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Sample records for electric double layer

  1. Electric fields and double layers in plasmas

    NASA Technical Reports Server (NTRS)

    Singh, Nagendra; Thiemann, H.; Schunk, R. W.

    1987-01-01

    Various mechanisms for driving double layers in plasmas are briefly described, including applied potential drops, currents, contact potentials, and plasma expansions. Some dynamical features of the double layers are discussed. These features, as seen in simulations, laboratory experiments, and theory, indicate that double layers and the currents through them undergo slow oscillations which are determined by the ion transit time across an effective length of the system in which double layers form. It is shown that a localized potential dip forms at the low potential end of a double layer, which interrupts the electron current through it according to the Langmuir criterion, whenever the ion flux into the double is disrupted. The generation of electric fields perpendicular to the ambient magnetic field by contact potentials is also discussed. Two different situations were considered; in one, a low-density hot plasma is sandwiched between high-density cold plasmas, while in the other a high-density current sheet permeates a low-density background plasma. Perpendicular electric fields develop near the contact surfaces. In the case of the current sheet, the creation of parallel electric fields and the formation of double layers are also discussed when the current sheet thickness is varied. Finally, the generation of electric fields and double layers in an expanding plasma is discussed.

  2. Electric fields and double layers in plasmas

    NASA Astrophysics Data System (ADS)

    Singh, Nagendra; Thiemann, H.; Schunk, R. W.

    1987-05-01

    Various mechanisms for driving double layers in plasmas are briefly described, including applied potential drops, currents, contact potentials, and plasma expansions. Some dynamical features of the double layers are discussed. These features, as seen in simulations, laboratory experiments, and theory, indicate that double layers and the currents through them undergo slow oscillations which are determined by the ion transit time across an effective length of the system in which double layers form. It is shown that a localized potential dip forms at the low potential end of a double layer, which interrupts the electron current through it according to the Langmuir criterion, whenever the ion flux into the double is disrupted. The generation of electric fields perpendicular to the ambient magnetic field by contact potentials is also discussed. Two different situations were considered; in one, a low-density hot plasma is sandwiched between high-density cold plasmas, while in the other a high-density current sheet permeates a low-density background plasma. Perpendicular electric fields develop near the contact surfaces. In the case of the current sheet, the creation of parallel electric fields and the formation of double layers are also discussed when the current sheet thickness is varied. Finally, the generation of electric fields and double layers in an expanding plasma is discussed.

  3. Reversible Heating in Electric Double Layer Capacitors

    NASA Astrophysics Data System (ADS)

    Janssen, Mathijs; van Roij, René

    2017-03-01

    A detailed comparison is made between different viewpoints on reversible heating in electric double layer capacitors. We show in the limit of slow charging that a combined Poisson-Nernst-Planck and heat equation, first studied by d'Entremont and Pilon [J. Power Sources 246, 887 (2014), 10.1016/j.jpowsour.2013.08.024], recovers the temperature changes as predicted by the thermodynamic identity of Janssen et al. [Phys. Rev. Lett. 113, 268501 (2014), 10.1103/PhysRevLett.113.268501], and disagrees with the approximative model of Schiffer et al. [J. Power Sources 160, 765 (2006), 10.1016/j.jpowsour.2005.12.070] that predominates the literature. The thermal response to the adiabatic charging of supercapacitors contains information on electric double layer formation that has remained largely unexplored.

  4. Reversible Heating in Electric Double Layer Capacitors.

    PubMed

    Janssen, Mathijs; van Roij, René

    2017-03-03

    A detailed comparison is made between different viewpoints on reversible heating in electric double layer capacitors. We show in the limit of slow charging that a combined Poisson-Nernst-Planck and heat equation, first studied by d'Entremont and Pilon [J. Power Sources 246, 887 (2014)JPSODZ0378-775310.1016/j.jpowsour.2013.08.024], recovers the temperature changes as predicted by the thermodynamic identity of Janssen et al. [Phys. Rev. Lett. 113, 268501 (2014)PRLTAO0031-900710.1103/PhysRevLett.113.268501], and disagrees with the approximative model of Schiffer et al. [J. Power Sources 160, 765 (2006)JPSODZ0378-775310.1016/j.jpowsour.2005.12.070] that predominates the literature. The thermal response to the adiabatic charging of supercapacitors contains information on electric double layer formation that has remained largely unexplored.

