, molecule, or ion. These results should be helpful in developing a qualitative understanding of important processes that occur in supercritical water. 29 refs., 6 figs

  18. Enhancing Charge Carrier Lifetime in Metal Oxide Photoelectrodes through Mild Hydrogen Treatment

    KAUST Repository

    Jang, Ji-Wook

    2017-08-25

    Widespread application of solar water splitting for energy conversion is largely dependent on the progress in developing not only efficient but also cheap and scalable photoelectrodes. Metal oxides, which can be deposited with scalable techniques and are relatively cheap, are particularly interesting, but high efficiency is still hindered by the poor carrier transport properties (i.e., carrier mobility and lifetime). Here, a mild hydrogen treatment is introduced to bismuth vanadate (BiVO4), which is one of the most promising metal oxide photoelectrodes, as a method to overcome the carrier transport limitations. Time-resolved microwave and terahertz conductivity measurements reveal more than twofold enhancement of the carrier lifetime for the hydrogen-treated BiVO4, without significantly affecting the carrier mobility. This is in contrast to the case of tungsten-doped BiVO4, although hydrogen is also a donor type dopant in BiVO4. The enhancement in carrier lifetime is found to be caused by significant reduction of trap-assisted recombination, either via passivation or reduction of deep trap states related to vanadium antisite on bismuth or vanadium interstitials according to density functional theory calculations. Overall, these findings provide further insights on the interplay between defect modulation and carrier transport in metal oxides, which benefit the development of low-cost, highly-efficient solar energy conversion devices.

  19. Study of the Bulk Charge Carrier Dynamics in Anatase and Rutile TiO2 Single Crystals by Femtosecond Time Resolved Spectroscopy

    KAUST Repository

    Maity, Partha; Mohammed, Omar F.; Katsiev, Khabiboulakh; Idriss, Hicham

    2018-01-01

    as the best model for fundamental studies. Their ultrafast charge carrier dynamics especially on TiO2 anatase single crystal (the most active phase) are unresolved. Here femtosecond time resolved spectroscopy (TRS) was carried out to explore the dynamics

  20. Change in carrier type in high-k gate carbon nanotube field-effect transistors by interface fixed charges

    International Nuclear Information System (INIS)

    Moriyama, N; Ohno, Y; Kitamura, T; Kishimoto, S; Mizutani, T

    2010-01-01

    We study the phenomenon of change in carrier type in carbon nanotube field-effect transistors (CNFETs) caused by the atomic layer deposition (ALD) of a HfO 2 gate insulator. When a HfO 2 layer is deposited on a CNFET, the type of carrier changes from p-type to n-type. The so-obtained n-type device has good performance and stability in air. The conductivity of such a device with a channel length of 0.7 μm is 11% of the quantum conductance 4e 2 /h. The contact resistance for electron current is estimated to be 14 kΩ. The n-type conduction of this CNFET is maintained for more than 100 days. The change in carrier type is attributed to positive fixed charges introduced at the interface between the HfO 2 and SiO 2 layers. We also propose a novel technique to control the type of conduction by utilizing interface fixed charges; this technique is compatible with Si CMOS process technology.

  1. Multi-THz spectroscopy of mobile charge carriers in P3HT:PCBM on a sub-100 fs time scale

    DEFF Research Database (Denmark)

    Cooke, David G.; Krebs, Frederik C; Jepsen, Peter Uhd

    2013-01-01

    The dynamics of mobile charge carrier generation in polymer bulk heterojunction films is of vital importance to the development of more efficient organic photovoltaics. As with conventional semiconductors, the optical signatures of mobile carriers lie in the far-infrared (1-30 THz) although...

  2. Modeling charge collection efficiency degradation in partially depleted GaAs photodiodes using the 1- and 2-carrier Hecht equations

    International Nuclear Information System (INIS)

    Auden, E.C.; Vizkelethy, G.; Serkland, D.K.; Bossert, D.J.; Doyle, B.L.

    2017-01-01

    The Hecht equation can be used to model the nonlinear degradation of charge collection efficiency (CCE) in response to radiation-induced displacement damage in both fully and partially depleted GaAs photodiodes. CCE degradation is measured for laser-generated photocurrent as a function of fluence and bias in Al_0_._3Ga_0_._7As/GaAs/Al_0_._2_5Ga_0_._7_5As p-i-n photodiodes which have been irradiated with 12 MeV C and 7.5 MeV Si ions. CCE is observed to degrade more rapidly with fluence in partially depleted photodiodes than in fully depleted photodiodes. When the intrinsic GaAs layer is fully depleted, the 2-carrier Hecht equation describes CCE degradation as photogenerated electrons and holes recombine at defect sites created by radiation damage in the depletion region. If the GaAs layer is partially depleted, CCE degradation is more appropriately modeled as the sum of the 2-carrier Hecht equation applied to electrons and holes generated within the depletion region and the 1-carrier Hecht equation applied to minority carriers that diffuse from the field-free (non-depleted) region into the depletion region. Enhanced CCE degradation is attributed to holes that recombine within the field-free region of the partially depleted intrinsic GaAs layer before they can diffuse into the depletion region.

  3. Modeling charge collection efficiency degradation in partially depleted GaAs photodiodes using the 1- and 2-carrier Hecht equations

    Energy Technology Data Exchange (ETDEWEB)

    Auden, E.C., E-mail: eauden@sandia.gov; Vizkelethy, G.; Serkland, D.K.; Bossert, D.J.; Doyle, B.L.

    2017-05-15

    The Hecht equation can be used to model the nonlinear degradation of charge collection efficiency (CCE) in response to radiation-induced displacement damage in both fully and partially depleted GaAs photodiodes. CCE degradation is measured for laser-generated photocurrent as a function of fluence and bias in Al{sub 0.3}Ga{sub 0.7}As/GaAs/Al{sub 0.25}Ga{sub 0.75}As p-i-n photodiodes which have been irradiated with 12 MeV C and 7.5 MeV Si ions. CCE is observed to degrade more rapidly with fluence in partially depleted photodiodes than in fully depleted photodiodes. When the intrinsic GaAs layer is fully depleted, the 2-carrier Hecht equation describes CCE degradation as photogenerated electrons and holes recombine at defect sites created by radiation damage in the depletion region. If the GaAs layer is partially depleted, CCE degradation is more appropriately modeled as the sum of the 2-carrier Hecht equation applied to electrons and holes generated within the depletion region and the 1-carrier Hecht equation applied to minority carriers that diffuse from the field-free (non-depleted) region into the depletion region. Enhanced CCE degradation is attributed to holes that recombine within the field-free region of the partially depleted intrinsic GaAs layer before they can diffuse into the depletion region.

  4. Biomolecular electrostatics and solvation: a computational perspective.

    Science.gov (United States)

    Ren, Pengyu; Chun, Jaehun; Thomas, Dennis G; Schnieders, Michael J; Marucho, Marcelo; Zhang, Jiajing; Baker, Nathan A

    2012-11-01

    An understanding of molecular interactions is essential for insight into biological systems at the molecular scale. Among the various components of molecular interactions, electrostatics are of special importance because of their long-range nature and their influence on polar or charged molecules, including water, aqueous ions, proteins, nucleic acids, carbohydrates, and membrane lipids. In particular, robust models of electrostatic interactions are essential for understanding the solvation properties of biomolecules and the effects of solvation upon biomolecular folding, binding, enzyme catalysis, and dynamics. Electrostatics, therefore, are of central importance to understanding biomolecular structure and modeling interactions within and among biological molecules. This review discusses the solvation of biomolecules with a computational biophysics view toward describing the phenomenon. While our main focus lies on the computational aspect of the models, we provide an overview of the basic elements of biomolecular solvation (e.g. solvent structure, polarization, ion binding, and non-polar behavior) in order to provide a background to understand the different types of solvation models.

  5. Dependence of the carrier mobility and trapped charge limited conduction on silver nanoparticles embedment in doped polypyrrole nanostructures

    Science.gov (United States)

    Biswas, Swarup; Dutta, Bula; Bhattacharya, Subhratanu

    2013-10-01

    The present article demonstrates an intensive study upon the temperature dependent current density (J)-voltage (V) characteristics of moderately doped polypyrrole nanostructure and its silver nanoparticles incorporated nanocomposites. Analysis of the measured J-V characteristics of different synthesized nano-structured samples within a wide temperature range revealed that the electrical conduction behavior followed a trapped charge-limited conduction and a transition of charge transport mechanism from deep exponential trap limited conduction to shallow traps limited conduction had been occurred due to the incorporation of silver nanoparticles within the polypyrrole matrix. A direct evaluation of carrier mobility as a function of electric field and temperature from the measured J-V characteristics illustrates that the incorporation of silver nanoparticles within the polypyrrole matrix enhances the carrier mobility at a large extent by reducing the concentration of traps within the polypyrrole matrix. The calculated mobility is consistent with the Poole-Frenkel form for the electrical field up to a certain temperature range. The nonlinear low temperature dependency of mobility of all the nanostructured samples was explained by Mott variable range hopping conduction mechanisms. Quantitative information regarding the charge transport parameters obtained from the above study would help to extend optimization strategies for the fabrication of new organic semiconducting nano-structured devices.

  6. Effects of carrier concentrations on the charge transport properties in monolayer silicene

    International Nuclear Information System (INIS)

    Abidin, B I; Yeoh, K H; Yong, T K; Ong, D S

    2017-01-01

    Using analytical band Monte Carlo approach, we have carried out a systematic study on the effects of carrier concentrations on the steady-state and transient electron transports that occur within a monolayer silicene. In particular, we have observed the following: First at steady-state, the electron mobility reduces with higher carrier concentrations. Secondly, in the transient regime we found that the drift velocity overshoot can be controlled by varying the carrier concentrations. We uncover that at carrier concentration of 1  ×  10 13 cm −2 , the drift velocity overshoot can reach up to 3.8  ×  10 7 cm s −1 which is close to the steady-state drift velocity saturation of graphene. Thirdly, the distance of the velocity over shoot can be further extended with higher carrier concentrations. Our findings could be useful and can be used as benchmark for future development of nanoscale silicene based devices. (paper)

  7. Generation of reactive oxygen species and charge carriers in plasmonic photocatalytic Au@TiO2 nanostructures with enhanced activity.

    Science.gov (United States)

    He, Weiwei; Cai, Junhui; Jiang, Xiumei; Yin, Jun-Jie; Meng, Qingbo

    2018-06-13

    The combination of semiconductor and plasmonic nanostructures, endowed with high efficiency light harvesting and surface plasmon confinement, has been a promising way for efficient utilization of solar energy. Although the surface plasmon resonance (SPR) assisted photocatalysis has been extensively studied, the photochemical mechanism, e.g. the effect of SPR on the generation of reactive oxygen species and charge carriers, is not well understood. In this study, we take Au@TiO2 nanostructures as a plasmonic photocatalyst to address this critical issue. The Au@TiO2 core/shell nanostructures with tunable SPR property were synthesized by the templating method with post annealing thermal treatment. It was found that Au@TiO2 nanostructures exhibit enhanced photocatalytic activity in either sunlight or visible light (λ > 420 nm). Electron spin resonance spectroscopy with spin trapping and spin labeling was used to investigate the enhancing effect of Au@TiO2 on the photo-induced reactive oxygen species and charge carriers. The formation of Au@TiO2 core/shell nanostructures resulted in a dramatic increase in light-induced generation of hydroxyl radicals, singlet oxygen, holes and electrons, as compared with TiO2 alone. This enhancement under visible light (λ > 420 nm) irradiation may be dominated by SPR induced local electrical field enhancement, while the enhancement under sunlight irradiation is dominated by the higher electron transfer from TiO2 to Au. These results unveiled that the superior photocatalytic activity of Au@TiO2 nanostructures correlates with enhanced generation of reactive oxygen species and charge carriers.

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

    Energy Technology Data Exchange (ETDEWEB)

    Lim, Eunju, E-mail: elim@dankook.ac.kr, E-mail: taguchi.d.aa@m.titech.ac.jp, E-mail: iwamoto@pe.titech.ac.jp [Department of Applied Physics, Institute of Nanosensor and Biotechnology, Dankook University, Jukjeon-dong, Gyeonggi-do 448-701 (Korea, Republic of); Taguchi, Dai, E-mail: elim@dankook.ac.kr, E-mail: taguchi.d.aa@m.titech.ac.jp, E-mail: iwamoto@pe.titech.ac.jp; Iwamoto, Mitsumasa, E-mail: elim@dankook.ac.kr, E-mail: taguchi.d.aa@m.titech.ac.jp, E-mail: iwamoto@pe.titech.ac.jp [Department of Physical Electronics, Tokyo Institute of Technology 2-12-1, O-okayama, Meguro-ku, Tokyo 152-8552 (Japan)

    2014-08-18

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

  9. The quantic distribution of mobile carriers in a surface charge coupled device

    International Nuclear Information System (INIS)

    Ionescu, M.

    1977-01-01

    The quantic distribution of the electrons in a surface charge coupled device (CCD), for a MIS structure with a real insulator (finite difference energy between the conduction bands of the insulator and of the semiconductor) is presented. A fundamental limitation of the charge transfer in a surface CCD is obtained. (author)

  10. Charge carrier mobility in poly[methyl(phenyl)silylene] studied by time-resolved terahertz spectroscopy and molecular modeling

    Czech Academy of Sciences Publication Activity Database

    Němec, Hynek; Kratochvílová, Irena; Kužel, Petr; Šebera, Jakub; Kochalska, Anna; Nožár, Juraj; Nešpůrek, Stanislav

    2011-01-01

    Roč. 13, č. 7 (2011), s. 2850-2856 ISSN 1463-9076 R&D Projects: GA ČR(CZ) GP202/09/P099; GA ČR GA203/08/1594; GA AV ČR KAN401770651; GA MŠk LC512; GA ČR(CZ) GAP304/10/1951 Institutional research plan: CEZ:AV0Z10100520; CEZ:AV0Z40500505 Keywords : molecular electronics * THz spectroscopy * charge carrier mobility Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 3.573, year: 2011

  11. Two-frequency method for measuring Hall emf in high-resistive materials with charge-carrier low mobility

    International Nuclear Information System (INIS)

    Aleksandrov, A.L.; Vedeneev, A.S.; Gulyaev, I.B.; Zhdan, A.G.

    1982-01-01

    A facility for measuring Hall emf in high-resistive materials with low mobility of charge carriers by the two-frequency method using digital synchronous integration is described. The facility permits to detect the minimum Hall emf approxamatety equat to 5 μV at approximatety equal to 1 T Ohm of the investigated.sample resistance during the measuring time of approximately equal to 2000 s. Sensitivity by Hall mobility makes up >= 0.01 cm 2 /Vxs at the same measuring time. Measuring results of the Hall emf on GaAs monocrystals, CdSe films and island film of gold are presented

  12. Probing surface states in PbS nanocrystal films using pentacene field effect transistors: controlling carrier concentration and charge transport in pentacene.

    Science.gov (United States)

    Park, Byoungnam; Whitham, Kevin; Bian, Kaifu; Lim, Yee-Fun; Hanrath, Tobias

    2014-12-21

    We used a bilayer field effect transistor (FET) consisting of a thin PbS nanocrystals (NCs) film interfaced with vacuum-deposited pentacene to probe trap states in NCs. We interpret the observed threshold voltage shift in context of charge carrier trapping by PbS NCs and relate the magnitude of the threshold voltage shift to the number of trapped carriers. We explored a series of NC surface ligands to modify the interface between PbS NCs and pentacene and demonstrate the impact of interface chemistry on charge carrier density and the FET mobility in a pentacene FET.

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

    Energy Technology Data Exchange (ETDEWEB)

    Vukmirovic, Nenad; Wang, Lin-Wang

    2009-11-10

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

  14. Chemical vapour deposition diamond. Charge carrier movement at low temperatures and use in time-critical applications

    International Nuclear Information System (INIS)

    Jansen, Hendrik

    2013-09-01

    Diamond, a wide band gap semiconductor with exceptional electrical properties, has found its way in diverse fields of application reaching from the usage as a sensor material for beam loss monitors at particle accelerator facilities, over laser windows, to UV light sensors in space applications, e.g. for space weather forecasting. Though often used at room temperature, little is known about the charge transport in diamond towards liquid helium temperatures. In this work the method of the transient current technique is employed at temperatures between room temperature and 2 K. The temperature and electric field strength dependence of the pulse shape, the charge carrier transit time, the drift velocity, the saturation velocity, and the low-field mobility is measured in detector-grade scCVD diamond. Furthermore, the usability of diamond in time-critical applications is tested, and the main results are presented.

  15. Nanocrystals in the glass and centers of localization of free charge carriers in the thick-film resistors

    International Nuclear Information System (INIS)

    Abdurakhmanov, G.

    2012-01-01

    Conduction mechanism of doped silicate glass (DSG) based on existence of nanocrystals in the glass is proposed. These nanocrystals act as localization centers of free charge carriers. Random distribution of the nanocrystal's sizes and distances between them leads to charge transport by variable length hopping. It is shown that dopant atoms generate the narrow impurity subband of 0.03 eV in width. This subband joins close to the glass valence band top or slightly (less than 0.01 eV) separated from the last. What is why the hopping mechanism coexists with thermal activation one and at low temperatures (T -n ), 0.25 800 K) structure transitions of nanocrystals take place and conductivity of DSG decreases sharply. Beyond of the minimum of conductivity (above 1000 K) energy gap is formed between the impurity subband and the valence band top of glass, so DSG behaves like a typical semiconductor. (author)

  16. Chemical Vapour Deposition Diamond - Charge Carrier Movement at Low Temperatures and Use in Time-Critical Applications

    CERN Document Server

    Jansen, Hendrik; Pernegger, Heinz

    Diamond, a wide band gap semiconductor with exceptional electrical properties, has found its way in diverse fields of application reaching from the usage as a sensor material for beam loss monitors at particle accelerator facilities, to laser windows, to UV light sensors in space applications, e.g. for space weather forecasting. Though often used at room temperature, little is known about the charge transport in diamond towards liquid helium temperatures. In this work the method of the transient current technique is employed at temperatures between room temperature and 2 K. The temperature and electric field strength dependence of the pulse shape, the charge carrier transit time, the drift velocity, the saturation velocity, and the low-field mobility is measured in detector-grade scCVD diamond. Furthermore, the usability of diamond in time-critical applications is tested, and the main results are presented.

  17. Charge transport in organic transistors accounting for a wide distribution of carrier energies, Part I : Theory

    NARCIS (Netherlands)

    Torricelli, F.

    2012-01-01

    An extended theory of carrier hopping transport in organic transistors is proposed. According to many experimental studies, the density of localized states in organic thin-film transistors can be described by a double-exponential function. In this work, using a percolation model of hopping, the

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

    Science.gov (United States)

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

    2016-04-28

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

  19. Impact of charge carrier injection on single-chain photophysics of conjugated polymers

    Energy Technology Data Exchange (ETDEWEB)

    Hofmann, Felix J.; Vogelsang, Jan, E-mail: jan.vogelsang@physik.uni-regensburg.de; Lupton, John M. [Institut für Experimentelle und Angewandte Physik, Universität Regensburg, Universitätsstrasse 31, 93053 Regensburg (Germany)

    2016-06-27

    Charges in conjugated polymer materials have a strong impact on the photophysics and their interaction with the primary excited state species has to be taken into account in understanding device properties. Here, we employ single-molecule spectroscopy to unravel the influence of charges on several photoluminescence (PL) observables. The charges are injected either stochastically by a photochemical process or deterministically in a hole-injection sandwich device configuration. We find that upon charge injection, besides a blue-shift of the PL emission and a shortening of the PL lifetime due to quenching and blocking of the lowest-energy chromophores, the non-classical photon arrival time distribution of the multichromophoric chain is modified towards a more classical distribution. Surprisingly, the fidelity of photon antibunching deteriorates upon charging, whereas one would actually expect the opposite: the number of chromophores to be reduced. A qualitative model is presented to explain the observed PL changes. The results are of interest to developing a microscopic understanding of the intrinsic charge-exciton quenching interaction in devices.

  20. Charge-carrier selective electrodes for organic bulk heterojunction solar cell by contact-printed siloxane oligomers

    International Nuclear Information System (INIS)

    Hwang, Hyun-Sik; Khang, Dahl-Young

    2015-01-01

    ‘Smart’ (or selective) electrode for charge carriers, both electrons and holes, in organic bulk-heterojunction (BHJ) solar cells using insertion layers made of hydrophobically-recovered and contact-printed siloxane oligomers between electrodes and active material has been demonstrated. The siloxane oligomer insertion layer has been formed at a given interface simply by conformally-contacting a cured slab of polydimethylsiloxane stamp for less than 100 s. All the devices, either siloxane oligomer printed at one interface only or printed at both interfaces, showed efficiency enhancement when compared to non-printed ones. The possible mechanism that is responsible for the observed efficiency enhancement has been discussed based on the point of optimum symmetry and photocurrent analysis. Besides its simplicity and large-area applicability, the demonstrated contact-printing technique does not involve any vacuum or wet processing steps and thus can be very useful for the roll-based, continuous production scheme for organic BHJ solar cells. - Highlights: • Carrier-selective insertion layer in organic bulk heterojunction solar cells • Simple contact-printing of siloxane oligomers improves cell efficiency. • Printed siloxane layer reduces carrier recombination at electrode surfaces. • Siloxane insertion layer works equally well at both electrode surfaces. • Patterned PDMS stamp shortens the printing time within 100 s

  1. Charge carrier dynamics in PMMA-LiClO4 based polymer electrolytes plasticized with different plasticizers

    Science.gov (United States)

    Pal, P.; Ghosh, A.

    2017-07-01

    We have studied the charge carrier dynamics in poly(methylmethacrylate)-LiClO4 polymer electrolytes plasticized with different plasticizers such as ethylene carbonate (EC), propylene carbonate (PC), polyethylene glycol (PEG), and dimethyl carbonate (DMC). We have measured the broadband complex conductivity spectra of these electrolytes in the frequency range of 0.01 Hz-3 GHz and in the temperature range of 203 K-363 K and analyzed the conductivity spectra in the framework of the random barrier model by taking into account the contribution of the electrode polarization observed at low frequencies and/or at high temperatures. It is observed that the temperature dependences of the ionic conductivity and relaxation time follow the Vogel-Tammann-Fulcher relation for all plasticized electrolytes. We have also performed the scaling of the conductivity spectra, which indicates that the charge carrier dynamics is almost independent of temperature and plasticizers in a limited frequency range. The existence of nearly constant loss in these electrolytes has been observed at low temperatures and/or high frequencies. We have studied the dielectric relaxation in these electrolytes using electric modulus formalism and obtained the stretched exponent and the decay function. We have observed less cooperative ion dynamics in electrolytes plasticized with DMC compared to electrolytes plasticized with EC, PC, and PEG.

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

    Science.gov (United States)

    Pal, P.; Ghosh, A.

    2016-07-01

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

  3. Effects of low charge carrier wave function overlap on internal quantum efficiency in GaInN quantum wells

    Energy Technology Data Exchange (ETDEWEB)

    Netzel, Carsten; Hoffmann, Veit; Wernicke, Tim; Knauer, Arne; Weyers, Markus [Ferdinand-Braun-Institut fuer Hoechstfrequenztechnik, Gustav-Kirchhoff-Strasse 4, 12489 Berlin (Germany); Kneissl, Michael [Ferdinand-Braun-Institut fuer Hoechstfrequenztechnik, Gustav-Kirchhoff-Strasse 4, 12489 Berlin (Germany); Institut fuer Festkoerperphysik, Technische Universitaet Berlin, Hardenbergstrasse 36, 10623 Berlin (Germany)

    2010-07-15

    To determine relevant processes affecting the internal quantum efficiency in GaInN quantum well structures, we have studied the temperature and excitation power dependent photoluminescence intensity for quantum wells with different well widths on (0001) c-plane GaN and for quantum wells on nonpolar (11-20) a-plane GaN. In thick polar quantum wells, the quantum confined Stark effect (QCSE) causes a stronger intensity decrease with increasing temperature as long as the radiative recombination dominates. At higher temperatures, when the nonradiative recombination becomes more important, thick polar quantum wells feature a lower relative intensity decrease than thinner polar or nonpolar quantum wells. Excitation power dependent photoluminescence points to a transition from a recombination of excitons to a bimolecular recombination of uncorrelated charge carriers for thick polar quantum wells in the same temperature range. This transition might contribute to the limitation of nonradiative recombination by a reduced diffusivity of charge carriers. (copyright 2010 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  4. Determination of energy band diagram and charge carrier mobility of white emitting polymer from optical, electrical and impedance spectroscopy

    Energy Technology Data Exchange (ETDEWEB)

    Mohd Sarjidan, M.A., E-mail: mohd.arif@um.edu.my; Mohd Mokhtar, H.A.; Abd Majid, W.H., E-mail: q3haliza@um.edu.my

    2015-03-15

    A single-layer white polymer light-emitting device (WPLED) has been fabricated using spin coating technique. The device was constructed as ITO/PEDOT:PSS(50 nm)/SPW-111(50 nm)/LiF(1 nm)/Al(100 nm). Indium tin oxide (ITO) and poly(3,4-ethylenedioxythiophene) Polystyrene sulfonate (PEDOT:PSS) are used as the transparent anode. SPW-111 is fabricated as a white emissive layer and lithium fluoride (LiF) and aluminum (Al) are used as reflecting cathode. Energy band diagram of the device was estimated from a combination of ultraviolet–visible (UV–vis) and current–voltage (J–V) analyses. Charge carrier mobility (μ) of PLED was evaluated using negative differential susceptance (−ΔB) method from impedance spectroscopy (IS) analysis. The calculated μ of the SPW-111 device is in the magnitude of 10{sup −6} cm{sup 2}/V/s. - Highlights: • Single layer PLED has been fabricated with spin-coating technique and device performance has been evaluated. • Energy band diagram of the SPW-111 is estimated from optical and electrical analyses. • Charge carrier mobility of the SPW-111 materials is obtained by impedance spectroscopy.

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

    Energy Technology Data Exchange (ETDEWEB)

    Pal, P.; Ghosh, A., E-mail: sspag@iacs.res.in [Department of Solid State Physics, Indian Association for the Cultivation of Science, Jadavpur, Kolkata 700032 (India)

    2016-07-28

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

  6. Experimental evidence for importance of Hund's exchange interaction for incoherence of charge carriers in iron-based superconductors

    Science.gov (United States)

    Fink, J.; Rienks, E. D. L.; Thirupathaiah, S.; Nayak, J.; van Roekeghem, A.; Biermann, S.; Wolf, T.; Adelmann, P.; Jeevan, H. S.; Gegenwart, P.; Wurmehl, S.; Felser, C.; Büchner, B.

    2017-04-01

    Angle-resolved photoemission spectroscopy is used to study the scattering rates of charge carriers from the hole pockets near Γ in the iron-based high-Tc hole-doped superconductors KxBa1 -xFe2As2 , x =0.4 , and KxEu1 -xFe2As2 , x =0.55 , and the electron-doped compound Ba (Fe1-xCox) 2As2 , x =0.075 . The scattering rate for any given band is found to depend linearly on the energy, indicating a non-Fermi-liquid regime. The scattering rates in the hole-doped compound are considerably higher than those in the electron-doped compounds. In the hole-doped systems the scattering rate of the charge carriers of the inner hole pocket is about three times higher than the binding energy, indicating that the spectral weight is heavily incoherent. The strength of the scattering rates and the difference between electron- and hole-doped compounds signals the importance of Hund's exchange coupling for correlation effects in these iron-based high-Tc superconductors. The experimental results are in qualitative agreement with theoretical calculations in the framework of combined density functional dynamical mean-field theory.

  7. Revealing charge carrier dynamics in squaraine:[6, 6]-phenyl-C 71-butyric acid methyl ester based organic solar cells

    Science.gov (United States)

    Rana, Aniket; Sharma, Chhavi; Prabhu, Deepak D.; Kumar, Mahesh; Karuvath, Yoosaf; Das, Suresh; Chand, Suresh; Singh, Rajiv K.

    2018-04-01

    Ultrafast charge carrier dynamics as well as the generation of polaron pair in squaraine (SQ) and squaraine:[6,6]-phenyl-C 71-butyric acid methyl ester (SQ:PCBM71) have been studied using ultrafast transient absorption spectroscopy (UTAS). The current study reveals that the pure SQ exhibits the creation of singlet and triplet states; however, incorporation of PCBM71 in SQ results in the formation of polaron pairs with ˜550ps lifetime, which in turn leads to the creation of free electrons in the device. We show that the considerable increment in monomolecular and bimolecular recombination in SQ:PCBM71 compared to pure SQ which describes the interfacial compatibility of SQ and PCBMC71 molecules. The present work not only provides the information about the carrier generation in SQ and SQ:PCBM71 but also gives the facts relating to the effect of PCBM71 mixing into the SQ which is very significant because the SQ has donor-acceptor-donor (D-A-D) structure and mixing one more acceptor can introduce more complex recombinations in the blend. These findings have been complimented by the charge transport study in the device using impedance spectroscopy. The various important transport parameters are transit time (τt), diffusion constant (Dn), global mobility (μ) and carrier lifetime (τr). The values of these parameters are 26.38 μs, 4.64x10-6 cm2s-1, 6.12x10-6 cm2V-1s-1 and 399 μs, respectively. To the best of our knowledge such study related to SQ is not present in the literature comprehensively.

  8. Picosecond charge transport in rutile at high carrier densities studiedby transient terahertz spectroscopy

    Czech Academy of Sciences Publication Activity Database

    Zajac, Vít; Němec, Hynek; Kužel, Petr

    2016-01-01

    Roč. 94, č. 11 (2016), 1-9, č. článku 115206. ISSN 1098-0121 R&D Projects: GA ČR GA13-12386S Institutional support: RVO:68378271 Keywords : terahertz spectroscopy * charge transport * TiO 2 * rutile * ultrafast spectroscopy Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 3.736, year: 2014

  9. Charge Carrier Dynamics and pH Effect on Optical Properties of Anionic and Cationic Porphyrin-Graphene Oxide Composites

    Science.gov (United States)

    Bajjou, O.; Bakour, A.; Khenfouch, M.; Baitoul, M.; Mothudi, B.; Maaza, M.; Faulques, E.

    2018-02-01

    Composites of graphene oxide (GO) functionalized with Sn(V) tetrakis (4-pyridyl)porphyrin (SnTPyP2+) and meso-tetrakis(4-phenylsulfonic acid)porphyrin (H4TPPS4 2- ) were prepared at different pH values.Successful synthesis of water-soluble stable suspension of GO-SnTPyP2+ and GO-H4TPPS4 2-was confirmed using various spectroscopic techniques, including scanning electronic microscopy (SEM), Raman spectroscopy, and ultraviolet-visible (UV-Vis) absorption. Variation of the pH was found to strongly influence the optical properties of the GO-SnTPyP2+ and GO-H4TPPS4 2-composites, as demonstrated by the UV-Vis absorption results. Steady-state photoluminescence (PL) and time-resolved PL (TRPL) results for both composites showed PL quenching and decrease in the exciton mean lifetime, suggesting strong excited-state interactions between the different components. Moreover, charge carrier dynamics study revealed that insertion of GO into both porphyrin derivatives led to faster mean lifetime for excitons with a slight advantage in the case of the cationic porphyrin-GO composite, making it a better choice for charge separation applications thanks to the higher efficiency of charge/energy transfer interactions.

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

    Science.gov (United States)

    Sun, Baichuan; Barnard, Amanda S

    2016-08-07

    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.

  11. Feature of polaronic charge carriers in polysilanes: Experimental and theoretical approach

    Czech Academy of Sciences Publication Activity Database

    Nešpůrek, Stanislav; Kochalska, Anna; Nožár, Juraj; Kadashchuk, A.; Fishchuk, I. I.; Sworakowski, J.; Kajzar, F.

    2010-01-01

    Roč. 521, - (2010), s. 72-83 ISSN 1542-1406. [International Conference on Frontiers of Polymers and Advanced Materials /10./. Santiago, 27.09.2009-02.10.2009] R&D Projects: GA AV ČR IAA100100622; GA AV ČR KAN400720701 Institutional research plan: CEZ:AV0Z40500505 Keywords : binding energy * charge mobility * hopping transport Subject RIV: CD - Macromolecular Chemistry Impact factor: 0.543, year: 2010

  12. Charge Carrier Dynamics of Methylammonium Lead-Iodide Perovskite Solar Cells

    OpenAIRE

    Neukom, Martin Thomas

    2016-01-01

    Transient opto-electrical measurements of methylammonium lead iodide (MALI) perovskite solar cells (PSCs) are performed and analyzed in order to elucidate the operating mechanisms. The current response to a light pulse or voltage pulse shows an extraordinarily broad dynamic range covering 9 orders of magnitude in time - from microseconds to minutes - until steady-state is reached. Evidence of a slowly changing charge density at the perovskite layer boundaries is found, which is most probably ...

  13. Understanding charge carrier relaxation processes in terbium arsenide nanoparticles using transient absorption spectroscopy

    Science.gov (United States)

    Vanderhoef, Laura R.

    Erbium arsenide nanoparticles epitaxially grown within III-V semiconductors have been shown to improve the performance of devices for applications ranging from thermoelectrics to THz pulse generation. The small size of rare-earth nanoparticles suggests that interesting electronic properties might emerge as a result of both spatial confinement and surface states. However, ErAs nanoparticles do not exhibit any signs of quantum confinement or an emergent bandgap, and these experimental observations are understood from theory. The incorporation of other rare-earth monopnictide nanoparticles into III-V hosts is a likely path to engineering carrier excitation, relaxation and transport dynamics for optoelectronic device applications. However, the electronic structure of these other rare-earth monopnictide nanoparticles remains poorly understood. The objective of this research is to explore the electronic structure and optical properties of III-V materials containing novel rare-earth monopnictides. We use ultrafast pump-probe spectroscopy to investigate the electronic structure of TbAs nanoparticles in III-V hosts. We start with TbAs:GaAs, which was expected to be similar to ErAs:GaAs. We study the dynamics of carrier relaxation into the TbAs states using optical pump terahertz probe transient absorption spectroscopy. By analyzing how the carrier relaxation rates depend on pump fluence and sample temperature, we conclude that the TbAs states are saturable. Saturable traps suggest the existence of a bandgap for TbAs nanoparticles, in sharp contrast with previous results for ErAs. We then apply the same experimental technique to two samples of TbAs nanoparticles in InGaAs with different concentrations of TbAs. We observe similar relaxation dynamics associated with trap saturation, though the ability to resolve these processes is contingent upon a high enough TbAs concentration in the sample. We have also constructed an optical pump optical probe transient absorption

  14. In-situ analysis of microwave conductivity and impedance spectroscopy for evaluation of charge carrier dynamics at interfaces

    Science.gov (United States)

    Choi, Wookjin; Inoue, Junichi; Tsutsui, Yusuke; Sakurai, Tsuneaki; Seki, Shu

    2017-11-01

    A unique concerted analysis comprising non-contact microwave conductivity measurements and impedance spectroscopy was developed to simultaneously assess the charge carrier mobility and injection barriers. The frequency dependence of the microwave conductivity as well as the electrical current was analyzed by applying sinusoidal voltage to determine the equivalent circuit parameters. Based on the temperature dependence of the circuit parameters, the energy of the injection barrier was estimated to be 0.4 eV with the Richardson-Schottky model, and the band-like transport was confirmed with the negative temperature coefficient with the β value of 1.4 in the intra-layer conduction of C8-BTBT. In contrast, the increase in the resistance of the C8-BTBT layer with decreasing temperature implied the occurrence of hopping-like transport in the inter-layer conduction of C8-BTBT.

  15. High charge carrier density at the NaTaO3/SrTiO3 hetero-interface

    KAUST Repository

    Nazir, Safdar

    2011-08-05

    The formation of a (quasi) two-dimensional electron gas between the band insulators NaTaO3 and SrTiO3 is studied by means of the full-potential linearized augmented plane-wave method of density functional theory. Optimization of the atomic positions points to only small changes in the chemical bonding at the interface. Both the p-type (NaO)−/(TiO2)0 and n-type (TaO2)+/(SrO)0 interfaces are found to be metallic with high charge carrier densities. The effects of O vacancies are discussed. Spin-polarized calculations point to the formation of isolated O 2pmagnetic moments, located in the metallic region of the p-type interface.

  16. Magnetic dipole self-organization of charge carriers in high-temperature superconductors and kinetics of phase transformation

    CERN Document Server

    Voronov, A V; Shuvalov, V V

    2001-01-01

    The phenomenological model, describing the magnetic dipole self-organization of charge carriers (formation of so-called stripe-structures and energy gap in the states spectrum), is designed for interpreting the data on the nonstationary nonlinear spectroscopy of the high-temperature superconductors. It is shown that after fast heating of the superconducting sample the kinetics of the subsequent phase transition depends on the initial temperature T. The destruction of the stripe-structures at low overheating T* < T < T sub m approx = (1.4-1.5)T*, whereby T sub c and T* approx = T sub c are the temperatures of transition into the superconducting state and formation of the stripe-structures occurs slowly (the times above 10 sup - sup 9 s) in spite of practically instantaneous disappearance of the superconductivity

  17. Effect of dye-doped concentration on the charge carrier recombination in molecularly doped organic light-emitting devices

    Energy Technology Data Exchange (ETDEWEB)

    Chen Jiangshan; Ma Dongge [State Key Laboratory of Polymer Physics and Chemistry, Changchun Institute of Applied Chemistry, Graduate School of the Chinese Academy of Sciences, Changchun 130022 (China)

    2006-05-21

    The effect of the concentration of 4-(dicyanomethylene)-2-t-butyl-6- (1, 1, 7, 7-tetramethyljulolidyl-9-enyl)-4H-pyran (DCJTB) as dopant in tris(8-hydroxyquinoline) aluminium (Alq{sub 3}) on the charge carrier recombination was studied by transient electroluminescence (EL). The electron-hole recombination coefficient ({gamma}) was determined from the long-time component of the temporal decay of the EL intensity after a rectangular voltage pulse was turned off. It was found that the coefficient monotonically decreased with an increase in the DCJTB-doping concentration. The monotonic decrease is attributed to concentration quenching on the excitons and coincided well with the reduction of the EL efficiency.

  18. Study of the Bulk Charge Carrier Dynamics in Anatase and Rutile TiO2 Single Crystals by Femtosecond Time Resolved Spectroscopy

    KAUST Repository

    Maity, Partha

    2018-04-02

    Understanding of the fundamentals behind charge carriers of photo-catalytic materials are still illusive hindering progress in our quest for renewable energy. TiO2 anatase and rutile are the most understood phases in photo-catalysis and serve as the best model for fundamental studies. Their ultrafast charge carrier dynamics especially on TiO2 anatase single crystal (the most active phase) are unresolved. Here femtosecond time resolved spectroscopy (TRS) was carried out to explore the dynamics of photo-excited charge carriers’ recombination in anatase single crystal, for the first time using pump fluence effects, and compares it to that of the rutile single crystal. A significant difference in charge carrier recombination rates between both crystals is observed. We found that the time constants for carrier recombination are two orders of magnitude slower for anatase (101) when compared to those of rutile (110). Moreover, bulk defects introduced by reduction of the samples via annealing in ultra-high vacuum resulted in faster recombination rates for both polymorphs. Both states (fresh and reduced) probed by pump fluence dependence measurements revealed that the major recombination channel in fresh and reduced anatase and reduced rutile is the first-order Shockley–Reed mediated. However, for fresh rutile, third-body Auger recombination was observed, attributed to the presence of higher density of intrinsic charge carriers. At all excitation wavelengths and fluence investigated, anatase (101) single crystal show longer charge carrier lifetime when compared to rutile (110) single. This may explain the superiority of the anatase phase for the electron transfer H+ reduction to molecular hydrogen.

  19. Determination of charge carrier mobility of hole transporting polytriarylamine-based diodes

    International Nuclear Information System (INIS)

    Barea, Eva M.; Garcia-Belmonte, Germa; Sommer, Michael; Huettner, Sven; Bolink, Henk J.; Thelakkat, Mukundan

    2010-01-01

    Hole transport properties of three different side chain poly(triarylamines) have been determined by means of the analysis of steady-state current-voltage characteristics using co-planar diode structures. The interpretation is based on space-charge limited models with field-dependent mobility. Mobilities between ∼ 10 -8 and 10 -6 cm 2 V -1 s -1 are obtained. The highest mobility is achieved for poly(tetraphenylbenzidine) devices and the lowest for poly(triphenylamine) devices. Electron-rich methoxy substituents increase the mobility of poly(triphenylamine)s. A comparison of the mobility values with those obtained using organic field-effect transistors is also given.