  5. Electrical power generation by mechanically modulating electrical double layers.

    PubMed

    Moon, Jong Kyun; Jeong, Jaeki; Lee, Dongyun; Pak, Hyuk Kyu

    2013-01-01

    Since Michael Faraday and Joseph Henry made their great discovery of electromagnetic induction, there have been continuous developments in electrical power generation. Most people today get electricity from thermal, hydroelectric, or nuclear power generation systems, which use this electromagnetic induction phenomenon. Here we propose a new method for electrical power generation, without using electromagnetic induction, by mechanically modulating the electrical double layers at the interfacial areas of a water bridge between two conducting plates. We find that when the height of the water bridge is mechanically modulated, the electrical double layer capacitors formed on the two interfacial areas are continuously charged and discharged at different phases from each other, thus generating an AC electric current across the plates. We use a resistor-capacitor circuit model to explain the results of this experiment. This observation could be useful for constructing a micro-fluidic power generation system in the near future.

  6. Electric fields and double layers in plasmas

    NASA Astrophysics Data System (ADS)

    Singh, Nagendra; Thiemann, H.; Schunk, R. W.

    1987-05-01

    Various mechanisms for driving double layers (DLs) in plasmas are described, including applied potential drops, currents, contact potentials, and plasma expansions. Somne dynamic features of the DLs are discussed; and it is demonstrated that DLs and the currents through them undergo slow oscillations, determined by the ion transit time across an effective length of the system in which the DLs form. It is shown that a localized potential dip forms at the low potential end of a DL, which interrupts the electron current through it according to the Langmuir criterion whenever the ion flux into the DL is disrupted. Also considered is the generation of electric fields perpendicular to the ambient magnetic field by contact potentials.

  7. Electrical Power Generation by Mechanically Modulating Electrical Double Layers

    NASA Astrophysics Data System (ADS)

    Pak, Hyuk Kyu; Moon, Jong Kyun

    2014-11-01

    Since Michael Faraday and Joseph Henry made their great discovery of electromagnetic induction, there have been continuous developments in electrical power generation. Most people today get electricity from thermal, hydroelectric, or nuclear power generation systems, which use this electromagnetic induction phenomenon. Here we propose a new method for electrical power generation, without using electromagnetic induction, by mechanically modulating the electrical double layers at the interfacial areas of a water bridge between two conducting plates. We find that when the height of the water bridge is mechanically modulated, the electrical double layer capacitors formed on the two interfacial areas are continuously charged and discharged at different phases from each other, thus generating an AC electric current across the plates. We use a resistor-capacitor circuit model to explain the results of this experiment. This observation could be useful for constructing a micro-fluidic power generation system and for understanding the interfacial charge distribution in solid-liquid interfaces in the near future. This work was supported by Center for Soft and Living Matter through IBS prgram in Korea.

  8. Challenges facing lithium batteries and electrical double-layer capacitors.

    PubMed

    Choi, Nam-Soon; Chen, Zonghai; Freunberger, Stefan A; Ji, Xiulei; Sun, Yang-Kook; Amine, Khalil; Yushin, Gleb; Nazar, Linda F; Cho, Jaephil; Bruce, Peter G

    2012-10-01

    Energy-storage technologies, including electrical double-layer capacitors and rechargeable batteries, have attracted significant attention for applications in portable electronic devices, electric vehicles, bulk electricity storage at power stations, and "load leveling" of renewable sources, such as solar energy and wind power. Transforming lithium batteries and electric double-layer capacitors requires a step change in the science underpinning these devices, including the discovery of new materials, new electrochemistry, and an increased understanding of the processes on which the devices depend. The Review will consider some of the current scientific issues underpinning lithium batteries and electric double-layer capacitors.