  20. Charge carrier dynamics investigation of CuInS{sub 2} quantum dots films using injected charge extraction by linearly increasing voltage (i-CELIV): the role of ZnS Shell

    Energy Technology Data Exchange (ETDEWEB)

    Bi, Ke; Sui, Ning; Zhang, Liquan; Wang, Yinghui, E-mail: yinghui-wang@outlook.com; Liu, Qinghui, E-mail: liuqinghui@jlu.edu.cn; Tan, Mingrui [Jilin University, Femtosecond Laser Laboratory, Key Laboratory of Physics and Technology for Advanced Batteries (Ministry of Education), College of Physics (China); Zhou, Qiang [Jilin University, Key Laboratory of Superhard Materials, College of Physics (China); Zhang, Hanzhuang, E-mail: zhanghz@jlu.edu.cn [Jilin University, Femtosecond Laser Laboratory, Key Laboratory of Physics and Technology for Advanced Batteries (Ministry of Education), College of Physics (China)

    2016-12-15

    The role of ZnS shell on the photo-physical properties within CuInS{sub 2}/ZnS quantum dots (QDs) is carefully studied in optoelectronic devices. Linearly increasing voltage technique has been employed to investigate the charge carrier dynamics of both CuInS{sub 2} and CuInS{sub 2}/ZnS QDs films. This study shows that charge carriers follow a similar behavior of monomolecular recombination in this film, with their charge transfer rate correlates to the increase of applied voltage. It turns out that the ZnS shell could affect the carrier diffusion process through depressing the trapping states and would build up a potential barrier.

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

    Science.gov (United States)

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

    2016-09-01

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

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

    Science.gov (United States)

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

    2016-02-01

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

  3. Interplay Between Side Chain Pattern, Polymer Aggregation, and Charge Carrier Dynamics in PBDTTPD:PCBM Bulk-Heterojunction Solar Cells

    KAUST Repository

    Dyer-Smith, Clare

    2015-05-01

    Poly(benzo[1,2-b:4,5-b′]dithiophene–alt–thieno[3,4-c]pyrrole-4,6-dione) (PBDTTPD) polymer donors with linear side-chains yield bulk-heterojunction (BHJ) solar cell power conversion efficiencies (PCEs) of about 4% with phenyl-C71-butyric acid methyl ester (PC71BM) as the acceptor, while a PBDTTPD polymer with a combination of branched and linear substituents yields a doubling of the PCE to 8%. Using transient optical spectroscopy it is shown that while the exciton dissociation and ultrafast charge generation steps are not strongly affected by the side chain modifications, the polymer with branched side chains exhibits a decreased rate of nongeminate recombination and a lower fraction of sub-nanosecond geminate recombination. In turn the yield of long-lived charge carriers increases, resulting in a 33% increase in short circuit current (J sc). In parallel, the two polymers show distinct grazing incidence X-ray scattering spectra indicative of the presence of stacks with different orientation patterns in optimized thin-film BHJ devices. Independent of the packing pattern the spectroscopic data also reveals the existence of polymer aggregates in the pristine polymer films as well as in both blends which trap excitons and hinder their dissociation.

  4. Kinetic Monte Carlo Modeling of Charge Carriers in Organic Electronic Devices: Suppression of the Self-Interaction Error

    KAUST Repository

    Li, Haoyuan

    2017-05-18

    Kinetic Monte Carlo (KMC) simulations have emerged as an important tool to help improve the efficiency of organic electronic devices by providing a better understanding of their device physics. In the KMC simulation of an organic device, the reliability of the results depends critically on the accuracy of the chosen charge-transfer rates, which are themselves strongly influenced by the site-energy differences. These site-energy differences include components coming from the electrostatic forces present in the system, which are often evaluated through electric potentials described by the Poisson equation. Here we show that the charge-carrier self-interaction errors that appear when evaluating the site-energy differences can lead to unreliable simulation results. To eliminate these errors, we propose two approaches that are also found to reduce the impact of finite-size effects. As a consequence, reliable results can be obtained at reduced computational costs. The proposed methodologies can be extended to other device simulation techniques as well.

  5. Determination of charge carrier mobility of hole transporting polytriarylamine-based diodes

    Energy Technology Data Exchange (ETDEWEB)

    Barea, Eva M. [Photovoltaic and Optoelectronic Devices Group, Departament de Fisica, Universitat Jaume I, 12071 Castello (Spain); Garcia-Belmonte, Germa, E-mail: garciag@uji.e [Photovoltaic and Optoelectronic Devices Group, Departament de Fisica, Universitat Jaume I, 12071 Castello (Spain); Sommer, Michael; Huettner, Sven [Applied Functional Polymers, Universitaet Bayreuth, 95440 Bayreuth (Germany); Bolink, Henk J. [Molecular Science Institute-Universitat de Valencia, Poligon La Coma s/n, 46980 Paterna, Valencia (Spain); Thelakkat, Mukundan, E-mail: mukundan.thelakkat@uni-bayreuth.d [Applied Functional Polymers, Universitaet Bayreuth, 95440 Bayreuth (Germany)

    2010-04-02

    Hole transport properties of three different side chain poly(triarylamines) have been determined by means of the analysis of steady-state current-voltage characteristics using co-planar diode structures. The interpretation is based on space-charge limited models with field-dependent mobility. Mobilities between {approx} 10{sup -8} and 10{sup -6} cm{sup 2} V{sup -1} s{sup -1} are obtained. The highest mobility is achieved for poly(tetraphenylbenzidine) devices and the lowest for poly(triphenylamine) devices. Electron-rich methoxy substituents increase the mobility of poly(triphenylamine)s. A comparison of the mobility values with those obtained using organic field-effect transistors is also given.

  6. Effect of trapping of charge carriers on the resolution of Ge(Li) detectors

    International Nuclear Information System (INIS)

    Venturini, Luzia

    1979-01-01

    In this work a measurement is described of the variation of the resolution of a Ge(Li) detector as a function of the position of irradiation of a collimated gamma-ray beam. Also the variation of the resolution has been measured as a function of the applied detector voltage, using a collimated and a non-collimated gamma-ray beam. The measurement indicate that in the process of charge collection loss of holes predominates and the best resolution is obtained in the middle of the compensated region. It has been verified that, in the case of a collimated gamma beam the detector resolution improves with increasing detector bias up to at least 5100 Volts. For a non-collimated gamma beam, however, the resolution reaches a constant value at about 4400 Volts. The dependence of resolution on the position of irradiation can be accounted for by introducing a local ionization factor different from the usual position independent Fano factor. (author)

  7. Shape-Tunable Charge Carrier Dynamics at the Interfaces between Perovskite Nanocrystals and Molecular Acceptors

    KAUST Repository

    Ahmed, Ghada H.

    2016-09-19

    Hybrid organic/inorganic perovskites have recently emerged as an important class of materials and have exhibited remarkable performance in photovoltaics. To further improve their device efficiency, an insightful understanding of the interfacial charge transfer (CT) process is required. Here, we report the first direct experimental observation of the tremendous effect that the shape of perovskite nanocrystals (NCs) has on interfacial CT in the presence of a molecular acceptor. A dramatic change in CT dynamics at the interfaces of three different NC shapes, spheres, platelets, and cubes, is recorded. Our results clearly demonstrate that the mechanism of CT is significantly affected by the NC shape. More importantly, the results demonstrate that complexation on the NC surface acts as an additional driving force not only to tune the CT dynamics but also to control the reaction mechanism at the interface. This observation opens a new venue for further developing perovskite NCs-based applications.

  8. Shape-Tunable Charge Carrier Dynamics at the Interfaces between Perovskite Nanocrystals and Molecular Acceptors

    KAUST Repository

    Ahmed, Ghada H.; Liu, Jiakai; Parida, Manas R.; Banavoth, Murali; Bose, Riya; AlYami, Noktan; Hedhili, Mohamed N.; Peng, Wei; Pan, Jun; Besong, Tabot M.D.; Bakr, Osman; Mohammed, Omar F.

    2016-01-01

    Hybrid organic/inorganic perovskites have recently emerged as an important class of materials and have exhibited remarkable performance in photovoltaics. To further improve their device efficiency, an insightful understanding of the interfacial charge transfer (CT) process is required. Here, we report the first direct experimental observation of the tremendous effect that the shape of perovskite nanocrystals (NCs) has on interfacial CT in the presence of a molecular acceptor. A dramatic change in CT dynamics at the interfaces of three different NC shapes, spheres, platelets, and cubes, is recorded. Our results clearly demonstrate that the mechanism of CT is significantly affected by the NC shape. More importantly, the results demonstrate that complexation on the NC surface acts as an additional driving force not only to tune the CT dynamics but also to control the reaction mechanism at the interface. This observation opens a new venue for further developing perovskite NCs-based applications.

  9. Theoretical models of the spin-dependent charge-carrier dynamics in metals and semiconductors

    International Nuclear Information System (INIS)

    Krauss, Michael

    2010-01-01

    This thesis is concerned with spin-dependent carrier dynamics in semiconductors and metals. We are especially interested in the dynamics on ultrashort timescales, which can be driven by ultrashort optical excitation, and use of a theoretical description in terms of the dynamical spin-density matrix. The first part of this thesis is concerned with spin-dependent carrier dynamics in bulk GaAs. For conduction electrons in GaAs, the most important mechanisms, by which an electron spin polarization can be destroyed, are the Dyakonov-Perel and Bir-Aronov-Pikus mechanisms. For the Dyakonov-Perel effect, our treatment is the first calculation of the dynamics of the spindensity matrix for bulk GaAs. From our microsopic calculation, we extract spin-dephasing times. In particular, we can describe the dependence of the spin-dephasing time for a wide range of n-doping concentrations and explain the spin-dephasing dynamics in and out of the motional-narrowing regime. For the Bir-Aronov-Pikus mechanism, i.e., the exchange interaction of electronics with holes, approximate relaxation times for limiting cases were derived about 30 years ago. We show that these approaches provide an incomplete picture of spin relaxation, and are only valid for high or low densities, whereas the microscopic calculation is capable of explaining the electronic dynamics also for intermediate doping densities, which are most interesting for typical experiments. The spin-dependent hole dynamics in GaAs is much faster than that of electrons, because the p-like hole bands experience the spin-orbit interaction directly, rather than through the interaction with other bands. The resulting spin relaxation is sometimes referred to as an Elliott-Yafet mechanism. For the first time, we present results for the microscopic dynamics of this mechanism for holes in bulk GaAs, and we discuss the different results that may be obtained with different measurement techniques. We also analyze the importance of ''spin hot

  10. Molecular dynamics study of the solvation of an alpha-helical transmembrane peptide by DMSO

    NARCIS (Netherlands)

    Duarte, A.M.; Mierlo, van C.P.M.; Hemminga, M.A.

    2008-01-01

    10-ns molecular dynamics study of the solvation of a hydrophobic transmembrane helical peptide in dimethyl sulfoxide (DMSO) is presented. The objective is to analyze how this aprotic polar solvent is able to solvate three groups of amino acid residues (i.e., polar, apolar, and charged) that are

  11. High-resolution charge carrier mobility mapping of heterogeneous organic semiconductors

    Science.gov (United States)

    Button, Steven W.; Mativetsky, Jeffrey M.

    2017-08-01

    Organic electronic device performance is contingent on charge transport across a heterogeneous landscape of structural features. Methods are therefore needed to unravel the effects of local structure on overall electrical performance. Using conductive atomic force microscopy, we construct high-resolution out-of-plane hole mobility maps from arrays of 5000 to 16 000 current-voltage curves. To demonstrate the efficacy of this non-invasive approach for quantifying and mapping local differences in electrical performance due to structural heterogeneities, we investigate two thin film test systems, one bearing a heterogeneous crystal structure [solvent vapor annealed 5,11-Bis(triethylsilylethynyl)anthradithiophene (TES-ADT)—a small molecule organic semiconductor] and one bearing a heterogeneous chemical composition [p-DTS(FBTTh2)2:PC71BM—a high-performance organic photovoltaic active layer]. TES-ADT shows nearly an order of magnitude difference in hole mobility between semicrystalline and crystalline areas, along with a distinct boundary between the two regions, while p-DTS(FBTTh2)2:PC71BM exhibits subtle local variations in hole mobility and a nanoscale domain structure with features below 10 nm in size. We also demonstrate mapping of the built-in potential, which plays a significant role in organic light emitting diode and organic solar cell operation.

  12. Selective contacts drive charge extraction in quantum dot solids via asymmetry in carrier transfer kinetics

    KAUST Repository

    Mora-Sero, Ivan; Bertoluzzi, Luca; Gonzalez-Pedro, Victoria; Gimenez, Sixto; Fabregat-Santiago, Francisco; Kemp, Kyle W.; Sargent, Edward H.; Bisquert, Juan

    2013-01-01

    Colloidal quantum dot solar cells achieve spectrally selective optical absorption in a thin layer of solution-processed, size-effect tuned, nanoparticles. The best devices built to date have relied heavily on drift-based transport due to the action of an electric field in a depletion region that extends throughout the thickness of the quantum dot layer. Here we study for the first time the behaviour of the best-performing class of colloidal quantum dot films in the absence of an electric field, by screening using an electrolyte. We find that the action of selective contacts on photovoltage sign and amplitude can be retained, implying that the contacts operate by kinetic preferences of charge transfer for either electrons or holes. We develop a theoretical model to explain these experimental findings. The work is the first to present a switch in the photovoltage in colloidal quantum dot solar cells by purposefully formed selective contacts, opening the way to new strategies in the engineering of colloidal quantum dot solar cells. © 2013 Macmillan Publishers Limited. All rights reserved.

  13. Field enhanced charge carrier reconfiguration in electronic and ionic coupled dynamic polymer resistive memory

    International Nuclear Information System (INIS)

    Zhao Junhui; Thomson, Douglas J; Freund, Michael S; Pilapil, Matt; Pillai, Rajesh G; Aminur Rahman, G M

    2010-01-01

    Dynamic resistive memory devices based on a conjugated polymer composite (PPy 0 DBS - Li + (PPy: polypyrrole; DBS - : dodecylbenzenesulfonate)), with field-driven ion migration, have been demonstrated. In this work the dynamics of these systems has been investigated and it has been concluded that increasing the applied field can dramatically increase the rate at which information can be 'written' into these devices. A conductance model using space charge limited current coupled with an electric field induced ion reconfiguration has been successfully utilized to interpret the experimentally observed transient conducting behaviors. The memory devices use the rising and falling transient current states for the storage of digital states. The magnitude of these transient currents is controlled by the magnitude and width of the write/read pulse. For the 500 nm length devices used in this work an increase in 'write' potential from 2.5 to 5.5 V decreased the time required to create a transient conductance state that can be converted into the digital signal by 50 times. This work suggests that the scaling of these devices will be favorable and that 'write' times for the conjugated polymer composite memory devices will decrease rapidly as ion driving fields increase with decreasing device size.

  14. Selective contacts drive charge extraction in quantum dot solids via asymmetry in carrier transfer kinetics

    KAUST Repository

    Mora-Sero, Ivan

    2013-08-12

    Colloidal quantum dot solar cells achieve spectrally selective optical absorption in a thin layer of solution-processed, size-effect tuned, nanoparticles. The best devices built to date have relied heavily on drift-based transport due to the action of an electric field in a depletion region that extends throughout the thickness of the quantum dot layer. Here we study for the first time the behaviour of the best-performing class of colloidal quantum dot films in the absence of an electric field, by screening using an electrolyte. We find that the action of selective contacts on photovoltage sign and amplitude can be retained, implying that the contacts operate by kinetic preferences of charge transfer for either electrons or holes. We develop a theoretical model to explain these experimental findings. The work is the first to present a switch in the photovoltage in colloidal quantum dot solar cells by purposefully formed selective contacts, opening the way to new strategies in the engineering of colloidal quantum dot solar cells. © 2013 Macmillan Publishers Limited. All rights reserved.

  15. Exploring the validity and limitations of the Mott-Gurney law for charge-carrier mobility determination of semiconducting thin-films

    Science.gov (United States)

    Röhr, Jason A.; Moia, Davide; Haque, Saif A.; Kirchartz, Thomas; Nelson, Jenny

    2018-03-01

    Using drift-diffusion simulations, we investigate the voltage dependence of the dark current in single carrier devices typically used to determine charge-carrier mobilities. For both low and high voltages, the current increases linearly with the applied voltage. Whereas the linear current at low voltages is mainly due to space charge in the middle of the device, the linear current at high voltage is caused by charge-carrier saturation due to a high degree of injection. As a consequence, the current density at these voltages does not follow the classical square law derived by Mott and Gurney, and we show that for trap-free devices, only for intermediate voltages, a space-charge-limited drift current can be observed with a slope that approaches a value of two. We show that, depending on the thickness of the semiconductor layer and the size of the injection barriers, the two linear current-voltage regimes can dominate the whole voltage range, and the intermediate Mott-Gurney regime can shrink or disappear. In this case, which will especially occur for thicknesses and injection barriers typical of single-carrier devices used to probe organic semiconductors, a meaningful analysis using the Mott-Gurney law will become unachievable, because a square-law fit can no longer be achieved, resulting in the mobility being substantially underestimated. General criteria for when to expect deviations from the Mott-Gurney law when used for analysis of intrinsic semiconductors are discussed.

  16. Exploring the validity and limitations of the Mott-Gurney law for charge-carrier mobility determination of semiconducting thin-films.

    Science.gov (United States)

    Röhr, Jason A; Moia, Davide; Haque, Saif A; Kirchartz, Thomas; Nelson, Jenny

    2018-03-14

    Using drift-diffusion simulations, we investigate the voltage dependence of the dark current in single carrier devices typically used to determine charge-carrier mobilities. For both low and high voltages, the current increases linearly with the applied voltage. Whereas the linear current at low voltages is mainly due to space charge in the middle of the device, the linear current at high voltage is caused by charge-carrier saturation due to a high degree of injection. As a consequence, the current density at these voltages does not follow the classical square law derived by Mott and Gurney, and we show that for trap-free devices, only for intermediate voltages, a space-charge-limited drift current can be observed with a slope that approaches a value of two. We show that, depending on the thickness of the semiconductor layer and the size of the injection barriers, the two linear current-voltage regimes can dominate the whole voltage range, and the intermediate Mott-Gurney regime can shrink or disappear. In this case, which will especially occur for thicknesses and injection barriers typical of single-carrier devices used to probe organic semiconductors, a meaningful analysis using the Mott-Gurney law will become unachievable, because a square-law fit can no longer be achieved, resulting in the mobility being substantially underestimated. General criteria for when to expect deviations from the Mott-Gurney law when used for analysis of intrinsic semiconductors are discussed.

  17. Improved film morphology reduces charge carrier recombination into the triplet excited state in a small bandgap polymer-fullerene photovoltaic cell

    NARCIS (Netherlands)

    Di Nuzzo, D.; Aguirre de Miguel, A.; Shahid, M.; Gevaerts, Veronique; Meskers, S.C.J.; Janssen, R.A.J.

    2010-01-01

    The use of diiodooctane as processing additive for construction of PCPDTBT:PCBM solar cells results in a profound change in photophysical behavior of this blend. In the improved morphology obtained with the additive, recombination of charge carriers to the lowest triplet excited state is suppressed.

  18. Insights into the charge carrier terahertz mobility in polyfluorenes from large-scale atomistic simulations and time-resolved terahertz spectroscopy

    Czech Academy of Sciences Publication Activity Database

    Vukmirović, N.; Ponseca, C.S.; Němec, Hynek; Yartsev, A.; Sundström, V.

    2012-01-01

    Roč. 116, č. 37 (2012), s. 19665-1972 ISSN 1932-7447 Institutional research plan: CEZ:AV0Z10100520 Keywords : charge carrier mobility * time-resolved terahertz spectroscopy * multiscale atomistic calculations Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 4.814, year: 2012

  19. Ultra-fast charge carrier dynamics across the spectrum of an optical gain media based on InAs/AlGaInAs/InP quantum dots

    Directory of Open Access Journals (Sweden)

    I. Khanonkin

    2017-03-01

    Full Text Available The charge carrier dynamics of improved InP-based InAs/AlGaInAs quantum dot (QD semiconductor optical amplifiers are examined employing the multi-wavelength ultrafast pump-probe measurement technique. The transient transmission response of the continuous wave probe shows interesting dynamical processes during the initial 2-3 ps after the pump pulse, when carriers originating from two photon absorption contribute the least to the recovery. The effects of optical excitations and electrical bias levels on the recovery dynamics of the gain in energetically different QDs are quantified and discussed. The experimental observations are validated qualitatively using a comprehensive finite-difference time-domain model by recording the time evolution of the charge carriers in the QDs ensemble following the pulse.

  20. Charge carrier transport mechanisms in perovskite CdTiO3 fibers

    Directory of Open Access Journals (Sweden)

    Z. Imran

    2014-06-01

    Full Text Available Electrical transport properties of electrospun cadmium titanate (CdTiO3 fibers have been investigated using ac and dc measurements. Air annealing of as spun fibers at 1000 °C yielded the single phase perovskite fibers having diameter ∼600 nm - 800 nm. Both the ac and dc electrical measurements were carried out at temperatures from 200 K – 420 K. The complex impedance plane plots revealed a single semicircular arc which indicates the interfacial effect due to grain boundaries of fibers. The dielectric properties obey the Maxwell-Wagner theory of interfacial polarization. In dc transport study at low voltages, data show Ohmic like behavior followed by space charge limited current (SCLC with traps at higher voltages at all temperatures (200 K – 420 K. Trap density in our fibers system is Nt = 6.27 × 1017 /cm3. Conduction mechanism in the sample is governed by 3-D variable range hopping (VRH from 200 K – 300 K. The localized density of states were found to be N(EF = 5.51 × 1021 eV−1 cm−3 at 2 V. Other VRH parameters such as hopping distance (Rhop and hopping energy (Whop were also calculated. In the high temperature range of 320 K – 420 K, conductivity follows the Arrhenius law. The activation energy found at 2 V is 0.10 eV. Temperature dependent and higher values of dielectric constant make the perovskite CdTiO3 fibers efficient material for capacitive energy storage devices.

  1. Emission and Dynamics of Charge Carriers in Uncoated and Organic/Metal Coated Semiconductor Nanowires

    Science.gov (United States)

    Kaveh Baghbadorani, Masoud

    In this dissertation, the dynamics of excitons in hybrid metal/organic/nanowire structures possessing nanometer thick deposited molecular and metal films on top of InP and GaAs nanowire (NW) surfaces were investigated. Optical characterizations were carried out as a function of the semiconductor NW material, design, NW size and the type and thickness of the organic material and metal used. Hybrid organic and plasmonic semiconductor nanowire heterostructures were fabricated using organic molecular beam deposition technique. I investigated the photon emission of excitons in 150 nm diameter polytype wurtzite/zincblende InP NWs and the influence of a few ten nanometer thick organic and metal films on the emission using intensity- and temperature-dependent time-integrated and time resolved (TR) photoluminescence (PL). The plasmonic NWs were coated with an Aluminum quinoline (Alq3) interlayer and magnesium-silver (Mg0.9:Ag0.1) top layer. In addition, the nonlinear optical technique of heterodyne four-wave mixing was used (in collaboration with Prof. Wolfgang Langbein, University of Cardiff) to study incoherent and coherent carrier relaxation processes on bare nanowires on a 100 femtosecond time-scale. Alq3 covered NWs reveal a stronger emission and a longer decay time of exciton transitions indicating surface state passivation at the Alq3/NW interface. Alq3/Mg:Ag NWs reveal a strong quenching of the exciton emission which is predominantly attributed to Forster energy-transfer from excitons to plasmon oscillations in the metal cluster film. Changing the Mg:Ag to gold and the organic Alq3 spacer layer to PTCDA leads to a similar behavior, but the PL quenching is strongly increased. The observed behavior is attributed to a more continuous gold deposition leading to an increased Forster energy transfer and to a metal induced band-bending. I also investigated ensembles of bare and gold/Alq3 coated GaAs-AlGaAs-GaAs core shell NWs of 130 nm diameter. Plasmonic NWs with Au

  2. Screening in crystalline liquids protects energetic carriers in hybrid perovskites

    Science.gov (United States)

    Zhu, Haiming; Miyata, Kiyoshi; Fu, Yongping; Wang, Jue; Joshi, Prakriti; Niesner, Daniel; Williams, Kristopher; Jin, Song; Zhu, Xiaoyang

    Hybrid lead halide perovskites exhibit carrier properties that resemble those of pristine nonpolar semiconductors despite static and dynamic disorder, but how carriers are protected from efficient scattering with charged defects and optical phonons is unknown. Here, we reveal the carrier protection mechanism by comparing three single-crystal lead bromide perovskites: CH3NH3PbBr3, CH(NH2)2PbBr3, and CsPbBr3. We observed hot fluorescence emission from energetic carriers with 102 picosecond lifetimes in CH3NH3PbBr3 or CH(NH,SUB>2)2PbBr3, but not in CsPbBr3. The hot fluorescence is correlated with liquid-like molecular reorientational motions, suggesting that dynamic screening protects energetic carriers via solvation or large polaron formation on time scales competitive with that of ultrafast cooling. Similar protections likely exist for band-edge carriers. The long-lived energetic carriers may enable hot-carrier solar cells with efficiencies exceeding the Shockley-Queisser limit. This work was supported by U.S. Department of Energy Grant ER46980, National Science Foundation, Grant DMR 1420634 (MRSEC), and Department of Energy Award DE-FG02-09ER46664.

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

    Science.gov (United States)

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

    2014-08-01

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

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

    Directory of Open Access Journals (Sweden)

    Christian Wehrenfennig

    2014-08-01

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

  5. Facile synthesis of bismuth oxyhalide nanosheet films with distinct conduction type and photo-induced charge carrier behavior

    Science.gov (United States)

    Jia, Huimin; He, Weiwei; Zhang, Beibei; Yao, Lei; Yang, Xiaokai; Zheng, Zhi

    2018-05-01

    A modified successive ionic layer adsorption and reaction (SILAR) method was developed to fabricate 2D ordered BiOX (X = CI, Br, I) nanosheet array films on FTO substrates at room temperature. The formation of BiOX films were characterized by X-ray powder diffraction (XRD), scanning electron microscopy (SEM), high resolution transmission electron microscopy (HRTEM), UV-vis absorption spectroscopy, and X-ray photoelectron spectroscopy (XPS). The semiconductor surface states determine the type of semiconductor. Although BiOCI, BiOBr and BiOI belong to the bismuth oxyhalide semiconductor family and possess similar crystal and electronic structures, they show different conductivity types due to their respective surface states. Mott-Schottky curve results demonstrate that the BiOCl and BiOI nanosheet arrays display n-type semiconductor properties, while the BiOBr films exhibit p-type semiconductor properties. Assisted by surface photovoltage (SPV) and transient photovoltage (TPV) techniques, the photoinduced charge transfer dynamics on the surface/interface of the BiOX/FTO nanosheet films were systematically and comparatively investigated. As revealed by the results, both the separation and transfer dynamics of the photo-induced carrier are influenced by film thickness.

  6. On the radiative recombination and tunneling of charge carriers in SiGe/Si heterostructures with double quantum wells

    Energy Technology Data Exchange (ETDEWEB)

    Yablonsky, A. N., E-mail: yablonsk@ipmras.ru; Zhukavin, R. Kh.; Bekin, N. A.; Novikov, A. V.; Yurasov, D. V.; Shaleev, M. V. [Russian Academy of Sciences, Institute for Physics of Microstructures (Russian Federation)

    2016-12-15

    For SiGe/Si(001) epitaxial structures with two nonequivalent SiGe quantum wells separated by a thin Si barrier, the spectral and time characteristics of interband photoluminescence corresponding to the radiative recombination of excitons in quantum wells are studied. For a series of structures with two SiGe quantum wells different in width, the characteristic time of tunneling of charge carriers (holes) from the narrow quantum well, distinguished by a higher exciton recombination energy, to the wide quantum well is determined as a function of the Si barrier thickness. It is shown that the time of tunneling of holes between the Si{sub 0.8}5Ge{sub 0.15} layers with thicknesses of 3 and 9 nm steadily decreases from ~500 to <5 ns, as the Si barrier thickness is reduced from 16 to 8 nm. At intermediate Si barrier thicknesses, an increase in the photoluminescence signal from the wide quantum well is observed, with a characteristic time of the same order of magnitude as the luminescence decay time of the narrow quantum well. This supports the observation of the effect of the tunneling of holes from the narrow to the wide quantum well. A strong dependence of the tunneling time of holes on the Ge content in the SiGe layers at the same thickness of the Si barrier between quantum wells is observed, which is attributed to an increase in the effective Si barrier height.

  7. On the tin impurity in the thermoelectric compound ZnSb: Charge-carrier generation and compensation

    Energy Technology Data Exchange (ETDEWEB)

    Prokofieva, L. V., E-mail: lprokofieva496@gmail.com; Konstantinov, P. P.; Shabaldin, A. A. [Russian Academy of Sciences, Ioffe Physical–Technical Institute (Russian Federation)

    2016-06-15

    The technique for measuring the Hall coefficient and electrical conductivity in the thermal cycling mode is used to study the effect of the Sn impurity on the microstructure and properties of pressed ZnSb samples. Tin was introduced as an excess component (0.1 and 0.2 at %) and as a substitutional impurity for Zn and Sb atoms in a concentration of (2–2.5) at % The temperature dependences of the parameters of lightly doped samples are fundamentally like similar curves for ZnSb with 0.1 at % of Cu. The highest Hall concentration, 1.4 × 10{sup 19} cm{sup –3} at 300 K, is obtained upon the introduction of 0.1 at % of Sn; the dimensionless thermoelectric figure of merit attains its maximum value of 0.85 at 660 K. The experimental data are discussed under the assumption of two doping mechanisms, which are effective in different temperature ranges, with zinc vacancies playing the decisive role of acceptor centers. In two ZnSb samples with SnSb and ZnSn additives, the charge-carrier compensation effect is observed; this effect depends on temperature and markedly changes with doping type. As in p-type A{sup IV}–B{sup VI} materials with a low Sn content, hole compensation can be attributed to atomic recharging Sn{sup 2+} → Sn{sup 4+}. Types of compensating complexes are considered.

  8. High-frequency conductivity of optically excited charge carriers in hydrogenated nanocrystalline silicon investigated by spectroscopic femtosecond pump–probe reflectivity measurements

    Energy Technology Data Exchange (ETDEWEB)

    He, Wei [University of Birmingham, School of Physics and Astronomy, Birmingham B15 2TT (United Kingdom); Yurkevich, Igor V. [Aston University, Nonlinearity and Complexity Research Group, Birmingham B4 7ET (United Kingdom); Zakar, Ammar [University of Birmingham, School of Physics and Astronomy, Birmingham B15 2TT (United Kingdom); Kaplan, Andrey, E-mail: a.kaplan.1@bham.ac.uk [University of Birmingham, School of Physics and Astronomy, Birmingham B15 2TT (United Kingdom)

    2015-10-01

    We report an investigation into the high-frequency conductivity of optically excited charge carriers far from equilibrium with the lattice. The investigated samples consist of hydrogenated nanocrystalline silicon films grown on a thin film of silicon oxide on top of a silicon substrate. For the investigation, we used an optical femtosecond pump–probe setup to measure the reflectance change of a probe beam. The pump beam ranged between 580 and 820 nm, whereas the probe wavelength spanned 770 to 810 nm. The pump fluence was fixed at 0.6 mJ/cm{sup 2}. We show that at a fixed delay time of 300 fs, the conductivity of the excited electron–hole plasma is described well by a classical conductivity model of a hot charge carrier gas found at Maxwell–Boltzmann distribution, while Fermi–Dirac statics is not suitable. This is corroborated by values retrieved from pump–probe reflectance measurements of the conductivity and its dependence on the excitation wavelength and carrier temperature. The conductivity decreases monotonically as a function of the excitation wavelength, as expected for a nondegenerate charge carrier gas. - Highlights: • We study high‐frequency conductivity of excited hydrogenated nanocrystalline silicon. • Reflectance change was measured as a function of pump and probe wavelength. • Maxwell–Boltzmann transport theory was used to retrieve the conductivity. • The conductivity decreases monotonically as a function of the pump wavelength.

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

    Science.gov (United States)

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

    2015-01-28

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

  10. Interfacial solvation thermodynamics

    International Nuclear Information System (INIS)

    Ben-Amotz, Dor

    2016-01-01

    Previous studies have reached conflicting conclusions regarding the interplay of cavity formation, polarizability, desolvation, and surface capillary waves in driving the interfacial adsorptions of ions and molecules at air–water interfaces. Here we revisit these questions by combining exact potential distribution results with linear response theory and other physically motivated approximations. The results highlight both exact and approximate compensation relations pertaining to direct (solute–solvent) and indirect (solvent–solvent) contributions to adsorption thermodynamics, of relevance to solvation at air–water interfaces, as well as a broader class of processes linked to the mean force potential between ions, molecules, nanoparticles, proteins, and biological assemblies. (paper)

  11. Optimization of the charge-carrier injection in organic light-emitting diodes; Optimierung der Ladungstraegerinjektion in organische Leuchtdioden

    Energy Technology Data Exchange (ETDEWEB)

    Krause, Ralf

    2009-07-01

    Nowadays based on resource shortage and climate warming there is a big interest in the use of power-saving lighting sources. Therefore the research on white organic light emitting devices (OLEDs) has gained importance during the last years. To obtain high power efficiencies in OLEDs it is necessary to provide low driving voltages. That can be realised by the use of doped transport layers, in which donors and acceptors are coevaporated with organic transport materials. In this thesis I discuss novel p-type and n-type doping materials for small organic molecules which decrease the ohmic loss in organic transport layers used in OLEDs. This reduction of the resistance is caused by an increase of the intrinsic charge carrier density and therefore an increase of the conductivity. First single layer devices are used to analyse the properties of potential doping materials by varying the doping concentration. The tested p-doping materials are commercially available metal oxides (MoO{sub 3} and Re{sub 2}O{sub 7}) and metal-organic complexes. Both metal oxides show a strong conductivity improvement of up to 7 orders of magnitude. The investigated n-doping materials are alkali salts, metal-organic and organic complexes. Among the alkali salts Cs{sub 2}CO{sub 3} is the best material in test with a conductivity enhancement of up to 7 orders of magnitude. For this material class I focused on the question whether the metal cation or the organic anion causes the doping effect. Using similar Caesium salts differently strong doping effects were obtained. Therefore I came to the conclusion that beside the metal cation also the anion plays a role for the doping effect. Secondly I performed a series of multilayer devices for two doping materials (Re{sub 2}O{sub 7} as acceptor and Cs{sub 2}CO{sub 3} as donor) to separate the transport and injection enhancement. The results show that a doped transport layer improves the hole or electron injection into an undoped material by several orders

  12. Low temperature luminescence and charge carrier trapping in a cryogenic scintillator Li{sub 2}MoO{sub 4}

    Energy Technology Data Exchange (ETDEWEB)

    Spassky, D.A., E-mail: deris2002@mail.ru [Institute of Physics, University of Tartu, Ravila 14c, 50411 Tartu (Estonia); Skobeltsyn Institute of Nuclear Physics, Moscow State University, 119991 Moscow (Russian Federation); Nagirnyi, V. [Institute of Physics, University of Tartu, Ravila 14c, 50411 Tartu (Estonia); Savon, A.E. [Skobeltsyn Institute of Nuclear Physics, Moscow State University, 119991 Moscow (Russian Federation); Kamenskikh, I.A. [Physics Faculty, Moscow State University, 119991 Moscow (Russian Federation); Barinova, O.P.; Kirsanova, S.V. [D. Mendeleyev University of Chemical Technology of Russia, 125047 Moscow (Russian Federation); Grigorieva, V.D.; Ivannikova, N.V.; Shlegel, V.N. [Nikolaev Institute of Inorganic Chemistry, SB RAS, 630090 Novosibirsk (Russian Federation); Aleksanyan, E. [Institute of Physics, University of Tartu, Ravila 14c, 50411 Tartu (Estonia); A.Alikhanyan National Science Laboratory, 2 Br. Alikhanyan Str., 0036 Yerevan (Armenia); Yelisseyev, A.P. [Sobolev Institute of Geology and Mineralogy, SB RAS, 630090 Novosibirsk (Russian Federation); Belsky, A. [Institute of Light and Matter, CNRS, University Lyon1, 69622 Villeurbanne (France)

    2015-10-15

    The luminescence and optical properties of promising cryogenic scintillator Li{sub 2}MoO{sub 4} were studied in the temperature region of 2–300 K. The data on luminescence spectra and decay characteristics, excitation spectra, thermostimulated luminescence curves and spectra as well as transmission and reflectivity spectra are presented for the single crystals grown by two different procedures, the conventional Czochralski method and the low-temperature gradient Czochralski technique. The bandgap of Li{sub 2}MoO{sub 4} is estimated from the analysis of transmission, luminescence excitation and reflectivity spectra. Up to three luminescence bands with the maxima at 1.98, 2.08 and 2.25 eV are detected in the emission spectra of crystals and their origin is discussed. In the thermoluminescence curves of both studied crystals, two high-intensity peaks were observed at 22 and 42 K, which are ascribed to the thermal release of self-trapped charge carriers. The coexistence of self-trapped electrons and holes allows one to explain the poor scintillation light yield of Li{sub 2}MoO{sub 4} at low temperatures. - Highlights: • Single crystals of Li{sub 2}MoO{sub 4} were grown by two methods. • The transparency cutoff (~4.3 eV) and bandgap values (<4.9 eV) are estimated. • The emission 2.08 eV is ascribed to self-trapped excitons and quenches at T>7 K. • Shallow traps considerably influence the energy transfer to emission centres. • Co-existence of self-trapped holes and electrons results in a low light yield.

  13. A possibility for generation of two species of charge carriers along main-chain and side-chains for a π-conjugated polymer

    International Nuclear Information System (INIS)

    Kudo, Yuki; Kawabata, Kohsuke; Goto, Hiromasa

    2013-01-01

    Iodide doping produces charge carriers in π-conjugated polymers. Solitons can be generated in the case of polyacetylene, and polarons in the case of aromatic-type conjugated polymers. We synthesized a conjugated main-chain/side-chain polymer, which consists of polyene in the main-chain and aromatic-type conjugated units in the side-chains. Based on the SSH (Su, Schrieffer, Heeger) theoretical model of solitons in one-dimensional conjugated polymers, we experimentally carried out chemical doping to the main-chain/side-chains conjugated polymer. Generation of the charge carriers was examined by electron spin resonance spectroscopy. This study may lead to realization of a dual doping system of solitons and polarons in π-conjugation expanded to two-dimensional directions in polymers.

  14. Non-contact, non-destructive, quantitative probing of interfacial trap sites for charge carrier transport at semiconductor-insulator boundary

    Energy Technology Data Exchange (ETDEWEB)

    Choi, Wookjin; Miyakai, Tomoyo; Sakurai, Tsuneaki; Saeki, Akinori [Department of Applied Chemistry, Graduate School of Engineering, Osaka University, Suita 565-0871 (Japan); Yokoyama, Masaaki [Kaneka Fundamental Technology Research Alliance Laboratories, Graduate School of Engineering, Osaka University, Suita 565-0871 (Japan); Seki, Shu, E-mail: seki@chem.eng.osaka-u.ac.jp [Department of Applied Chemistry, Graduate School of Engineering, Osaka University, Suita 565-0871 (Japan); Kaneka Fundamental Technology Research Alliance Laboratories, Graduate School of Engineering, Osaka University, Suita 565-0871 (Japan)

    2014-07-21

    The density of traps at semiconductor–insulator interfaces was successfully estimated using microwave dielectric loss spectroscopy with model thin-film organic field-effect transistors. The non-contact, non-destructive analysis technique is referred to as field-induced time-resolved microwave conductivity (FI-TRMC) at interfaces. Kinetic traces of FI-TRMC transients clearly distinguished the mobile charge carriers at the interfaces from the immobile charges trapped at defects, allowing both the mobility of charge carriers and the number density of trap sites to be determined at the semiconductor-insulator interfaces. The number density of defects at the interface between evaporated pentacene on a poly(methylmethacrylate) insulating layer was determined to be 10{sup 12 }cm{sup −2}, and the hole mobility was up to 6.5 cm{sup 2} V{sup −1} s{sup −1} after filling the defects with trapped carriers. The FI-TRMC at interfaces technique has the potential to provide rapid screening for the assessment of interfacial electronic states in a variety of semiconductor devices.

  15. Efficient charge carriers induced by extra outer-shell electrons in iron-pnictides: a comparison between Ni- and Co-doped CaFeAsF

    International Nuclear Information System (INIS)

    Zhang Min; Yu Yi; Tan Shun; Zhang Yuheng; Zhang Changjin; Zhang Lei; Qu Zhe; Ling Langsheng; Xi, Chuanying

    2010-01-01

    A comprehensive study of the difference between CaFe 1-x Ni x AsF and CaFe 1-x Co x AsF systems has been carried out by measuring the efficient charge carrier concentration, the valence states and the superconducting phase diagram. It is found that at the same doping level, Ni doping introduces nearly twice the number of charge carriers as Co doping. However, x-ray absorption near-edge spectroscopy measurements reveal that the valence state of Fe in both systems is close to 2, indicating that there is no valence mismatch. We suggest that the charge carriers in CaFe 1-x M x AsF (M=transition metal elements) are not induced by valence mismatch but come from the difference in the number of outer-shell electrons. We also suggest that with Ni and Co doping, the systems change from a multi-band material in the underdoped regions to a single-band state in the overdoped regions.

  16. Electrical resistivities and solvation enthalpies for solutions of salts in liquid alkali metals

    International Nuclear Information System (INIS)

    Hubberstey, P.; Dadd, A.T.

    1982-01-01

    An empirical correlation is shown to exist between the resistivity coefficients drho/dc for solutes in liquid alkali metals and the corresponding solvation enthalpies Usub(solvn) of the neutral gaseous solute species. Qualitative arguments based on an electrostatic solvation model in which the negative solute atom is surrounded by a solvation sphere of positive solvent ion cores are used to show that both parameters are dependent on the charge density of the solute atom and hence on the extent of charge transfer from solvent to solute. Thus as the charge density of the solute increases, the solvation enthalpy increases regularly and the resistivity coefficients pass through a maximum to give the observed approximately parabolic drho/dc versus Usub(solvn) relationship. (Auth.)

  17. The impact of Au doping on the charge carrier dynamics at the interfaces between cationic porphyrin and silver nanoclusters

    KAUST Repository

    Almansaf, Abdulkhaleq A.

    2017-02-04

    We explore the impact of Au doping on the charge transfer dynamics between the positively charged porphyrin (TMPyP) and negatively charged silver nanoclusters (Ag29 NCs). Our transient absorption (TA) spectroscopic results demonstrate that the interfacial charge transfer, the intersystem crossing and the triplet state lifetime of porphyrin can be tuned by the doping of Au atoms in Ag29 NCs. Additionally, we found that the electrostatic interaction between the negative charge of the cluster and the positive charge on the TMPyP is the driving force that brings them close to each other for complex formation and subsequently facilitates the transfer process.

  18. The impact of Au doping on the charge carrier dynamics at the interfaces between cationic porphyrin and silver nanoclusters

    KAUST Repository

    Almansaf, Abdulkhaleq A.; Parida, Manas R.; Besong, Tabot M.D.; Maity, Partha; Bootharaju, Megalamane Siddaramappa; Bakr, Osman; Mohammed, Omar F.

    2017-01-01

    We explore the impact of Au doping on the charge transfer dynamics between the positively charged porphyrin (TMPyP) and negatively charged silver nanoclusters (Ag29 NCs). Our transient absorption (TA) spectroscopic results demonstrate that the interfacial charge transfer, the intersystem crossing and the triplet state lifetime of porphyrin can be tuned by the doping of Au atoms in Ag29 NCs. Additionally, we found that the electrostatic interaction between the negative charge of the cluster and the positive charge on the TMPyP is the driving force that brings them close to each other for complex formation and subsequently facilitates the transfer process.

  19. Charge-carrier dynamics in polycrystalline thin-film CuIn{sub 1−x}Ga{sub x}Se{sub 2} photovoltaic devices after pulsed laser excitation: Interface and space-charge region analysis

    Energy Technology Data Exchange (ETDEWEB)

    Kuciauskas, Darius; Li, Jian V.; Kanevce, Ana; Guthrey, Harvey; Contreras, Miguel; Pankow, Joel; Dippo, Pat; Ramanathan, Kannan [National Renewable Energy Laboratory, 15013 Denver West Parkway, Golden, Colorado 80401-3305 (United States)

    2015-05-14

    We used time-resolved photoluminescence (TRPL) spectroscopy to analyze time-domain and spectral-domain charge-carrier dynamics in CuIn{sub 1−x}Ga{sub x}Se{sub 2} (CIGS) photovoltaic (PV) devices. This new approach allowed detailed characterization for the CIGS/CdS buffer interface and for the space-charge region. We find that dynamics at the interface is dominated by diffusion, where the diffusion rate is several times greater than the thermionic emission or interface recombination rate. In the space-charge region, the electric field of the pn junction has the largest effect on the carrier dynamics. Based on the minority-carrier (electron) drift-rate dependence on the electric field strength, we estimated drift mobility in compensated CuIn{sub 1−x}Ga{sub x}Se{sub 2} (with x ≈ 0.3) as 22 ± 2 cm{sup 2}(Vs){sup −1}. Analysis developed in this study could be applied to evaluate interface and junction properties of PV and other electronic devices. For CIGS PV devices, TRPL spectroscopy could contribute to understanding effects due to absorber compositional grading, which is one of the focus areas in developing record-efficiency CIGS solar cells.

  20. Mobility of charge carriers in electron-irradiated crystals of n-type Hg0.8Cd0.2Te

    International Nuclear Information System (INIS)

    Voitsekhovskii, A.V.; Kiryushkin, E.M.; Kokhanenko, A.P.; Kurbanov, K.R.; Lilenko, Yu.V.

    1988-01-01

    We present the results of an investigation of the behavior of the mobility of the charge carriers in Hg 1-x Cd x Te crystals with n-type conduction as a function of the dose of irradiation by electrons with an energy of 3.0 MeV at 300 K and the initial content of defects in the material. The complex character of the variation of the mobility of the electrons as a function of the dose observed when crystals of n-Hg 1-x Cd x Te (x ∼ 0.20) with different initial concentrations of defects are irradiated by fast electrons has been attributed to the influence of the factors of the shielding of the ionized scattering centers by electrons and the additional scattering of the charge carriers on the radiation defects. Good agreement between the experimental and calculated plots of the dependence of the mobility of electrons on the irradiation dose has been obtained with consideration of a model of the simultaneous introduction of donor (single charged) and acceptor (doubly charged) defects into a narrow-band semiconductor characterized by a degenerate and nonparabolic conduction band

  1. Interfacial dynamic surface traps of lead sulfide (PbS) nanocrystals: test-platform for interfacial charge carrier traps at the organic/inorganic functional interface

    Science.gov (United States)

    Kim, Youngjun; Ko, Hyungduk; Park, Byoungnam

    2018-04-01

    Nanocrystal (NC) size and ligand dependent dynamic trap formation of lead sulfide (PbS) NCs in contact with an organic semiconductor were investigated using a pentacene/PbS field effect transistor (FET). We used a bilayer pentacene/PbS FET to extract information of the surface traps of PbS NCs at the pentacene/PbS interface through the field effect-induced charge carrier density measurement in the threshold and subthreshold regions. PbS size and ligand dependent trap properties were elucidated by the time domain and threshold voltage measurements in which threshold voltage shift occurs by carrier charging and discharging in the trap states of PbS NCs. The observed threshold voltage shift is interpreted in context of electron trapping through dynamic trap formation associated with PbS NCs. To the best of our knowledge, this is the first demonstration of the presence of interfacial dynamic trap density of PbS NC in contact with an organic semiconductor (pentacene). We found that the dynamic trap density of the PbS NC is size dependent and the carrier residence time in the specific trap sites is more sensitive to NC size variation than to NC ligand exchange. The probing method presented in the study offers a means to investigate the interfacial surface traps at the organic-inorganic hetero-junction, otherwise understanding of the buried surface traps at the functional interface would be elusive.

  2. Negative differential mobility for negative carriers as revealed by space charge measurements on crosslinked polyethylene insulated model cables

    International Nuclear Information System (INIS)

    Teyssedre, G.; Laurent, C.; Vu, T. T. N.

    2015-01-01

    Among features observed in polyethylene materials under relatively high field, space charge packets, consisting in a pulse of net charge that remains in the form of a pulse as it crosses the insulation, are repeatedly observed but without complete theory explaining their formation and propagation. Positive charge packets are more often reported, and the models based on negative differential mobility(NDM) for the transport of holes could account for some charge packets phenomenology. Conversely, NDM for electrons transport has never been reported so far. The present contribution reports space charge measurements by pulsed electroacoustic method on miniature cables that are model of HVDC cables. The measurements were realized at room temperature or with a temperature gradient of 10 °C through the insulation under DC fields on the order 30–60 kV/mm. Space charge results reveal systematic occurrence of a negative front of charges generated at the inner electrode that moves toward the outer electrode at the beginning of the polarization step. It is observed that the transit time of the front of negative charge increases, and therefore the mobility decreases, with the applied voltage. Further, the estimated mobility, in the range 10 −14 –10 −13  m 2  V −1  s −1 for the present results, increases when the temperature increases for the same condition of applied voltage. The features substantiate the hypothesis of negative differential mobility used for modelling space charge packets

  3. Negative differential mobility for negative carriers as revealed by space charge measurements on crosslinked polyethylene insulated model cables

    Science.gov (United States)

    Teyssedre, G.; Vu, T. T. N.; Laurent, C.

    2015-12-01

    Among features observed in polyethylene materials under relatively high field, space charge packets, consisting in a pulse of net charge that remains in the form of a pulse as it crosses the insulation, are repeatedly observed but without complete theory explaining their formation and propagation. Positive charge packets are more often reported, and the models based on negative differential mobility(NDM) for the transport of holes could account for some charge packets phenomenology. Conversely, NDM for electrons transport has never been reported so far. The present contribution reports space charge measurements by pulsed electroacoustic method on miniature cables that are model of HVDC cables. The measurements were realized at room temperature or with a temperature gradient of 10 °C through the insulation under DC fields on the order 30-60 kV/mm. Space charge results reveal systematic occurrence of a negative front of charges generated at the inner electrode that moves toward the outer electrode at the beginning of the polarization step. It is observed that the transit time of the front of negative charge increases, and therefore the mobility decreases, with the applied voltage. Further, the estimated mobility, in the range 10-14-10-13 m2 V-1 s-1 for the present results, increases when the temperature increases for the same condition of applied voltage. The features substantiate the hypothesis of negative differential mobility used for modelling space charge packets.

  4. Tungsten-based nanomaterials (WO{sub 3} & Bi{sub 2}WO{sub 6}): Modifications related to charge carrier transfer mechanisms and photocatalytic applications

    Energy Technology Data Exchange (ETDEWEB)

    Girish Kumar, S., E-mail: girichem@yahoo.co.in; Koteswara Rao, K.S.R., E-mail: raoksrk@gmail.com

    2015-11-15

    Graphical abstract: - Highlights: • Photocatalytic applications of WO{sub 3} and Bi{sub 2}WO{sub 6} based nanomaterial are reviewed. • Modifications to improve their performance are highlighted. • Charge carrier generation–separation–recombination is discussed. • Challenges and future prospects in this area are addressed. - Abstract: Heterogeneous photocatalysis is an ideal green energy technology for the purification of wastewater. Although titania dominates as the reference photocatalyst, its wide band gap is a bottleneck for extended utility. Thus, search for non-TiO{sub 2} based nanomaterials has become an active area of research in recent years. In this regard, visible light absorbing polycrystalline WO{sub 3} (2.4–2.8 eV) and Bi{sub 2}WO{sub 6} (2.8 eV) with versatile structure-electronic properties has gained considerable interest to promote the photocatalytic reactions. These materials are also explored in selective functional group transformation in organic reactions, because of low reduction and oxidation potential of WO{sub 3} CB and Bi{sub 2}WO{sub 6} VB, respectively. In this focused review, various strategies such as foreign ion doping, noble metal deposition and heterostructuring with other semiconductors designed for efficient photocatalysis is discussed. These modifications not only extend the optical response to longer wavelengths, but also prolong the life-time of the charge carriers and strengthen the photocatalyst stability. The changes in the surface-bulk properties and the charge carrier transfer dynamics associated with each modification correlating to the high activity are emphasized. The presence of oxidizing agents, surface modification with Cu{sup 2+} ions and synthesis of exposed facets to promote the degradation rate is highlighted. In depth study on these nanomaterials is likely to sustain interest in wastewater remediation and envisaged to signify in various green energy applications.

  5. Unraveling Unprecedented Charge Carrier Mobility through Structure Property Relationship of Four Isomers of Didodecyl[1]benzothieno[3,2-b][1]benzothiophene.

    Science.gov (United States)

    Tsutsui, Yusuke; Schweicher, Guillaume; Chattopadhyay, Basab; Sakurai, Tsuneaki; Arlin, Jean-Baptiste; Ruzié, Christian; Aliev, Almaz; Ciesielski, Artur; Colella, Silvia; Kennedy, Alan R; Lemaur, Vincent; Olivier, Yoann; Hadji, Rachid; Sanguinet, Lionel; Castet, Frédéric; Osella, Silvio; Dudenko, Dmytro; Beljonne, David; Cornil, Jérôme; Samorì, Paolo; Seki, Shu; Geerts, Yves H

    2016-09-01

    The structural and electronic properties of four isomers of didodecyl[1]-benzothieno[3,2-b][1]benzothiophene (C12-BTBT) have been investigated. Results show the strong impact of the molecular packing on charge carrier transport and electronic polarization properties. Field-induced time-resolved microwave conductivity measurements unravel an unprecedented high average interfacial mobility of 170 cm(2) V(-1) s(-1) for the 2,7-isomer, holding great promise for the field of organic electronics. © 2016 The Authors. Published by WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  6. Experimental investigation of the excess charge and time constant of minority carriers in the thin diffused layer of 0.1 Ohm-cm silicon solar cells

    Science.gov (United States)

    Godlewski, M. P.; Brandhorst, H. W., Jr.; Lindholm, F. A.; Sah, C. T.

    1976-01-01

    The observed low open-circuit voltage in 0.1 Ohm-cm solar cells is probably related to an excessively high diode saturation current. Theoretical studies conducted by Lindholm et al. (1975) and by Godlewski et al. (1975) have shown that a high saturation current could be produced by either high recombination rates or bandgap narrowing effects. A description is given of an investigation which shows that bandgap narrowing effects have a first order significance in determining the charge carrier transport controlling the open-circuit voltage of 0.1 Ohm-cm silicon solar cells.

  7. Effect of degree of order of silicon dioxide on localization processes of non-equilibrium charge carriers under the influence of gamma-radiation

    CERN Document Server

    Garibov, A A; Agaev, T N

    1999-01-01

    The effect of the degree of order of SiO sub 2 on the localization process of non-equilibrium charge carriers (NCC) when exposed to gamma-quanta at 77 K has been investigated. It has been found that with decreasing SiO sub 2 structure degree of order, a localization probability of NCC increases. A contribution of surface defect states in SiO sub 2 to localization, migration and recombination annihilation processes of NCC induced by ionizing radiation has been determined.

  8. Two-dimensional analytical model of double-gate tunnel FETs with interface trapped charges including effects of channel mobile charge carriers

    Science.gov (United States)

    Xu, Huifang; Dai, Yuehua

    2017-02-01

    A two-dimensional analytical model of double-gate (DG) tunneling field-effect transistors (TFETs) with interface trapped charges is proposed in this paper. The influence of the channel mobile charges on the potential profile is also taken into account in order to improve the accuracy of the models. On the basis of potential profile, the electric field is derived and the expression for the drain current is obtained by integrating the BTBT generation rate. The model can be used to study the impact of interface trapped charges on the surface potential, the shortest tunneling length, the drain current and the threshold voltage for varying interface trapped charge densities, length of damaged region as well as the structural parameters of the DG TFET and can also be utilized to design the charge trapped memory devices based on TFET. The biggest advantage of this model is that it is more accurate, and in its expression there are no fitting parameters with small calculating amount. Very good agreements for both the potential, drain current and threshold voltage are observed between the model calculations and the simulated results. Project supported by the National Natural Science Foundation of China (No. 61376106), the University Natural Science Research Key Project of Anhui Province (No. KJ2016A169), and the Introduced Talents Project of Anhui Science and Technology University.

  9. Time-resolved terahertz spectroscopy of charge carrier dynamics in the chalcogenide glass As30Se30Te40 [Invited

    DEFF Research Database (Denmark)

    Wang, Tianwu; Romanova, Elena A.; Abdel-Moneim, Nabil

    2016-01-01

    absorption bands at 2-3 and 5-8 THz were observed. TRTS reveals an ultrafast relaxation process of the photoinduced carrier response, well described by a rate equation model with a finite concentration of mid-bandgap trap states for self-trapped excitons. The photoinduced conductivity can be well described...

  10. Negative differential mobility for negative carriers as revealed by space charge measurements on crosslinked polyethylene insulated model cables

    Energy Technology Data Exchange (ETDEWEB)

    Teyssedre, G., E-mail: gilbert.teyssedre@laplace.univ-tlse.fr; Laurent, C. [Université de Toulouse, UPS, INPT, LAPLACE (Laboratoire Plasma et Conversion d' Energie), 118 route de Narbonne, F-31062 Toulouse cedex 9 (France); CNRS, LAPLACE, F-31062 Toulouse (France); Vu, T. T. N. [Université de Toulouse, UPS, INPT, LAPLACE (Laboratoire Plasma et Conversion d' Energie), 118 route de Narbonne, F-31062 Toulouse cedex 9 (France); Electric Power University, 235 Hoang Quoc Viet, 10000 Hanoi (Viet Nam)

    2015-12-21

    Among features observed in polyethylene materials under relatively high field, space charge packets, consisting in a pulse of net charge that remains in the form of a pulse as it crosses the insulation, are repeatedly observed but without complete theory explaining their formation and propagation. Positive charge packets are more often reported, and the models based on negative differential mobility(NDM) for the transport of holes could account for some charge packets phenomenology. Conversely, NDM for electrons transport has never been reported so far. The present contribution reports space charge measurements by pulsed electroacoustic method on miniature cables that are model of HVDC cables. The measurements were realized at room temperature or with a temperature gradient of 10 °C through the insulation under DC fields on the order 30–60 kV/mm. Space charge results reveal systematic occurrence of a negative front of charges generated at the inner electrode that moves toward the outer electrode at the beginning of the polarization step. It is observed that the transit time of the front of negative charge increases, and therefore the mobility decreases, with the applied voltage. Further, the estimated mobility, in the range 10{sup −14}–10{sup −13} m{sup 2} V{sup −1} s{sup −1} for the present results, increases when the temperature increases for the same condition of applied voltage. The features substantiate the hypothesis of negative differential mobility used for modelling space charge packets.

  11. Light absorption in thin quantizing semiconductor wires with non-parabolic law of dispersion of charge carriers

    International Nuclear Information System (INIS)

    Djotian, A.P.; Kazarian, E.M.; Karakashinian, Y.V.

    1993-01-01

    Interband absorption of light in a quantizing wire with non-parabolic dispersion law of charge carries, as well as energy spectrum and state densities are studied. The effect of Coulomb interaction between particles on the spectral curve of interband absorption is considered. Non-parabolic dispersion law of charge carries leads to an essential displacement of absorption line to ground state of one-dimensional exciton. 7 refs

  12. Photocatalytic hydrogen generation enhanced by band gap narrowing and improved charge carrier mobility in AgTaO3 by compensated co-doping.

    Science.gov (United States)

    Li, Min; Zhang, Junying; Dang, Wenqiang; Cushing, Scott K; Guo, Dong; Wu, Nianqiang; Yin, Penggang

    2013-10-14

    The correlation of the electronic band structure with the photocatalytic activity of AgTaO3 has been studied by simulation and experiments. Doping wide band gap oxide semiconductors usually introduces discrete mid-gap states, which extends the light absorption but has limited benefit for photocatalytic activity. Density functional theory (DFT) calculations show that compensated co-doping in AgTaO3 can overcome this problem by increasing the light absorption and simultaneously improving the charge carrier mobility. N/H and N/F co-doping can delocalize the discrete mid-gap states created by sole N doping in AgTaO3, which increases the band curvature and the electron-to-hole effective mass ratio. In particular, N/F co-doping creates a continuum of states that extend the valence band of AgTaO3. N/F co-doping thus improves the light absorption without creating the mid-gap states, maintaining the necessary redox potentials for water splitting and preventing from charge carrier trapping. The experimental results have confirmed that the N/F-codoped AgTaO3 exhibits a red-shift of the absorption edge in comparison with the undoped AgTaO3, leading to remarkable enhancement of photocatalytic activity toward hydrogen generation from water.

  13. Terahertz response of two-dimensional charge carrier systems in GaAs-based heterostructures; Terahertz-Antwort von zweidimensionalen Ladungstraegersystemen in GaAs-basierten Heterostrukturen

    Energy Technology Data Exchange (ETDEWEB)

    Grunwald, Torben

    2009-12-17

    This thesis deals with the THz response of two-dimensional charge carrier systems in different semiconductor heterostructures under varying conditions. The utilized spectrometer is suitable for time-resolved optical pump - THz probe experiments, as well as for optical pump-probe experiments in the near infrared for identical conditions. It allows the investigation of the transverse dielectric function of both, a (GaIn)As/GaAs quantum well and a two-dimensional electron gas in a GaAs-based heterostructure. First, the THz response of an electron-hole plasma is examined for different carrier densities. The plasma is generated by interband transitions in a (GaIn)As/GaAs quantum well. The measured transverse dielectric function reveals that the plasma behaves in accordance with the classical Drude oscillator model. It also conforms to the microscopic theory of the THz response of corresponding many-body systems. Evidence of a plasma resonance in the negative imaginary part of the inverse dielectric function is found. The squared peak frequency of the resonance is proportional to the carrier density of the plasma. This behavior corresponds to the plasma frequency of a three-dimensional plasma. Overall, it can be shown that the transverse THz response of a two-dimensional electron-hole plasma behaves like the response of a three-dimensional plasma. Therefore, the transversal THz response of an electron-hole plasma seems to be independent of the dimension of the charge carrier system. Secondly, the behavior of the quantum well for a 1s-exciton dominated carrier system is investigated. A good agreement between experiment and microscopic theory is obtained for the dielectric function. The negative imaginary part of the inverse dielectric function shows a resonance at the intraexcitonic 1s-2p transition frequency, even in weakly excited excitonic systems. Increasing the carrier density leads to a plasma-like behavior of the system. However, in these densities a significant

  14. Model of Organic Solar Cell Photocurrent Including the Effect of Charge Accumulation at Interfaces and Non-Uniform Carrier Generation

    DEFF Research Database (Denmark)

    Torto, Lorenzo; Cester, Andrea; Rizzo, Antonio

    2017-01-01

    We developed an improved model to fit the photocurrent density versus voltage in organic solar cells. The model has been validated by fitting data from P3HT:PCBM solar cells. Our model quantitatively accounts for the band bending near the electrodes caused by charge accumulation in the active layer...

  15. Localized vs. delocalized character of charge carriers in LaAlO3/SrTiO3 heterostructure

    Energy Technology Data Exchange (ETDEWEB)

    Zhou, Kejin; Schlappa, Justine; Strocov, Vladimir; Frison, Ruggero; Patthey, Luc; Schmitt, Thorsten [Paul Scherrer Institut, CH-5232 Villigen PSI (Switzerland); Radovic, Milan [Laboratory for Synchrotron and Neutron Spectroscopy, Ecole Polytechnique Federale de Lausanne, CH-1015 Lausanne (Switzerland); Paul Scherrer Institut, CH-5232 Villigen PSI (Switzerland); Mesot, Joel [Paul Scherrer Institut, CH-5232 Villigen PSI (Switzerland); Laboratory for Synchrotron and Neutron Spectroscopy, Ecole Polytechnique Federale de Lausanne, CH-1015 Lausanne (Switzerland)

    2011-07-01

    Oxide heterostructures have been attracting great attention due to extraordinary phenomena occurring at the interface and their potential application for device design. A particularly fascinating system is the two-dimensional conductive interface between the band insulators LaAlO{sub 3} (LAO) and SrTiO{sub 3} (STO), which can be even driven to magnetic and superconducting phases at low temperatures. Resonant inelastic X-ray scattering at Ti L-edges is particularly suitable to address the electronic structure of its interface since the Ti{sup 3+} states clearly display strong dd excitations while Ti{sup 4+} states exhibit only elastic emission in the low energy loss regime. Our studies on LAO/STO superlattices prepared by pulsed laser deposition unambiguously reveal the presence of both localized and delocalized Ti 3d carriers generated during the building of the LAO/STO interfaces. Systematic studies on samples before and after annealing under O{sub 2} atmosphere and high temperature show that the dual character carriers can be either induced by electron transfer due to the polar-discontinuity or by oxygen vacancies defects. Oxygen vacancies and electronic reconstruction are equivalent in balancing the built-up electric potential.

  16. Investigation of charges carrier density in phosphorus and boron doped SiNx:H layers for crystalline silicon solar cells

    International Nuclear Information System (INIS)

    Paviet-Salomon, B.; Gall, S.; Slaoui, A.

    2013-01-01

    Highlights: ► We investigate the properties of phosphorus and boron-doped silicon nitride films. ► Phosphorus-doped layers yield higher lifetimes than undoped ones. ► The fixed charges density decreases when increasing the films phosphorus content. ► Boron-doped films feature very low lifetimes. ► These doped layers are of particular interest for crystalline silicon solar cells. -- Abstract: Dielectric layers are of major importance in crystalline silicon solar cells processing, especially as anti-reflection coatings and for surface passivation purposes. In this paper we investigate the fixed charge densities (Q fix ) and the effective lifetimes (τ eff ) of phosphorus (P) and boron (B) doped silicon nitride layers deposited by plasma-enhanced chemical vapour deposition. P-doped layers exhibit a higher τ eff than standard undoped layers. In contrast, B-doped layers exhibit lower τ eff . A strong Q fix decrease is to be seen when increasing the P content within the film. Based on numerical simulations we also demonstrate that the passivation obtained with P- and B-doped layers are limited by the interface states rather than by the fixed charges

  17. Ionic Liquids: Radiation Chemistry, Solvation Dynamics and Reactivity Patterns

    International Nuclear Information System (INIS)

    Wishart, J.F.

    2011-01-01

    Ionic liquids (ILs) are a rapidly expanding family of condensed-phase media with important applications in energy production, nuclear fuel and waste processing, improving the efficiency and safety of industrial chemical processes, and pollution prevention. ILs generally have low volatilities and are combustion-resistant, highly conductive, recyclable and capable of dissolving a wide variety of materials. They are finding new uses in chemical synthesis, catalysis, separations chemistry, electrochemistry and other areas. Ionic liquids have dramatically different properties compared to conventional molecular solvents, and they provide a new and unusual environment to test our theoretical understanding of primary radiation chemistry, charge transfer and other reactions. We are interested in how IL properties influence physical and dynamical processes that determine the stability and lifetimes of reactive intermediates and thereby affect the courses of reactions and product distributions. We study these issues by characterization of primary radiolysis products and measurements of their yields and reactivity, quantification of electron solvation dynamics and scavenging of electrons in different states of solvation. From this knowledge we wish to learn how to predict radiolytic mechanisms and control them or mitigate their effects on the properties of materials used in nuclear fuel processing, for example, and to apply IL radiation chemistry to answer questions about general chemical reactivity in ionic liquids that will aid in the development of applications listed above. Very early in our radiolysis studies it became evident that the slow solvation dynamics of the excess electron in ILs (which vary over a wide viscosity range) increase the importance of pre-solvated electron reactivity and consequently alter product distributions and subsequent chemistry. This difference from conventional solvents has profound effects on predicting and controlling radiolytic yields

  18. Optimization of charge-carrier generation in amorphous-silicon thin-film tandem solar cell backed by two-dimensional metallic surface-relief grating

    Science.gov (United States)

    Civiletti, Benjamin J.; Anderson, Tom H.; Ahmad, Faiz; Monk, Peter B.; Lakhtakia, Akhlesh

    2017-08-01

    The rigorous coupled-wave approach was implemented in a three-dimensional setting to calculate the chargecarrier-generation rate in a thin-film solar cell with multiple amorphous-silicon p-i-n junctions. The solar cell comprised a front antireflection window; three electrically isolated p-i-n junctions in tandem; and a periodically corrugated silver back-reflector with hillock-shaped corrugations arranged on a hexagonal lattice. The differential evolution algorithm (DEA) was used to maximize the charge-carrier-generation rate over a set of selected optical and electrical parameters. This optimization exercise minimized the bandgap of the topmost i-layer but all other parameters turned out to be uninfluential. More importantly, the exercise led to a configuration that would very likely render the solar cell inefficient. Therefore, another optimization exercise was conducted to maximize power density. The resulting configuration was optimal over all parameters.

  19. Energy spectrum of charge carriers in TlIn{sub 1–x}Yb{sub x}Te{sub 2} solid solutions

    Energy Technology Data Exchange (ETDEWEB)

    Aliev, F. F., E-mail: farzali@physics.ab.az [Azerbaijan National Academy of Sciences, Institute of Physics (Azerbaijan); Agaeva, U. M.; Zarbaliev, M. M., E-mail: zarbalievmm51@mail.ru [Sumqayit State University (Azerbaijan)

    2016-10-15

    The temperature dependences of the electrical conductivity σ(T), the Hall coefficient R(T), and the thermoelectric coefficient α(T) are investigated in TlIn{sub 1–x}Yb{sub x}Te{sub 2} (0 < x < 0.10) solid solutions at 80–1000K. From the kinetic parameters, the effective masses of electrons and holes are determined. The obtained experimental data on σ(T) and α(T) are interpreted within the context of a model with one and two types of charge carriers. It is established that, since x = 0.05, the TlIn{sub 1–x}Yb{sub x}Te{sub 2} solid solutions belong to the class of narrow-gap semiconductors that have high matrix elements of interaction.

  20. Comparison of modification strategies towards enhanced charge carrier separation and photocatalytic degradation activity of metal oxide semiconductors (TiO2, WO3 and ZnO)

    Science.gov (United States)

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

    2017-01-01

    Metal oxide semiconductors (TiO2, WO3 and ZnO) finds unparalleled opportunity in wastewater purification under UV/visible light, largely encouraged by their divergent admirable features like stability, non-toxicity, ease of preparation, suitable band edge positions and facile generation of active oxygen species in the aqueous medium. However, the perennial failings of these photocatalysts emanates from the stumbling blocks like rapid charge carrier recombination and meager visible light response. In this review, tailoring the surface-bulk electronic structure through the calibrated and veritable approaches such as impurity doping, deposition with noble metals, sensitizing with other compounds (dyes, polymers, inorganic complexes and simple chelating ligands), hydrogenation process (annealing under hydrogen atmosphere), electronic integration with other semiconductors, modifying with carbon nanostructures, designing with exposed facets and tailoring with hierarchical morphologies to overcome their critical drawbacks are summarized. Taking into account the materials intrinsic properties, the pros and cons together with similarities and striking differences for each strategy in specific to TiO2, WO3 & ZnO are highlighted. These subtlety enunciates the primacy for improving the structure-electronic properties of metal oxides and credence to its fore in the practical applications. Future research must focus on comparing the performances of ZnO, TiO2 and WO3 in parallel to get insight into their photocatalytic behaviors. Such comparisons not only reveal the changed surface-electronic structure upon various modifications, but also shed light on charge carrier dynamics, free radical generation, structural stability and compatibility for photocatalytic reactions. It is envisioned that these cardinal tactics have profound implications and can be replicated to other semiconductor photocatalysts like CeO2, In2O3, Bi2O3, Fe2O3, BiVO4, AgX, BiOX (X = Cl, Br & I), Bi2WO6, Bi2MoO6

  1. Method to quantify the delocalization of electronic states in amorphous semiconductors and its application to assessing charge carrier mobility of p -type amorphous oxide semiconductors

    Science.gov (United States)

    de Jamblinne de Meux, A.; Pourtois, G.; Genoe, J.; Heremans, P.

    2018-01-01

    Amorphous semiconductors are usually characterized by a low charge carrier mobility, essentially related to their lack of long-range order. The development of such material with higher charge carrier mobility is hence challenging. Part of the issue comes from the difficulty encountered by first-principles simulations to evaluate concepts such as the electron effective mass for disordered systems since the absence of periodicity induced by the disorder precludes the use of common concepts derived from condensed matter physics. In this paper, we propose a methodology based on first-principles simulations that partially solves this problem, by quantifying the degree of delocalization of a wave function and of the connectivity between the atomic sites within this electronic state. We validate the robustness of the proposed formalism on crystalline and molecular systems and extend the insights gained to disordered/amorphous InGaZnO4 and Si. We also explore the properties of p -type oxide semiconductor candidates recently reported to have a low effective mass in their crystalline phases [G. Hautier et al., Nat. Commun. 4, 2292 (2013), 10.1038/ncomms3292]. Although in their amorphous phase none of the candidates present a valence band with delocalization properties matching those found in the conduction band of amorphous InGaZnO4, three of the seven analyzed materials show some potential. The most promising candidate, K2Sn2O3 , is expected to possess in its amorphous phase a slightly higher hole mobility than the electron mobility in amorphous silicon.

  2. Charge-carrier transport in epitactical strontium titanate layers for the application in superconducting components; Ladungstraegertransport in epitaktischen Strontiumtitanat-Schichten fuer den Einsatz in supraleitenden Bauelementen

    Energy Technology Data Exchange (ETDEWEB)

    Grosse, Veit

    2011-02-01

    In this thesis thin STO layers were epitactically deposited on YBCO for a subsequent electrical characterization. YBCO layers with a roughness of less than 2 nm (RMS), good out-of-plane orientation with a half-width in the rocking curve in the range (0.2..0.3) at only slightly diminished critical temperature could be reached. The STO layers exhibited also very good crystallographic properties. The charge-carrier transport in STO is mainly dominated by interface-limited processes. By means of an in thesis newly developed barrier model thereby the measured dependencies j(U,T) respectively {sigma}(U,T) could be described very far-reachingly. At larger layer thicknesses and low temperatures the charge-carrier transport succeeds by hopping processes. So in the YBCO/STO/YBCO system the variable-range hopping could be identified as dominating transport process. Just above U>10 V a new behaviour is observed, which concerning its temperature dependence however is also tunnel-like. The STO layers exhibit here very large resistances, so that fields up to 10{sup 7}..10{sup 8} V/m can be reached without flowing of significant leakage currents through the barrier. In the system YBCO/STO/Au the current transport can be principally in the same way as in the YBCO/STO/YBCO system. The special shape and above all the asymmetry of the barrier however work out very distinctly. It could be shown that at high temperatures according to the current direction a second barrier on the opposite electrode must be passed. So often observed breakdown effects can be well described. For STO layer-thicknesses in the range around 25 nm in the whole temperature range studied inelastic tunneling over chains of localized states was identified as dominating transport process. It could however for the first time be shown that at very low temperatures in the STO layers Coulomb blockades can be formed.

  3. Modelos contínuos do solvente: fundamentos Continuum solvation models: fundamentals

    Directory of Open Access Journals (Sweden)

    Josefredo R. Pliego Jr

    2006-06-01

    Full Text Available Continuum solvation models are nowadays widely used in the modeling of solvent effects and the range of applications goes from the calculation of partition coefficients to chemical reactions in solution. The present work presents a detailed explanation of the physical foundations of continuum models. We discuss the polarization of a dielectric and its representation through the volume and surface polarization charges. The Poisson equation for a dielectric was obtained and we have also derived and discuss the apparent surface charge method and its application for free energy of solvation calculations.

  4. Polyoxovanadate-alkoxide clusters as multi-electron charge carriers for symmetric non-aqueous redox flow batteries.

    Science.gov (United States)

    VanGelder, L E; Kosswattaarachchi, A M; Forrestel, P L; Cook, T R; Matson, E M

    2018-02-14

    Non-aqueous redox flow batteries have emerged as promising systems for large-capacity, reversible energy storage, capable of meeting the variable demands of the electrical grid. Here, we investigate the potential for a series of Lindqvist polyoxovanadate-alkoxide (POV-alkoxide) clusters, [V 6 O 7 (OR) 12 ] (R = CH 3 , C 2 H 5 ), to serve as the electroactive species for a symmetric, non-aqueous redox flow battery. We demonstrate that the physical and electrochemical properties of these POV-alkoxides make them suitable for applications in redox flow batteries, as well as the ability for ligand modification at the bridging alkoxide moieties to yield significant improvements in cluster stability during charge-discharge cycling. Indeed, the metal-oxide core remains intact upon deep charge-discharge cycling, enabling extremely high coulombic efficiencies (∼97%) with minimal overpotential losses (∼0.3 V). Furthermore, the bulky POV-alkoxide demonstrates significant resistance to deleterious crossover, which will lead to improved lifetime and efficiency in a redox flow battery.

  5. Measurement of the drift mobilities and the mobility-lifetime products of charge carriers in a CdZnTe crystal by using a transient pulse technique

    International Nuclear Information System (INIS)

    Cho, H Y; Kwon, Y K; Lee, C S; Lee, J H; Moon, J Y

    2011-01-01

    In this work we present results on the measurement of the drift mobility and the mobility-lifetime product of charge carriers in a 16-pixellated CdZnTe detector. For the determination of an interaction position based on the pulse rise-time method in a CZT detector, it is necessary to characterize the transport properties governed by drift mobility and lifetime for electrons and holes. In order to extract the transport properties of an electron and a hole, we bombarded 5.5-MeV alpha particles from a 241 Am source and 81-keV gamma rays emitted from a 133 Ba source on the negatively biased contact of the CZT detector. A time-of-flight (TOF) method was used to measure the electron drift mobility at room temperature whose value turned out to be 906.4 cm 2 /Vc s. With the Hecht's equation, the electron mobility-lifetime product was also determined from the bias-dependent alpha response and was equal to (9.88 ± 2.33) x 10 -3 cm 2 /V. On the other hand, the hole mobility-lifetime product was evaluated by a model based on the average charge collection efficiency which accounts for the absorption probability with a given photon energy. By using a single parameter fitting of the model, we obtained the hole mobility-lifetime product of (8.28 ± 0.17) x 10 -4 cm 2 /V.

  6. Performance of hybrid p-type vertical transistors with poly(N-vinylcarbazole) as emitter and the transfer mechanism of charge carriers through the base

    International Nuclear Information System (INIS)

    Huang, Jinying; Ma, Dongge; Hümmelgen, Ivo A

    2013-01-01

    We report hybrid vertical architecture p-type transistors with poly(N-vinylcarbazole) as the emitter, p-type silicon as the collector and Al:Ca alloy layer as the base. The investigation of the common-base and common-emitter characteristics clearly demonstrates that the devices operate as permeable-base transistors (PBTs). The PBTs show common-base current gain α of 0.98 at −V BC = 1.5 V and common-emitter gain β of over 100. Atomic force microscope images of the base layer show an uneven surface, showing that the annealing does not dissolve the charge trap states but offers ‘pinholes’ for the oxidation in-depth even through the whole base layer. In this case, the charge carriers must tunnel the thin oxidized layer, and then are collected. It is clearly seen that there exists a barrier against holes injection from the base to the collector semiconductor at the interface, and the further oxidation caused by exposing the devices in air changes the operational mode of the resulting devices from the PBT to the metal-base transistor. (paper)

  7. Corrosion Thermodynamics of Magnesium and Alloys from First Principles as a Function of Solvation

    Science.gov (United States)

    Limmer, Krista; Williams, Kristen; Andzelm, Jan

    Thermodynamics of corrosion processes occurring on magnesium surfaces, such as hydrogen evolution and water dissociation, have been examined with density functional theory (DFT) to evaluate the effect of impurities and dilute alloying additions. The modeling of corrosion thermodynamics requires examination of species in a variety of chemical and electronic states in order to accurately represent the complex electrochemical corrosion process. In this study, DFT calculations for magnesium corrosion thermodynamics were performed with two DFT codes (VASP and DMol3), with multiple exchange-correlation functionals for chemical accuracy, as well as with various levels of implicit and explicit solvation for surfaces and solvated ions. The accuracy of the first principles calculations has been validated against Pourbaix diagrams constructed from solid, gas and solvated charged ion calculations. For aqueous corrosion, it is shown that a well parameterized implicit solvent is capable of accurately representing all but the first coordinating layer of explicit water for charged ions.

  8. Role of Dispersive Fluorous Interaction in the Solvation Dynamics of the Perfluoro Group Containing Molecules.

    Science.gov (United States)

    Mondal, Saptarsi; Chaterjee, Soumit; Halder, Ritaban; Jana, Biman; Singh, Prashant Chandra

    2017-08-17

    Perfluoro group containing molecules possess an important self-aggregation property through the fluorous (F···F) interaction which makes them useful for diverse applications such as medicinal chemistry, separation techniques, polymer technology, and biology. In this article, we have investigated the solvation dynamics of coumarin-153 (C153) and coumarin-6H (C6H) in ethanol (ETH), 2-fluoroethanol (MFE), and 2,2,2-trifluoroethanol (TFE) using the femtosecond upconversion technique and molecular dynamics (MD) simulation to understand the role of fluorous interaction between the solute and solvent molecules in the solvation dynamics of perfluoro group containing molecules. The femtosecond upconversion data show that the time scales of solvation dynamics of C6H in ETH, MFE, and TFE are approximately the same whereas the solvation dynamics of C153 in TFE is slow as compared to that of ETH and MFE. It has also been observed that the time scale of solvation dynamics of C6H in ETH and MFE is higher than that of C153 in the same solvents. MD simulation results show a qualitative agreement with the experimental data in terms of the time scale of the slow components of the solvation for all the systems. The experimental and simulation studies combined lead to the conclusion that the solvation dynamics of C6H in all solvents as well as C153 in ETH and MFE is mostly governed by the charge distribution of ester moieties (C═O and O) of dye molecules whereas the solvation of C153 in TFE is predominantly due to the dispersive fluorous interaction (F···F) between the perfluoro groups of the C153 and solvent molecules.

  9. A novel research approach on the dynamic properties of photogenerated charge carriers at Ag{sub 2}S quantum-dots-sensitized TiO{sub 2} films by a frequency-modulated surface photovoltage technology

    Energy Technology Data Exchange (ETDEWEB)

    Zhang, Yu; Zhang, Wei [Liaoning Key Laboratory for Green Synthesis and Preparative Chemistry of Advanced Materials, College of Chemistry, Liaoning University, Shenyang 110036 (China); Xie, Tengfeng; Wang, Dejun [College of Chemistry, Jilin University, Changchun 130012 (China); Song, Xi-Ming, E-mail: songlab@lnu.edu.cn [Liaoning Key Laboratory for Green Synthesis and Preparative Chemistry of Advanced Materials, College of Chemistry, Liaoning University, Shenyang 110036 (China)

    2013-09-01

    Graphical abstract: The changed SPV with chopping frequencies indicate the separation speeds of photogenerated charge carriers in different films. - Highlights: • Ag{sub 2}S-sensitized TiO{sub 2} films show good photoelectric responses in visible-light region. • Frequency-modulated SPV give dynamic information and evidence of Ag{sub 2}S QDSSCs’ performance. • Frequency-modulated SPV can supply complementary information in the study of Ag{sub 2}S ODSSCs. - Abstract: Ag{sub 2}S quantum-dots-sensitized TiO{sub 2} films with different amount of Ag{sub 2}S were fabricated by a successive ionic layer adsorption and reaction (SILAR) method. The separation and transport of photogenerated charge carriers at different spectral regions were studied by the frequency-modulated surface photovoltage technology. Some novel dynamic information of photogenerated charge carriers in a wide spectral range is found. The results indicate that the rate and direction of separation (diffusion) for photogenerated charge carriers are closely related to the performance of quantum-dots-sensitized solar cells (QDSSCs) based on the Ag{sub 2}S/TiO{sub 2} nano-structure.