  9. A review of molecular modelling of electric double layer capacitors.

    PubMed

    Burt, Ryan; Birkett, Greg; Zhao, X S

    2014-04-14

    Electric double-layer capacitors are a family of electrochemical energy storage devices that offer a number of advantages, such as high power density and long cyclability. In recent years, research and development of electric double-layer capacitor technology has been growing rapidly, in response to the increasing demand for energy storage devices from emerging industries, such as hybrid and electric vehicles, renewable energy, and smart grid management. The past few years have witnessed a number of significant research breakthroughs in terms of novel electrodes, new electrolytes, and fabrication of devices, thanks to the discovery of innovative materials (e.g. graphene, carbide-derived carbon, and templated carbon) and the availability of advanced experimental and computational tools. However, some experimental observations could not be clearly understood and interpreted due to limitations of traditional theories, some of which were developed more than one hundred years ago. This has led to significant research efforts in computational simulation and modelling, aimed at developing new theories, or improving the existing ones to help interpret experimental results. This review article provides a summary of research progress in molecular modelling of the physical phenomena taking place in electric double-layer capacitors. An introduction to electric double-layer capacitors and their applications, alongside a brief description of electric double layer theories, is presented first. Second, molecular modelling of ion behaviours of various electrolytes interacting with electrodes under different conditions is reviewed. Finally, key conclusions and outlooks are given. Simulations on comparing electric double-layer structure at planar and porous electrode surfaces under equilibrium conditions have revealed significant structural differences between the two electrode types, and porous electrodes have been shown to store charge more efficiently. Accurate electrolyte and

  10. Capacitance of carbon-based electrical double-layer capacitors.

    PubMed

    Ji, Hengxing; Zhao, Xin; Qiao, Zhenhua; Jung, Jeil; Zhu, Yanwu; Lu, Yalin; Zhang, Li Li; MacDonald, Allan H; Ruoff, Rodney S

    2014-01-01

    Experimental electrical double-layer capacitances of porous carbon electrodes fall below ideal values, thus limiting the practical energy densities of carbon-based electrical double-layer capacitors. Here we investigate the origin of this behaviour by measuring the electrical double-layer capacitance in one to five-layer graphene. We find that the capacitances are suppressed near neutrality, and are anomalously enhanced for thicknesses below a few layers. We attribute the first effect to quantum capacitance effects near the point of zero charge, and the second to correlations between electrons in the graphene sheet and ions in the electrolyte. The large capacitance values imply gravimetric energy storage densities in the single-layer graphene limit that are comparable to those of batteries. We anticipate that these results shed light on developing new theoretical models in understanding the electrical double-layer capacitance of carbon electrodes, and on opening up new strategies for improving the energy density of carbon-based capacitors.

  11. Capacitance of carbon-based electrical double-layer capacitors

    NASA Astrophysics Data System (ADS)

    Ji, Hengxing; Zhao, Xin; Qiao, Zhenhua; Jung, Jeil; Zhu, Yanwu; Lu, Yalin; Zhang, Li Li; MacDonald, Allan H.; Ruoff, Rodney S.

    2014-02-01

    Experimental electrical double-layer capacitances of porous carbon electrodes fall below ideal values, thus limiting the practical energy densities of carbon-based electrical double-layer capacitors. Here we investigate the origin of this behaviour by measuring the electrical double-layer capacitance in one to five-layer graphene. We find that the capacitances are suppressed near neutrality, and are anomalously enhanced for thicknesses below a few layers. We attribute the first effect to quantum capacitance effects near the point of zero charge, and the second to correlations between electrons in the graphene sheet and ions in the electrolyte. The large capacitance values imply gravimetric energy storage densities in the single-layer graphene limit that are comparable to those of batteries. We anticipate that these results shed light on developing new theoretical models in understanding the electrical double-layer capacitance of carbon electrodes, and on opening up new strategies for improving the energy density of carbon-based capacitors.