  10. The effect of charge carrier and doping site on thermoelectric properties of Mg2Sn0.75Ge0.25

    International Nuclear Information System (INIS)

    Saparamadu, Udara; Mao, Jun; Dahal, Keshab; Zhang, Hao; Tian, Fei; Song, Shaowei; Liu, Weishu; Ren, Zhifeng

    2017-01-01

    Mg 2 Sn 0.75 Ge 0.25 has been recently demonstrated to be a promising thermoelectric material for power generation in the temperature range from room temperature to 723 K because of the high power factor of ∼54 μW cm −1  K −2 upon Sb doping to the Sn site. The enhanced density of states effective mass and weak electron scattering from the alloying effect are believed to be the main reasons for the high power factor (PF) and hence high figure of merit (ZT). In this study, it is shown that the right choice of carrier donor also plays an important role in obtaining high power factor. The effect of carrier donors Y and La at Mg-site and Bi and P at Sn-site in Mg 2 Sn 0.75 Ge 0.25 is systematically investigated. It is found that charge donors at the Sn-site are much more effective than at the Mg-site in enhancing PF and ZT. Bi doped Mg 2 Sn 0.73 Bi 0.02 Ge 0.25 shows a peak ZT of ∼1.4 at 673 K, a peak PF of ∼54 μW cm −1  K −2 at 577 K, which resulted in an engineering figure of merit (ZT) eng of ∼0.76 and (PF) eng of ∼2.05 W m −1  K −1 for cold side fixed at 323 K and hot side at 723 K.

  11. Ionic Liquids: Radiation Chemistry, Solvation Dynamics and Reactivity Patterns

    International Nuclear Information System (INIS)

    Wishart, J.F.

    2008-01-01

    Ionic liquids (ILs) are a rapidly expanding family of condensed-phase media with important applications in energy production, nuclear fuel and waste processing, improving the efficiency and safety of industrial chemical processes, and pollution prevention. ILs are generally nonvolatile, noncombustible, highly conductive, recyclable and capable of dissolving a wide variety of materials. They are finding new uses in chemical synthesis, catalysis, separations chemistry, electrochemistry and other areas. Ionic liquids have dramatically different properties compared to conventional molecular solvents, and they provide a new and unusual environment to test our theoretical understanding of charge transfer and other reactions. We are interested in how IL properties influence physical and dynamical processes that determine the stability and lifetimes of reactive intermediates and thereby affect the courses of chemical reactions and product distributions. Successful use of ionic liquids in radiation-filled environments, where their safety advantages could be significant, requires an understanding of ionic liquid radiation chemistry. For example, characterizing the primary steps of IL radiolysis will reveal radiolytic degradation pathways and suggest ways to prevent them or mitigate their effects on the properties of the material. An understanding of ionic liquid radiation chemistry will also facilitate pulse radiolysis studies of general chemical reactivity in ILs, which will aid in the development of applications listed above. Very early in our radiolysis studies it became evident that slow solvation dynamics of the excess electron in ILs (which vary over a wide viscosity range) increases the importance of pre-solvated electron reactivity and consequently alters product distributions. Parallel studies of IL solvation phenomena using coumarin-153 dynamic Stokes shifts and polarization anisotropy decay rates are done to compare with electron solvation studies and to evaluate

  12. IONIC LIQUIDS: RADIATION CHEMISTRY, SOLVATION DYNAMICS AND REACTIVITY PATTERNS

    International Nuclear Information System (INIS)

    WISHART, J.F.

    2007-01-01

    energy production, nuclear fuel and waste processing, improving the efficiency and safety of industrial chemical processes, and pollution prevention. ILs are generally nonvolatile, noncombustible, highly conductive, recyclable and capable of dissolving a wide variety of materials. They are finding new uses in chemical synthesis, catalysis, separations chemistry, electrochemistry and other areas. Ionic liquids have dramatically different properties compared to conventional molecular solvents, and they provide a new and unusual environment to test our theoretical understanding of charge transfer and other reactions. We are interested in how IL properties influence physical and dynamical processes that determine the stability and lifetimes of reactive intermediates and thereby affect the courses of chemical reactions and product distributions. Successful use of ionic liquids in radiation-filled environments, where their safety advantages could be significant, requires an understanding of ionic liquid radiation chemistry. For example, characterizing the primary steps of IL radiolysis will reveal radiolytic degradation pathways and suggest ways to prevent them or mitigate their effects on the properties of the material. An understanding of ionic liquid radiation chemistry will also facilitate pulse radiolysis studies of general chemical reactivity in ILs, which will aid in the development of applications listed above. Very early in our radiolysis studies it became evident that slow solvation dynamics of the excess electron in ILs (which vary over a wide viscosity range) increases the importance of pre-solvated electron reactivity and consequently alters product distributions. Parallel studies of IL solvation phenomena using coumarin-153 dynamic Stokes shifts and polarization anisotropy decay rates are done to compare with electron solvation studies and to evaluate the influence of ILs on charge transport processes. Methods. Picosecond pulse radiolysis studies at BNL

  13. Updated Abraham solvation parameters for polychlorinated biphenyls

    NARCIS (Netherlands)

    van Noort, P.C.M.; Haftka, J.J.H.; Parsons, J.R.

    2010-01-01

    This study shows that the recently published polychlorinated biphenyl (PCB) Abraham solvation parameters predict PCB air−n-hexadecane and n-octanol−water partition coefficients very poorly, especially for highly ortho-chlorinated congeners. Therefore, an updated set of PCB solvation parameters was

  14. Updated Abraham solvation parameters for polychlorinated biphenyls

    NARCIS (Netherlands)

    Noort, van P.C.M.; Haftka, J.J.H.; Parsons, J.R.

    2010-01-01

    This study shows that the recently published polychlorinated biphenyl (PCB) Abraham solvation parameters predict PCB air-n-hexadecane and n-octanol-water partition coefficients very poorly, especially for highly ortho-chlorinated congeners. Therefore, an updated set of PCB solvation parameters was

  15. Benzonitrile: Electron affinity, excited states, and anion solvation

    Science.gov (United States)

    Dixon, Andrew R.; Khuseynov, Dmitry; Sanov, Andrei

    2015-10-01

    We report a negative-ion photoelectron imaging study of benzonitrile and several of its hydrated, oxygenated, and homo-molecularly solvated cluster anions. The photodetachment from the unsolvated benzonitrile anion to the X ˜ 1 A 1 state of the neutral peaks at 58 ± 5 meV. This value is assigned as the vertical detachment energy (VDE) of the valence anion and the upper bound of adiabatic electron affinity (EA) of benzonitrile. The EA of the lowest excited electronic state of benzonitrile, a ˜ 3 A 1 , is determined as 3.41 ± 0.01 eV, corresponding to a 3.35 eV lower bound for the singlet-triplet splitting. The next excited state, the open-shell singlet A ˜ 1 A 1 , is found about an electron-volt above the triplet, with a VDE of 4.45 ± 0.01 eV. These results are in good agreement with ab initio calculations for neutral benzonitrile and its valence anion but do not preclude the existence of a dipole-bound state of similar energy and geometry. The step-wise and cumulative solvation energies of benzonitrile anions by several types of species were determined, including homo-molecular solvation by benzonitrile, hydration by 1-3 waters, oxygenation by 1-3 oxygen molecules, and mixed solvation by various combinations of O2, H2O, and benzonitrile. The plausible structures of the dimer anion of benzonitrile were examined using density functional theory and compared to the experimental observations. It is predicted that the dimer anion favors a stacked geometry capitalizing on the π-π interactions between the two partially charged benzonitrile moieties.

  16. First principles analysis of the CDW instability of single-layer 1T-TiSe2 and its evolution with charge carrier density

    Science.gov (United States)

    Guster, Bogdan; Canadell, Enric; Pruneda, Miguel; Ordejón, Pablo

    2018-04-01

    We present a density functional theory study of the electronic structure of single-layer TiSe2, and focus on the charge density wave (CDW) instability present on this 2D material. We explain the 2× 2 periodicity of the CDW from the phonon band structure of the undistorted crystal, which is unstable under one of the phonon modes at the M point. This can be understood in terms of a partial band gap opening at the Fermi level, which we describe on the basis of the symmetry of the involved crystal orbitals, leading to an energy gain upon the displacement of the atoms following the phonon mode in a 2  ×  1 structure. Furthermore, the combination of the corresponding phonons for the three inequivalent M points of the Brillouin zone leads to the 2  ×  2 distortion characteristic of the CDW state. This leads to a further opening of a full gap, which reduces the energy of the 2  ×  2 structure compared to the 2  ×  1 one of a single M point phonon, and makes the CDW structure the most stable one. We also analyze the effect of charge injection into the layer on the structural instability. We predict that the 2  ×  2 structure only survives for a certain range of doping levels, both for electrons and for holes, as doping reduces the energy gain due to the gap opening. We predict the transition from the commensurate 2  ×  2 distortion to an incommensurate one with increasing wavelength upon increasing the doping level, followed by the appearance of the undistorted 1  ×  1 structure for larger carrier concentrations.

  17. Equilibrium and nonequilibrium solvation and solute electronic structure

    International Nuclear Information System (INIS)

    Kim, H.J.; Hynes, J.T.

    1990-01-01

    When a molecular solute is immersed in a polar and polarizable solvent, the electronic wave function of the solute system is altered compared to its vacuum value; the solute electronic structure is thus solvent-dependent. Further, the wave function will be altered depending upon whether the polarization of the solvent is or is not in equilibrium with the solute charge distribution. More precisely, while the solvent electronic polarization should be in equilibrium with the solute electronic wave function, the much more sluggish solvent orientational polarization need not be. We call this last situation non-equilibrium solvation. We outline a nonlinear Schroedinger equation approach to these issues

  18. Design of suitable carrier buffer for free-flow zone electrophoresis by charge-to-mass ratio and band broadening analysis.

    Science.gov (United States)

    Kong, Fan-Zhi; Yang, Ying; He, Yu-Chen; Zhang, Qiang; Li, Guo-Qing; Fan, Liu-Yin; Xiao, Hua; Li, Shan; Cao, Cheng-Xi

    2016-09-01

    In this work, charge-to-mass ratio (C/M) and band broadening analyses were combined to provide better guidance for the design of free-flow zone electrophoresis carrier buffer (CB). First, the C/M analyses of hemoglobin and C-phycocyanin (C-PC) under different pH were performed by CLC Protein Workbench software. Second, band dispersion due to the initial bandwidth, diffusion, and hydrodynamic broadening were discussed, respectively. Based on the analyses of the C/M and band broadening, a better guidance for preparation of free-flow zone electrophoresis CB was obtained. Series of experiments were performed to validate the proposed method. The experimental data showed high accordance with our prediction allowing the CB to be prepared easily with our proposed method. To further evaluate this method, C-PC was purified from crude extracts of Spirulina platensis with the selected separation condition. Results showed that C-PC was well separated from other phycobiliproteins that have similar physicochemical properties, and analytical grade product with purity up to 4.5 (A620/A280) was obtained. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  19. Solvates of silico-12-molybdic acid with alcohols

    International Nuclear Information System (INIS)

    Punchuk, I.N.; Chuvaev, V.F.

    1984-01-01

    With the aim of investigating interaction processes of solid heteropolyacids and organic compounds, solvates are prepared. Solvates are products of adding gaseous methanol, ethanol and isopropanol to silico-12-molybdic acid. The compounds are studied by IR and PMR spectroscopy methods. Possible models for solvate structure are considered, as well as their connection with solvate properties and thermal decomposition

  20. Terahertz radiation on the base of accelerated charge carriers in GaAs; Terahertz-Strahlung auf der Basis beschleunigter Ladungstraeger in GaAs

    Energy Technology Data Exchange (ETDEWEB)

    Dreyhaupt, Andre

    2008-07-01

    Electromagnetic radiation in the frequency range between about 100 GHz and 5 THz can be used for spectroscopy and microscopy, but it is also promising for security screening and even wireless communication. In the present thesis a planar photoconducting large-area THz radiation source is presented. The device exhibits outstanding properties, in particular high THz field strength and generation efficiency and large spectral bandwidth with short THz pulse length. The THz emission is based on acceleration and deceleration of photoexcited carriers in semiconductor substrates. A metallic interdigitated structure at the surface of semi-insulating GaAs provides the electrodes of an Auston switch. In a biased structure photoexcited charge carriers are accelerated. Hence electromagnetic waves are emitted. An appropriately structured second metallization, electrically isolated from the electrodes, prevents destructive interference of the emitted waves. The structure investigated here combines several advantages of different conventional photoconducting THz sources. First, it provides high electric acceleration fields at moderate voltages owing to the small electrode separation. Second, the large active area in the mm2 range allows excitation by large optical powers of some mW. Optical excitation with near-infrared femtosecond lasers is possible with repetition rates in the GHz range. The presented results point out the excellent characteristics regarding the emitted THz field strength, average power, spectral properties, and easy handling of the interdigitated structure in comparison to various conventional emitter structures. Various modifications of the semiconductor substrate and the optimum excitation conditions were investigated. In the second part of this thesis the dynamic conductivity of GaAs/Al{sub x}Ga{sub 1-x}As superlattices in an applied static electric field was investigated with time-resolved THz spectroscopy. The original goal was to explore whether the

  1. Hydrophilic Solvation Dominates the Terahertz Fingerprint of Amino Acids in Water.

    Science.gov (United States)

    Esser, Alexander; Forbert, Harald; Sebastiani, Federico; Schwaab, Gerhard; Havenith, Martina; Marx, Dominik

    2018-02-01

    Spectroscopy in the terahertz frequency regime is a sensitive tool to probe solvation-induced effects in aqueous solutions. Yet, a systematic understanding of spectral lineshapes as a result of distinct solvation contributions remains terra incognita. We demonstrate that modularization of amino acids in terms of functional groups allows us to compute their distinct contributions to the total terahertz response. Introducing the molecular cross-correlation analysis method provides unique access to these site-specific contributions. Equivalent groups in different amino acids lead to look-alike spectral contributions, whereas side chains cause characteristic but additive complexities. Specifically, hydrophilic solvation of the zwitterionic groups in valine and glycine leads to similar terahertz responses which are fully decoupled from the side chain. The terahertz response due to H-bonding within the large hydrophobic solvation shell of valine turns out to be nearly indistinguishable from that in bulk water in direct comparison to the changes imposed by the charged functional groups that form strong H-bonds with their hydration shells. Thus, the hydrophilic groups and their solvation shells dominate the terahertz absorption difference, while on the same intensity scale, the influence of hydrophobic water can be neglected.

  2. Improving accuracy of electrochemical capacitance and solvation energetics in first-principles calculations

    Science.gov (United States)

    Sundararaman, Ravishankar; Letchworth-Weaver, Kendra; Schwarz, Kathleen A.

    2018-04-01

    Reliable first-principles calculations of electrochemical processes require accurate prediction of the interfacial capacitance, a challenge for current computationally efficient continuum solvation methodologies. We develop a model for the double layer of a metallic electrode that reproduces the features of the experimental capacitance of Ag(100) in a non-adsorbing, aqueous electrolyte, including a broad hump in the capacitance near the potential of zero charge and a dip in the capacitance under conditions of low ionic strength. Using this model, we identify the necessary characteristics of a solvation model suitable for first-principles electrochemistry of metal surfaces in non-adsorbing, aqueous electrolytes: dielectric and ionic nonlinearity, and a dielectric-only region at the interface. The dielectric nonlinearity, caused by the saturation of dipole rotational response in water, creates the capacitance hump, while ionic nonlinearity, caused by the compactness of the diffuse layer, generates the capacitance dip seen at low ionic strength. We show that none of the previously developed solvation models simultaneously meet all these criteria. We design the nonlinear electrochemical soft-sphere solvation model which both captures the capacitance features observed experimentally and serves as a general-purpose continuum solvation model.

  3. Understanding Lithium Solvation and Diffusion through Topological Analysis of First-Principles Molecular Dynamics

    Energy Technology Data Exchange (ETDEWEB)

    Bhatia, Harsh [Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States); Gyulassy, Attila [Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States); Ong, Mitchell [Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States); Lordi, Vincenzo [Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States); Draeger, Erik [Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States); Pask, John [Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States); Pascucci, Valerio [Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States); Bremer, Peer -Timo [Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)

    2016-09-27

    The performance of lithium-ion batteries is strongly influenced by the ionic conductivity of the electrolyte, which depends on the speed at which Li ions migrate across the cell and relates to their solvation structure. The choice of solvent can greatly impact, both, the solvation and diffusivity of Li ions. In this work, we present our application of the topological techniques to extract and predict such behavior in the data generated by the first-principles molecular dynamics simulation of Li ions in an important organic solvent -ethylene carbonate. More specifically, we use the scalar topology of the electron charge density field to analyze the evolution of the solvation structures. This allows us to derive a parameter-free bond definition for lithium-oxygen bonds, to provide a quantitative measure for bond strength, and to understand the regions of influence of each atom in the simulation. This has provided new insights into how and under what conditions certain bonds may form and break. As a result, we can identify and, more importantly, predict, unstable configurations in solvation structures. This can be very useful in understanding when small changes to the atoms' movements can cause significantly different bond structures to evolve. Ultimately, this promises to allow scientists to explore lithium ion solvation and diffusion more systematically, with the aim of new insights and potentially accelerating the calculations themselves.

  4. Ambipolar charge carrier transport in organic semiconductor blends of C{sub 60} and CuPc; Ambipolarer Ladungstransport in organischen Halbleiter-Mischschichten bestehend aus C{sub 60} und CuPc

    Energy Technology Data Exchange (ETDEWEB)

    Bronner, Markus

    2008-06-20

    In this work ambipolar charge carrier transport is realised in organic field effect transistors using mixtures of p-conductive copper phthalocyanine and n-conductive buckminster fullerene as active layer. These blends are known from research on organic solar cells and can be considered as a model system for ambipolar transport. The field effect mobilities for electrons and holes can be adjusted by the variation of the mixing ratio. Thereby balanced mobilities for both charge carrier types are possible. In this work the variation of mobility, threshold voltage and electronic energy levels with the mixing ratio is discussed. The charge carrier mobilities are strongly reduced upon dilution of the respective conducting phase by the other species. This shows that transport of each carrier species occurs by percolation through the respective phase in the blend. A strong correlation between contact resistance and mobility indicates that carrier injection is diffusion limited. A charge redistribution in the copper phthalocyanine causes a hole accumulation at the organic/organic interface and affects thereby the threshold voltage for holes. The electronic structure was investigated by photoelectron spectroscopy. It was found that there is no chemical reaction between the different materials. The common work function of these blends changes linearly between the work functions of the neat materials. Moreover, a constant ionisation potential for the highest occupied molecular orbitals of the two materials and the core levels is obtained. Furthermore ambipolar inverters using mixed organic semiconductor layers were made and compared to complementary inverters consisting of discrete p- and n-channel transistors. The experimental findings and concomitant simulations demonstrate the need for balanced electron and hole mobilities in order to achieve symmetric inverter characteristics. However, they also reveal the superior performance of true complementary logic inverters towards

  5. Ionic liquids: radiation chemistry, solvation dynamics and reactivity patterns

    International Nuclear Information System (INIS)

    Wishart, J.F.; Funston, A.M.; Szreder, T.

    2006-01-01

    Ionic liquids (ILs) are a rapidly expanding family of condensed-phase media with important applications in energy production, nuclear fuel and waste processing, improving the efficiency and safety of industrial chemical processes, and pollution prevention. ILs are nonvolatile, noncombustible, highly conductive, recyclable and capable of dissolving a wide variety of materials. They are finding new uses in chemical synthesis, catalysis, separations chemistry, electrochemistry and other areas. Ionic liquids have dramatically different properties compared to conventional molecular solvents, and they provide a new and unusual environment to test our theoretical understanding of charge transfer and other reactions. We are interested in how IL properties influence physical and dynamical processes that determine the stability and lifetimes of reactive intermediates and thereby affect the courses of chemical reactions and product distributions. Successful use of ionic liquids in radiation-filled environments, where their safety advantages could be significant, requires an understanding of ionic liquid radiation chemistry. For example, characterizing the primary steps of IL radiolysis will reveal radiolytic degradation pathways and suggest ways to prevent them or mitigate their effects on the properties of the material. An understanding of ionic liquid radiation chemistry will also facilitate pulse radiolysis studies of general chemical reactivity in ILs, which will aid in the development of energy production, chemical industry and environmental applications. Pulse radiolysis of [R 4 N][NTf 2 ] [R 4 N][N(CN) 2 ], and [R 4 P][N(CN) 2 ] ionic liquids produces solvated electrons that absorb over a broad range in the near infrared and persisting for hundreds of nanoseconds. Systematic cation variation shows that solvated electron's spectroscopic properties depend strongly on the lattice structure of the ionic liquid. Very early in our radiolysis studies it became evident that

  6. 1 SUPPLEMENTARY INFORMATION Nonpolar Solvation Dynamics ...

    Indian Academy of Sciences (India)

    IITP

    . S. NP. ( t. ) ( )t. SNeqm. NP. (a). (b). Figure S2. (a) Nonequilibrium solvation response functions calculated after averaging over different number of nonequilibrium trajectories. The response function converges after averaging over more than ...

  7. Solvated electron structure in glassy matrices

    International Nuclear Information System (INIS)

    Kevan, L.

    1981-01-01

    Current knowledge of the detailed geometrical structure of solvated electrons in aqueous and organic media is summarized. The geometry of solvated electrons in glassy methanol, ethanol, and 2-methyltetrahydrofuran is discussed. Advanced electron magnetic resonance methods and development of new methods of analysis of electron spin echo modulation patterns, second moment line shapes, and forbidden photon spin-flip transitions for paramagnetic species in these disordered systems are discussed. 66 references are cited

  8. Phonon and free-charge carrier properties in group-III nitride heterostructures investigated by spectroscopic ellipsometry and optical Hall effect

    Science.gov (United States)

    Schoeche, Stefan

    The material class of group-III nitrides gained tremendous technological importance for optoelectronic and high-power/high-frequency amplification devices. Tunability of the direct band gap from 0.65 eV (InN) to 6.2 eV (AlN) by alloying, high breakthrough voltages and intrinsic mobilities, as well as the formation of highly mobile 2d electron gases (2DEG) at heterointerfaces make these compounds ideal for many applications. GaN and Ga-rich alloys are well studied and current research is mainly device-oriented. For example, choice and quality of the gate dielectric significantly influence device performance in high-electron mobility transistors (HEMT) which utilize highly mobile 2DEGs at heterointerfaces. Experimental access to the 2DEG channel properties without influence from parasitic currents or contact properties are desirable. In- and Al-rich ternary alloys are less explored than Ga-rich compounds. For InN and In-rich alloys, while many material parameters such as stiffness constants or effective mass values are largely unknown, reliable p-type doping is a major challenge, also because p-type conducting channels are buried within highly conductive n-type material formed at the surface and interfaces preventing electrical characterization. For AlN and high-Al content alloys, doping mechanisms are not understood and reliable fabrication of material with high free-charge carrier (FCC) concentrations was achieved just recently. Difficulties to form ohmic contacts impair electrical measurements and optical characterization is impeded by lack of high-energy excitation sources. In this work, spectroscopic ellipsometry over the wide spectral range from the THz to VUV in combination with optical Hall effect (generalized ellipsometry with applied magnetic field) from THz to MIR are applied in order to investigate the phonon modes and FCC properties in group-III nitride heterostructures. Adequate model descriptions and analysis strategies are introduced which allow

  9. Comparison of modification strategies towards enhanced charge carrier separation and photocatalytic degradation activity of metal oxide semiconductors (TiO{sub 2}, WO{sub 3} and ZnO)

    Energy Technology Data Exchange (ETDEWEB)

    Kumar, S. Girish [Department of Physics, Indian Institute of Science, Bengaluru, 560012 Karnataka (India); Department of Chemistry, School of Engineering and Technology, CMR University, Bengaluru, 562149, Karnataka (India); Rao, K.S.R. Koteswara, E-mail: raoksrk@gmail.com [Department of Physics, Indian Institute of Science, Bengaluru, 560012 Karnataka (India)

    2017-01-01

    Graphical abstract: Semiconductor metal oxides: Modifications, charge carrier dynamics and photocatalysis. - Highlights: • TiO{sub 2}, WO{sub 3} and ZnO based photocatalysis is reviewed. • Advances to improve the efficiency are emphasized. • Differences and similarities in the modifications are highlighted. • Charge carrier dynamics for each strategy are discussed. - Abstract: Metal oxide semiconductors (TiO{sub 2}, WO{sub 3} and ZnO) finds unparalleled opportunity in wastewater purification under UV/visible light, largely encouraged by their divergent admirable features like stability, non-toxicity, ease of preparation, suitable band edge positions and facile generation of active oxygen species in the aqueous medium. However, the perennial failings of these photocatalysts emanates from the stumbling blocks like rapid charge carrier recombination and meager visible light response. In this review, tailoring the surface-bulk electronic structure through the calibrated and veritable approaches such as impurity doping, deposition with noble metals, sensitizing with other compounds (dyes, polymers, inorganic complexes and simple chelating ligands), hydrogenation process (annealing under hydrogen atmosphere), electronic integration with other semiconductors, modifying with carbon nanostructures, designing with exposed facets and tailoring with hierarchical morphologies to overcome their critical drawbacks are summarized. Taking into account the materials intrinsic properties, the pros and cons together with similarities and striking differences for each strategy in specific to TiO{sub 2}, WO{sub 3} & ZnO are highlighted. These subtlety enunciates the primacy for improving the structure-electronic properties of metal oxides and credence to its fore in the practical applications. Future research must focus on comparing the performances of ZnO, TiO{sub 2} and WO{sub 3} in parallel to get insight into their photocatalytic behaviors. Such comparisons not only reveal

  10. Thermodynamics of sublimation and solvation for bicyclo-derivatives of 1,3-thiazine

    International Nuclear Information System (INIS)

    Ol’khovich, Marina V.; Blokhina, Svetlana V.; Sharapova, Angelica V.; Perlovich, German L.; Proshin, Alexey N.

    2013-01-01

    Highlights: • Temperature dependencies of saturated vapor pressure of new bicyclo-derivatives were obtained. • Thermodynamic functions of sublimation and solvation were calculated. • The correlations between thermodynamic functions and molecular descriptors are discussed. - Abstract: Temperature dependencies of saturated vapor pressure of novel bicyclo-derivatives of 1,3-thiazine with methoxy- and carbonyl-substituents have been obtained by method of transference by means of an inert gas carrier. Thermodynamic functions of sublimation have been calculated. Correlations between thermodynamic functions of sublimation and thermophysical properties of the substances and molecular descriptors have been established. The enthalpies of solvation of compounds were calculated using the measured values of enthalpies of sublimation and of standard enthalpies of solution in hexane and buffer

  11. Influence of temperature and molecular structure on ionic liquid solvation layers.

    Science.gov (United States)

    Wakeham, Deborah; Hayes, Robert; Warr, Gregory G; Atkin, Rob

    2009-04-30

    Atomic force microscopy (AFM) force profiling is used to investigate the structure of adsorbed and solvation layers formed on a mica surface by various room temperature ionic liquids (ILs) ethylammonium nitrate (EAN), ethanolammonium nitrate (EtAN), ethylammonium formate (EAF), propylammonium formate (PAF), ethylmethylammonium formate (EMAF), and dimethylethylammonium formate (DMEAF). At least seven layers are observed for EAN at 14 degrees C (melting point 13 degrees C), decreasing as the temperature is increased to 30 degrees C due to thermal energy disrupting solvophobic forces that lead to segregation of cation alkyl tails from the charged ammonium and nitrate moieties. The number and properties of the solvation layers can also be controlled by introducing an alcohol moiety to the cation's alkyl tail (EtAN), or by replacing the nitrate anion with formate (EAF and PAF), even leading to the detection of distinct cation and anion sublayers. Substitution of primary by secondary or tertiary ammonium cations reduces the number of solvation layers formed, and also weakens the cation layer adsorbed onto mica. The observed solvation and adsorbed layer structures are discussed in terms of the intermolecular cohesive forces within the ILs.

  12. Strong Stretching of Poly(ethylene glycol) Brushes Mediated by Ionic Liquid Solvation.

    Science.gov (United States)

    Han, Mengwei; Espinosa-Marzal, Rosa M

    2017-09-07

    We have measured forces between mica surfaces coated with a poly(ethylene glycol) (PEG) brush solvated by a vacuum-dry ionic liquid, 1-ethyl-3-methyl imidazolium bis(trifluoromethylsulfonyl)imide, with a surface forces apparatus. At high grafting density, the solvation mediated by the ionic liquid causes the brush to stretch twice as much as in water. Modeling of the steric repulsion indicates that PEG behaves as a polyelectrolyte; the hydrogen bonding between ethylene glycol and the imidazolium cation seems to effectively charge the polymer brush, which justifies the strong stretching. Importantly, under strong polymer compression, solvation layers are squeezed out at a higher rate than for the neat ionic liquid. We propose that the thermal fluctuations of the PEG chains, larger in the brush than in the mushroom configuration, maintain the fluidity of the ionic liquid under strong compression, in contrast to the solid-like squeezing-out behavior of the neat ionic liquid. This is the first experimental study of the behavior of a polymer brush solvated by an ionic liquid under nanoconfinement.

  13. Structural aspects of the solvation shell of lysine and acetylated lysine: A Car-Parrinello and classical molecular dynamics investigation

    International Nuclear Information System (INIS)

    Carnevale, V.; Raugei, S.

    2009-01-01

    Lysine acetylation is a post-translational modification, which modulates the affinity of protein-protein and/or protein-DNA complexes. Its crucial role as a switch in signaling pathways highlights the relevance of charged chemical groups in determining the interactions between water and biomolecules. A great effort has been recently devoted to assess the reliability of classical molecular dynamics simulations in describing the solvation properties of charged moieties. In the spirit of these investigations, we performed classical and Car-Parrinello molecular dynamics simulations on lysine and acetylated-lysine in aqueous solution. A comparative analysis between the two computational schemes is presented with a focus on the first solvation shell of the charged groups. An accurate structural analysis unveils subtle, yet statistically significant, differences which are discussed in connection to the significant electronic density charge transfer occurring between the solute and the surrounding water molecules.

  14. The effects of metallicity, radiation field and dust extinction on the charge state of PAHs in diffuse clouds: implications for the DIB carrier

    NARCIS (Netherlands)

    Cox, N.L.J.; Spaans, M.

    2006-01-01

    Context.The unidentified diffuse interstellar bands (DIB) are observed throughout the Galaxy, the Local Group and beyond. Their carriers are possibly related to complex carbonaceous gas-phase molecules, such as (cationic) polycyclic aromatic hydrocarbons and fullerenes. Aims.In order to reveal the

  15. The effects of metallicity, radiation field and dust extinction on the charge state of PAHs in diffuse clouds : implications for the DIB carrier

    NARCIS (Netherlands)

    Cox, NLJ; Spaans, M

    Context. The unidentified diffuse interstellar bands (DIB) are observed throughout the Galaxy, the Local Group and beyond. Their carriers are possibly related to complex carbonaceous gas-phase molecules, such as (cationic) polycyclic aromatic hydrocarbons and fullerenes. Aims. In order to reveal the

  16. Solvated protein-DNA docking using HADDOCK

    Energy Technology Data Exchange (ETDEWEB)

    Dijk, Marc van; Visscher, Koen M.; Kastritis, Panagiotis L.; Bonvin, Alexandre M. J. J., E-mail: a.m.j.j.bonvin@uu.nl [Utrecht University, Bijvoet Center for Biomolecular Research, Faculty of Science-Chemistry (Netherlands)

    2013-05-15

    Interfacial water molecules play an important role in many aspects of protein-DNA specificity and recognition. Yet they have been mostly neglected in the computational modeling of these complexes. We present here a solvated docking protocol that allows explicit inclusion of water molecules in the docking of protein-DNA complexes and demonstrate its feasibility on a benchmark of 30 high-resolution protein-DNA complexes containing crystallographically-determined water molecules at their interfaces. Our protocol is capable of reproducing the solvation pattern at the interface and recovers hydrogen-bonded water-mediated contacts in many of the benchmark cases. Solvated docking leads to an overall improvement in the quality of the generated protein-DNA models for cases with limited conformational change of the partners upon complex formation. The applicability of this approach is demonstrated on real cases by docking a representative set of 6 complexes using unbound protein coordinates, model-built DNA and knowledge-based restraints. As HADDOCK supports the inclusion of a variety of NMR restraints, solvated docking is also applicable for NMR-based structure calculations of protein-DNA complexes.

  17. Solvated protein–DNA docking using HADDOCK

    International Nuclear Information System (INIS)

    Dijk, Marc van; Visscher, Koen M.; Kastritis, Panagiotis L.; Bonvin, Alexandre M. J. J.

    2013-01-01

    Interfacial water molecules play an important role in many aspects of protein–DNA specificity and recognition. Yet they have been mostly neglected in the computational modeling of these complexes. We present here a solvated docking protocol that allows explicit inclusion of water molecules in the docking of protein–DNA complexes and demonstrate its feasibility on a benchmark of 30 high-resolution protein–DNA complexes containing crystallographically-determined water molecules at their interfaces. Our protocol is capable of reproducing the solvation pattern at the interface and recovers hydrogen-bonded water-mediated contacts in many of the benchmark cases. Solvated docking leads to an overall improvement in the quality of the generated protein–DNA models for cases with limited conformational change of the partners upon complex formation. The applicability of this approach is demonstrated on real cases by docking a representative set of 6 complexes using unbound protein coordinates, model-built DNA and knowledge-based restraints. As HADDOCK supports the inclusion of a variety of NMR restraints, solvated docking is also applicable for NMR-based structure calculations of protein–DNA complexes.

  18. Solvated protein-DNA docking using HADDOCK

    NARCIS (Netherlands)

    van Dijk, Marc; Visscher, Koen M; Bonvin, Alexandre M.J.J; Kastritis, Panagiotis L.

    2013-01-01

    Interfacial water molecules play an important role in many aspects of protein-DNA specificity and recognition. Yet they have been mostly neglected in the computational modeling of these complexes. We present here a solvated docking protocol that allows explicit inclusion of water molecules in the

  19. Partial solvation parameters and LSER molecular descriptors

    International Nuclear Information System (INIS)

    Panayiotou, Costas

    2012-01-01

    Graphical abstract: The one-to-one correspondence of LSER molecular descriptors and partial solvation parameters (PSPs) for propionic acid. Highlights: ► Quantum-mechanics based development of a new QSPR predictive method. ► One-to-one correspondence of partial solvation parameters and LSER molecular descriptors. ► Development of alternative routes for the determination of partial solvation parameters and solubility parameters. ► Expansion and enhancement of solubility parameter approach. - Abstract: The partial solvation parameters (PSP) have been defined recently, on the basis of the insight derived from modern quantum chemical calculations, in an effort to overcome some of the inherent restrictions of the original definition of solubility parameter and expand its range of applications. The present work continues along these lines and introduces two new solvation parameters, the van der Waals and the polarity/refractivity ones, which may replace both of the former dispersion and polar PSPs. Thus, one may use either the former scheme of PSPs (dispersion, polar, acidic, and basic) or, equivalently, the new scheme (van der Waals, polarity/refractivity, acidic, basic). The new definitions are made in a simple and straightforward manner and, thus, the strength and appeal of the widely accepted concept of solubility parameter is preserved. The inter-relations of the various PSPs are critically discussed and their values are tabulated for a variety of common substances. The advantage of the new scheme of PSPs is the bridge that makes with the corresponding Abraham’s LSER descriptors. With this bridge, one may exchange information between PSPs, LSER experimental scales, and quantum mechanics calculations such as via the COSMO-RS theory. The proposed scheme is a predictive one and it is applicable to, both, homo-solvated and hetero-solvated compounds. The new scheme is tested for the calculation of activity coefficients at infinite dilution, for octanol

  20. Dynamics of Interfacial Charge Transfer States and Carriers Separation in Dye-Sensitized Solar Cells: A Time-Resolved Terahertz Spectroscopy Study

    OpenAIRE

    Brauer, Jan C.; Marchioro, Arianna; Paraecattil, Arun A.; Oskouei, Ahmad A.; Moser, Jacques-E.

    2015-01-01

    Electron injection from a photoexcited molecular sensitizer into a wide-bandgap semiconductor is the primary step toward charge separation in dye-sensitized solar cells (DSSCs). According to the current understanding of DSSCs functioning mechanism, charges are separated directly during this primary electron transfer process, yielding hot conduction band electrons in the semiconductor and positive holes localized on oxidized dye molecules at the surface. Comparing results of ultrafast transien...

  1. Boosting the Visible-Light Photoactivity of BiOCl/BiVO4/N-GQD Ternary Heterojunctions Based on Internal Z-Scheme Charge Transfer of N-GQDs: Simultaneous Band Gap Narrowing and Carrier Lifetime Prolonging.

    Science.gov (United States)

    Zhu, Mingyue; Liu, Qian; Chen, Wei; Yin, Yuanyuan; Ge, Lan; Li, Henan; Wang, Kun

    2017-11-08

    The efficient separation of photogenerated electron-hole pairs in photoactive materials is highly desired, allowing their transfer to specific sites for undergoing redox reaction in various applications. The construction of ternary heterojunctions is a practical strategy to enhance the migration of photogenerated electron that realizes the synergistic effect of multicomponents rather than the simple overlay of single component. Here, we demonstrate an available way to fabricate new BiOCl/BiVO 4 /nitrogen-doped graphene quantum dot (N-GQD) ternary heterojunctions that exhibit higher efficiency in charge separation than any binary heterojunction or pure material under visible-light irradiation. UV-vis diffuse reflectance spectroscopy demonstrated that the proposed BiOCl/BiVO 4 /N-GQD ternary heterojunctions possess the narrower band gap energy. More importantly, the ternary heterojunctions reveal the prolonged lifetime of photogenerated charges and enhanced the separation efficiency of photogenerated electron-hole pairs, which may be ascribed to sensitization based on an internal Z-scheme charge transfer at the interface of N-GQDs with oxygen functional groups. Furthermore, we examine the photoactive performance of proposed ternary heterojunctions in aqueous solution by using the photodegradation of bisphenol A as a model system and BiOCl/BiVO 4 /N-GQD ternary heterojunctions also display a dramatically enhanced photodegradation rate. The proposed charge separation and transfer process of BiOCl/BiVO 4 /N-GQD ternary heterojunctions for the enhanced photoactivity were deduced by electrochemical measurements, photoluminescence, and electron spin resonance. The results demonstrate that a Z-scheme charge process was formed between BiOCl/BiVO 4 binary heterojunctions and N-GQDs, leading to an efficient charge carrier separation and strong photocatalytic ability. Notably, this work may assist in a better understanding of the role of N-GQDs in kinds of heterojunctions

  2. Advanced dielectric continuum model of preferential solvation

    Science.gov (United States)

    Basilevsky, Mikhail; Odinokov, Alexey; Nikitina, Ekaterina; Grigoriev, Fedor; Petrov, Nikolai; Alfimov, Mikhail

    2009-01-01

    A continuum model for solvation effects in binary solvent mixtures is formulated in terms of the density functional theory. The presence of two variables, namely, the dimensionless solvent composition y and the dimensionless total solvent density z, is an essential feature of binary systems. Their coupling, hidden in the structure of the local dielectric permittivity function, is postulated at the phenomenological level. Local equilibrium conditions are derived by a variation in the free energy functional expressed in terms of the composition and density variables. They appear as a pair of coupled equations defining y and z as spatial distributions. We consider the simplest spherically symmetric case of the Born-type ion immersed in the benzene/dimethylsulfoxide (DMSO) solvent mixture. The profiles of y(R ) and z(R ) along the radius R, which measures the distance from the ion center, are found in molecular dynamics (MD) simulations. It is shown that for a given solute ion z(R ) does not depend significantly on the composition variable y. A simplified solution is then obtained by inserting z(R ), found in the MD simulation for the pure DMSO, in the single equation which defines y(R ). In this way composition dependences of the main solvation effects are investigated. The local density augmentation appears as a peak of z(R ) at the ion boundary. It is responsible for the fine solvation effects missing when the ordinary solvation theories, in which z =1, are applied. These phenomena, studied for negative ions, reproduce consistently the simulation results. For positive ions the simulation shows that z ≫1 (z =5-6 at the maximum of the z peak), which means that an extremely dense solvation shell is formed. In such a situation the continuum description fails to be valid within a consistent parametrization.

  3. Electrochemical behaviours of Eu(III/E(II and Ce(IV/Ce(III in H3PO4-H2O media : solvation and complexation reactions

    Directory of Open Access Journals (Sweden)

    Belqat B.

    2018-01-01

    Full Text Available Many kinds of rare earth elements (REE such as europium and cerium have been make them essential elements in many high-tech components. The electrochemical studies can be presented as an interesting indication for europium and cerium extraction from phosphoric solutions, including solvation and complexation reactions. The normal redox potentials of Eu3+/Eu2+ and Ce4+/Ce3+ systems have been determined in H3PO4-H2O media with various phosphoric acid concentration. The solvation of these elements in phosphoric media is characterized by their transfer activity coefficients "f" calculated from the corresponding normal redox potentials. The corresponding solvation increases with increasing the H3PO4 concentration. For each REE, the electrochemical properties depend on its number of charges and on its basic properties. Results suggest that solvation and complexation of REE phosphates are important in controlling REE concentration.

  4. Charge carrier transport in Cu(In,Ga)Se2 thin-film solar-cells studied by electron beam induced current and temperature and illumination dependent current voltage analysis

    International Nuclear Information System (INIS)

    Nichterwitz, Melanie

    2012-01-01

    This work contributes to the understanding of generation dependent charge-carrier transport properties in Cu(In,Ga)Se 2 (CIGSe)/ CdS/ ZnO solar cells and a consistent model for the electronic band diagram of the heterojunction region of the device is developed. Cross section electron-beam induced current (EBIC) and temperature and illumination dependent current voltage (IV) measurements are performed on CIGSe solar cells with varying absorber layer compositions and CdS thickness. For a better understanding of possibilities and limitations of EBIC measurements applied on CIGSe solar cells, detailed numerical simulations of cross section EBIC profiles for varying electron beam and solar cell parameters are performed and compared to profiles obtained from an analytical description. Especially the effects of high injection conditions are considered. Even though the collection function of the solar cell is not independent of the generation function of the electron beam, the local electron diffusion length in CIGSe can still be extracted. Grain specific values ranging from (480±70) nm to (2.3±0.2) μm are determined for a CuInSe 2 absorber layer and a value of (2.8±0.3) μm for CIGSe with a Ga-content of 0.3. There are several models discussed in literature to explain generation dependent charge carrier transport, all assuming a high acceptor density either located in the CIGSe layer close to the CIGSe/CdS interface (p + layer), within the CdS layer or at the CdS/ZnO interface. In all models, a change in charge carrier collection properties is caused by a generation dependent occupation probability of the acceptor type defect state and the resulting potential distribution throughout the device. Numerical simulations of EBIC and IV data are performed with parameters according to these models. The model that explains the experimental data best is that of a p + layer at the CIGSe/CdS interface and acceptor type defect states at the CdS/ZnO interface. The p + layer leads

  5. Infrared spectroscopy of model electrochemical interfaces in ultrahigh vacuum: some implications for ionic and chemisorbate solvation at electrode surfaces

    Science.gov (United States)

    Villegas, Ignacio; Kizhakevariam, Naushad; Weaver, Michael J.

    1995-07-01

    The utility of infrared reflection-absorption spectroscopy (IRAS) for examining structure and bonding for model electrochemical interfaces in ultrahigh vacuum (UHV) is illustrated, focusing specifically on the solvation of cations and chemisorbed carbon monoxide on Pt(111). These systems were chosen partly in view of the availability of IRAS data (albeit limited to chemisorbate vibrations) for the corresponding in-situ metal-solution interfaces, enabling direct spectral comparisons to be made with the "UHV electrochemical model" systems. Kelvin probe measurements of the metal-UHV surface potential changes (ΔΦ) attending alterations in the interfacial composition are also described: these provide the required link to the in-situ electrode potentials as well as yielding additional insight into surface solvation. Variations in the negative electronic charge density and, correspondingly, in the cation surface concentration (thereby mimicking charge-induced alterations in the electrode potential below the potential of zero charge) are achieved by potassium atom dosage onto Pt(111). Of the solvents selected for discussion here — deuterated water, methanol, and acetonitrile — the first two exhibit readily detectable vibrational bands which provide information on the ionic solvation structure. Progressively dosing these solvents onto Pt(111) in the presence of low potassium coverages yields marked alterations in the solvent vibrational bands which can be understood in terms of sequential cation solvation. Comparison between these spectra for methanol with analogous data for sequential methanol solvation of gas-phase alkali cations enables the influence of the interfacial environment to be assessed. The effects of solvating chemisorbed CO are illustrated for acetonitrile; the markedly larger shifts in CO frequencies and binding sites for dilute CO adlayers can be accounted for in terms of short-range coadsorbate interactions in addition to longer-range Stark effects

  6. Silver atom solvation and desolvation in ice matrices: study of solvation shell geometry by electron spin resonance and electron spin echo methods

    Energy Technology Data Exchange (ETDEWEB)

    Kevan, L; Narayana, P A

    1978-01-01

    Results of studies of the solvation shell structure of silver atoms in ice matrix at 4/sup 0/K by electron spin resonance (ESR) and electron spin echo spectrometry are reported. Drastic change in the hyperfine coupling constant of the silver atom was noted when the silver atom initially produced at 4/sup 0/K was warmed to 77/sup 0/K and reexamined by ESR at 4/sup 0/K. This suggested a very drastic rearrangement of the water molecules surrounding the silver atom. The geometric arrangement of water molecules around the silver atom produced at 4/sup 0/K was what would be expected for a solvated silver ion, indicating that no rearrangement had occurred after the silver atom formed. The addition of a little thermal excitation (heating to 77/sup 0/K) results in the geometry changes than can be explained by assuming either that a water molecule rotates around one of its OH bands or by the development of a hydrogen bond between the silver atom and one of the first solvation shell water molecules. Optical excitation in the absorption band of the silver atom in the ice matrix at 400nm resulted in desolvation of the silver ion or a reversion to the structure originally obtained by reaction of solver salts in ic matrix with radiation produced electrons. This was best explained by a charge transfer mechanism. (BLM)

  7. Photoinduced electron transfer and solvation in iodide-doped acetonitrile clusters.

    Science.gov (United States)

    Ehrler, Oli T; Griffin, Graham B; Young, Ryan M; Neumark, Daniel M

    2009-04-02

    We have used ultrafast time-resolved photoelectron imaging to measure charge transfer dynamics in iodide-doped acetonitrile clusters I(-)(CH(3)CN)(n) with n = 5-10. Strong modulations of vertical detachment energies were observed following charge transfer from the halide, allowing interpretation of the ongoing dynamics. We observe a sharp drop in the vertical detachment energy (VDE) within 300-400 fs, followed by a biexponential increase that is complete by approximately 10 ps. Comparison to theory suggests that the iodide is internally solvated and that photodetachment results in formation of a diffuse electron cloud in a confined cavity. We interpret the initial drop in VDE as a combination of expansion of the cavity and localization of the excess electron on one or two solvent molecules. The subsequent increase in VDE is attributed to a combination of the I atom leaving the cavity and rearrangement of the acetonitrile molecules to solvate the electron. The n = 5-8 clusters then show a drop in VDE of around 50 meV on a much longer time scale. The long-time VDEs are consistent with those of (CH(3)CN)(n)(-) clusters with internally solvated electrons. Although the excited-state created by the pump pulse decays by emission of a slow electron, no such decay is seen by 200 ps.

  8. The effect of the Grain-Boundary and surface scattering of charge carriers on electrical conductance of thin V and Re films

    International Nuclear Information System (INIS)

    Lakh, Kh.G.; Stasyuk, Z.V.

    1994-01-01

    Size effects in electrical conductivity and the Hall coefficient of thin V and Re films have been investigated. An analysis of experimental data was made within the framework of modified Mayadas -Shatzkes and Tellier - Tosser - Pichard models. The parameters of charge transport for V and Re have been found

  9. A comparative study on charge carrier recombination across the junction region of Cu2ZnSn(S,Se4 and Cu(In,GaSe2 thin film solar cells

    Directory of Open Access Journals (Sweden)

    Mohammad Abdul Halim

    2016-03-01

    Full Text Available A comparative study with focusing on carrier recombination properties in Cu2ZnSn(S,Se4 (CZTSSe and the CuInGaSe2 (CIGS solar cells has been carried out. For this purpose, electroluminescence (EL and also bias-dependent time resolved photoluminescence (TRPL using femtosecond (fs laser source were performed. For the similar forward current density, the EL-intensity of the CZTSSe sample was obtained significantly lower than that of the CIGS sample. Primarily, it can be attributed to the existence of excess amount of non-radiative recombination center in the CZTSSe, and/or CZTSSe/CdS interface comparing to that of CIGS sample. In case of CIGS sample, TRPL decay time was found to increase with the application of forward-bias. This can be attributed to the reduced charge separation rate resulting from the reduced electric-field at the junction. However, in CZTSSe sample, TRPL decay time has been found almost independent under the forward and reverse-bias conditions. This phenomenon indicates that the charge recombination rate strongly dominates over the charge separation rate across the junction of the CZTSSe sample. Finally, temperature dependent VOC suggests that interface related recombination in the CZTSSe solar cell structure might be one of the major factors that affect EL-intensity and also, TRPL decay curves.

  10. A comparative study on charge carrier recombination across the junction region of Cu{sub 2}ZnSn(S,Se){sub 4} and Cu(In,Ga)Se{sub 2} thin film solar cells

    Energy Technology Data Exchange (ETDEWEB)

    Halim, Mohammad Abdul, E-mail: halimtsukuba2012@gmail.com; Islam, Muhammad Monirul; Luo, Xianjia; Sakurai, Takeaki; Akimoto, Katsuhiro [Institute of Applied Physics, University of Tsukuba, Tsukuba, Ibaraki 305-8573 (Japan); Sakai, Noriyuki; Kato, Takuya; Sugimoto, Hiroki [Energy Solution Business Center, Showa Shell Sekiyu K.K., Minato, Tokyo 135-8074 (Japan); Tampo, Hitoshi; Shibata, Hajime; Niki, Shigeru [National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba, Ibaraki 305-8568 (Japan)

    2016-03-15

    A comparative study with focusing on carrier recombination properties in Cu{sub 2}ZnSn(S,Se){sub 4} (CZTSSe) and the CuInGaSe{sub 2} (CIGS) solar cells has been carried out. For this purpose, electroluminescence (EL) and also bias-dependent time resolved photoluminescence (TRPL) using femtosecond (fs) laser source were performed. For the similar forward current density, the EL-intensity of the CZTSSe sample was obtained significantly lower than that of the CIGS sample. Primarily, it can be attributed to the existence of excess amount of non-radiative recombination center in the CZTSSe, and/or CZTSSe/CdS interface comparing to that of CIGS sample. In case of CIGS sample, TRPL decay time was found to increase with the application of forward-bias. This can be attributed to the reduced charge separation rate resulting from the reduced electric-field at the junction. However, in CZTSSe sample, TRPL decay time has been found almost independent under the forward and reverse-bias conditions. This phenomenon indicates that the charge recombination rate strongly dominates over the charge separation rate across the junction of the CZTSSe sample. Finally, temperature dependent V{sub OC} suggests that interface related recombination in the CZTSSe solar cell structure might be one of the major factors that affect EL-intensity and also, TRPL decay curves.

  11. Recent results on solvation dynamics of electron and spur reactions of solvated electron in polar solvents studied by femtosecond laser spectroscopy and picosecond pulse radiolysis

    International Nuclear Information System (INIS)

    Mostafavi, M.

    2006-01-01

    . Nevertheless, the results show that the effect of the molecular structure of the solvents on solvation dynamics of electron is not negligible. The first study of picosecond pulse radiolysis of neat tetrahydrofuran (THF) by pulse-probe method was performed using the ELYSE picosecond pulse electron facility. ELYSE is a laser triggered electron accelerator that delivers at repetition rate of 1-50 Hz, electron pulses with a duration 5-15 ps, a charge of 2-7 nC and a kinetic energy tuneable in the range 2-9 MeV. The pulse- probe study of neat THF shows a fast decay of absorbance at 790 nm within 2.5 ns (Figure 2). This decay is assigned to the solvated electron. From the decay we deduced the time dependent G-value of solvated electron in the picosecond time range. The ratio between the initial absorbance (at 30 ps) and at 2.5 ns is about 2. In similar conditions, the same ratio in water and in the alcohols is 1.15, 1.25, respectively. In fact, the G-value of solvated electron in THF is much more time dependent that those in polar solvents like water and alcohols. We compared the time dependent G value for solvated electron between two methods: direct time resolved measurement and scavenging method. The analysis suggests either that the initial yield in THF (at zero time) is lower than in water or that a very fast decay occurs within the electron pulse.Eventually, the first pulse radiolysis measurements at picosecond range and at elevated temperature in water is studied by pulse-probe method using a high temperature high pressure cell. This study is done in collaboration with the Radiolysis laboratory of CEA/Saclay. The kinetics of the hydrated electron are found to be temperature dependent (Figure 3) and are qualitatively in agreement with radiolytic yield values obtained at elevated temperature after spur reactions. Assuming the same initial G value at picosecond time range for different temperatures, we deduce that at 350 degree C the yield at nanosecond range becomes almost the

  12. Relaxation dynamics following transition of solvated electrons

    International Nuclear Information System (INIS)

    Barnett, R.B.; Landman, U.; Nitzan, A.

    1989-01-01

    Relaxation dynamics following an electronic transition of an excess solvated electron in clusters and in bulk water is studied using an adiabatic simulation method. In this method the solvent evolves classically and the electron is constrained to a specified state. The coupling between the solvent and the excess electron is evaluated via the quantum expectation value of the electron--water molecule interaction potential. The relaxation following excitation (or deexcitation) is characterized by two time scales: (i) a very fast (/similar to/20--30 fs) one associated with molecular rotations in the first solvation shell about the electron, and (ii) a slower stage (/similar to/200 fs), which is of the order of the longitudinal dielectric relaxation time. The fast relaxation stage exhibits an isotope effect. The spectroscopical consequences of the relaxation dynamics are discussed

  13. Generalized Born Models of Macromolecular Solvation Effects

    Science.gov (United States)

    Bashford, Donald; Case, David A.

    2000-10-01

    It would often be useful in computer simulations to use a simple description of solvation effects, instead of explicitly representing the individual solvent molecules. Continuum dielectric models often work well in describing the thermodynamic aspects of aqueous solvation, and approximations to such models that avoid the need to solve the Poisson equation are attractive because of their computational efficiency. Here we give an overview of one such approximation, the generalized Born model, which is simple and fast enough to be used for molecular dynamics simulations of proteins and nucleic acids. We discuss its strengths and weaknesses, both for its fidelity to the underlying continuum model and for its ability to replace explicit consideration of solvent molecules in macromolecular simulations. We focus particularly on versions of the generalized Born model that have a pair-wise analytical form, and therefore fit most naturally into conventional molecular mechanics calculations.

  14. Interfacial Charge-Carrier Trapping in CH3NH3PbI3-Based Heterolayered Structures Revealed by Time-Resolved Photoluminescence Spectroscopy.

    Science.gov (United States)

    Yamada, Yasuhiro; Yamada, Takumi; Shimazaki, Ai; Wakamiya, Atsushi; Kanemitsu, Yoshihiko

    2016-06-02

    The fast-decaying component of photoluminescence (PL) under very weak pulse photoexcitation is dominated by the rapid relaxation of the photoexcited carriers into a small number of carrier-trapping defect states. Here, we report the subnanosecond decay of the PL under excitation weaker than 1 nJ/cm(2) both in CH3NH3PbI3-based heterostructures and bare thin films. The trap-site density at the interface was evaluated on the basis of the fluence-dependent PL decay profiles. It was found that high-density defects determining the PL decay dynamics are formed near the interface between CH3NH3PbI3 and the hole-transporting Spiro-OMeTAD but not at the CH3NH3PbI3/TiO2 interface and the interior regions of CH3NH3PbI3 films. This finding can aid the fabrication of high-quality heterointerfaces, which are required improving the photoconversion efficiency of perovskite-based solar cells.

  15. Theory of optical spectra of solvated electrons

    International Nuclear Information System (INIS)

    Kestner, N.R.

    1975-01-01

    During the last few years better theoretical models of solvated electron have been developed. These models allow one to calculate a priori the observable properties of the trapped electron. One of the most important and most widely determined properties is the optical spectrum. In this paper we consider the predictions of the theories not only as to the band maximum but line shape and width. In addition we will review how the theories predict these will depend on the solvent, pressure, temperature, and solvent density. In all cases extensive comparisons will be made with experimental work. In addition four new areas will be explored and recent results will be presented. These concern electrons in dense polar gases, the time development of the solvated electron spectrum, solvated electrons in mixed solvents, and photoelectron emission spectra (PEE) as it relates to higher excited states. This paper will review all recent theoretical calculations and present a critical review of the present status and future developments which are anticipated. The best theories are quite successful in predicting trends, and qualitative agreement concerning band maximum. The theory is still weak in predicting line shape and line width

  16. Preferential solvation: dividing surface vs excess numbers.

    Science.gov (United States)

    Shimizu, Seishi; Matubayasi, Nobuyuki

    2014-04-10

    How do osmolytes affect the conformation and configuration of supramolecular assembly, such as ion channel opening and actin polymerization? The key to the answer lies in the excess solvation numbers of water and osmolyte molecules; these numbers are determinable solely from experimental data, as guaranteed by the phase rule, as we show through the exact solution theory of Kirkwood and Buff (KB). The osmotic stress technique (OST), in contrast, purposes to yield alternative hydration numbers through the use of the dividing surface borrowed from the adsorption theory. However, we show (i) OST is equivalent, when it becomes exact, to the crowding effect in which the osmolyte exclusion dominates over hydration; (ii) crowding is not the universal driving force of the osmolyte effect (e.g., actin polymerization); (iii) the dividing surface for solvation is useful only for crowding, unlike in the adsorption theory which necessitates its use due to the phase rule. KB thus clarifies the true meaning and limitations of the older perspectives on preferential solvation (such as solvent binding models, crowding, and OST), and enables excess number determination without any further assumptions.

  17. Preferential Solvation of an Asymmetric Redox Molecule

    Energy Technology Data Exchange (ETDEWEB)

    Han, Kee Sung; Rajput, Nav Nidhi; Vijayakumar, M.; Wei, Xiaoliang; Wang, Wei; Hu, Jian Z.; Persson, Kristin A.; Mueller, Karl T.

    2016-12-15

    The fundamental correlations between inter-molecular interactions, solvation structure and functionality of electrolytes are in many cases unknown, particularly for multi-component liquid systems. In this work, we explore such correlations by investigating the complex interplay between solubility and solvation structure for the electrolyte system comprising N-(ferrocenylmethyl)-N,N-dimethyl-N-ethylammonium bistrifluoromethylsulfonimide (Fc1N112-TFSI) dissolved in a ternary carbonate solvent mixture using combined NMR relaxation and computational analyses. Probing the evolution of the solvent-solvent, ion-solvent and ion-ion interactions with an increase in solute concentration provides a molecular level understanding of the solubility limit of the Fc1N112-TFSI system. An increase in solute con-centration leads to pronounced Fc1N112-TFSI contact-ion pair formation by diminishing solvent-solvent and ion-solvent type interactions. At the solubility limit, the precipitation of solute is initiated through agglomeration of contact-ion pairs due to overlapping solvation shells.

  18. Conductometric determination of solvation numbers of alkali metal cations

    International Nuclear Information System (INIS)

    Fialkov, Yu.Ya.; Gorbachev, V.Yu.; Chumak, V.L.

    1997-01-01

    Theories describing the interrelation of ion mobility with their effective radii in solutions are considered. Possibility of using these theories for determination the solvation numbers n s of some ions is estimated. According to conductometric data values of n s are calculated for alkali metal ions in propylene carbonate. The data obtained are compared with solvation numbers determined with the use of entropies of ions solvation. Change of n s values within temperature range 273.15-323.15 K is considered. Using literature data the effect of crystallographic radii of cations and medium permittivity on the the values of solvation numbers of cations are analyzed. (author)

  19. Influence of Silver and Gold Nanoparticles and Thin Layers on Charge Carrier Generation in InGaN/GaN Multiple Quantum Well Structures and Crystalline Zinc Oxide Films

    Science.gov (United States)

    Mezdrogina, M. M.; Vinogradov, A. Ya.; Kozhanova, Yu. V.; Levitskii, V. S.

    2018-04-01

    It has been shown that Ag and Au nanoparticles and thin layers influence charge carrier generation in InGaN/GaN multiple quantum well structures and crystalline ZnO films owing to the surface morphology heterogeneity of the semiconductors. When nanoparticles 10 films, the radiation intensity has turned out to grow considerably because of a plasmon resonance with the participation of localized plasmons. The application of Ag or Au layers on the surface of the structures strongly attenuates the radiation. When Ag and Au nanoparticles are applied on crystalline ZnO films obtained by rf magnetron sputtering, the radiation intensity in the short-wavelength part of the spectrum increases insignificantly because of their highly heterogeneous surface morphology.

  20. The role of solvation in the binding selectivity of the L-type calcium channel.

    Science.gov (United States)

    Boda, Dezső; Henderson, Douglas; Gillespie, Dirk

    2013-08-07

    We present grand canonical Monte Carlo simulation results for a reduced model of the L-type calcium channel. While charged residues of the protein amino acids in the selectivity filter are treated explicitly, most of the degrees of freedom (including the rest of the protein and the solvent) are represented by their dielectric response, i.e., dielectric continua. The new aspect of this paper is that the dielectric coefficient in the channel is different from that in the baths. The ions entering the channel, thus, cross a dielectric boundary at the entrance of the channel. Simulating this case has been made possible by our recent methodological development [D. Boda, D. Henderson, B. Eisenberg, and D. Gillespie, J. Chem. Phys. 135, 064105 (2011)]. Our main focus is on the effect of solvation energy (represented by the Born energy) on monovalent vs. divalent ion selectivity in the channel. We find no significant change in selectivity by changing the dielectric coefficient in the channel because the larger solvation penalty is counterbalanced by the enhanced Coulomb attraction inside the channel as soon as we use the Born radii (fitted to experimental hydration energies) to compute the solvation penalty from the Born equation.

  1. Modifying Poisson equation for near-solute dielectric polarization and solvation free energy

    Energy Technology Data Exchange (ETDEWEB)

    Yang, Pei-Kun, E-mail: peikun@isu.edu.tw

    2016-06-15

    Highlights: • We modify the Poisson equation. • The dielectric polarization was calculated from the modified Poisson equation. • The solvation free energies of the solutes were calculated from the dielectric polarization. • The calculated solvation free energies were similar to those obtained from MD simulations. - Abstract: The dielectric polarization P is important for calculating the stability of protein conformation and the binding affinity of protein–protein/ligand interactions and for exploring the nonthermal effect of an external electric field on biomolecules. P was decomposed into the product of the electric dipole moment per molecule p; bulk solvent density N{sub bulk}; and relative solvent molecular density g. For a molecular solute, 4πr{sup 2}p(r) oscillates with the distance r to the solute, and g(r) has a large peak in the near-solute region, as observed in molecular dynamics (MD) simulations. Herein, the Poisson equation was modified for computing p based on the modified Gauss’s law of Maxwell’s equations, and the potential of the mean force was used for computing g. For one or two charged atoms in a water cluster, the solvation free energies of the solutes obtained by these equations were similar to those obtained from MD simulations.

  2. Elucidating the Solvation Structure and Dynamics of Lithium Polysulfides Resulting from Competitive Salt and Solvent Interactions

    Energy Technology Data Exchange (ETDEWEB)

    Rajput, Nav Nidhi; Murugesan, Vijayakumar; Shin, Yongwoo; Han, Kee Sung; Lau, Kah Chun; Chen, Junzheng; Liu, Jun; Curtiss, Larry A.; Mueller, Karl T.; Persson, Kristin A.

    2017-04-10

    Fundamental molecular level understanding of functional properties of liquid solutions provides an important basis for designing optimized electrolytes for numerous applica-tions. In particular, exhaustive knowledge of solvation structure, stability and transport properties is critical for developing stable electrolytes for fast charging and high energy density next-generation energy storage systems. Here we report the correlation between solubility, solvation structure and translational dynamics of a lithium salt (Li-TFSI) and polysulfides species using well-benchmarked classical molecular dynamics simulations combined with nuclear magnetic resonance (NMR). It is observed that the polysulfide chain length has a significant effect on the ion-ion and ion-solvent interaction as well as on the diffusion coefficient of the ionic species in solution. In particular, extensive cluster formation is observed in lower order poly-sulfides (Sx2-; x≤4), whereas the longer polysulfides (Sx2-; x>4) show high solubility and slow dynamics in the solu-tion. It is observed that optimal solvent/salt ratio is essen-tial to control the solubility and conductivity as the addi-tion of Li salt increases the solubility but decreases the mo-bility of the ionic species. This work provides a coupled theoretical and experimental study of bulk solvation struc-ture and transport properties of multi-component electro-lyte systems, yielding design metrics for developing optimal electrolytes with improved stability and solubility.

  3. Elucidating the charge carrier separation and working mechanism of CH3NH3PbI(3-x)Cl(x) perovskite solar cells.

    Science.gov (United States)

    Edri, Eran; Kirmayer, Saar; Mukhopadhyay, Sabyasachi; Gartsman, Konstantin; Hodes, Gary; Cahen, David

    2014-03-11

    Developments in organic-inorganic lead halide-based perovskite solar cells have been meteoric over the last 2 years, with small-area efficiencies surpassing 15%. We address the fundamental issue of how these cells work by applying a scanning electron microscopy-based technique to cell cross-sections. By mapping the variation in efficiency of charge separation and collection in the cross-sections, we show the presence of two prime high efficiency locations, one at/near the absorber/hole-blocking-layer, and the second at/near the absorber/electron-blocking-layer interfaces, with the former more pronounced. This 'twin-peaks' profile is characteristic of a p-i-n solar cell, with a layer of low-doped, high electronic quality semiconductor, between a p- and an n-layer. If the electron blocker is replaced by a gold contact, only a heterojunction at the absorber/hole-blocking interface remains.

  4. Unravelling charge carrier dynamics in protonated g-C3N4 interfaced with carbon nanodots as co-catalysts toward enhanced photocatalytic CO2 reduction: A combined experimental and first-principles DFT study

    Institute of Scientific and Technical Information of China (English)

    Wee-Jun Ong; Lutfi Kurnianditia Putri; Yoong-Chuen Tan; Lling-Lling Tan; Neng Li; Yun Hau Ng; Xiaoming Wen; Siang-Piao Chai

    2017-01-01

    In this work,we demonstrated the successful construction of metal-free zerodimensional/two-dimensional carbon nanodot (CND)-hybridized protonated g-C3N4 (pCN) (CND/pCN) heterojunction photocatalysts by means of electrostatic attraction.We experimentally found that CNDs with an average diameter of 4.4 nm were uniformly distributed on the surface of pCN using electron microscopy analysis.The CND/pCN-3 sample with a CND content of 3 wt.% showed the highest catalytic activity in the CO2 photoreduction process under visible and simulated solar light.Thisprocess results in the evolution of CH4 and CO.The total amounts of CH4 and CO generated by the CND/pCN-3 photocatalyst after 10 h of visible-light activity were found to be 29.23 and 58.82 μmol·gcatalyst-1,respectively.These values were 3.6 and 2.28 times higher,respectively,than the amounts generated when using pCN alone.The corresponding apparent quantum efficiency (AQE) was calculated to be 0.076%.Furthermore,the CND/pCN-3 sample demonstrated high stability and durability after four consecutive photoreaction cycles,with no significant decrease in the catalytic activity.The significant improvement in the photoactivity using CND/pCN-3 was attributed to the synergistic interaction between pCN and CNDs.This synergy allows the effective migration of photoexcited electrons from pCN to CNDs via wellcontacted heterojunction interfaces,which retards the charge recombination.This was confirmed by photoelectrochemical measurements,and steady-state and time-resolved photoluminescence analyses.The first-principles density functional theory (DFT) calculations were consistent with our experimental results,and showed that the work function of CNDs (5.56 eV) was larger than that of pCN (4.66 eV).This suggests that the efficient shuttling of electrons from the conduction band of pCN to CNDs hampers the recombination of electron-hole pairs.This significantly increased the probability of free charge carriers reducing CO2 to CH4

  5. Radionuclide carrier

    International Nuclear Information System (INIS)

    Hartman, F.A.; Kretschmar, H.C.; Tofe, A.J.

    1978-01-01

    A physiologically acceptable particulate radionuclide carrier is described. It comprises a modified anionic starch derivative with 0.1% to 1.5% by weight of a reducing agent and 1 to 20% by weight of anionic substituents

  6. Carrier Screening

    Science.gov (United States)

    ... How accurate is carrier screening? No test is perfect. In a small number of cases, test results ... in which an egg is removed from a woman’s ovary, fertilized in a laboratory with the man’s ...

  7. Nonpolar solvation dynamics for a nonpolar solute in room ...

    Indian Academy of Sciences (India)

    Sandipa Indra

    2018-01-30

    Jan 30, 2018 ... Keywords. Solvation dynamics; nonpolar solvation; ionic liquid; molecular dynamics; linear response theory. 1. ... J. Chem. Sci. (2018) 130:3 spectrum of the excited probe molecule for imida- .... Therefore, the solute and the RTIL ions interact only ... interval of 30 ps from a long equilibrium trajectory of dura-.

  8. Abacavir methanol 2.5-solvate

    Directory of Open Access Journals (Sweden)

    Phuong-Truc T. Pham

    2009-08-01

    Full Text Available The structure of abacavir (systematic name: {(1S,4R-4-[2-amino-6-(cyclopropylamino-9H-purin-9-yl]cyclopent-2-en-1-yl}methanol, C14H18N6O·2.5CH3OH, consists of hydrogen-bonded ribbons which are further held together by additional hydrogen bonds involving the hydroxyl group and two N atoms on an adjacent purine. The asymmetric unit also contains 2.5 molecules of methanol solvate which were grossly disordered and were excluded using SQUEEZE subroutine in PLATON [Spek, (2009. Acta Cryst. D65, 148–155].

  9. Rotation and solvation of ammonium ion

    International Nuclear Information System (INIS)

    Perrin, C.L.; Gipe, R.K.

    1987-01-01

    From nitrogen-15 spin-lattice relaxation times and nuclear Overhauser enhancements, the rotational correlations time tau/sub c/ for 15 NH 4 + was determined in s series of solvents. Values of tau/sub c/ range from 0.46 to 20 picoseconds. The solvent dependent of tau/sub c/ cannot be explained in terms of solvent polarity, molecular dipole moment, solvent basicity, solvent dielectric relaxation, or solvent viscosity. The rapid rotation and the variation with solvent can be accounted for by a model that involves hydrogen bonding of an NH proton to more than one solvent molecule in a disordered solvation environment. 25 references, 1 table

  10. Influence of the Compositional Grading on Concentration of Majority Charge Carriers in Near-Surface Layers of n(p)-HgCdTe Grown by Molecular Beam Epitaxy

    Science.gov (United States)

    Voitsekhovskii, A. V.; Nesmelov, S. N.; Dzyadukh, S. M.

    2018-02-01

    The capacitive characteristics of metal-insulator-semiconductor (MIS) structures based on the compositionally graded Hg1-xCdxTe created by molecular beam epitaxy have been experimentally investigated in a wide temperature range (8-77 K). A program has been developed for numerical simulation of ideal capacitance-voltage (C-V) characteristics in the low-frequency and high-frequency approximations. The concentrations of the majority carriers in the near-surface semiconductor layer are determined from the values of the capacitances in the minima of low-frequency C-V curves. For MIS structures based on p-Hg1-xCdxTe, the effect of the presence of the compositionally graded layer on the hole concentration in the near-surface semiconductor layer, determined from capacitive measurements, has not been established. Perhaps this is due to the fact that the concentration of holes in the near-surface layer largely depends on the type of dielectric coating and the regimes of its application. For MIS structures based on n-Hg1-x Cd x Te (x = 0.22-0.23) without a graded-gap layer, the electron concentration determined by the proposed method is close to the average concentration determined by the Hall measurements. The electron concentration in the near-surface semiconductor layer of the compositionally graded n-Hg1-x Cd x Te (x = 0.22-0.23) found from the minimum capacitance value is much higher than the average electron concentration determined by the Hall measurements. The results are qualitatively explained by the creation of additional intrinsic donor-type defects in the near-surface compositionally graded layer of n-Hg1-x Cd x Te.

  11. Organic solvation of intercalated cations in V/sub 2/O/sub 5/ xerogels

    International Nuclear Information System (INIS)

    Lemordant, D.; Bouhaouss, A.; Aldbert, P.; Baffier, N.

    1986-01-01

    V/sub 2/O/sub 5/ xerogels (V/sub 2/O/sub 5/, 1.6H/sub 2/O) undergo a topotactic reversible exchange reaction at room temperature in organic solvents containing monovalent alkali or divalent (Mn/sup 2+/) cations. Basal spacing are dependent on solvent type and charge-to-radius ratio of guest cations. From the interlayer distances, two solvation stages have been inferred, depending on the nature of the solvent and of the cation, except with Cs/sup +/ for which no intracrystalline swelling by organic solvents is observed

  12. Computational Study of Geometry, Solvation Free Energy, Dipole Moment, Polarizability, Hyperpolarizability and Molecular Properties of 2-Methylimidazole

    Directory of Open Access Journals (Sweden)

    Mohammad Firoz Khan

    2016-12-01

    Full Text Available Ab initio calculations were carried out to study the geometry, solvation free energy, dipole moment, molecular electrostatic potential (MESP, Mulliken and Natural charge distribution, polarizability, hyperpolarizability, Natural Bond Orbital (NBO energetic and different molecular properties like global reactivity descriptors (chemical hardness, softness, chemical potential, electronegativity, electrophilicity index of 2-methylimidazole. B3LYP/6-31G(d,p level of theory was used to optimize the structure both in the gas phase and in solution. The solvation free energy, dipole moment and molecular properties were calculated by applying the Solvation Model on Density (SMD in four solvent systems, namely water, dimethylsulfoxide (DMSO, n-octanol and chloroform. The computed bond distances, bond angles and dihedral angles of 2-methylimidazole agreed reasonably well with the experimental data except for C(2-N(1, C(4-C(5 and N(1-H(7 bond lengths and N(1-C(5-C(4 bond angle. The solvation free energy, dipole moment, polarizability, first order hyperpolarizability, chemical potential, electronegativity and electrophilicity index of 2-methylimidazole increased on going from non-polar to polar solvents. Chemical hardness also increased with increasing polarity of the solvent and the opposite relation was found in the case of softness. These results provide better understanding of the stability and reactivity of 2-methylimidazole in different solvent systems.

  13. A Low-Energy-Gap Thienochrysenocarbazole Dye for Highly Efficient Mesoscopic Titania Solar Cells: Understanding the Excited State and Charge Carrier Dynamics.

    Science.gov (United States)

    Wang, Junting; Xie, Xinrui; Weng, Guorong; Yuan, Yi; Zhang, Jing; Wang, Peng

    2018-05-09

    Maintaining both a high external quantum efficiency and a large open-circuit photovoltage of dye-sensitized solar cells (DSSCs) is a crucial challenge in the process of developing narrow-energy-gap dyes for the capture of infrared solar photons. Herein, we report two donor-acceptor organic dyes, C294 and C295, with a polycyclic heteroaromatic unit, 6,11-dihydrothieno[3',2':8,9]chryseno[10,11,12,1-bcdefg]carbazole (TCC), as the central module of the electron donor, and ethylbenzothiadiazole-benzioc acid as the electron acceptor. The interfacial charge recombination was successfully mitigated by introducing an additional branched aliphatic chain in C295. Furthermore, the O⋅⋅⋅S nonbonding interaction between the oxygen atom of the alkoxy group and the sulfur atom of the thiophene in C295 controlled the conformation of C295, resulting in a narrow energy-gap. Time-resolved spectroscopic measurements on C294 and the model dye C272 indicated that the elevation of the HOMO energy level decreased the kinetics and yield of hole injection owing to a reduction in the driving force and that the shortened excited-state lifetime caused by the narrowing of the energy gap was unfavorable for electron injection. By fine tuning the composition of the electrolyte, C294 and C295 eventually achieved high power conversion efficiencies of 11.5 % and 12.4 %, respectively, under full sunlight of air mass 1.5 global conditions. © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

  14. Fabrication of a Co(OH)2/ZnCr LDH "p-n" Heterojunction Photocatalyst with Enhanced Separation of Charge Carriers for Efficient Visible-Light-Driven H2 and O2 Evolution.

    Science.gov (United States)

    Sahoo, Dipti Prava; Nayak, Susanginee; Reddy, K Hemalata; Martha, Satyabadi; Parida, Kulamani

    2018-04-02

    Photocatalytic generation of H 2 and O 2 by water splitting remains a great challenge for clean and sustainable energy. Taking into the consideration promising heterojunction photocatalysts, analogous energy issues have been mitigated to a meaningful extent. Herein, we have architectured a highly efficient bifunctional heterojunction material, i.e., p-type Co(OH) 2 platelets with an n-type ZnCr layered double hydroxide (LDH) by an ultrasonication method. Primarily, the Mott-Schottky measurements confirmed the n- and p-type semiconductive properties of LDH and CH material, respectively, with the construction of a p-n heterojunction. The high resolution transmission electron microscopy results suggest that surface modification of ZnCr LDH by Co(OH) 2 hexagonal platelets could form a fabulous p-n interfacial region that significantly decreases the energy barrier for O 2 and H 2 production by effectively separating and transporting photoinduced charge carriers, leading to enhanced photoreactivity. A deep investigation into the mechanism shows that a 30 wt % Co(OH) 2 -modified ZnCr LDH sample liberates maximum H 2 and O 2 production in 2 h, i.e., 1115 and 560 μmol, with apparent conversion efficiencies of H 2 and O 2 evolution of 13.12% and 6.25%, respectively. Remarkable photocatalytic activity with energetic charge pair transfer capability was illustrated by electrochemical impedance spectroscopy, linear sweep voltammetry, and photoluminescence spectra. The present study clearly suggests that low-cost Co(OH) 2 platelets are the most crucial semiconductors to provide a new p-n heterojunction photocatalyst for photocatalytic H 2 and O 2 production on the platform of ZnCr LDH.

  15. Solvation of hydrocarbons in aqueous-organic mixtures

    International Nuclear Information System (INIS)

    Sedov, I.A.; Magsumov, T.I.; Solomonov, B.N.

    2016-01-01

    Highlights: • Thermodynamic functions of solvation in mixtures of water with acetone and acetonitrile are measured at T = 298.15 K. • Solvation of n-octane and toluene in aqueous-organic mixtures is studied. • When increasing water content, Gibbs free energies grow up steadily, while enthalpies have a maximum. • Hydrocarbons are preferentially solvated with organic cosolvent even in mixtures with rather high water content. • Acetonitrile suppresses the hydrophobic effect less than acetone. - Abstract: We study the solvation of two hydrocarbons, n-octane and toluene, in binary mixtures of water with organic cosolvents. Two polar aprotic cosolvents that are miscible with water in any proportions, acetonitrile and acetone, were considered. We determine the magnitudes of thermodynamic functions of dissolution and solvation at T = 298.15 K in the mixtures with various compositions. Solution calorimetry was used to measure the enthalpies of solution, and GC headspace analysis was applied to obtain limiting activity coefficients of solutes in the studied systems. For the first time, the enthalpies of solution of alkane in the mixtures with high water content were measured directly. We observed well-pronounced maxima of the dependencies of enthalpies of solvation from the composition of solvent and no maxima for the Gibbs free energies of solvation. Two factors are concluded to be important to explain the observed tendencies: high energy cost of reorganization of binary solvent upon insertion of solute molecules and preferential surrounding of hydrocarbons with the molecules of organic cosolvent. Enthalpy-entropy compensation leads to a steady growth of the Gibbs free energies with increasing water content. On the other hand, consideration of the plots of the Gibbs free energy against enthalpy of solvation clearly shows that the solvation properties are changed dramatically after addition of a rather small amount of organic cosolvents. It is shown that they

  16. Solvation of lithium ion in dimethoxyethane and propylene carbonate

    Science.gov (United States)

    Chaban, Vitaly

    2015-07-01

    Solvation of the lithium ion (Li+) in dimethoxyethane (DME) and propylene carbonate (PC) is of scientific significance and urgency in the context of lithium-ion batteries. I report PM7-MD simulations on the composition of Li+ solvation shells (SH) in a few DME/PC mixtures. The equimolar mixture features preferential solvation by PC, in agreement with classical MD studies. However, one DME molecule is always present in the first SH, supplementing the cage formed by five PC molecules. As PC molecules get removed, DME gradually substitutes vacant places. In the PC-poor mixtures, an entire SH is populated by five DME molecules.