  12. Double Layers in Astrophysics

    NASA Technical Reports Server (NTRS)

    Williams, Alton C. (Editor); Moorehead, Tauna W. (Editor)

    1987-01-01

    Topics addressed include: laboratory double layers; ion-acoustic double layers; pumping potential wells; ion phase-space vortices; weak double layers; electric fields and double layers in plasmas; auroral double layers; double layer formation in a plasma; beamed emission from gamma-ray burst source; double layers and extragalactic jets; and electric potential between plasma sheet clouds.

  13. Electric Double-Layer Capacitors Applying to Voltage Sag Compensator

    NASA Astrophysics Data System (ADS)

    Nara, Hidetaka

    Recently the electric double-layer capacitor (EDLC) which is rapidly charged and discharged and offers long life, maintenance-free, has been developed as a new energy storage element. Therefore, we developed the uninterruptible power supply as voltage sag compensator utilizing EDLC. This paper describes an abstract of EDLC and applying to voltage sag compensation.

  14. Superconductivity in Electric Double Layer Capacitor under Pressure

    NASA Astrophysics Data System (ADS)

    McCann, Duncan; Misek, Martin; Kamenev, Konstantin; Huxley, Andrew

    2015-03-01

    Chemical doping generally provides the most common method for tuning into the superconducting state of a material yet can be difficult to control and also potentially introduces structural disorder complicating the underlying physics. Electric Double Layer devices however provide a means to electrostatically dope materials with high electric fields allowing continuous tuning of a 2D superconducting state thus avoiding such issues. One such device is the Electric Double Layer Capacitor which can detect the onset of superconductivity through AC magnetisation measurements. We make use of a similar device in an attempt to electrostatically dope and tune the superconductivity in the cuprate compound La1.93Sr0.07CuO4 as well as investigating whether application of pressure improves its efficiency.

  15. Development and current status of electric double-layer capacitors

    SciTech Connect

    Morimoto, Takeshi; Hiratsuka, Kazuya; Sanada, Yasuhiro; Kurihara, Kaname

    1995-12-31

    An electric double layer capacitor (EDLC) based on the charge storage at the interface between a high surface area carbon electrode and an electrolyte solution is widely used as maintenance-free power source for IC memories and microcomputers. New applications for electric double-layer capacitors have been proposed in recent years. The popularity of these devices is derived from their high energy density relative to conventional capacitors and their long cycle life and high power density relative to batteries. In this paper a classification and a characteristics of industrially produced Japanese small EDLCs are reviewed. Structure and performance of power capacitors under development as well as materials and performance of industrially produced small capacitors are discussed.

  16. Insights from theory and simulation on the electrical double layer.

    PubMed

    Henderson, Douglas; Boda, Dezso

    2009-05-28

    Despite the fact that our conceptual understanding of the electrical double layer has advanced during the past few decades, the interpretation of experimental and applied work is still largely based on the venerable Poisson-Boltzmann theory of Gouy, Chapman and Stern. This is understandable since this theory is simple and analytic. However, it is not very accurate because the atomic/molecular nature of the ions/solvent and their correlations are ignored. Simulation and some theoretical studies by ourselves and others that have advanced our understanding are discussed. These studies show that the GCS theory predicts a narrow double layer with monotonic profiles. This is not correct. The double layer is wider, and there can be substantial layering that would be even more pronounced if explicit solvent molecules are considered. For many years, experimental studies of the double layer have been directed to the use of electrochemistry as an analytical tool. This is acceptable for analytic chemistry studies. However, the understanding of electrochemical reactions that typically occur at the electrode surface, where simulation and theory indicate that the GCS theory can have substantial errors, requires modern approaches. New, fundamental experimental studies that would lead to deeper insights using more novel systems would be desirable. Further, biophysics is an interesting field. Recent studies of the selectivity of ion channels and of the adsorption of ions in a binding sites of a protein have shown that the linearized GCS theory has substantial errors.

  17. Flexible nanoporous tunable electrical double layer biosensors for sweat diagnostics.

    PubMed

    Munje, Rujuta D; Muthukumar, Sriram; Panneer Selvam, Anjan; Prasad, Shalini

    2015-09-30

    An ultra-sensitive and highly specific electrical double layer (EDL) modulated biosensor, using nanoporous flexible substrates for wearable diagnostics is demonstrated with the detection of the stress biomarker cortisol in synthetic and human sweat. Zinc oxide thin film was used as active region in contact with the liquid i.e. synthetic and human sweat containing the biomolecules. Cortisol detection in sweat was accomplished by measuring and quantifying impedance changes due to modulation of the double layer capacitance within the electrical double layer through the application of a low orthogonally directed alternating current (AC) electric field. The EDL formed at the liquid-semiconductor interface was amplified in the presence of the nanoporous flexible substrate allowing for measuring the changes in the alternating current impedance signal due to the antibody-hormone interactions at diagnostically relevant concentrations. High sensitivity of detection of 1 pg/mL or 2.75 pmol cortisol in synthetic sweat and 1 ng/mL in human sweat is demonstrated with these novel biosensors. Specificity in synthetic sweat was demonstrated using a cytokine IL-1β. Cortisol detection in human sweat was demonstrated over a concentration range from 10-200 ng/mL.

  18. Flexible nanoporous tunable electrical double layer biosensors for sweat diagnostics

    NASA Astrophysics Data System (ADS)

    Munje, Rujuta D.; Muthukumar, Sriram; Panneer Selvam, Anjan; Prasad, Shalini

    2015-09-01

    An ultra-sensitive and highly specific electrical double layer (EDL) modulated biosensor, using nanoporous flexible substrates for wearable diagnostics is demonstrated with the detection of the stress biomarker cortisol in synthetic and human sweat. Zinc oxide thin film was used as active region in contact with the liquid i.e. synthetic and human sweat containing the biomolecules. Cortisol detection in sweat was accomplished by measuring and quantifying impedance changes due to modulation of the double layer capacitance within the electrical double layer through the application of a low orthogonally directed alternating current (AC) electric field. The EDL formed at the liquid-semiconductor interface was amplified in the presence of the nanoporous flexible substrate allowing for measuring the changes in the alternating current impedance signal due to the antibody-hormone interactions at diagnostically relevant concentrations. High sensitivity of detection of 1 pg/mL or 2.75 pmol cortisol in synthetic sweat and 1 ng/mL in human sweat is demonstrated with these novel biosensors. Specificity in synthetic sweat was demonstrated using a cytokine IL-1β. Cortisol detection in human sweat was demonstrated over a concentration range from 10-200 ng/mL.

  19. Flexible nanoporous tunable electrical double layer biosensors for sweat diagnostics

    PubMed Central

    Munje, Rujuta D.; Muthukumar, Sriram; Panneer Selvam, Anjan; Prasad, Shalini

    2015-01-01

    An ultra-sensitive and highly specific electrical double layer (EDL) modulated biosensor, using nanoporous flexible substrates for wearable diagnostics is demonstrated with the detection of the stress biomarker cortisol in synthetic and human sweat. Zinc oxide thin film was used as active region in contact with the liquid i.e. synthetic and human sweat containing the biomolecules. Cortisol detection in sweat was accomplished by measuring and quantifying impedance changes due to modulation of the double layer capacitance within the electrical double layer through the application of a low orthogonally directed alternating current (AC) electric field. The EDL formed at the liquid-semiconductor interface was amplified in the presence of the nanoporous flexible substrate allowing for measuring the changes in the alternating current impedance signal due to the antibody-hormone interactions at diagnostically relevant concentrations. High sensitivity of detection of 1 pg/mL or 2.75 pmol cortisol in synthetic sweat and 1 ng/mL in human sweat is demonstrated with these novel biosensors. Specificity in synthetic sweat was demonstrated using a cytokine IL-1β. Cortisol detection in human sweat was demonstrated over a concentration range from 10–200 ng/mL. PMID:26420511

  20. Optical and Electrical Characteristics of Graphene Double Layer Formed by a Double Transfer of Graphene Single Layers.