  17. Modeling solvation effects in real-space and real-time within density functional approaches

    Energy Technology Data Exchange (ETDEWEB)

    Delgado, Alain [Istituto Nanoscienze - CNR, Centro S3, via Campi 213/A, 41125 Modena (Italy); Centro de Aplicaciones Tecnológicas y Desarrollo Nuclear, Calle 30 # 502, 11300 La Habana (Cuba); Corni, Stefano; Pittalis, Stefano; Rozzi, Carlo Andrea [Istituto Nanoscienze - CNR, Centro S3, via Campi 213/A, 41125 Modena (Italy)

    2015-10-14

    The Polarizable Continuum Model (PCM) can be used in conjunction with Density Functional Theory (DFT) and its time-dependent extension (TDDFT) to simulate the electronic and optical properties of molecules and nanoparticles immersed in a dielectric environment, typically liquid solvents. In this contribution, we develop a methodology to account for solvation effects in real-space (and real-time) (TD)DFT calculations. The boundary elements method is used to calculate the solvent reaction potential in terms of the apparent charges that spread over the van der Waals solute surface. In a real-space representation, this potential may exhibit a Coulomb singularity at grid points that are close to the cavity surface. We propose a simple approach to regularize such singularity by using a set of spherical Gaussian functions to distribute the apparent charges. We have implemented the proposed method in the OCTOPUS code and present results for the solvation free energies and solvatochromic shifts for a representative set of organic molecules in water.

  18. Comparison of the Marcus and Pekar partitions in the context of non-equilibrium, polarizable-continuum solvation models

    International Nuclear Information System (INIS)

    You, Zhi-Qiang; Herbert, John M.; Mewes, Jan-Michael; Dreuw, Andreas

    2015-01-01

    The Marcus and Pekar partitions are common, alternative models to describe the non-equilibrium dielectric polarization response that accompanies instantaneous perturbation of a solute embedded in a dielectric continuum. Examples of such a perturbation include vertical electronic excitation and vertical ionization of a solution-phase molecule. Here, we provide a general derivation of the accompanying polarization response, for a quantum-mechanical solute described within the framework of a polarizable continuum model (PCM) of electrostatic solvation. Although the non-equilibrium free energy is formally equivalent within the two partitions, albeit partitioned differently into “fast” versus “slow” polarization contributions, discretization of the PCM integral equations fails to preserve certain symmetries contained in these equations (except in the case of the conductor-like models or when the solute cavity is spherical), leading to alternative, non-equivalent matrix equations. Unlike the total equilibrium solvation energy, however, which can differ dramatically between different formulations, we demonstrate that the equivalence of the Marcus and Pekar partitions for the non-equilibrium solvation correction is preserved to high accuracy. Differences in vertical excitation and ionization energies are <0.2 eV (and often <0.01 eV), even for systems specifically selected to afford a large polarization response. Numerical results therefore support the interchangeability of the Marcus and Pekar partitions, but also caution against relying too much on the fast PCM charges for interpretive value, as these charges differ greatly between the two partitions, especially in polar solvents

  19. Comparison of the Marcus and Pekar partitions in the context of non-equilibrium, polarizable-continuum solvation models

    Energy Technology Data Exchange (ETDEWEB)

    You, Zhi-Qiang; Herbert, John M., E-mail: herbert@chemistry.ohio-state.edu [Department of Chemistry and Biochemistry, The Ohio State University, Columbus, Ohio 43210 (United States); Mewes, Jan-Michael; Dreuw, Andreas [Interdisciplinary Center for Scientific Computing, Ruprechts-Karls University, Im Neuenheimer Feld 368, 69120 Heidelberg (Germany)

    2015-11-28

    The Marcus and Pekar partitions are common, alternative models to describe the non-equilibrium dielectric polarization response that accompanies instantaneous perturbation of a solute embedded in a dielectric continuum. Examples of such a perturbation include vertical electronic excitation and vertical ionization of a solution-phase molecule. Here, we provide a general derivation of the accompanying polarization response, for a quantum-mechanical solute described within the framework of a polarizable continuum model (PCM) of electrostatic solvation. Although the non-equilibrium free energy is formally equivalent within the two partitions, albeit partitioned differently into “fast” versus “slow” polarization contributions, discretization of the PCM integral equations fails to preserve certain symmetries contained in these equations (except in the case of the conductor-like models or when the solute cavity is spherical), leading to alternative, non-equivalent matrix equations. Unlike the total equilibrium solvation energy, however, which can differ dramatically between different formulations, we demonstrate that the equivalence of the Marcus and Pekar partitions for the non-equilibrium solvation correction is preserved to high accuracy. Differences in vertical excitation and ionization energies are <0.2 eV (and often <0.01 eV), even for systems specifically selected to afford a large polarization response. Numerical results therefore support the interchangeability of the Marcus and Pekar partitions, but also caution against relying too much on the fast PCM charges for interpretive value, as these charges differ greatly between the two partitions, especially in polar solvents.

  20. Zero-point energy effects in anion solvation shells.

    Science.gov (United States)

    Habershon, Scott

    2014-05-21

    By comparing classical and quantum-mechanical (path-integral-based) molecular simulations of solvated halide anions X(-) [X = F, Cl, Br and I], we identify an ion-specific quantum contribution to anion-water hydrogen-bond dynamics; this effect has not been identified in previous simulation studies. For anions such as fluoride, which strongly bind water molecules in the first solvation shell, quantum simulations exhibit hydrogen-bond dynamics nearly 40% faster than the corresponding classical results, whereas those anions which form a weakly bound solvation shell, such as iodide, exhibit a quantum effect of around 10%. This observation can be rationalized by considering the different zero-point energy (ZPE) of the water vibrational modes in the first solvation shell; for strongly binding anions, the ZPE of bound water molecules is larger, giving rise to faster dynamics in quantum simulations. These results are consistent with experimental investigations of anion-bound water vibrational and reorientational motion.

  1. Proton solvation and proton transfer in chemical and electrochemical processes

    International Nuclear Information System (INIS)

    Lengyel, S.; Conway, B.E.

    1983-01-01

    This chapter examines the proton solvation and characterization of the H 3 O + ion, proton transfer in chemical ionization processes in solution, continuous proton transfer in conductance processes, and proton transfer in electrode processes. Topics considered include the condition of the proton in solution, the molecular structure of the H 3 O + ion, thermodynamics of proton solvation, overall hydration energy of the proton, hydration of H 3 O + , deuteron solvation, partial molal entropy and volume and the entropy of proton hydration, proton solvation in alcoholic solutions, analogies to electrons in semiconductors, continuous proton transfer in conductance, definition and phenomenology of the unusual mobility of the proton in solution, solvent structure changes in relation to anomalous proton mobility, the kinetics of the proton-transfer event, theories of abnormal proton conductance, and the general theory of the contribution of transfer reactions to overall transport processes

  2. Ultrafast transient-absorption of the solvated electron in water

    International Nuclear Information System (INIS)

    Kimura, Y.; Alfano, J.C.; Walhout, P.K.; Barbara, P.F.

    1994-01-01

    Ultrafast near infrared (NIR)-pump/variable wavelength probe transient-absorption spectroscopy has been performed on the aqueous solvated electron. The photodynamics of the solvated electron excited to its p-state are qualitatively similar to previous measurements of the dynamics of photoinjected electrons at high energy. This result confirms the previous interpretation of photoinjected electron dynamics as having a rate-limiting bottleneck at low energies presumably involving the p-state

  3. Estimation of abraham solvation equation coefficients for hydrogen bond formation from abraham solvation parameters for solute activity and basicity

    NARCIS (Netherlands)

    Noort, van P.C.M.

    2013-01-01

    Abraham solvation equations find widespread use in environmental chemistry and pharmaco-chemistry. The coefficients in these equations, which are solvent (system) descriptors, are usually determined by fitting experimental data. To simplify the determination of these coefficients in Abraham

  4. Charge carrier dynamics in photovoltaic materials

    NARCIS (Netherlands)

    Jensen, S.A.

    2014-01-01

    We employ the experimental technique THz Time Domain spectroscopy (THz-TDS) to study the optoelectronic properties of potential photovoltaic materials. This all-optical method is useful for probing photoconductivities in a range of materials on ultrafast timescales without the application of

  5. Water-enhanced solvation of organics

    Energy Technology Data Exchange (ETDEWEB)

    Lee, Jane H. [Univ. of California, Berkeley, CA (United States)

    1993-07-01

    Water-enhanced solvation (WES) was explored for Lewis acid solutes in Lewis base organic solvents, to develop cheap extract regeneration processes. WES for solid solutes was determined from ratios of solubilities of solutes in water-sat. and low-water solvent; both were determined from solid-liquid equilibrium. Vapor-headspace analysis was used to determine solute activity coefficients as function of organic phase water concentration. WES magnitudes of volatile solutes were normalized, set equal to slope of log γs vs xw/xs curve. From graph shape Δ(log γs) represents relative change in solute activity coefficient. Solutes investigated by vapor-headspace analysis were acetic acid, propionic acid, ethanol, 1,2-propylene glycol, 2,3-butylene glycol. Monocarboxylic acids had largest decrease in activity coefficient with water addition followed by glycols and alcohols. Propionic acid in cyclohexanone showed greatest water-enhancement Δ(log γacid)/Δ(xw/xacid) = -0.25. In methylcyclohexanone, the decrease of the activity coefficient of propionic acid was -0.19. Activity coefficient of propionic acid in methylcyclohexanone stopped decreasing once the water reached a 2:1 water to acid mole ratio, implying a stoichiometric relation between water, ketone, and acid. Except for 2,3-butanediol, activity coefficients of the solutes studied decreased monotonically with water content. Activity coefficient curves of ethanol, 1,2-propanediol and 2,3-butanediol did not level off at large water/solute mole ratio. Solutes investigated by solid-liquid equilibrium were citric acid, gallic acid, phenol, xylenols, 2-naphthol. Saturation concentration of citric acid in anhydrous butyl acetate increased from 0.0009 to 0.087 mol/L after 1.3 % (g/g) water co-dissolved into organic phase. Effect of water-enhanced solvation for citric acid is very large but very small for phenol and its derivatives.

  6. Aircraft Carriers

    DEFF Research Database (Denmark)

    Nødskov, Kim; Kværnø, Ole

    as their purchases of aircraft carrier systems, makes it more than likely that the country is preparing such an acquisition. China has territorial disputes in the South China Sea over the Spratly Islands and is also worried about the security of its sea lines of communications, by which China transports the majority......, submarines, aircraft and helicopters, is not likely to be fully operational and war-capable until 2020, given the fact that China is starting from a clean sheet of paper. The United States of America (USA), the United Kingdom (UK), Russia and India are currently building or have made decisions to build new...

  7. Extending the Solvation-Layer Interface Condition Continum Electrostatic Model to a Linearized Poisson-Boltzmann Solvent.

    Science.gov (United States)

    Molavi Tabrizi, Amirhossein; Goossens, Spencer; Mehdizadeh Rahimi, Ali; Cooper, Christopher D; Knepley, Matthew G; Bardhan, Jaydeep P

    2017-06-13

    We extend the linearized Poisson-Boltzmann (LPB) continuum electrostatic model for molecular solvation to address charge-hydration asymmetry. Our new solvation-layer interface condition (SLIC)/LPB corrects for first-shell response by perturbing the traditional continuum-theory interface conditions at the protein-solvent and the Stern-layer interfaces. We also present a GPU-accelerated treecode implementation capable of simulating large proteins, and our results demonstrate that the new model exhibits significant accuracy improvements over traditional LPB models, while reducing the number of fitting parameters from dozens (atomic radii) to just five parameters, which have physical meanings related to first-shell water behavior at an uncharged interface. In particular, atom radii in the SLIC model are not optimized but uniformly scaled from their Lennard-Jones radii. Compared to explicit-solvent free-energy calculations of individual atoms in small molecules, SLIC/LPB is significantly more accurate than standard parametrizations (RMS error 0.55 kcal/mol for SLIC, compared to RMS error of 3.05 kcal/mol for standard LPB). On parametrizing the electrostatic model with a simple nonpolar component for total molecular solvation free energies, our model predicts octanol/water transfer free energies with an RMS error 1.07 kcal/mol. A more detailed assessment illustrates that standard continuum electrostatic models reproduce total charging free energies via a compensation of significant errors in atomic self-energies; this finding offers a window into improving the accuracy of Generalized-Born theories and other coarse-grained models. Most remarkably, the SLIC model also reproduces positive charging free energies for atoms in hydrophobic groups, whereas standard PB models are unable to generate positive charging free energies regardless of the parametrized radii. The GPU-accelerated solver is freely available online, as is a MATLAB implementation.

  8. Cluster expansion of the solvation free energy difference: Systematic improvements in the solvation of single ions

    Science.gov (United States)

    Pliego, Josefredo R.

    2017-07-01

    The cluster expansion method has been used in the imperfect gas theory for several decades. This paper proposes a cluster expansion of the solvation free energy difference. This difference, which results from a change in the solute-solvent potential energy, can be written as the logarithm of a finite series. Similar to the Mayer function, the terms in the series are related to configurational integrals, which makes the integrand relevant only for configurations of the solvent molecules close to the solute. In addition, the terms involve interaction of solute with one, two, and so on solvent molecules. The approach could be used for hybrid quantum mechanical and molecular mechanics methods or mixed cluster-continuum approximation. A simple form of the theory was applied for prediction of pKa in methanol; the results indicated that three explicit methanol molecules and the dielectric continuum lead to a root of mean squared error (RMSE) of only 1.3 pKa units, whereas the pure continuum solvation model based on density method leads to a RMSE of 6.6 pKa units.

  9. Terahertz carrier dynamics in graphene and graphene nanostructures

    DEFF Research Database (Denmark)

    Jensen, Søren A.; Turchinovich, Dmitry; Tielrooij, Klaas Jan

    2014-01-01

    Photoexcited charge carriers in 2D graphene and in 1D graphene nanostructures were studied with optical pump-THz probe spectroscopy. We find efficient hot-carrier multiplication in 2D graphene, and predominantly free carrier early time response in 1D nanostructures. © 2014 OSA....

  10. Order and correlation contributions to the entropy of hydrophobic solvation

    Energy Technology Data Exchange (ETDEWEB)

    Liu, Maoyuan; Besford, Quinn Alexander; Mulvaney, Thomas; Gray-Weale, Angus, E-mail: gusgw@gusgw.net [School of Chemistry, The University of Melbourne, Victoria 3010 (Australia)

    2015-03-21

    The entropy of hydrophobic solvation has been explained as the result of ordered solvation structures, of hydrogen bonds, of the small size of the water molecule, of dispersion forces, and of solvent density fluctuations. We report a new approach to the calculation of the entropy of hydrophobic solvation, along with tests of and comparisons to several other methods. The methods are assessed in the light of the available thermodynamic and spectroscopic information on the effects of temperature on hydrophobic solvation. Five model hydrophobes in SPC/E water give benchmark solvation entropies via Widom’s test-particle insertion method, and other methods and models are tested against these particle-insertion results. Entropies associated with distributions of tetrahedral order, of electric field, and of solvent dipole orientations are examined. We find these contributions are small compared to the benchmark particle-insertion entropy. Competitive with or better than other theories in accuracy, but with no free parameters, is the new estimate of the entropy contributed by correlations between dipole moments. Dipole correlations account for most of the hydrophobic solvation entropy for all models studied and capture the distinctive temperature dependence seen in thermodynamic and spectroscopic experiments. Entropies based on pair and many-body correlations in number density approach the correct magnitudes but fail to describe temperature and size dependences, respectively. Hydrogen-bond definitions and free energies that best reproduce entropies from simulations are reported, but it is difficult to choose one hydrogen bond model that fits a variety of experiments. The use of information theory, scaled-particle theory, and related methods is discussed briefly. Our results provide a test of the Frank-Evans hypothesis that the negative solvation entropy is due to structured water near the solute, complement the spectroscopic detection of that solvation structure by

  11. Standard electrode potential, Tafel equation, and the solvation thermodynamics.

    Science.gov (United States)

    Matyushov, Dmitry V

    2009-06-21

    Equilibrium in the electronic subsystem across the solution-metal interface is considered to connect the standard electrode potential to the statistics of localized electronic states in solution. We argue that a correct derivation of the Nernst equation for the electrode potential requires a careful separation of the relevant time scales. An equation for the standard metal potential is derived linking it to the thermodynamics of solvation. The Anderson-Newns model for electronic delocalization between the solution and the electrode is combined with a bilinear model of solute-solvent coupling introducing nonlinear solvation into the theory of heterogeneous electron transfer. We therefore are capable of addressing the question of how nonlinear solvation affects electrochemical observables. The transfer coefficient of electrode kinetics is shown to be equal to the derivative of the free energy, or generalized force, required to shift the unoccupied electronic level in the bulk. The transfer coefficient thus directly quantifies the extent of nonlinear solvation of the redox couple. The current model allows the transfer coefficient to deviate from the value of 0.5 of the linear solvation models at zero electrode overpotential. The electrode current curves become asymmetric in respect to the change in the sign of the electrode overpotential.

  12. Solvation structures of lithium halides in methanol–water mixtures

    International Nuclear Information System (INIS)

    Sarkar, Atanu; Dixit, Mayank Kumar; Tembe, B.L.

    2015-01-01

    Highlights: • Potentials of mean force for Li + -halides are calculated in methanol–water mixtures. • Stable CIP for x methanol = 1.0 becomes unstable at and below x methanol = 0.75. • The Li + ion is preferentially solvated by methanol molecules. • The halide ions are preferentially solvated by water molecules. - Abstract: The potentials of mean force (PMFs) for the ion pairs, Li + −Cl − , Li + −Br − and Li + −I − have been calculated in five methanol–water compositions. The results obtained are verified by trailing the trajectories and calculating the ion pair distance residence times. Local structures around the ions are studied using the radial distribution functions, density profiles, orientational correlation functions, running coordination numbers and excess coordination numbers. The major change in PMF is observed as the methanol mole fraction (x methanol ) is changed from 1.0 to 0.75. The stable contact ion pair occurring for x methanol = 1.0 becomes unstable at and below x methanol = 0.75. The preferential solvation data show that the halide ions are always preferentially solvated by water molecules. Although the lithium ion is preferentially solvated by methanol molecules, there is significant affinity towards water molecules as well

  13. Intensity of f-f bands of neodymium chloride alcohol solvates

    International Nuclear Information System (INIS)

    Bukietynska, K.; Jezowski-Trzebiatowska, B.; Keller, B.

    1981-01-01

    Recent results revealed that in alcohol solutions of lanthanide chlorides, at least in the case of Eu 3+ and Yb 3+ ions, there exist mixed solvates, i.e. both chloride ions and solvent molecules are present in the Ln 3+ ion first coordination sphere. This conclusion was drawn from an analysis of the charge transfer transitions in the spectra of Eu 3+ and Yb 3+ chlorides in alcohols (methyl, ethyl, n-propyl), where two separate C.T.bands were observed and identified as C.T. transitions from the alcohol molecule and chloride ion to the Ln 3+ ion. In our previous paper we have reported that the energy of the first f-d transition in the Pr 3+ chloride alcohol solvates varied for different alcohols. These data also confirmed our suggestion that alcohol molecules are present in the first coordination sphere of the lanthanide ion. In the work reported here, we have tried to apply the intensity analysis method to the solution spectra of neodymium chloride dissolved in simple aliphatic alcohols like methanol, ethanol and n-propanol. Experimental details are given. Results are presented and discussed. (author)

  14. Development and application of QM/MM methods to study the solvation effects and surfaces

    Energy Technology Data Exchange (ETDEWEB)

    Dibya, Pooja Arora [Iowa State Univ., Ames, IA (United States)

    2010-01-01

    Quantum mechanical (QM) calculations have the advantage of attaining high-level accuracy, however QM calculations become computationally inefficient as the size of the system grows. Solving complex molecular problems on large systems and ensembles by using quantum mechanics still poses a challenge in terms of the computational cost. Methods that are based on classical mechanics are an inexpensive alternative, but they lack accuracy. A good trade off between accuracy and efficiency is achieved by combining QM methods with molecular mechanics (MM) methods to use the robustness of the QM methods in terms of accuracy and the MM methods to minimize the computational cost. Two types of QM combined with MM (QM/MM) methods are the main focus of the present dissertation: the application and development of QM/MM methods for solvation studies and reactions on the Si(100) surface. The solvation studies were performed using a discreet solvation model that is largely based on first principles called the effective fragment potential method (EFP). The main idea of combining the EFP method with quantum mechanics is to accurately treat the solute-solvent and solvent-solvent interactions, such as electrostatic, polarization, dispersion and charge transfer, that are important in correctly calculating solvent effects on systems of interest. A second QM/MM method called SIMOMM (surface integrated molecular orbital molecular mechanics) is a hybrid QM/MM embedded cluster model that mimics the real surface.3 This method was employed to calculate the potential energy surfaces for reactions of atomic O on the Si(100) surface. The hybrid QM/MM method is a computationally inexpensive approach for studying reactions on larger surfaces in a reasonably accurate and efficient manner. This thesis is comprised of four chapters: Chapter 1 describes the general overview and motivation of the dissertation and gives a broad background of the computational methods that have been employed in this work

  15. Grid inhomogeneous solvation theory: hydration structure and thermodynamics of the miniature receptor cucurbit[7]uril.

    Science.gov (United States)

    Nguyen, Crystal N; Young, Tom Kurtzman; Gilson, Michael K

    2012-07-28

    The displacement of perturbed water upon binding is believed to play a critical role in the thermodynamics of biomolecular recognition, but it is nontrivial to unambiguously define and answer questions about this process. We address this issue by introducing grid inhomogeneous solvation theory (GIST), which discretizes the equations of inhomogeneous solvation theory (IST) onto a three-dimensional grid situated in the region of interest around a solute molecule or complex. Snapshots from explicit solvent simulations are used to estimate localized solvation entropies, energies, and free energies associated with the grid boxes, or voxels, and properly summing these thermodynamic quantities over voxels yields information about hydration thermodynamics. GIST thus provides a smoothly varying representation of water properties as a function of position, rather than focusing on hydration sites where solvent is present at high density. It therefore accounts for full or partial displacement of water from sites that are highly occupied by water, as well as for partly occupied and water-depleted regions around the solute. GIST can also provide a well-defined estimate of the solvation free energy and therefore enables a rigorous end-states analysis of binding. For example, one may not only use a first GIST calculation to project the thermodynamic consequences of displacing water from the surface of a receptor by a ligand, but also account, in a second GIST calculation, for the thermodynamics of subsequent solvent reorganization around the bound complex. In the present study, a first GIST analysis of the molecular host cucurbit[7]uril is found to yield a rich picture of hydration structure and thermodynamics in and around this miniature receptor. One of the most striking results is the observation of a toroidal region of high water density at the center of the host's nonpolar cavity. Despite its high density, the water in this toroidal region is disfavored energetically and

  16. Difference rule-a new thermodynamic principle: prediction of standard thermodynamic data for inorganic solvates.

    Science.gov (United States)

    Jenkins, H Donald Brooke; Glasser, Leslie

    2004-12-08

    We present a quite general thermodynamic "difference" rule, derived from thermochemical first principles, quantifying the difference between the standard thermodynamic properties, P, of a solid n-solvate (or n-hydrate), n-S, containing n molecules of solvate, S (water or other) and the corresponding solid parent (unsolvated) salt: [P[n-solvate] - P[parent

  17. Water Evaporation and Conformational Changes from Partially Solvated Ubiquitin

    Directory of Open Access Journals (Sweden)

    Saravana Prakash Thirumuruganandham

    2010-01-01

    Full Text Available Using molecular dynamics simulation, we study the evaporation of water molecules off partially solvated ubiquitin. The evaporation and cooling rates are determined for a molecule at the initial temperature of 300 K. The cooling rate is found to be around 3 K/ns, and decreases with water temperature in the course of the evaporation. The conformation changes are monitored by studying a variety of intermediate partially solvated ubiquitin structures. We find that ubiquitin shrinks with decreasing hydration shell and exposes more of its hydrophilic surface area to the surrounding.

  18. Dipole moments of molecules solvated in helium nanodroplets

    International Nuclear Information System (INIS)

    Stiles, Paul L.; Nauta, Klaas; Miller, Roger E.

    2003-01-01

    Stark spectra are reported for hydrogen cyanide and cyanoacetylene solvated in helium nanodroplets. The goal of this study is to understand the influence of the helium solvent on measurements of the permanent electric dipole moment of a molecule. We find that the dipole moments of the helium solvated molecules, calculated assuming the electric field is the same as in vacuum, are slightly smaller than the well-known gas-phase dipole moments of HCN and HCCCN. A simple elliptical cavity model quantitatively accounts for this difference, which arises from the dipole-induced polarization of the helium

  19. Theoretical-experimental study of the solvation enthalpy of acetone in dilute aqueous solution

    International Nuclear Information System (INIS)

    Arroyo, S. Tolosa; Martin, J.A. Sanson; Garcia, A. Hidalgo

    2005-01-01

    The present paper describes molecular dynamics simulations of aqueous solutions at infinite dilution with acetone as solute. Lennard-Jones with electrostatic term (12-6-1 potentials) were employed to describe the solute-solvent interactions. The Morokuma decomposition scheme of ab initio interaction energies at the SCF level and the ESIE charges on the solute atoms were used to reproduce the exchange and Coulomb electrostatic contributions of the solute-water interaction potential. Some extensions, such as including the dispersion component evaluated at MP2 level, were added to the traditional calculation procedures in order to improve the results of the solvation enthalpy. The results obtained with the EX-DIS-ES model were compared with the experimental calorimetry values, the observed agreement being acceptable

  20. On the relation between Marcus theory and ultrafast spectroscopy of solvation kinetics

    Science.gov (United States)

    Roy, Santanu; Galib, Mirza; Schenter, Gregory K.; Mundy, Christopher J.

    2018-01-01

    The phenomena of solvent exchange control the process of solvating ions, protons, and charged molecules. Building upon our extension of Marcus' philosophy of electron transfer, we provide a new perspective of ultrafast solvent exchange mechanism around ions measurable by two-dimensional infrared (2DIR) spectroscopy. In this theory, solvent rearrangement drives an ion-bound water to an activated state of higher coordination number, triggering ion-water separation that leads to the solvent-bound state of the water molecule. This ion-bound to solvent-bound transition rate for a BF4--water system is computed using ab initio molecular dynamics and Marcus theory, and is found to be in excellent agreement with the 2DIR measurement.

  1. Differential geometry based solvation model II: Lagrangian formulation.

    Science.gov (United States)

    Chen, Zhan; Baker, Nathan A; Wei, G W

    2011-12-01

    Solvation is an elementary process in nature and is of paramount importance to more sophisticated chemical, biological and biomolecular processes. The understanding of solvation is an essential prerequisite for the quantitative description and analysis of biomolecular systems. This work presents a Lagrangian formulation of our differential geometry based solvation models. The Lagrangian representation of biomolecular surfaces has a few utilities/advantages. First, it provides an essential basis for biomolecular visualization, surface electrostatic potential map and visual perception of biomolecules. Additionally, it is consistent with the conventional setting of implicit solvent theories and thus, many existing theoretical algorithms and computational software packages can be directly employed. Finally, the Lagrangian representation does not need to resort to artificially enlarged van der Waals radii as often required by the Eulerian representation in solvation analysis. The main goal of the present work is to analyze the connection, similarity and difference between the Eulerian and Lagrangian formalisms of the solvation model. Such analysis is important to the understanding of the differential geometry based solvation model. The present model extends the scaled particle theory of nonpolar solvation model with a solvent-solute interaction potential. The nonpolar solvation model is completed with a Poisson-Boltzmann (PB) theory based polar solvation model. The differential geometry theory of surfaces is employed to provide a natural description of solvent-solute interfaces. The optimization of the total free energy functional, which encompasses the polar and nonpolar contributions, leads to coupled potential driven geometric flow and PB equations. Due to the development of singularities and nonsmooth manifolds in the Lagrangian representation, the resulting potential-driven geometric flow equation is embedded into the Eulerian representation for the purpose of

  2. Ab initio studies on the solvation, electronic structures and intracluster reactions in M(+)L(n), with M(+)=magnesium and calcium singly-charged ions, L=water, methanol, ammonia, and n=1-6, and the elimination of a hydrogen atom in H atom in hydrated sodium clusters

    Science.gov (United States)

    Chan, Ka Wai

    The solvation and electronic structures of M+Ln, with M+ = Mg+ and Cat, L = H2O, CH 3OH and NH3, n=1-6 were investigated by ab initio calculations using G03 package and density functional theory based ab initio molecular dynamics (AIMD) simulations with projector augmented-wave (PAW) method and a planewave basis set using Vienna Ab initio Simulation Package (VASP). Furthermore, ab initio studies on the intracluster reactions of Mg+ and Ca+ ions with different solvent molecules, H2O, CH3OH and NH3, were also done using G03 package. Finally, the elimination of a H atom in Na(H2O)n was studied. Such studies on the interactions and reactivity in gas clusters can provide insights into their analogies existing in condense phase. Interactions of Mg+ and Ca+ ions in different solvent molecules, H2O, CH3OH and NH3, were calculated with B3LYP and MP2 methods with basis sets 6-31+g** and 6-311+g**. A systematic comparison on the structures and reactivities of these clusters should provide a better understanding on the interplay of the ion-solvent, solvent-solvent, and electron-solvent interactions. It can provide a better understanding on the structures and bonding of complexes having analogies to those existing in condense phase. For Mg+(CH3OH)n and Ca+(CH 3OH)n, both H-elimination from OH/CH bond and CH3-elimination were investigated. H-elimination from O---H bond becomes more accessible for large cluster due to the diffusion of electron density to O---H bond. Studies on the H-elimination in Mg+(NH3)n and H-elimination from C---H bond in Mg+(CH3OH) n show that the reaction barriers flatten above 20 kcal/mol as n reaches 4 and above. These calculation results prove that the source of loss of H atom in ground state Mg+(CH3OH)n should be through the O---H bond rather than through the C---H bond. Compared to Mg+(CH3OH)n, the reaction barriers for H-elimination in Mg+(NH3)n is much larger, which is in consistent with the experimental observation of little H-elimination for Mg

  3. Thermodynamics of solvation and solvophobic effect in formamide

    International Nuclear Information System (INIS)

    Sedov, I.A.; Stolov, M.A.; Solomonov, B.N.

    2013-01-01

    Highlights: • Enthalpies of solution of apolar organic compounds in formamide were measured. • Gibbs free energies of solution were experimentally determined. • Influence of the solvophobic effect on solvation thermodynamics was studied. • Thermodynamic features of solutions in formamide resemble those of aqueous solutions. -- Abstract: Using semi-adiabatic calorimetry, we measured the enthalpies of solution for various low-polar compounds including alkanes, aromatic hydrocarbons and their halogenated derivatives in formamide at temperature of 298 K. For the same compounds, the values of limiting activity coefficients in formamide were determined using GC headspace analysis at 298 K, and Gibbs free energies of solution and solvation were calculated. Based on these data and the available literature values of the Gibbs free energy of solvation in formamide for a number of other low-polar solutes, a study of the solvophobic effect in this solvent is performed, and its resemblance to the hydrophobic effect in aqueous solutions is demonstrated. It is shown that the contribution of the solvophobic effect into the solvation Gibbs free energy in formamide is much higher than that in aliphatic alcohols, but lower than that in water. Like in water, the magnitude of this contribution for different solutes linearly increases with the solute molecular volume. Solvophobic effect also significantly affects the enthalpies of dissolution in formamide, causing them to be more negative in the case of alkanes and more positive in the case of arenes

  4. Isotope effect in enthalpy of solvation of the lithium ion

    International Nuclear Information System (INIS)

    Krestov, G.A.; Egorov, G.I.; Korolev, V.P.

    1989-01-01

    At 298.15 K, the authors determined the standard enthalpies of solution for 6 LiCl and 7 LiCl in water, heavy water, dimethylsulfoxide (DMSO) and aqueous solutions of DMSO. The authors have established that solvation of 6 Li + is differentiated in water and DMSO to a greater degree than for 7 Li +

  5. The solvation of carbohydrates in dimethylsulfoxide and water

    International Nuclear Information System (INIS)

    Berger, S.; Diaz, M.D.; Horwat, Ch.

    1999-01-01

    The solvation of sucrose and other carbohydrates in DMSO and water is probed by intermolecular NOE measurements. The NOE effects are interpreted in terms of specific binding of the solvent to certain sites of the molecules. It is shown that DMSO attaches to specific sites of the sucrose molecule, whereas for water such a clear differentiation cannot be proven. (author)

  6. Microscopic picture of the aqueous solvation of glutamic acid

    NARCIS (Netherlands)

    Leenders, E.J.M.; Bolhuis, P.G.; Meijer, E.J.

    2008-01-01

    We present molecular dynamics simulations of glutamic acid and glutamate solvated in water, using both density functional theory (DFT) and the Gromos96 force field. We focus on the microscopic aspects of the solvation−particularly on the hydrogen bond structures and dynamics−and investigate the

  7. On the coupling between molecular diffusion and solvation shell exchange

    DEFF Research Database (Denmark)

    Møller, Klaus Braagaard; Rey, Rossend; Masia, Marco

    2005-01-01

    The connection between diffusion and solvent exchanges between first and second solvation shells is studied by means of molecular dynamics simulations and analytic calculations, with detailed illustrations for water exchange for the Li+ and Na+ ions, and for liquid argon. First, two methods...

  8. Comparison between implicit and hybrid solvation methods for the ...

    Indian Academy of Sciences (India)

    Administrator

    Both implicit solvation method (dielectric polarizable continuum model, DPCM) and hybrid ... the free energy change (ΔGsol) as per the PCM ... Here the gas phase change is written as ΔGg = ΔEelec + ..... bution to the field of electrochemistry.

  9. Polarizability and Aqueous Solvation of the Sulfate Dianion

    Czech Academy of Sciences Publication Activity Database

    Jungwirth, Pavel; Curtis, J. E.; Tobias, D. J.

    2003-01-01

    Roč. 367, - (2003), s. 704-710 ISSN 0009-2614 R&D Projects: GA MŠk LN00A032 Institutional research plan: CEZ:AV0Z4040901 Keywords : polarizability * aqueous solvation * dianion Subject RIV: CF - Physical ; Theoretical Chemistry Impact factor: 2.438, year: 2003

  10. Solvation Dynamics in Different Phases of the Lyotropic Liquid Crystalline System.

    Science.gov (United States)

    Roy, Bibhisan; Satpathi, Sagar; Gavvala, Krishna; Koninti, Raj Kumar; Hazra, Partha

    2015-09-03

    Reverse hexagonal (HII) liquid crystalline material based on glycerol monooleate (GMO) is considered as a potential carrier for drugs and other important biomolecules due to its thermotropic phase change and excellent morphology. In this work, the dynamics of encapsulated water, which plays important role in stabilization and formation of reverse hexagonal mesophase, has been investigated by time dependent Stokes shift method using Coumarin-343 as a solvation probe. The formation of the reverse hexagonal mesophase (HII) and transformation to the L2 phase have been monitored using small-angle X-ray scattering and polarized light microscopy experiments. REES studies suggest the existence of different polar regions in both HII and L2 systems. The solvation dynamics study inside the reverse hexagonal (HII) phase reveals the existence of two different types of water molecules exhibiting dynamics on a 120-900 ps time scale. The estimated diffusion coefficients of both types of water molecules obtained from the observed dynamics are in good agreement with the measured diffusion coefficient collected from the NMR study. The calculated activation energy is found to be 2.05 kcal/mol, which is associated with coupled rotational-translational water relaxation dynamics upon the transition from "bound" to "quasi-free" state. The observed ∼2 ns faster dynamics of the L2 phase compared to the HII phase may be associated with both the phase transformation as well as thermotropic effect on the relaxation process. Microviscosities calculated from time-resolved anisotropy studies infer that the interface is almost ∼22 times higher viscous than the central part of the cylinder. Overall, our results reveal the unique dynamical features of water inside the cylinder of reverse hexagonal and inverse micellar phases.

  11. Investigation of radiative charging of dielectrics irradiated by ions

    International Nuclear Information System (INIS)

    Dergobuzov, K.A.; Yalovets, A.P.

    1994-01-01

    Within the framework of the Gusel'nikov mathematical model are fulflled numerical investigations of charging dielectrics irradiated with ions and atoms. The model accounts for dynamics of quasi-free charge carriers of each sign with account of processes of dielectrics ionization with a beam, charge recombination and charge drift in an electric fields. The effective mobility of charge carriers is determined with account for its dependence on the dose rate

  12. Spectroscopic and computational studies of ionic clusters as models of solvation and atmospheric reactions

    Science.gov (United States)

    Kuwata, Keith T.

    Ionic clusters are useful as model systems for the study of fundamental processes in solution and in the atmosphere. Their structure and reactivity can be studied in detail using vibrational predissociation spectroscopy, in conjunction with high level ab initio calculations. This thesis presents the applications of infrared spectroscopy and computation to a variety of gas-phase cluster systems. A crucial component of the process of stratospheric ozone depletion is the action of polar stratospheric clouds (PSCs) to convert the reservoir species HCl and chlorine nitrate (ClONO2) to photochemically labile compounds. Quantum chemistry was used to explore one possible mechanism by which this activation is effected: Cl- + ClONO2 /to Cl2 + NO3- eqno(1)Correlated ab initio calculations predicted that the direct reaction of chloride ion with ClONO2 is facile, which was confirmed in an experimental kinetics study. In the reaction a weakly bound intermediate Cl2-NO3- is formed, with ~70% of the charge localized on the nitrate moiety. This enables the Cl2-NO3- cluster to be well solvated even in bulk solution, allowing (1) to be facile on PSCs. Quantum chemistry was also applied to the hydration of nitrosonium ion (NO+), an important process in the ionosphere. The calculations, in conjunction with an infrared spectroscopy experiment, revealed the structure of the gas-phase clusters NO+(H2O)n. The large degree of covalent interaction between NO+ and the lone pairs of the H2O ligands is contrasted with the weak electrostatic bonding between iodide ion and H2O. Finally, the competition between ion solvation and solvent self-association is explored for the gas-phase clusters Cl/-(H2O)n and Cl-(NH3)n. For the case of water, vibrational predissociation spectroscopy reveals less hydrogen bonding among H2O ligands than predicted by ab initio calculations. Nevertheless, for n /ge 5, cluster structure is dominated by water-water interactions, with Cl- only partially solvated by the

  13. A polarizable QM/MM approach to the molecular dynamics of amide groups solvated in water

    Energy Technology Data Exchange (ETDEWEB)

    Schwörer, Magnus; Wichmann, Christoph; Tavan, Paul, E-mail: tavan@physik.uni-muenchen.de [Lehrstuhl für BioMolekulare Optik, Ludwig-Maximilians Universität München, Oettingenstr. 67, 80538 München (Germany)

    2016-03-21

    The infrared (IR) spectra of polypeptides are dominated by the so-called amide bands. Because they originate from the strongly polar and polarizable amide groups (AGs) making up the backbone, their spectral positions sensitively depend on the local electric fields. Aiming at accurate computations of these IR spectra by molecular dynamics (MD) simulations, which derive atomic forces from a hybrid quantum and molecular mechanics (QM/MM) Hamiltonian, here we consider the effects of solvation in bulk liquid water on the amide bands of the AG model compound N-methyl-acetamide (NMA). As QM approach to NMA we choose grid-based density functional theory (DFT). For the surrounding MM water, we develop, largely based on computations, a polarizable molecular mechanics (PMM) model potential called GP6P, which features six Gaussian electrostatic sources (one induced dipole, five static partial charge distributions) and, therefore, avoids spurious distortions of the DFT electron density in hybrid DFT/PMM simulations. Bulk liquid GP6P is shown to have favorable properties at the thermodynamic conditions of the parameterization and beyond. Lennard-Jones (LJ) parameters of the DFT fragment NMA are optimized by comparing radial distribution functions in the surrounding GP6P liquid with reference data obtained from a “first-principles” DFT-MD simulation. Finally, IR spectra of NMA in GP6P water are calculated from extended DFT/PMM-MD trajectories, in which the NMA is treated by three different DFT functionals (BP, BLYP, B3LYP). Method-specific frequency scaling factors are derived from DFT-MD simulations of isolated NMA. The DFT/PMM-MD simulations with GP6P and with the optimized LJ parameters then excellently predict the effects of aqueous solvation and deuteration observed in the IR spectra of NMA. As a result, the methods required to accurately compute such spectra by DFT/PMM-MD also for larger peptides in aqueous solution are now at hand.

  14. A solvated electron lithium electrode for secondary batteries

    Science.gov (United States)

    Sammells, A. F.; Semkow, K. W.

    1986-09-01

    Attention is given to a novel method for the achievement of high electro-chemical reversibility in Li-based nonaqueous cells, using a liquid negative electrode that consists of Li dissolved in liquid ammonia as a solvated electron Li electrode. The containment of this liquid negative active material from direct contact to a liquid nonaqueous electrolyte in the positive electrode compartment was realized through the use of a Li-intercalated, electronically conducting ceramic membrane.

  15. Tris[2-(deuteriomethylsulfanylphenyl]phosphine deuteriochloroform 0.125-solvate

    Directory of Open Access Journals (Sweden)

    Seik Weng Ng

    2008-05-01

    Full Text Available The title deuterated tripodal phosphine, C21H12D9PS3·0.125CDCl3, crystallizes as two independent molecules, one of which lies on a general position and the other about a threefold rotation axis, and as a deuteriochloroform solvate. The solvent molecule is disordered about a site of symmetry 3, so that the ratio of phosphine to solvent is 8:1. The P atom adopts a pyramidal coordination geometry.

  16. Solvation dynamics of lithium salts in wet nitrobenzene

    Czech Academy of Sciences Publication Activity Database

    Moakes, G.; Gelbaum, L. T.; Leisen, J.; Janata, J.; Mareček, Vladimír

    2006-01-01

    Roč. 593, 1-2 (2006), s. 111-118 ISSN 0022-0728 R&D Projects: GA ČR GA203/03/0822 Grant - others:Georgia Research Alliance(US) GRA.CG06.D Institutional research plan: CEZ:AV0Z40400503 Keywords : solvation * NMR * FTIR * nitrobenzene/water * solvatomers Subject RIV: CF - Physical ; Theoretical Chemistry Impact factor: 2.339, year: 2006

  17. Comparison of solvation dynamics of electrons in four polyols

    Energy Technology Data Exchange (ETDEWEB)

    Lampre, I.; Pernot, P.; Bonin, J. [Laboratoire de Chimie Physique/ELYSE, Universite Paris-Sud 11, UMR 8000, Bat. 349, Orsay F-91405 (France); CNRS, Orsay F-91405 (France); Mostafavi, M. [Laboratoire de Chimie Physique/ELYSE, Universite Paris-Sud 11, UMR 8000, Bat. 349, Orsay F-91405 (France); CNRS, Orsay F-91405 (France)], E-mail: mehran.mostafavi@lcp.u-psud.fr

    2008-10-15

    Using pump-probe transient absorption spectroscopy, we studied the solvation dynamics of the electron in liquid polyalcohols: ethane-1,2-diol, propane-1,2-diol, propane-1,3-diol and propane-1,2,3-triol. Time-resolved absorption spectra ranging from 440 to 720 nm were measured. Our study shows that the excess electron in the diols presents an intense and wide absorption band in the visible and near-IR spectral domain at early time after two-photon ionization of the neat solvent. Then, for the first tens of picoseconds, the electron spectrum shifts toward the blue domain and its bandwidth decreases as the red part of the initial spectrum rapidly drops, while the blue part hardly evolves. In contrast, in the triol, the absorption spectrum of the electron is early situated in the visible range after the pump pulse and then solely evolves in the red part. The Bayesian data analysis of the observed picosecond solvation dynamics with different models is in favor of a heterogeneous continuous relaxation. That is corroborated by the analogy between the change in the absorption band with increasing time or decreasing temperature. That tends to indicate a similar organization disorder of the solvent. Moreover, the electron solvation dynamics is very fast in propane-1,2,3-triol despite its high viscosity and highlight the role of the OH-group in that process.

  18. Improvements to the APBS biomolecular solvation software suite.

    Science.gov (United States)

    Jurrus, Elizabeth; Engel, Dave; Star, Keith; Monson, Kyle; Brandi, Juan; Felberg, Lisa E; Brookes, David H; Wilson, Leighton; Chen, Jiahui; Liles, Karina; Chun, Minju; Li, Peter; Gohara, David W; Dolinsky, Todd; Konecny, Robert; Koes, David R; Nielsen, Jens Erik; Head-Gordon, Teresa; Geng, Weihua; Krasny, Robert; Wei, Guo-Wei; Holst, Michael J; McCammon, J Andrew; Baker, Nathan A

    2018-01-01

    The Adaptive Poisson-Boltzmann Solver (APBS) software was developed to solve the equations of continuum electrostatics for large biomolecular assemblages that have provided impact in the study of a broad range of chemical, biological, and biomedical applications. APBS addresses the three key technology challenges for understanding solvation and electrostatics in biomedical applications: accurate and efficient models for biomolecular solvation and electrostatics, robust and scalable software for applying those theories to biomolecular systems, and mechanisms for sharing and analyzing biomolecular electrostatics data in the scientific community. To address new research applications and advancing computational capabilities, we have continually updated APBS and its suite of accompanying software since its release in 2001. In this article, we discuss the models and capabilities that have recently been implemented within the APBS software package including a Poisson-Boltzmann analytical and a semi-analytical solver, an optimized boundary element solver, a geometry-based geometric flow solvation model, a graph theory-based algorithm for determining pK a values, and an improved web-based visualization tool for viewing electrostatics. © 2017 The Protein Society.

  19. Enthalpy-entropy compensation: the role of solvation.

    Science.gov (United States)

    Dragan, Anatoliy I; Read, Christopher M; Crane-Robinson, Colyn

    2017-05-01

    Structural modifications to interacting systems frequently lead to changes in both the enthalpy (heat) and entropy of the process that compensate each other, so that the Gibbs free energy is little changed: a major barrier to the development of lead compounds in drug discovery. The conventional explanation for such enthalpy-entropy compensation (EEC) is that tighter contacts lead to a more negative enthalpy but increased molecular constraints, i.e., a compensating conformational entropy reduction. Changes in solvation can also contribute to EEC but this contribution is infrequently discussed. We review long-established and recent cases of EEC and conclude that the large fluctuations in enthalpy and entropy observed are too great to be a result of only conformational changes and must result, to a considerable degree, from variations in the amounts of water immobilized or released on forming complexes. Two systems exhibiting EEC show a correlation between calorimetric entropies and local mobilities, interpreted to mean conformational control of the binding entropy/free energy. However, a substantial contribution from solvation gives the same effect, as a consequence of a structural link between the amount of bound water and the protein flexibility. Only by assuming substantial changes in solvation-an intrinsically compensatory process-can a more complete understanding of EEC be obtained. Faced with such large, and compensating, changes in the enthalpies and entropies of binding, the best approach to engineering elevated affinities must be through the addition of ionic links, as they generate increased entropy without affecting the enthalpy.

  20. Carrier population control and surface passivation in solar cells

    KAUST Repository

    Cuevas, Andres; Wan, Yimao; Yan, Di; Samundsett, Christian; Allen, Thomas; Zhang, Xinyu; Cui, Jie; Bullock, James

    2018-01-01

    Controlling the concentration of charge carriers near the surface is essential for solar cells. It permits to form regions with selective conductivity for either electrons or holes and it also helps to reduce the rate at which they recombine

  1. Thermodynamic functions of ion solvation in normal alcohols of aliphatic series

    International Nuclear Information System (INIS)

    Sergeeva, I.A.

    1978-01-01

    Thermodynamic functions of ion solvation of alkali, alkaline earth metals and halogenides in 9 alcohols are calculated using the earlier suggested method. It is shown that summary values are in good accord with experimental ones, the deviations do not surpass 0-5%, solvation energies of one and the same electrolyte in the series of n-alcohols do not change, enthalpy and entropy of solvation increase from lower alcohols to higher ones

  2. Effect of Solvation on Electron Detachment and Excitation Energies of a Green Fluorescent Protein Chromophore Variant.

    Science.gov (United States)

    Bose, Samik; Chakrabarty, Suman; Ghosh, Debashree

    2016-05-19

    Hybrid quantum mechanics/molecular mechanics (QM/MM) is applied to the fluorinated green fluorescent protein (GFP) chromophore (DFHBDI) in its deprotonated form to understand the solvatochromic shifts in its vertical detachment energy (VDE) and vertical excitation energy (VEE). This variant of the GFP chromophore becomes fluorescent in an RNA environment and has a wide range of applications in biomedical and biochemical fields. From microsolvation studies, we benchmark (with respect to full QM) the accuracy of our QM/MM calculations with effective fragment potential (EFP) as the MM method of choice. We show that while the solvatochromic shift in the VEE is minimal (0.1 eV blue shift) and its polarization component is only 0.03 eV, the effect of the solvent on the VDE is quite large (3.85 eV). We also show by accurate calculations on the solvatochromic shift of the VDE that polarization accounts for ∼0.23 eV and therefore cannot be neglected. The effect of the counterions on the VDE of the deprotonated chromophore in solvation is studied in detail, and a charge-smearing scheme is suggested for charged chromophores.

  3. CL 14: Solvation structure and dynamics of room temperature ionic liquids

    International Nuclear Information System (INIS)

    Musat, Raluca M.; Polyansky, Dmitriy; Crowell, Robert A.; Thomas, Marie; Wishart, James F.; Takahashi, Kenji; Katsumura, Yosuke

    2010-01-01

    Room temperature ionic liquids (RTILs) have emerged as a new class of solvents that, due to their unique properties (e.g., low volatility, large electrochemical window, high conductivity, etc.), have several potential applications. Among these are their possible use in nuclear fuel reprocessing, dye sensitized solar cells, and CO 2 sequestration. The properties of a given class of RTILs depend strongly on the choice of the counter anion. In this contribution we present new results using both static and time-resolved EXAFS (ca. 1 ns resolution) and time resolved optical absorption spectroscopy on a series of bromide containing imidazolium salts. The static results provide detailed information of the solvation shell of the bromide ion while the time-resolved data shed light on the nature and chemical behavior of the lowest lying charge transfer band, the physical motion of the bromine atom and its conversion to di-bromide. The photochemistry of the charge transfer (CT) band of the room temperature ionic liquid 1-hexyl-3-methylimidazolium bromide is investigated using ultrafast transient absorption spectroscopy (TA) in the near-IR and steady state UV absorption. Irradiation of the CT band at 266 nm results in the steady state production of di-bromide which absorbs strongly at 266 nm. It is shown that this photoproduct, which is apparently very stable, adversely affects ultrafast transient absorption measurements. Flowing and simultaneously translating the sample mitigates this effect and reveals new transient species and dynamics within the detection window of 850 nm to 1250 nm. (authors)

  4. Multiple time step molecular dynamics in the optimized isokinetic ensemble steered with the molecular theory of solvation: Accelerating with advanced extrapolation of effective solvation forces

    International Nuclear Information System (INIS)

    Omelyan, Igor; Kovalenko, Andriy

    2013-01-01

    We develop efficient handling of solvation forces in the multiscale method of multiple time step molecular dynamics (MTS-MD) of a biomolecule steered by the solvation free energy (effective solvation forces) obtained from the 3D-RISM-KH molecular theory of solvation (three-dimensional reference interaction site model complemented with the Kovalenko-Hirata closure approximation). To reduce the computational expenses, we calculate the effective solvation forces acting on the biomolecule by using advanced solvation force extrapolation (ASFE) at inner time steps while converging the 3D-RISM-KH integral equations only at large outer time steps. The idea of ASFE consists in developing a discrete non-Eckart rotational transformation of atomic coordinates that minimizes the distances between the atomic positions of the biomolecule at different time moments. The effective solvation forces for the biomolecule in a current conformation at an inner time step are then extrapolated in the transformed subspace of those at outer time steps by using a modified least square fit approach applied to a relatively small number of the best force-coordinate pairs. The latter are selected from an extended set collecting the effective solvation forces obtained from 3D-RISM-KH at outer time steps over a broad time interval. The MTS-MD integration with effective solvation forces obtained by converging 3D-RISM-KH at outer time steps and applying ASFE at inner time steps is stabilized by employing the optimized isokinetic Nosé-Hoover chain (OIN) ensemble. Compared to the previous extrapolation schemes used in combination with the Langevin thermostat, the ASFE approach substantially improves the accuracy of evaluation of effective solvation forces and in combination with the OIN thermostat enables a dramatic increase of outer time steps. We demonstrate on a fully flexible model of alanine dipeptide in aqueous solution that the MTS-MD/OIN/ASFE/3D-RISM-KH multiscale method of molecular dynamics

  5. Hot-carrier effects on irradiated deep submicron NMOSFET

    International Nuclear Information System (INIS)

    Cui Jiangwei; Zheng Qiwen; Yu Xuefeng; Cong Zhongchao; Zhou Hang; Guo Qi; Wen Lin; Wei Ying; Ren Diyuan

    2014-01-01

    We investigate how γ exposure impacts the hot-carrier degradation in deep submicron NMOSFET with different technologies and device geometries for the first time. The results show that hot-carrier degradations on irradiated devices are greater than those without irradiation, especially for narrow channel device. The reason is attributed to charge traps in STI, which then induce different electric field and impact ionization rates during hot-carrier stress. (semiconductor devices)

  6. Charge Transport Along Phenylenevinylene Molecular Wires

    OpenAIRE

    2006-01-01

    Abstract A model to calculate the mobility of charges along molecular wires is presented. The model is based on the tight-binding approximation and combines a quantum mechanical description of the charge with a classical description of the structural degrees of freedom. It is demonstrated that the average mobility of charge carriers along molecular wires can be obtained by time-propagation of states which are initially localised. The model is used to calculate the mobility of charg...

  7. Continuum model of non-equilibrium solvation and solvent effect on ultra-fast processes

    International Nuclear Information System (INIS)

    Li Xiangyuan; Fu Kexiang; Zhu Quan

    2006-01-01

    In the past 50 years, non-equilibrium solvation theory for ultra-fast processes such as electron transfer and light absorption/emission has attracted particular interest. A great deal of research efforts was made in this area and various models which give reasonable qualitative descriptions for such as solvent reorganization energy in electron transfer and spectral shift in solution, were developed within the framework of continuous medium theory. In a series of publications by the authors, we clarified that the expression of the non-equilibrium electrostatic free energy that is at the dominant position of non-equilibrium solvation and serves as the basis of various models, however, was incorrectly formulated. In this work, the authors argue that reversible charging work integration was inappropriately applied in the past to an irreversible path linking the equilibrium or the non-equilibrium state. Because the step from the equilibrium state to the nonequilibrium state is factually thermodynamically irreversible, the conventional expression for non-equilibrium free energy that was deduced in different ways is unreasonable. Here the authors derive the non-equilibrium free energy to a quite different form according to Jackson integral formula. Such a difference throws doubts to the models including the famous Marcus two-sphere model for solvent reorganization energy of electron transfer and the Lippert-Mataga equation for spectral shift. By introducing the concept of 'spring energy' arising from medium polarizations, the energy constitution of the non-equilibrium state is highlighted. For a solute-solvent system, the authors separate the total electrostatic energy into different components: the self-energies of solute charge and polarized charge, the interaction energy between them and the 'spring energy' of the solvent polarization. With detailed reasoning and derivation, our formula for non-equilibrium free energy can be reached through different ways. Based on the

  8. Ab initio joint density-functional theory of solvated electrodes, with model and explicit solvation

    Science.gov (United States)

    Arias, Tomas

    2015-03-01

    the electrochemical context and how it is needed for realistic description of solvated electrode systems [], and how simple ``implicit'' polarized continuum methods fail radically in this context. Finally, we shall present a series of results relevant to battery, supercapacitor, and solar-fuel systems, one of which has led to a recent invention disclosure for improving battery cycle lifetimes. Supported as a part of the Energy Materials Center at Cornell, an Energy Frontier Research Center funded by DOE/BES (award de-sc0001086) and by the New York State Division of Science, Technology and Innovation (NYSTAR, award 60923).

  9. Carrier dynamics in graphene. Ultrafast many-particle phenomena

    Energy Technology Data Exchange (ETDEWEB)

    Malic, E.; Brem, S.; Jago, R. [Department of Physics, Chalmers University of Technology, Goeteborg (Sweden); Winzer, T.; Wendler, F.; Knorr, A. [Institut fuer Theoretische Physik, Technische Universitaet Berlin (Germany); Mittendorff, M.; Koenig-Otto, J.C.; Schneider, H.; Helm, M.; Winnerl, S. [Helmholtz-Zentrum Dresden-Rossendorf, Dresden (Germany); Ploetzing, T.; Neumaier, D. [Advanced Microelectronic Center Aachen, AMO GmbH, Aachen (Germany)

    2017-11-15

    Graphene is an ideal material to study fundamental Coulomb- and phonon-induced carrier scattering processes. Its remarkable gapless and linear band structure opens up new carrier relaxation channels. In particular, Auger scattering bridging the valence and the conduction band changes the number of charge carriers and gives rise to a significant carrier multiplication - an ultrafast many-particle phenomenon that is promising for the design of highly efficient photodetectors. Furthermore, the vanishing density of states at the Dirac point combined with ultrafast phonon-induced intraband scattering results in an accumulation of carriers and a population inversion suggesting the design of graphene-based terahertz lasers. Here, we review our work on the ultrafast carrier dynamics in graphene and Landau-quantized graphene is presented providing a microscopic view on the appearance of carrier multiplication and population inversion. (copyright 2017 by WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

  10. Charged triblock copolymer self-assembly into charged micelles

    Science.gov (United States)

    Chen, Yingchao; Zhang, Ke; Zhu, Jiahua; Wooley, Karen; Pochan, Darrin; Department of Material Science; Engineering University of Delaware Team; Department of Chemistry Texas A&M University Collaboration

    2011-03-01

    Micelles were formed through the self-assembly of amphiphlic block copolymer poly(acrylic acid)-block-poly(methyl acrylate)-block-polystyrene (PAA-PMA-PS). ~Importantly, the polymer is complexed with diamine molecules in pure THF solution prior to water titration solvent processing-a critical aspect in the control of final micelle geometry. The addition of diamine triggers acid-base complexation ~between the carboxylic acid PAA side chains and amines. ~Remarkably uniform spheres were found to form close-packed patterns when forced into dried films and thin, solvated films when an excess of amine was used in the polymer assembly process. Surface properties and structural features of these hexagonal-packed spherical micelles with charged corona have been explored by various characterization methods including Transmission Electron Microscopy (TEM), cryogenic TEM, z-potential analysis and Dynamic Light Scattering. The forming mechanism for this pattern and morphology changes against external stimulate such as salt will be discussed.

  11. Charge imbalance

    International Nuclear Information System (INIS)

    Clarke, J.

    1981-01-01

    This article provides a long theoretical development of the main ideas of charge imbalance in superconductors. Concepts of charge imbalance and quasiparticle charge are introduced, especially in regards to the use of tunnel injection in producing and detecting charge imbalance. Various mechanisms of charge relaxation are discussed, including inelastic scattering processes, elastic scattering in the presence of energy-gap anisotropy, and various pair-breaking mechanisms. In each case, present theories are reviewed in comparison with experimental data

  12. Separation and recombinatiuon of charge carriers in solar cells with a nanostructured ZnO electrode; Trennung und Rekombination von Ladungstraegern in Solarzellen mit nanostrukturierter ZnO-Elektrode

    Energy Technology Data Exchange (ETDEWEB)

    Tornow, Julian

    2010-03-02

    The publication investigates electrodes consisting of ZnO nanorods deposited hydrothermally on conductive glass substrate (conductive glass). The electrodes are transparent to visible light and are sensitized for solar cell applications by a light-absorbing layer which in this case consists either of organometallic dye molecules (N3) or of an indium sulfide layer with a thickness of only a few nanometers. Electric contacts for the sensitized electrode are either made of a liquid electrolyte or of a perforated solid electrolyte. Methods of analysis were impedance spectroscopy, time-resolved photocurrent measurements, and time-resolved microwave photoconductivity. A high concentration of up to 10{sup 20} was found in the ZnO nanorods. The dye-sensitized solar cell showed exessively fast recombination with the oxydized dye molecules (sub-{mu}s) but a slow recombination rate with the oxydized redox ions of the electrolyte (ms). In the indium sulfide solar cells, the charges are separated at the contact with the ZnO nanorods while contact with the perforated CuSCN conductor is not charge-separating. Recombination takes place in indium sulfide, directly between the perforated conductor and ZnO, and also via the charge-separating contact with decreasing rates.

  13. Solvation quantities from a COSMO-RS equation of state

    International Nuclear Information System (INIS)

    Panayiotou, C.; Tsivintzelis, I.; Aslanidou, D.; Hatzimanikatis, V.

    2015-01-01

    Highlights: • Extension of the successful COSMO-RS model to an equation-of-state model. • Two scaling constants, obtained from atom-specific contributions. • Overall estimation of the solvation quantities and contributions. - Abstract: This work focuses on the extension of the successful COSMO-RS model of mixtures into an equation-of-state model of fluids and its application for the estimation of solvation/hydration quantities of a variety of chemical substances. These quantities include free-energies, enthalpies and entropies of hydration as well as the separate contributions to each of them. Emphasis is given on the estimation of contributions from the conformational changes of solutes upon solvation and the associated restructuring of solvent in its immediate neighborhood. COSMO-RS is a quantum-mechanics based group/segment contribution model in which the Quasi-Chemical (QC) approach is used for the description of the non-random distribution of interacting segments in the system. Thus, the equation-of-state development is done through such a QC framework. The new model will not need any adjustable parameters for the strong specific interactions, such as hydrogen bonds, since they will be provided by the quantum-mechanics based cosmo-files – a key feature of COSMO-RS model. It will need, however, one volumetric and one energy parameter per fluid, which are scaling constants or molecular descriptors of the fluid and are obtained from rather easily available data such as densities, boiling points, vapor pressures, heats of vaporization or second virial coefficients. The performance and the potential of the new equation-of-state model to become a fully predictive model are critically discussed

  14. Two-Dimensional Charge Transport in Disordered Organic Semiconductors

    NARCIS (Netherlands)

    Brondijk, J. J.; Roelofs, W. S. C.; Mathijssen, S. G. J.; Shehu, A.; Cramer, T.; Biscarini, F.; Blom, P. W. M.; de Leeuw, D. M.

    2012-01-01

    We analyze the effect of carrier confinement on the charge-transport properties of organic field-effect transistors. Confinement is achieved experimentally by the use of semiconductors of which the active layer is only one molecule thick. The two-dimensional confinement of charge carriers provides

  15. Extracting hot carriers from photoexcited semiconductor nanocrystals

    Energy Technology Data Exchange (ETDEWEB)

    Zhu, Xiaoyang

    2014-12-10

    This research program addresses a fundamental question related to the use of nanomaterials in solar energy -- namely, whether semiconductor nanocrystals (NCs) can help surpass the efficiency limits, the so-called “Shockley-Queisser” limit, in conventional solar cells. In these cells, absorption of photons with energies above the semiconductor bandgap generates “hot” charge carriers that quickly “cool” to the band edges before they can be utilized to do work; this sets the solar cell efficiency at a limit of ~31%. If instead, all of the energy of the hot carriers could be captured, solar-to-electric power conversion efficiencies could be increased, theoretically, to as high as 66%. A potential route to capture this energy is to utilize semiconductor nanocrystals. In these materials, the quasi-continuous conduction and valence bands of the bulk semiconductor become discretized due to confinement of the charge carriers. Consequently, the energy spacing between the electronic levels can be much larger than the highest phonon frequency of the lattice, creating a “phonon bottleneck” wherein hot-carrier relaxation is possible via slower multiphonon emission. For example, hot-electron lifetimes as long as ~1 ns have been observed in NCs grown by molecular beam epitaxy. In colloidal NCs, long lifetimes have been demonstrated through careful design of the nanocrystal interfaces. Due to their ability to slow electronic relaxation, semiconductor NCs can in principle enable extraction of hot carriers before they cool to the band edges, leading to more efficient solar cells.

  16. Solvation of the electron in alcohols studied using the Argonne picosecond pulse radiolysis system

    International Nuclear Information System (INIS)

    Jonah, C.D.; Kenney-Wallace, G.A.

    1979-01-01

    With a stroboscopic pulse radiolysis system, it is possible to measure the reactions of solvated electrons and dry electrons and the solvation time of electrons in alcohols from 20 psec to 350 psec. The solvation in alcohol and alcohol-alkane solutions is a complex process which depends on the microscopic structure of the fluid, so that the studies of solvation in alcohols as a function of temperature or as a function of the concentration of the alcohols must take into account the structure of the fluid being studied. The relaxation processes may not be dominant at low temperature. However, in room temperature alcohols, pre-existing traps are the dominant means of electron trapping. The extrapolation to water may be reasonable since water and alcohols both give similar final species. To obtain such idea of the solvation process in alcohols, the change of the absorption of electrons at 500 nm was measured. At very low concentration of alcohols in alkanes, electrons form a complex with a cluster of alcohol molecules, and the most probable size of this cluster is two alcohols (C 4 , C 10 ). The species formed is not solvated electrons, since the characteristic spectrum of solvated electrons is absent, and the conductivity of the species is far above that of solvated electrons. (Yamashita, S.)

  17. Studies of base pair sequence effects on DNA solvation based on all

    Indian Academy of Sciences (India)

    Detailed analyses of the sequence-dependent solvation and ion atmosphere of DNA are presented based on molecular dynamics (MD) simulations on all the 136 unique tetranucleotide steps obtained by the ABC consortium using the AMBER suite of programs. Significant sequence effects on solvation and ion localization ...

  18. Femtosecond spectroscopic study of the solvation of amphiphilic molecules by water

    NARCIS (Netherlands)

    Rezus, Y.L.A.; Bakker, H.J.

    2008-01-01

    We use polarization-resolved mid-infrared pump-probe spectroscopy to study the aqueous solvation of proline and N-methylacetamide. These molecules serve as models to study the solvation of proteins. We monitor the orientational dynamics of partly deuterated water molecules (HDO) that are present at

  19. Competitive solvation of (bis)(trifluoromethanesulfonyl)imide anion by acetonitrile and water

    DEFF Research Database (Denmark)

    Chaban, Vitaly

    2014-01-01

    Competitive solvation of an ion by two or more solvents is one of the key phenomena determining the identity of our world. Solvation in polar solvents frequently originates from non-additive non-covalent interactions. Pre-parametrized potentials poorly capture these interactions, unless the force...

  20. Time-dependent friction and solvation time correlation function

    International Nuclear Information System (INIS)

    Samanta, Alok; Ali, Sk Musharaf; Ghosh, Swapan K

    2005-01-01

    We have derived a new relation between the time-dependent friction and solvation time correlation function (STCF) for non-polar fluids. The friction values calculated using this relation and simulation results on STCF for a Lennard-Jones fluid are shown to have excellent agreement with the same obtained through mode-coupling theory. Also derived is a relation between the time-dependent dielectric friction and STCF for polar fluids. Routes are thus provided to obtain the time-dependent friction (non-polar as well as dielectric) from an experimentally measured quantity like STCF, even if the interparticle interaction potential is not known

  1. Role of trapped and solvated electrons in Ps formation

    International Nuclear Information System (INIS)

    Stepanov, S.V.; Byakov, V.M.; Mikhin, K.V.; He, C.; Hirade, T.

    2005-01-01

    Role of trapped and solvated electrons in Ps formation is discussed. Combination of thermalized positron with such electrons is possible from the view point of the energy balance and may results in Ps formation. This process proceeds during all e = lifetime matter. Fitting of raw experimental e + -e - annihilation spectra has to be based on an adequate physical input, which often leads to necessity of nonexponential deconvolution of the spectra. We have interpreted the Ps formation data in polyethylene, ethylene-methylmethacrylate and polymethylmethacrylate in dark and in light vs. tome of the measurement and temperature. parameters characterized accumulation of trapped electrons and their recombination with counter ions and positrons are obtained. (author)

  2. Electrochemical redox reactions in solvated silica sol-gel glass

    International Nuclear Information System (INIS)

    Opallo, M.

    2002-01-01

    The studies of electrochemical redox reactions in solvated silica sol-gel glass were reviewed. The methodology of the experiments with emphasis on the direct preparation of the solid electrolyte and the application ultra microelectrodes was described. Generally, the level of the electrochemical signal is not much below that observed in liquid electrolyte. The current depends on time elapsed after gelation, namely the longer time, the smaller current. The differences between electrochemical behaviour of the redox couples in monoliths and thin layers were described. (author)

  3. 47 CFR 11.42 - Participation by communications common carriers.

    Science.gov (United States)

    2010-10-01

    ... may, without charge, connect: (1) An originating source from the nearest service area to a selected... Emergency Action Termination, the common carriers shall disconnect the originating source and the... charge, connect an originating source from the nearest exchange to a selected Test Center and then to any...

  4. Mathematical analysis of the boundary-integral based electrostatics estimation approximation for molecular solvation: exact results for spherical inclusions.

    Science.gov (United States)

    Bardhan, Jaydeep P; Knepley, Matthew G

    2011-09-28

    We analyze the mathematically rigorous BIBEE (boundary-integral based electrostatics estimation) approximation of the mixed-dielectric continuum model of molecular electrostatics, using the analytically solvable case of a spherical solute containing an arbitrary charge distribution. Our analysis, which builds on Kirkwood's solution using spherical harmonics, clarifies important aspects of the approximation and its relationship to generalized Born models. First, our results suggest a new perspective for analyzing fast electrostatic models: the separation of variables between material properties (the dielectric constants) and geometry (the solute dielectric boundary and charge distribution). Second, we find that the eigenfunctions of the reaction-potential operator are exactly preserved in the BIBEE model for the sphere, which supports the use of this approximation for analyzing charge-charge interactions in molecular binding. Third, a comparison of BIBEE to the recent GBε theory suggests a modified BIBEE model capable of predicting electrostatic solvation free energies to within 4% of a full numerical Poisson calculation. This modified model leads to a projection-framework understanding of BIBEE and suggests opportunities for future improvements. © 2011 American Institute of Physics

  5. Structural Arrangement of Water Molecules around Highly Charged Nanoparticles: Molecular Dynamics Simulation

    International Nuclear Information System (INIS)

    Kim, Eunae; Yeom, Min Sun

    2014-01-01

    Molecular dynamics simulations were performed to understand the structural arrangement of water molecules around highly charged nanoparticles under aqueous conditions. The effect of two highly charged nanoparticles on the solvation charge asymmetry has been examined. We calculated the radial distribution functions of the components of water molecules around nanoparticles which have four charge types at two different salt concentrations. Even though the distributions of water molecules surrounding a sodium ion and a chloride ion are hardly affected by the charges of nanoparticles and the salt concentrations, those around highly charged nanoparticles are strongly influenced by the charges of nanoparticles, but hardly by the charges of nanoparticles and salt concentrations. We find that the distributions of hydrogen atoms in water molecules around one highly charged nanoparticle are dependent on the magnitude of the nanoparticle charge

  6. Charge transport and recombination in bulk heterojunction solar cells studied by the photoinduced charge extraction in linearly increasing voltage technique

    Science.gov (United States)

    Mozer, A. J.; Sariciftci, N. S.; Lutsen, L.; Vanderzande, D.; Österbacka, R.; Westerling, M.; Juška, G.

    2005-03-01

    Charge carrier mobility and recombination in a bulk heterojunction solar cell based on the mixture of poly[2-methoxy-5-(3,7-dimethyloctyloxy)-phenylene vinylene] (MDMO-PPV) and 1-(3-methoxycarbonyl)propyl-1-phenyl-(6,6)-C61 (PCBM) has been studied using the novel technique of photoinduced charge carrier extraction in a linearly increasing voltage (Photo-CELIV). In this technique, charge carriers are photogenerated by a short laser flash, and extracted under a reverse bias voltage ramp after an adjustable delay time (tdel). The Photo-CELIV mobility at room temperature is found to be μ =2×10-4cm2V-1s-1, which is almost independent on charge carrier density, but slightly dependent on tdel. Furthermore, determination of charge carrier lifetime and demonstration of an electric field dependent mobility is presented.

  7. Molecular modeling of nucleic Acid structure: electrostatics and solvation.

    Science.gov (United States)

    Bergonzo, Christina; Galindo-Murillo, Rodrigo; Cheatham, Thomas E

    2014-12-19

    This unit presents an overview of computer simulation techniques as applied to nucleic acid systems, ranging from simple in vacuo molecular modeling techniques to more complete all-atom molecular dynamics treatments that include an explicit representation of the environment. The third in a series of four units, this unit focuses on critical issues in solvation and the treatment of electrostatics. UNITS 7.5 & 7.8 introduced the modeling of nucleic acid structure at the molecular level. This included a discussion of how to generate an initial model, how to evaluate the utility or reliability of a given model, and ultimately how to manipulate this model to better understand its structure, dynamics, and interactions. Subject to an appropriate representation of the energy, such as a specifically parameterized empirical force field, the techniques of minimization and Monte Carlo simulation, as well as molecular dynamics (MD) methods, were introduced as a way of sampling conformational space for a better understanding of the relevance of a given model. This discussion highlighted the major limitations with modeling in general. When sampling conformational space effectively, difficult issues are encountered, such as multiple minima or conformational sampling problems, and accurately representing the underlying energy of interaction. In order to provide a realistic model of the underlying energetics for nucleic acids in their native environments, it is crucial to include some representation of solvation (by water) and also to properly treat the electrostatic interactions. These subjects are discussed in detail in this unit. Copyright © 2014 John Wiley & Sons, Inc.

  8. Molecular Dynamics Simulations on the solvation and interfacial behaviour of hydrophobic species. Applications to the TATB hypothesis and to the liquid/liquid extraction of cations to supercritical CO2

    International Nuclear Information System (INIS)

    Schurhammer, R.

    2001-12-01

    We report molecular dynamics studies on the solvation of charged hydrophobic molecules in pure liquids and at liquid / liquid interfaces. The first part of the thesis deals with the TATB hypothesis according to which the Asφ 4 + (TA + ) and Bφ 4 - (TB - ) ions have the same free energy of solvation in any solvent. The two ions are found to be solvated differently in pure liquids (water, chloroform, acetonitrile) as at a chloroform / water interface. These results are confirmed by free energy calculations and by simulations on iso-volume spherical S + and S - ions, which perfectly meet the TATB criteria. The many methodological tests performed show the importance of (i) the corrected treatment of 'long range interactions' (ii) the precise repartition of atomic charges (iii) the solvent models, especially for water, on the + / - charge discrimination by solvent. In the second part, in relation to the liquid / liquid extraction of cations from water to supercritical CO 2 , we report the behaviour of ions (Cs + , UO 2 2+ , Eu 3+ ), of un-complexed extractants molecules (tri-n-butylphosphate, calixarene), of their complexes with the cations and nitric acid at a preformed chloroform / water interface and during de-mixing simulations which started from a perfectly mixed CO 2 / water solutions. These studies demonstrate the importance of interfacial phenomena, of simulation conditions and acid and extractant concentrations, in assisted ion extraction to supercritical CO 2 . (author)

  9. Solvation of positive ions in water: the dominant role of water-water interaction

    International Nuclear Information System (INIS)

    Krekeler, Christian; Site, Luigi Delle

    2007-01-01

    Local polarization effects, induced by monovalent and divalent positive ions in water, influence (and in turn are influenced by) the large-scale structural properties of the solvent. Experiments can only distinguish this process of interplay in a generic qualitative way. Instead, first-principles calculations can address the question at both the electronic and atomistic scale, accounting for electronic polarization as well as geometrical conformations. For this reason we study the extension of the scales' interconnection by means of first-principle Car-Parrinello molecular dynamics applied to systems of different size. In this way we identify the general aspects dominating the physics of the first solvation shell and their connection to the effects related to the formation of the outer shells and eventually the bulk. We show that while the influence of the ions is extended to the first shell only, the water-water interaction is instead playing a dominant role even within the first shell independently of the size or the charge of the ion. (fast track communication)

  10. A dual cryogenic ion trap spectrometer for the formation and characterization of solvated ionic clusters

    Energy Technology Data Exchange (ETDEWEB)

    Marsh, Brett M.; Voss, Jonathan M.; Garand, Etienne, E-mail: egarand@chem.wisc.edu [Department of Chemistry, University of Wisconsin-Madison, 1101 University Avenue, Madison, Wisconsin 53706 (United States)

    2015-11-28

    A new experimental approach is presented in which two separate cryogenic ion traps are used to reproducibly form weakly bound solvent clusters around electrosprayed ions and messenger-tag them for single-photon infrared photodissociation spectroscopy. This approach thus enables the vibrational characterization of ionic clusters comprised of a solvent network around large and non-volatile ions. We demonstrate the capabilities of the instrument by clustering water, methanol, and acetone around a protonated glycylglycine peptide. For water, cluster sizes with greater than twenty solvent molecules around a single ion are readily formed. We further demonstrate that similar water clusters can be formed around ions having a shielded charge center or those that do not readily form hydrogen bonds. Finally, infrared photodissociation spectra of D{sub 2}-tagged GlyGlyH{sup +} ⋅ (H{sub 2}O){sub 1−4} are presented. They display well-resolved spectral features and comparisons with calculations reveal detailed information on the solvation structures of this prototypical peptide.

  11. Diffusive charge transport in graphene

    Science.gov (United States)

    Chen, Jianhao

    The physical mechanisms limiting the mobility of graphene on SiO 2 are studied and printed graphene devices on a flexible substrate are realized. Intentional addition of charged scattering impurities is used to study the effects of charged impurities. Atomic-scale defects are created by noble-gas ions irradiation to study the effect of unitary scatterers. The results show that charged impurities and atomic-scale defects both lead to conductivity linear in density in graphene, with a scattering magnitude that agrees quantitatively with theoretical estimates. While charged impurities cause intravalley scattering and induce a small change in the minimum conductivity, defects in graphene scatter electrons between the valleys and suppress the minimum conductivity below the metallic limit. Temperature-dependent measurements show that longitudinal acoustic phonons in graphene produce a small resistivity which is linear in temperature and independent of carrier density; at higher temperatures, polar optical phonons of the SiO2 substrate give rise to an activated, carrier density-dependent resistivity. Graphene is also made into high mobility transparent and flexible field effect device via the transfer-printing method. Together the results paint a complete picture of charge carrier transport in graphene on SiO2 in the diffusive regime, and show the promise of graphene as a novel electronic material that have potential applications not only on conventional inorganic substrates, but also on flexible substrates.

  12. Network topology for the formation of solvated electrons in binary CaO–Al2O3 composition glasses

    Science.gov (United States)

    Akola, Jaakko; Kohara, Shinji; Ohara, Koji; Fujiwara, Akihiko; Watanabe, Yasuhiro; Masuno, Atsunobu; Usuki, Takeshi; Kubo, Takashi; Nakahira, Atsushi; Nitta, Kiyofumi; Uruga, Tomoya; Weber, J. K. Richard; Benmore, Chris J.

    2013-01-01

    Glass formation in the CaO–Al2O3 system represents an important phenomenon because it does not contain typical network-forming cations. We have produced structural models of CaO–Al2O3 glasses using combined density functional theory–reverse Monte Carlo simulations and obtained structures that reproduce experiments (X-ray and neutron diffraction, extended X-ray absorption fine structure) and result in cohesive energies close to the crystalline ground states. The O–Ca and O–Al coordination numbers are similar in the eutectic 64 mol % CaO (64CaO) glass [comparable to 12CaO·7Al2O3 (C12A7)], and the glass structure comprises a topologically disordered cage network with large-sized rings. This topologically disordered network is the signature of the high glass-forming ability of 64CaO glass and high viscosity in the melt. Analysis of the electronic structure reveals that the atomic charges for Al are comparable to those for Ca, and the bond strength of Al–O is stronger than that of Ca–O, indicating that oxygen is more weakly bound by cations in CaO-rich glass. The analysis shows that the lowest unoccupied molecular orbitals occurs in cavity sites, suggesting that the C12A7 electride glass [Kim SW, Shimoyama T, Hosono H (2011) Science 333(6038):71–74] synthesized from a strongly reduced high-temperature melt can host solvated electrons and bipolarons. Calculations of 64CaO glass structures with few subtracted oxygen atoms (additional electrons) confirm this observation. The comparable atomic charges and coordination of the cations promote more efficient elemental mixing, and this is the origin of the extended cage structure and hosted solvated (trapped) electrons in the C12A7 glass. PMID:23723350

  13. Fractional charges

    International Nuclear Information System (INIS)

    Saminadayar, L.

    2001-01-01

    20 years ago fractional charges were imagined to explain values of conductivity in some materials. Recent experiments have proved the existence of charges whose value is the third of the electron charge. This article presents the experimental facts that have led theorists to predict the existence of fractional charges from the motion of quasi-particles in a linear chain of poly-acetylene to the quantum Hall effect. According to the latest theories, fractional charges are neither bosons nor fermions but anyons, they are submitted to an exclusive principle that is less stringent than that for fermions. (A.C.)

  14. Ultrafast carrier thermalization in lead iodide perovskite probed with two-dimensional electronic spectroscopy.

    Science.gov (United States)

    Richter, Johannes M; Branchi, Federico; Valduga de Almeida Camargo, Franco; Zhao, Baodan; Friend, Richard H; Cerullo, Giulio; Deschler, Felix

    2017-08-29

    In band-like semiconductors, charge carriers form a thermal energy distribution rapidly after optical excitation. In hybrid perovskites, the cooling of such thermal carrier distributions occurs on timescales of about 300 fs via carrier-phonon scattering. However, the initial build-up of the thermal distribution proved difficult to resolve with pump-probe techniques due to the requirement of high resolution, both in time and pump energy. Here, we use two-dimensional electronic spectroscopy with sub-10 fs resolution to directly observe the carrier interactions that lead to a thermal carrier distribution. We find that thermalization occurs dominantly via carrier-carrier scattering under the investigated fluences and report the dependence of carrier scattering rates on excess energy and carrier density. We extract characteristic carrier thermalization times from below 10 to 85 fs. These values allow for mobilities of 500 cm 2  V -1  s -1 at carrier densities lower than 2 × 10 19  cm -3 and limit the time for carrier extraction in hot carrier solar cells.Carrier-carrier scattering rates determine the fundamental limits of carrier transport and electronic coherence. Using two-dimensional electronic spectroscopy with sub-10 fs resolution, Richter and Branchi et al. extract carrier thermalization times of 10 to 85 fs in hybrid perovskites.

  15. Peptide-Carrier Conjugation

    DEFF Research Database (Denmark)

    Hansen, Paul Robert

    2015-01-01

    To produce antibodies against synthetic peptides it is necessary to couple them to a protein carrier. This chapter provides a nonspecialist overview of peptide-carrier conjugation. Furthermore, a protocol for coupling cysteine-containing peptides to bovine serum albumin is outlined....

  16. Air Carrier Traffic Statistics.

    Science.gov (United States)

    2013-11-01

    This report contains airline operating statistics for large certificated air carriers based on data reported to U.S. Department of Transportation (DOT) by carriers that hold a certificate issued under Section 401 of the Federal Aviation Act of 1958 a...