    PubMed

    Kim, Young Jun; Bae, Gi Yoon; Chun, Sungwoo; Park, Wanjun

    2016-03-01

    We demonstrate formation of double layer graphene by means of a double transfer using two single graphene layers grown by a chemical vapor deposition method. It is observed that shiftiness and broadness in the double-resonance of Raman scattering are much weaker than those of bilayer graphene formed naturally. Transport characteristics examined from transmission line measurements and field effect transistors show the similar behavior with those of single layer graphene. It indicates that interlayer separation, in electrical view, is large enough to avoid correlation between layers for the double layer structure. It is also observed from a transistor with the double layer graphene that molecules adsorpted on two inner graphene surfaces in the double layered structure are isolated and conserved from ambient environment.

  1. A novel vibrational energy harvester with electric double layer electrets

    NASA Astrophysics Data System (ADS)

    Ono, S.; Miwa, K.; Iori, J.; Mitsuya, H.; Ishibashi, K.; Sano, C.; Toshiyoshi, H.; Fujita, H.

    2016-11-01

    We propose a new type of vibrational energy harvester with an electric double layer (EDL) electrets. Instead of using any external bias-voltage source or dielectric layer on top of the metal electrode to sustain EDL, we succeed to anchor the ions to polymer network to form the EDL electrets. By changing contact area between the EDL electrets and the electrode, large electric current is generated in the circuit. Owing to extremely large capacitance of the EDL electret, vibrational energy harvesters have the unique capability to leverage the high- density charge accumulation to the electrode and obtained current density becomes as high as 200 μA/cm2 with output voltage of 1V even with low frequency vibrations as low as 1 Hz.

  2. Simulating Electric Double Layer Capacitance by Using Lattice Boltzmann Method

    NASA Astrophysics Data System (ADS)

    Sun, Ning; Gersappe, Dilip

    2015-03-01

    By using the Lattice Boltzmann Method (LBM) we studied diffuse-charge dynamics in electrochemical systems. We use the LBM to solve Poisson-Nernst-Planck equations (PNP) and Modified Poisson-Nernst-Planck equations (MPNP). The isotropic permittivity of electrolyte is modeled using the Booth model. The results show that both steric effect (MPNP) and isotropic permittivity (Booth model) can have large influence on diffuse-charge dynamics, especially when electrolyte concentration or applied potential is high. This model can be applied to simulate electric double layer capacitance of super capacitors with complex geometry and also incorporate other effects such as heat convection in a modular manner.

  3. Field-Induced Superconductivity in Electric Double Layer Transistors

    NASA Astrophysics Data System (ADS)

    Ueno, Kazunori; Shimotani, Hidekazu; Yuan, Hongtao; Ye, Jianting; Kawasaki, Masashi; Iwasa, Yoshihiro

    2014-03-01

    Electric field tuning of superconductivity has been a long-standing issue in solid state physics since the invention of the field-effect transistor (FET) in 1960. Owing to limited available carrier density in conventional FET devices, electric-field-induced superconductivity was believed to be possible in principle but impossible in practice. However, in the past several years, this limitation has been overcome by the introduction of an electrochemical concept, and electric-field-induced superconductivity has been realized. In the electric double layer (EDL) formed at the electrochemical interfaces, an extremely high electric field is generated and hence high-density charge carriers sufficient to induce superconductivity exist and are collectively used as a charge accumulation device known as an EDL capacitor. Field-induced superconductivity has been used to establish the relationship between Tc and carrier density and can now be used to search for new superconductors. Here, we review electric-field-induced superconductivity using an FET device, with a particular focus on the latest advances in EDL transistors.

  4. Performance of electric double layer capacitors with polymer gel electrolytes

    SciTech Connect

    Ishikawa, Masashi; Kishino, Takahiro; Katada, Naoji; Morita, Masayuki

    2000-07-01

    Polymer gel electrolytes consisting of poly(vinylidene fluoride) (PVdF), tetraethylammonium tetrafluoroborate (TEABF{sub 4}), and propylene carbonate (PC) as a plasticizer have been investigated for electric double layer capacitors. The PVdF gel electrolytes showed high ionic conductivity (ca. 6 mS/cm at 298 K). To assemble model capacitors with the PVdF gel electrolytes and activated carbon fiber cloth electrodes, a pair of the fixed electrodes was soaked in a precursor solution containing PC, PVdF, and TEABF{sub 4}, followed by evaporation of the PC solvent in a vacuum oven. The resulting gel electrolytes were in good contact with the electrodes. The model capacitors with the PVdF gel electrolytes showed a large value of capacitance and high coulombic efficiency in operation voltage ranges of 1--2 and 1--3 V. It is worth noting that the capacitors with the PVdF electrolytes showed long voltage retention in a self-discharge test. These good characteristics of the gel capacitors were comparable to those of typical double layer capacitors with a liquid organic electrolyte containing PC and TEABF{sub 4}; rather, the voltage retentivity of the PVdF gel capacitors was much superior to that of the capacitors with the organic electrolyte.

  5. Carbon additives for electrical double layer capacitor electrodes

    NASA Astrophysics Data System (ADS)

    Weingarth, D.; Cericola, D.; Mornaghini, F. C. F.; Hucke, T.; Kötz, R.

    2014-11-01

    Electrochemical double layer capacitors (EDLCs) are inherently high power devices when compared to rechargeable batteries. While capacitance and energy storage ability are mainly increased by optimizing the electrode active material or the electrolyte, the power capability could be improved by including conductive additives in the electrode formulations. This publication deals with the use of four different carbon additives - two carbon blacks and two graphites - in standard activated carbon based EDLC electrodes. The investigations include: (i) physical characterization of carbon powder mixtures such as surface area, press density, and electrical resistivity measurements, and (ii), electrochemical characterization via impedance spectroscopy and cyclic voltammetry of full cells made with electrodes containing 5 wt.% of carbon additive and compared to cells made with pure activated carbon electrodes in organic electrolyte. Improved cell performance was observed in both impedance and cyclic voltammetry responses. The results are discussed considering the main characteristics of the different carbon additives, and important considerations about electrode structure and processability are drawn.

  6. "Thermal Charging" Phenomenon in Electrical Double Layer Capacitors.

    PubMed

    Wang, Jianjian; Feng, Shien-Ping; Yang, Yuan; Hau, Nga Yu; Munro, Mary; Ferreira-Yang, Emerald; Chen, Gang

    2015-09-09

    Electrical double layer capacitors (EDLCs) are usually charged by applying a potential difference across the positive and negative electrodes. In this paper, we demonstrated that EDLCs can be charged by heating. An open circuit voltage of 80-300 mV has been observed by heating the supercapacitor to 65 °C. The charge generated at high temperature can be stored in the device after its returning to the room temperature, thus allowing the lighting up of LEDs by connecting the "thermally charged" supercapacitors in a series. The underlying mechanism is related to a thermo-electrochemical process that enhances the kinetics of Faradaic process at the electrode surface (e.g., surface redox reaction of functional group, or chemical adsorption/desorption of electrolyte ions) at higher temperature. Effects of "thermal charging" times, activation voltage, rate, and times on "thermally charged" voltage are studied and possible mechanisms are discussed.