  17. Air Carrier Traffic Statistics.

    Science.gov (United States)

    2012-07-01

    This report contains airline operating statistics for large certificated air carriers based on data reported to U.S. Department of Transportation (DOT) by carriers that hold a certificate issued under Section 401 of the Federal Aviation Act of 1958 a...

  18. Effect of trapping of charge carriers on the resolution of Ge(Li) detectors; Influencia da captura de portadores de cargas sobre a resolucao em detectores Ge(Li)

    Energy Technology Data Exchange (ETDEWEB)

    Venturini, Luzia

    1979-07-01

    In this work a measurement is described of the variation of the resolution of a Ge(Li) detector as a function of the position of irradiation of a collimated gamma-ray beam. Also the variation of the resolution has been measured as a function of the applied detector voltage, using a collimated and a non-collimated gamma-ray beam. The measurement indicate that in the process of charge collection loss of holes predominates and the best resolution is obtained in the middle of the compensated region. It has been verified that, in the case of a collimated gamma beam the detector resolution improves with increasing detector bias up to at least 5100 Volts. For a non-collimated gamma beam, however, the resolution reaches a constant value at about 4400 Volts. The dependence of resolution on the position of irradiation can be accounted for by introducing a local ionization factor different from the usual position independent Fano factor. (author)

  19. Model improvements to simulate charging in SEM

    Science.gov (United States)

    Arat, K. T.; Klimpel, T.; Hagen, C. W.

    2018-03-01

    Charging of insulators is a complex phenomenon to simulate since the accuracy of the simulations is very sensitive to the interaction of electrons with matter and electric fields. In this study, we report model improvements for a previously developed Monte-Carlo simulator to more accurately simulate samples that charge. The improvements include both modelling of low energy electron scattering and charging of insulators. The new first-principle scattering models provide a more realistic charge distribution cloud in the material, and a better match between non-charging simulations and experimental results. Improvements on charging models mainly focus on redistribution of the charge carriers in the material with an induced conductivity (EBIC) and a breakdown model, leading to a smoother distribution of the charges. Combined with a more accurate tracing of low energy electrons in the electric field, we managed to reproduce the dynamically changing charging contrast due to an induced positive surface potential.

  20. Nonextensive electron and ion dust charging currents

    International Nuclear Information System (INIS)

    Amour, Rabia; Tribeche, Mouloud

    2011-01-01

    The correct nonextensive electron and ion charging currents are presented for the first time based on the orbit motion limited approach. For -1< q<1, where q measures the amount of plasma nonextensivity, the nonextensive electron charging current is expressed in terms of the hypergeometric function. The variable dust charge is expressed in terms of the Lambert function and we take advantage of this transcendental function to investigate succinctly the effects of nonextensive charge carriers. The obtained formulas bring a possibility to build theories on nonlinear collective process in variable charge nonextensive dusty plasmas.

  1. Selective solvation extraction of gold from alkaline cyanide solution by alkyl phosphorus esters

    Energy Technology Data Exchange (ETDEWEB)

    Miller, J.D.; Wan, R.Y.; Mooiman, M.B.; Sibrell, P.L.

    1987-01-01

    Research efforts have shown that solvation extraction of gold from alkaline cyanide solution is possible by alkyl phosphorus esters. Both tributyl phosphate (TBP) and dibutyl butyl phosphonate (DBBP) appear to be effective extractants for gold and exhibit high loading capacities exceeding 30 gpl. Selective solvation extraction of gold from alkaline cyanide solution can be achieved with selectivity factors relative to other cyanoanions as high as 1000 under certain circumstances. Variables influencing the selectivity such as ionic strength, temperature, and extractant structure, are discussed in terms of the extraction chemistry, which seems to involve the solvation of a M dot, dot, dot Au(CN)2 ion pair.

  2. Solvation of ions in the gas-phase: a molecular dynamics simulation

    Science.gov (United States)

    Cabarcos, Orlando M.; Lisy, James M.

    1996-07-01

    Molecular dynamics simulations have been performed on the collision between a cesium ion and a cluster of twenty methanol molecules. This process, generating a solvated ion, was studied over a range (1 to 25 eV) of eight collision energies. Preliminary analysis of this gas phase solvation has included the distribution of final ion cluster sizes, fragmentation patterns, solvation timescales and energetics. Two distinct patterns have emerged: a ballistic penetration of the neutral cluster at the higher collision energies and an evaporative evolution of the cluster ion at lower collision energies.

  3. Solvation of graphite oxide in water-methanol binary polar solvents

    Energy Technology Data Exchange (ETDEWEB)

    You, Shujie; Yu, Junchun; Sundqvist, Bertil; Talyzin, Alexandr V. [Department of Physics, Umeaa University, SE-901 87 Umeaa (Sweden)

    2012-12-15

    The phase transition between two solvated phases was studied by DSC for graphite oxide (GO) powders immersed in water-methanol mixtures of various compositions. GO forms solid solvates with two different compositions when immersed in methanol. Reversible phase transition between two solvate states due to insertion/desertion of methanol monolayer occurs upon temperature variations. The temperature point and the enthalpy ({Delta}H) of the phase transition are maximal for pure methanol and decrease linearly with increase of water fraction up to 30%. (Copyright copyright 2012 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

  4. Selective nonspecific solvation under dielectric saturation and fluorescence spectra of dye solutions in binary solvents.

    Science.gov (United States)

    Bakhshiev, N G; Kiselev, M B

    1991-09-01

    The influence of selective nonspecific solvation on the fluorescence spectra of three substitutedN-methylphthalimides in a binary solvent system consisting of a nonpolar (n-heptane) and a polar (pyridine) component has been studied under conditions close to dielectric saturation. The substantially nonlinearity of the effect is confirmation that the spectral shifts of fluorescence bands depend on the number of polar solvent molecules involved in solvating the dye molecule. The measured fluorescence spectral shifts determined by substituting one nonpolar solvent molecula with a polar one in the proximity of the dye molecule agree quantitatively with the forecasts of the previously proposed semiempirical theory which describes this nonlinear solvation phenomenon.

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

    Energy Technology Data Exchange (ETDEWEB)

    Bagaev, V. S.; Krivobok, V. S., E-mail: krivobok@lebedev.ru; Nikolaev, S. N.; Onishchenko, E. E.; Pruchkina, A. A.; Aminev, D. F.; Skorikov, M. L. [Russian Academy of Sciences, Lebedev Physical Institute (Russian Federation); Lobanov, D. N.; Novikov, A. V. [Russian Academy of Sciences, Institute for Physics of Microstructures (Russian Federation)

    2013-11-15

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

  6. Charge mobility modification of semiconducting carbon nanotubes by intrinsic defects

    International Nuclear Information System (INIS)

    Bai, Hongcun; Ma, Yujia; Ma, Jinsuo; Mei, Jingnan; Tong, Yan; Ji, Yongqiang

    2017-01-01

    Charge carrier mobility is a central transport property in nanoscale electronics. Carbon nanotubes (CNTs) are supposed to have high carrier mobility. The preparation methods of CNTs have been greatly improved, but the defects always exist. This work presented first-principle investigations on the charge carrier mobility of carbon nanotubes containing several intrinsic defects. The charge carrier mobilities of zigzag (10, 0) tubes with Stone–Wales, mono vacant and 5/8/5 defects were studied as an example to explore the role of defects. Most carrier mobilities were decreased, but several values of mobility are unexpectedly increased upon the appearance of the defects. This interesting result is discussed based on the changes of the stretching modulus, the effective mass of the carrier and deformation potential constant induced by the defects. (paper)

  7. Trimesic acid dimethyl sulfoxide solvate: space group revision

    Directory of Open Access Journals (Sweden)

    Sylvain Bernès

    2008-07-01

    Full Text Available The structure of the title solvate, C9H6O6·C2H6OS, was determined 30 years ago [Herbstein, Kapon & Wasserman (1978. Acta Cryst. B34, 1613–1617], with data collected at room temperature, and refined in the space group P21. The present redetermination, based on high-resolution diffraction data, shows that the actual space group is more likely to be P21/m. The crystal structure contains layers of trimesic acid molecules lying on mirror planes. A mirror plane also passes through the S and O atoms of the solvent molecule. The molecules in each layer are interconnected through strong O—H...O hydrogen bonds, forming a two-dimensional supramolecular network within each layer. The donor groups are the hydroxyls of the trimesic acid molecules, while the acceptors are the carbonyl or the sulfoxide O atoms.

  8. Solvation thermodynamics of phenylalcohols in lamellar phase surfactant dispersions

    International Nuclear Information System (INIS)

    Martyniak, A.; Scheuermann, R.; Dilger, H.; Tucker, I.M.; Burkert, T.; Hashmi, A.S.K.; Vujosevic', D.; Roduner, E.

    2006-01-01

    The distribution and the stability of five phenylalcohols in a lamellar phase composed of simple bilayers separated by water at 298 and 348K is explored using avoided-level-crossing muon-spin resonance (ALC-μSR). The dependence of the alignment of the bilayer chains on temperature appears to be a crucial factor determining the phenylalcohol partitioning: increasing order of the surfactant tails leads to expulsion of the solute. Moreover, we observed a systematic trend, the longer the chain the deeper the phenyl group dips into the lipid bilayer. Recent studies have shown that the hydrophobic effect is adequate to describe membrane partitioning of small amphiphilic molecules. The solvation thermodynamic properties ΔG sol , ΔH sol , and ΔS sol which determine the solute transfer from the double layer into water prove that the distribution also strongly depends on shape, chemical nature and different structure of phenylalcohols

  9. Solvation thermodynamics of phenylalcohols in lamellar phase surfactant dispersions

    Energy Technology Data Exchange (ETDEWEB)

    Martyniak, A. [Institut fuer Physikalische Chemie, University of Stuttgart, Pfaffenwaldring 55, D-70569 Stuttgart (Germany); Scheuermann, R. [Laboratory for muon Spin Spectroscopy, Paul Scherrer Institute, CH-5232 Villigen (Switzerland); Dilger, H. [Institut fuer Physikalische Chemie, University of Stuttgart, Pfaffenwaldring 55, D-70569 Stuttgart (Germany); Tucker, I.M. [Unilever Research and Development, Port Sunlight, Wirral CH63 3JW (United Kingdom); Burkert, T. [Institut fuer Organische Chemie, University of Stuttgart, Pfaffenwaldring 55, D-70569 Stuttgart (Germany); Hashmi, A.S.K. [Institut fuer Organische Chemie, University of Stuttgart, Pfaffenwaldring 55, D-70569 Stuttgart (Germany); Vujosevic' , D. [Institut fuer Physikalische Chemie, University of Stuttgart, Pfaffenwaldring 55, D-70569 Stuttgart (Germany); Roduner, E. [Institut fuer Physikalische Chemie, University of Stuttgart, Pfaffenwaldring 55, D-70569 Stuttgart (Germany)]. E-mail: e.roduner@ipc.uni-stuttgart.de

    2006-03-31

    The distribution and the stability of five phenylalcohols in a lamellar phase composed of simple bilayers separated by water at 298 and 348K is explored using avoided-level-crossing muon-spin resonance (ALC-{mu}SR). The dependence of the alignment of the bilayer chains on temperature appears to be a crucial factor determining the phenylalcohol partitioning: increasing order of the surfactant tails leads to expulsion of the solute. Moreover, we observed a systematic trend, the longer the chain the deeper the phenyl group dips into the lipid bilayer. Recent studies have shown that the hydrophobic effect is adequate to describe membrane partitioning of small amphiphilic molecules. The solvation thermodynamic properties {delta}G{sub sol}, {delta}H{sub sol}, and {delta}S{sub sol} which determine the solute transfer from the double layer into water prove that the distribution also strongly depends on shape, chemical nature and different structure of phenylalcohols.

  10. MTS-MD of Biomolecules Steered with 3D-RISM-KH Mean Solvation Forces Accelerated with Generalized Solvation Force Extrapolation.

    Science.gov (United States)

    Omelyan, Igor; Kovalenko, Andriy

    2015-04-14

    We developed a generalized solvation force extrapolation (GSFE) approach to speed up multiple time step molecular dynamics (MTS-MD) of biomolecules steered with mean solvation forces obtained from the 3D-RISM-KH molecular theory of solvation (three-dimensional reference interaction site model with the Kovalenko-Hirata closure). GSFE is based on a set of techniques including the non-Eckart-like transformation of coordinate space separately for each solute atom, extension of the force-coordinate pair basis set followed by selection of the best subset, balancing the normal equations by modified least-squares minimization of deviations, and incremental increase of outer time step in motion integration. Mean solvation forces acting on the biomolecule atoms in conformations at successive inner time steps are extrapolated using a relatively small number of best (closest) solute atomic coordinates and corresponding mean solvation forces obtained at previous outer time steps by converging the 3D-RISM-KH integral equations. The MTS-MD evolution steered with GSFE of 3D-RISM-KH mean solvation forces is efficiently stabilized with our optimized isokinetic Nosé-Hoover chain (OIN) thermostat. We validated the hybrid MTS-MD/OIN/GSFE/3D-RISM-KH integrator on solvated organic and biomolecules of different stiffness and complexity: asphaltene dimer in toluene solvent, hydrated alanine dipeptide, miniprotein 1L2Y, and protein G. The GSFE accuracy and the OIN efficiency allowed us to enlarge outer time steps up to huge values of 1-4 ps while accurately reproducing conformational properties. Quasidynamics steered with 3D-RISM-KH mean solvation forces achieves time scale compression of conformational changes coupled with solvent exchange, resulting in further significant acceleration of protein conformational sampling with respect to real time dynamics. Overall, this provided a 50- to 1000-fold effective speedup of conformational sampling for these systems, compared to conventional MD

  11. Internal Charging

    Science.gov (United States)

    Minow, Joseph I.

    2014-01-01

    (1) High energy (>100keV) electrons penetrate spacecraft walls and accumulate in dielectrics or isolated conductors; (2) Threat environment is energetic electrons with sufficient flux to charge circuit boards, cable insulation, and ungrounded metal faster than charge can dissipate; (3) Accumulating charge density generates electric fields in excess of material breakdown strenght resulting in electrostatic discharge; and (4) System impact is material damage, discharge currents inside of spacecraft Faraday cage on or near critical circuitry, and RF noise.

  12. Theory of competitive solvation of polymers by two solvents and entropy-enthalpy compensation in the solvation free energy upon dilution with the second solvent.

    Science.gov (United States)

    Dudowicz, Jacek; Freed, Karl F; Douglas, Jack F

    2015-06-07

    We develop a statistical mechanical lattice theory for polymer solvation by a pair of relatively low molar mass solvents that compete for binding to the polymer backbone. A theory for the equilibrium mixture of solvated polymer clusters {AiBCj} and free unassociated molecules A, B, and C is formulated in the spirit of Flory-Huggins mean-field approximation. This theoretical framework enables us to derive expressions for the boundaries for phase stability (spinodals) and other basic properties of these polymer solutions: the internal energy U, entropy S, specific heat CV, extent of solvation Φsolv, average degree of solvation 〈Nsolv〉, and second osmotic virial coefficient B2 as functions of temperature and the composition of the mixture. Our theory predicts many new phenomena, but the current paper applies the theory to describe the entropy-enthalpy compensation in the free energy of polymer solvation, a phenomenon observed for many years without theoretical explanation and with significant relevance to liquid chromatography and other polymer separation methods.

  13. Charge transport in electrically doped amorphous organic semiconductors.

    Science.gov (United States)

    Yoo, Seung-Jun; Kim, Jang-Joo

    2015-06-01

    This article reviews recent progress on charge generation by doping and its influence on the carrier mobility in organic semiconductors (OSs). The doping induced charge generation efficiency is generally low in OSs which was explained by the integer charge transfer model and the hybrid charge transfer model. The ionized dopants formed by charge transfer between hosts and dopants can act as Coulomb traps for mobile charges, and the presence of Coulomb traps in OSs broadens the density of states (DOS) in doped organic films. The Coulomb traps strongly reduce the carrier hopping rate and thereby change the carrier mobility, which was confirmed by experiments in recent years. In order to fully understand the doping mechanism in OSs, further quantitative and systematic analyses of charge transport characteristics must be accomplished. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  14. Unusual solvation through both p-orbital lobes of a carbene carbon

    Energy Technology Data Exchange (ETDEWEB)

    Hadad, C. Z., E-mail: cacier.hadad@udea.edu.co [Grupo de Química-Física Teórica, Instituto de Química, Universidad de Antioquia, A. A. 1226 Medellín (Colombia); Jenkins, Samantha [College of Chemistry and Chemical Engineering, Hunan Normal University, Changsha, Hunan 410081 (China); Flórez, Elizabeth [Departamento de Ciencias Básicas, Universidad de Medellín, Carrera 87 N° 30-65, Medellín (Colombia)

    2015-03-07

    As a result of a configurational space search done to explain the experimental evidence of transient specific solvation of singlet fluorocarbene amide with tetrahydrofuran, we found that the most stable structures consist in a group in which each oxygen of two tetrahydrofuran molecules act as electron donor to its respective empty p-orbital lobe of the carbene carbon atom, located at each side of the carbene molecular plane. This kind of species, which to our knowledge has not been reported before, explains very well the particular experimental characteristics observed for the transient solvation of this system. We postulate that the simultaneous interaction to both p-orbital lobes seems to confer a special stability to the solvation complexes, because this situation moves away the systems from the proximity of the corresponding transition states for the ylide products. Additionally, we present an analysis of other solvation complexes and a study of the nature of the involved interactions.

  15. Entropic solvation force between surfaces modified by grafted chains: a density functional approach

    Directory of Open Access Journals (Sweden)

    O. Pizio

    2010-01-01

    Full Text Available The behavior of a hard sphere fluid in slit-like pores with walls modified by grafted chain molecules composed of hard sphere segments is studied using density functional theory. The chains are grafted to opposite walls via terminating segments forming pillars. The effects of confinement and of "chemical" modification of pore walls on the entropic solvation force are investigated in detail. We observe that in the absence of adsorbed fluid the solvation force is strongly repulsive for narrow pores and attractive for wide pores. In the presence of adsorbed fluid both parts of the curve of the solvation force may develop oscillatory behavior dependent on the density of pillars, the number of segments and adsorption conditions. Also, the size ratio between adsorbed fluid species and chain segments is of importance for the development of oscillations. The choice of these parameters is crucial for efficient manipulation of the solvation force as desired for pores of different width.

  16. Charge preamplifier

    International Nuclear Information System (INIS)

    Chaminade, R.; Passerieux, J.P.

    1961-01-01

    We describe a charge preamplifier having the following properties: - large open loop gain giving both stable gain and large input charge transfer; - stable input grid current with aging and without any adjustment; - fairly fast rise; - nearly optimum noise performance; - industrial material. (authors)

  17. Charge Meter

    Indian Academy of Sciences (India)

    Home; Journals; Resonance – Journal of Science Education; Volume 19; Issue 4. Charge Meter: Easy Way to Measure Charge and Capacitance: Some Interesting Electrostatic Experiments. M K Raghavendra V Venkataraman. Classroom Volume 19 Issue 4 April 2014 pp 376-390 ...

  18. Charging machine

    International Nuclear Information System (INIS)

    Medlin, J.B.

    1976-01-01

    A charging machine for loading fuel slugs into the process tubes of a nuclear reactor includes a tubular housing connected to the process tube, a charging trough connected to the other end of the tubular housing, a device for loading the charging trough with a group of fuel slugs, means for equalizing the coolant pressure in the charging trough with the pressure in the process tubes, means for pushing the group of fuel slugs into the process tube and a latch and a seal engaging the last object in the group of fuel slugs to prevent the fuel slugs from being ejected from the process tube when the pusher is removed and to prevent pressure liquid from entering the charging machine. 3 claims, 11 drawing figures

  19. Charge independence and charge symmetry

    Energy Technology Data Exchange (ETDEWEB)

    Miller, G A [Washington Univ., Seattle, WA (United States). Dept. of Physics; van Oers, W T.H. [Manitoba Univ., Winnipeg, MB (Canada). Dept. of Physics; [TRIUMF, Vancouver, BC (Canada)

    1994-09-01

    Charge independence and charge symmetry are approximate symmetries of nature, violated by the perturbing effects of the mass difference between up and down quarks and by electromagnetic interactions. The observations of the symmetry breaking effects in nuclear and particle physics and the implications of those effects are reviewed. (author). 145 refs., 3 tabs., 11 figs.

  20. Charge independence and charge symmetry

    International Nuclear Information System (INIS)

    Miller, G.A.

    1994-09-01

    Charge independence and charge symmetry are approximate symmetries of nature, violated by the perturbing effects of the mass difference between up and down quarks and by electromagnetic interactions. The observations of the symmetry breaking effects in nuclear and particle physics and the implications of those effects are reviewed. (author). 145 refs., 3 tabs., 11 figs

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

    Science.gov (United States)

    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.

  2. Charge transport and recombination in bulk heterojunction solar cells studied by the photoinduced charge extraction in linearly increasing voltage technique

    OpenAIRE

    Mozer, AJ; Sariciftci, NS; Osterbacka, R; Westerling, M; Juska, G; LUTSEN, Laurence; VANDERZANDE, Dirk

    2005-01-01

    Charge carrier mobility and recombination in a bulk heterojunction solar cell based on the mixture of poly[2-methoxy-5-(3,7-dimethyloctyloxy)-phenylene vinylene] (MDMO-PPV) and 1-(3-methoxycarbonyl)propyl-1-phenyl-(6,6)-C-61 (PCBM) has been studied using the novel technique of photoinduced charge carrier extraction in a linearly increasing voltage (Photo-CELIV). In this technique, charge carriers are photogenerated by a short laser flash, and extracted under a reverse bias voltage ramp after ...

  3. The dynamics of Ca2+ ions within the solvation shell of calbindin D9k.

    Directory of Open Access Journals (Sweden)

    Elad Project

    Full Text Available The encounter of a Ca(2+ ion with a protein and its subsequent binding to specific binding sites is an intricate process that cannot be fully elucidated from experimental observations. We have applied Molecular Dynamics to study this process with atomistic details, using Calbindin D9k (CaB as a model protein. The simulations show that in most of the time the Ca(2+ ion spends within the Debye radius of CaB, it is being detained at the 1st and 2nd solvation shells. While being detained near the protein, the diffusion coefficient of the ion is significantly reduced. However, due to the relatively long period of detainment, the ion can scan an appreciable surface of the protein. The enhanced propagation of the ion on the surface has a functional role: significantly increasing the ability of the ion to scan the protein's surface before being dispersed to the bulk. The contribution of this mechanism to Ca(2+ binding becomes significant at low ion concentrations, where the intervals between successive encounters with the protein are getting longer. The efficiency of the surface diffusion is affected by the distribution of charges on the protein's surface. Comparison of the Ca(2+ binding dynamics in CaB and its E60D mutant reveals that in the wild type (WT protein the carboxylate of E60 function as a preferred landing-site for the Ca(2+ arriving from the bulk, followed by delivering it to the final binding site. Replacement of the glutamate by aspartate significantly reduced the ability to transfer Ca(2+ ions from D60 to the final binding site, explaining the observed decrement in the affinity of the mutated protein to Ca(2+.

  4. Ionic Solution: What Goes Right and Wrong with Continuum Solvation Modeling.

    Science.gov (United States)

    Wang, Changhao; Ren, Pengyu; Luo, Ray

    2017-12-14

    Solvent-mediated electrostatic interactions were well recognized to be important in the structure and function of molecular systems. Ionic interaction is an important component in electrostatic interactions, especially in highly charged molecules, such as nucleic acids. Here, we focus on the quality of the widely used Poisson-Boltzmann surface area (PBSA) continuum models in modeling ionic interactions by comparing with both explicit solvent simulations and the experiment. In this work, the molality-dependent chemical potentials for sodium chloride (NaCl) electrolyte were first simulated in the SPC/E explicit solvent. Our high-quality simulation agrees well with both the previous study and the experiment. Given the free-energy simulations in SPC/E as the benchmark, we used the same sets of snapshots collected in the SPC/E solvent model for PBSA free-energy calculations in the hope to achieve the maximum consistency between the two solvent models. Our comparative analysis shows that the molality-dependent chemical potentials of NaCl were reproduced well with both linear PB and nonlinear PB methods, although nonlinear PB agrees better with SPC/E and the experiment. Our free-energy simulations also show that the presence of salt increases the hydrophobic effect in a nonlinear fashion, in qualitative agreement with previous theoretical studies of Onsager and Samaras. However, the lack of molality-dependency in the nonelectrostatics continuum models dramatically reduces the overall quality of PBSA methods in modeling salt-dependent energetics. These analyses point to further improvements needed for more robust modeling of solvent-mediated interactions by the continuum solvation frameworks.

  5. Boundary layer friction of solvate ionic liquids as a function of potential.

    Science.gov (United States)

    Li, Hua; Rutland, Mark W; Watanabe, Masayoshi; Atkin, Rob

    2017-07-01

    Atomic force microscopy (AFM) has been used to investigate the potential dependent boundary layer friction at solvate ionic liquid (SIL)-highly ordered pyrolytic graphite (HOPG) and SIL-Au(111) interfaces. Friction trace and retrace loops of lithium tetraglyme bis(trifluoromethylsulfonyl)amide (Li(G4) TFSI) at HOPG present clearer stick-slip events at negative potentials than at positive potentials, indicating that a Li + cation layer adsorbed to the HOPG lattice at negative potentials which enhances stick-slip events. The boundary layer friction data for Li(G4) TFSI shows that at HOPG, friction forces at all potentials are low. The TFSI - anion rich boundary layer at positive potentials is more lubricating than the Li + cation rich boundary layer at negative potentials. These results suggest that boundary layers at all potentials are smooth and energy is predominantly dissipated via stick-slip events. In contrast, friction at Au(111) for Li(G4) TFSI is significantly higher at positive potentials than at negative potentials, which is comparable to that at HOPG at the same potential. The similarity of boundary layer friction at negatively charged HOPG and Au(111) surfaces indicates that the boundary layer compositions are similar and rich in Li + cations for both surfaces at negative potentials. However, at Au(111), the TFSI - rich boundary layer is less lubricating than the Li + rich boundary layer, which implies that anion reorientations rather than stick-slip events are the predominant energy dissipation pathways. This is confirmed by the boundary friction of Li(G4) NO 3 at Au(111), which shows similar friction to Li(G4) TFSI at negative potentials due to the same cation rich boundary layer composition, but even higher friction at positive potentials, due to higher energy dissipation in the NO 3 - rich boundary layer.

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

    International Nuclear Information System (INIS)

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

    2010-01-01

    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.

  7. Dynamics of electron solvation in I-(CH3OH)n clusters (4 ≤n≤ 11)

    International Nuclear Information System (INIS)

    Young, Ryan M.; Yandell, Margaret A.; Neumark, Daniel M.

    2011-01-01

    The dynamics of electron solvation following excitation of the charge-transfer-to-solvent precursor state in iodide-doped methanol clusters, I - (CH 3 OH) n=4-11 , are studied with time-resolved photoelectron imaging. This excitation produces a I ... (CH 3 OH) n - cluster that is unstable with respect to electron autodetachment and whose autodetachment lifetime increases monotonically from ∼800 fs to 85 ps as n increases from 4 to 11. The vertical detachment energy (VDE) and width of the excited state feature in the photoelectron spectrum show complex time dependence during the lifetime of this state. The VDE decreases over the first 100-400 fs, then rises exponentially to a maximum with a ∼1 ps time constant, and finally decreases by as much as 180 meV with timescales of 3-20 ps. The early dynamics are associated with electron transfer from the iodide to the methanol cluster, while the longer-time changes in VDE are attributed to solvent reordering, possibly in conjunction with ejection of neutral iodine from the cluster. Changes in the observed width of the spectrum largely follow those of the VDEs; the dynamics of both are attributed to the major rearrangement of the solvent cluster during relaxation. The relaxation dynamics are interpreted as a reorientation of at least one methanol molecule and the disruption and formation of the solvent network in order to accommodate the excess charge.

  8. Dynamics of electron solvation in I(-)(CH3OH)n clusters (4 ≤ n ≤ 11).

    Science.gov (United States)

    Young, Ryan M; Yandell, Margaret A; Neumark, Daniel M

    2011-03-28

    The dynamics of electron solvation following excitation of the charge-transfer-to-solvent precursor state in iodide-doped methanol clusters, I(-)(CH(3)OH)(n = 4-11), are studied with time-resolved photoelectron imaging. This excitation produces a I···(CH(3)OH)(n)(-) cluster that is unstable with respect to electron autodetachment and whose autodetachment lifetime increases monotonically from ~800 fs to 85 ps as n increases from 4 to 11. The vertical detachment energy (VDE) and width of the excited state feature in the photoelectron spectrum show complex time dependence during the lifetime of this state. The VDE decreases over the first 100-400 fs, then rises exponentially to a maximum with a ~1 ps time constant, and finally decreases by as much as 180 meV with timescales of 3-20 ps. The early dynamics are associated with electron transfer from the iodide to the methanol cluster, while the longer-time changes in VDE are attributed to solvent reordering, possibly in conjunction with ejection of neutral iodine from the cluster. Changes in the observed width of the spectrum largely follow those of the VDEs; the dynamics of both are attributed to the major rearrangement of the solvent cluster during relaxation. The relaxation dynamics are interpreted as a reorientation of at least one methanol molecule and the disruption and formation of the solvent network in order to accommodate the excess charge.

  9. Duchenne muscular dystrophy carriers

    International Nuclear Information System (INIS)

    Matsumura, K.; Nakano, I.

    1989-01-01

    By means of magnetic resonance imaging (MRI), the proton spin-lattice relaxation times (T1 values) of the skeletal muscles were measured in Duchenne muscular dystrophy (DMD) carriers and normal controls. The bound water fraction (BWF) was calculated from the T1 values obtained, according to the fast proton diffusion model. In the DMD carriers, T1 values of the gluteus maximus and quadriceps femoris muscles were significantly higher, and BWFs of these muscles were significantly lower than in normal control. Degenerative muscular changes accompanied by interstitial edema were presumed responsible for this abnormality. No correlation was observed between the muscle T1 and serum creatine kinase values. The present study showed that MRI could be a useful method for studying the dynamic state of water in both normal and pathological skeletal muscles. Its possible utility for DMD carrier detection was discussed briefly. (orig.)

  10. Temperature Dependence of Charge Localization in High-Mobility, Solution-Crystallized Small Molecule Semiconductors Studied by Charge Modulation Spectroscopy

    DEFF Research Database (Denmark)

    Meneau, Aurélie Y. B.; Olivier, Yoann; Backlund, Tomas

    2016-01-01

    In solution-processable small molecule semiconductors, the extent of charge carrier wavefunction localization induced by dynamic disorder can be probed spectroscopically as a function of temperature using charge modulation spectroscopy (CMS). Here, it is shown based on combined fi eld-effect tran......In solution-processable small molecule semiconductors, the extent of charge carrier wavefunction localization induced by dynamic disorder can be probed spectroscopically as a function of temperature using charge modulation spectroscopy (CMS). Here, it is shown based on combined fi eld......-effect transistor and CMS measurements as a function of temperature that in certain molecular semiconductors, such as solution-processible pentacene, charge carriers become trapped at low temperatures in environments in which the charges become highly localized on individual molecules, while in some other molecules...

  11. Nonequilibrium quantum solvation with a time-dependent Onsager cavity

    Science.gov (United States)

    Kirchberg, H.; Nalbach, P.; Thorwart, M.

    2018-04-01

    We formulate a theory of nonequilibrium quantum solvation in which parameters of the solvent are explicitly depending on time. We assume in a simplest approach a spherical molecular Onsager cavity with a time-dependent radius. We analyze the relaxation properties of a test molecular point dipole in a dielectric solvent and consider two cases: (i) a shrinking Onsager sphere and (ii) a breathing Onsager sphere. Due to the time-dependent solvent, the frequency-dependent response function of the dipole becomes time-dependent. For a shrinking Onsager sphere, the dipole relaxation is in general enhanced. This is reflected in a temporally increasing linewidth of the absorptive part of the response. Furthermore, the effective frequency-dependent response function shows two peaks in the absorptive part which are symmetrically shifted around the eigenfrequency. By contrast, a breathing sphere reduces damping as compared to the static sphere. Interestingly, we find a non-monotonous dependence of the relaxation rate on the breathing rate and a resonant suppression of damping when both rates are comparable. Moreover, the linewidth of the absorptive part of the response function is strongly reduced for times when the breathing sphere reaches its maximal extension.

  12. Cluster Formation of Polyphilic Molecules Solvated in a DPPC Bilayer

    Directory of Open Access Journals (Sweden)

    Xiang-Yang Guo

    2017-10-01

    Full Text Available We analyse the initial stages of cluster formation of polyphilic additive molecules which are solvated in a dipalmitoylphosphatidylcholine (DPPC lipid bilayer. Our polyphilic molecules comprise an aromatic (trans-bilayer core domain with (out-of-bilayer glycerol terminations, complemented with a fluorophilic and an alkyl side chain, both of which are confined within the aliphatic segment of the bilayer. Large-scale molecular dynamics simulations (1 μ s total duration of a set of six of such polyphilic additives reveal the initial steps towards supramolecular aggregation induced by the specific philicity properties of the molecules. For our intermediate system size of six polyphiles, the transient but recurrent formation of a trimer is observed on a characteristic timescale of about 100 ns. The alkane/perfluoroalkane side chains show a very distinct conformational distribution inside the bilayer thanks to their different philicity, despite their identical anchoring in the trans-bilayer segment of the polyphile. The diffusive mobility of the polyphilic additives is about the same as that of the surrounding lipids, although it crosses both bilayer leaflets and tends to self-associate.

  13. Molecular hydrogen solvated in water – A computational study

    International Nuclear Information System (INIS)

    Śmiechowski, Maciej

    2015-01-01

    The aqueous hydrogen molecule is studied with molecular dynamics simulations at ambient temperature and pressure conditions, using a newly developed flexible and polarizable H 2 molecule model. The design and implementation of this model, compatible with an existing flexible and polarizable force field for water, is presented in detail. The structure of the hydration layer suggests that first-shell water molecules accommodate the H 2 molecule without major structural distortions and two-dimensional, radial-angular distribution functions indicate that as opposed to strictly tangential, the orientation of these water molecules is such that the solute is solvated with one of the free electron pairs of H 2 O. The calculated self-diffusion coefficient of H 2 (aq) agrees very well with experimental results and the time dependence of mean square displacement suggests the presence of caging on a time scale corresponding to hydrogen bond network vibrations in liquid water. Orientational correlation function of H 2 experiences an extremely short-scale decay, making the H 2 –H 2 O interaction potential essentially isotropic by virtue of rotational averaging. The inclusion of explicit polarizability in the model allows for the calculation of Raman spectra that agree very well with available experimental data on H 2 (aq) under differing pressure conditions, including accurate reproduction of the experimentally noted trends with solute pressure or concentration

  14. Preferential solvation and solvation shell composition of free base and protonated 5, 10, 15, 20-tetrakis(4-sulfonatophenyl)porphyrin in aqueous organic mixed solvents

    Science.gov (United States)

    Farajtabar, Ali; Jaberi, Fatemeh; Gharib, Farrokh

    2011-12-01

    The solvatochromic properties of the free base and the protonated 5, 10, 15, 20-tetrakis(4-sulfonatophenyl)porphyrin (TPPS) were studied in pure water, methanol, ethanol (protic solvents), dimethylsulfoxide, DMSO, (non-protic solvent), and their corresponding aqueous-organic binary mixed solvents. The correlation of the empirical solvent polarity scale ( ET) values of TPPS with composition of the solvents was analyzed by the solvent exchange model of Bosch and Roses to clarify the preferential solvation of the probe dyes in the binary mixed solvents. The solvation shell composition and the synergistic effects in preferential solvation of the solute dyes were investigated in terms of both solvent-solvent and solute-solvent interactions and also, the local mole fraction of each solvent composition was calculated in cybotactic region of the probe. The effective mole fraction variation may provide significant physico-chemical insights in the microscopic and molecular level of interactions between TPPS species and the solvent components and therefore, can be used to interpret the solvent effect on kinetics and thermodynamics of TPPS. The obtained results from the preferential solvation and solvent-solvent interactions have been successfully applied to explain the variation of equilibrium behavior of protonation of TPPS occurring in aqueous organic mixed solvents of methanol, ethanol and DMSO.

  15. Photo-generated carriers lose energy during extraction from polymer-fullerene solar cells

    KAUST Repository

    Melianas, Armantas

    2015-11-05

    In photovoltaic devices, the photo-generated charge carriers are typically assumed to be in thermal equilibrium with the lattice. In conventional materials, this assumption is experimentally justified as carrier thermalization completes before any significant carrier transport has occurred. Here, we demonstrate by unifying time-resolved optical and electrical experiments and Monte Carlo simulations over an exceptionally wide dynamic range that in the case of organic photovoltaic devices, this assumption is invalid. As the photo-generated carriers are transported to the electrodes, a substantial amount of their energy is lost by continuous thermalization in the disorder broadened density of states. Since thermalization occurs downward in energy, carrier motion is boosted by this process, leading to a time-dependent carrier mobility as confirmed by direct experiments. We identify the time and distance scales relevant for carrier extraction and show that the photo-generated carriers are extracted from the operating device before reaching thermal equilibrium.

  16. Density functional theory calculations of charge transport properties ...

    Indian Academy of Sciences (India)

    ZIRAN CHEN

    2017-08-04

    Aug 4, 2017 ... properties of 'plate-like' coronene topological structures ... Keywords. Organic semiconductors; density functional theory; charge carrier mobility; ambipolar transport; ..... nology Department of Sichuan Province (Grant Number.

  17. Asymmetric Carrier Random PWM

    DEFF Research Database (Denmark)

    Mathe, Laszlo; Lungeanu, Florin; Rasmussen, Peter Omand

    2010-01-01

    index. The flat motor current spectrum generates an acoustical noise close to the white noise, which may improve the acoustical performance of the drive. The new carrier wave is easy to implement digitally, without employing any external circuits. The modulation method can be used in open, as well...

  18. Willis H Carrier

    Indian Academy of Sciences (India)

    Home; Journals; Resonance – Journal of Science Education; Volume 17; Issue 2. Willis H. Carrier - Father of Air Conditioning. R V Simha. General Article Volume 17 Issue 2 February 2012 pp 117-138. Fulltext. Click here to view fulltext PDF. Permanent link: https://www.ias.ac.in/article/fulltext/reso/017/02/0117-0138 ...

  19. Tracking Ultrafast Carrier Dynamics in Single Semiconductor Nanowire Heterostructures

    Directory of Open Access Journals (Sweden)

    Taylor A.J.

    2013-03-01

    Full Text Available An understanding of non-equilibrium carrier dynamics in silicon (Si nanowires (NWs and NW heterostructures is very important due to their many nanophotonic and nanoelectronics applications. Here, we describe the first measurements of ultrafast carrier dynamics and diffusion in single heterostructured Si nanowires, obtained using ultrafast optical microscopy. By isolating individual nanowires, we avoid complications resulting from the broad size and alignment distribution in nanowire ensembles, allowing us to directly probe ultrafast carrier dynamics in these quasi-one-dimensional systems. Spatially-resolved pump-probe spectroscopy demonstrates the influence of surface-mediated mechanisms on carrier dynamics in a single NW, while polarization-resolved femtosecond pump-probe spectroscopy reveals a clear anisotropy in carrier lifetimes measured parallel and perpendicular to the NW axis, due to density-dependent Auger recombination. Furthermore, separating the pump and probe spots along the NW axis enabled us to track space and time dependent carrier diffusion in radial and axial NW heterostructures. These results enable us to reveal the influence of radial and axial interfaces on carrier dynamics and charge transport in these quasi-one-dimensional nanosystems, which can then be used to tailor carrier relaxation in a single nanowire heterostructure for a given application.

  20. Charge Transport in Spiro-OMeTAD Investigated through Space-Charge-Limited Current Measurements

    Science.gov (United States)

    Röhr, Jason A.; Shi, Xingyuan; Haque, Saif A.; Kirchartz, Thomas; Nelson, Jenny

    2018-04-01

    Extracting charge-carrier mobilities for organic semiconductors from space-charge-limited conduction measurements is complicated in practice by nonideal factors such as trapping in defects and injection barriers. Here, we show that by allowing the bandlike charge-carrier mobility, trap characteristics, injection barrier heights, and the shunt resistance to vary in a multiple-trapping drift-diffusion model, a numerical fit can be obtained to the entire current density-voltage curve from experimental space-charge-limited current measurements on both symmetric and asymmetric 2 ,2',7 ,7' -tetrakis(N ,N -di-4-methoxyphenylamine)-9 ,9' -spirobifluorene (spiro-OMeTAD) single-carrier devices. This approach yields a bandlike mobility that is more than an order of magnitude higher than the effective mobility obtained using analytical approximations, such as the Mott-Gurney law and the moving-electrode equation. It is also shown that where these analytical approximations require a temperature-dependent effective mobility to achieve fits, the numerical model can yield a temperature-, electric-field-, and charge-carrier-density-independent mobility. Finally, we present an analytical model describing trap-limited current flow through a semiconductor in a symmetric single-carrier device. We compare the obtained charge-carrier mobility and trap characteristics from this analytical model to the results from the numerical model, showing excellent agreement. This work shows the importance of accounting for traps and injection barriers explicitly when analyzing current density-voltage curves from space-charge-limited current measurements.