  7. Structure and dynamics of electrical double layers in organic electrolytes.

    PubMed

    Feng, Guang; Huang, Jingsong; Sumpter, Bobby G; Meunier, Vincent; Qiao, Rui

    2010-01-01

    The organic electrolyte of tetraethylammonium tetrafluoroborate (TEABF(4)) in the aprotic solvent of acetonitrile (ACN) is widely used in electrochemical systems such as electrochemical capacitors. In this paper, we examine the solvation of TEA(+) and BF(4)(-) in ACN, and the structure, capacitance, and dynamics of the electrical double layers (EDLs) in the TEABF(4-)ACN electrolyte using molecular dynamics simulations complemented with quantum density functional theory calculations. The solvation of TEA(+) and BF(4)(-) ions is found to be much weaker than that of small inorganic ions in aqueous solutions, and the ACN molecules in the solvation shell of both types of ions show only weak packing and orientational ordering. These solvation characteristics are caused by the large size, charge delocalization, and irregular shape (in the case of TEA(+) cation) of the ions. Near neutral electrodes, the double-layer structure in the organic electrolyte exhibits a rich organization: the solvent shows strong layering and orientational ordering, ions are significantly contact-adsorbed on the electrode, and alternating layers of cations/anions penetrate ca. 1.1 nm into the bulk electrolyte. The significant contact adsorption of ions and the alternating layering of cation/anion are new features found for EDLs in organic electrolytes. These features essentially originate from the fact that van der Waals interactions between organic ions and the electrode are strong and the partial desolvation of these ions occurs easily, as a result of the large size of the organic ions. Near charged electrodes, distinct counter-ion concentration peaks form, and the ion distribution cannot be described by the Helmholtz model or the Helmholtz + Poisson-Boltzmann model. This is because the number of counter-ions adsorbed on the electrode exceeds the number of electrons on the electrode, and the electrode is over-screened in parts of the EDL. The computed capacitances of the EDLs are in good

  8. Structure and dynamics of electrical double layers in organic electrolytes

    SciTech Connect

    Huang, Jingsong; Sumpter, Bobby G; Meunier, Vincent; Qiao, Rui; Feng, Guang

    2010-01-01

    The organic electrolyte of tetraethylammonium tetrafluoroborate (TEABF{sub 4}) in the aprotic solvent of acetonitrile (ACN) is widely used in electrochemical systems such as electrochemical capacitors. In this paper, we examine the solvation of TEA{sup +} and BF{sub 4}{sup -} in ACN, and the structure, capacitance, and dynamics of the electrical double layers (EDLs) in the TEABF{sub 4}-ACN electrolyte using molecular dynamics simulations complemented with quantum density functional theory calculations. The solvation of TEA+ and BF4- ions is found to be much weaker than that of small inorganic ions in aqueous solutions, and the ACN molecules in the solvation shell of both types of ions show only weak packing and orientational ordering. These solvation characteristics are caused by the large size, charge delocalization, and irregular shape (in the case of TEA+ cation) of the ions. Near neutral electrodes, the double-layer structure in the organic electrolyte exhibits a rich organization: the solvent shows strong layering and orientational ordering, ions are significantly contact-adsorbed on the electrode, and alternating layers of cations/anions penetrate ca. 1.1 nm into the bulk electrolyte. The significant contact adsorption of ions and the alternating layering of cation/anion are new features found for EDLs in organic electrolytes. These features essentially originate from the fact that van der Waals interactions between organic ions and the electrode are strong and the partial desolvation of these ions occurs easily, as a result of the large size of the organic ions. Near charged electrodes, distinct counter-ion concentration peaks form, and the ion distribution cannot be described by the Helmholtz model or the Helmholtz + Poisson-Boltzmann model. This is because the number of counter-ions adsorbed on the electrode exceeds the number of electrons on the electrode, and the electrode is over-screened in parts of the EDL. The computed capacitances of the EDLs are in

  9. Gate-Induced Superconductivity in Layered-Material-Based Electric Double Layer Transistors

    NASA Astrophysics Data System (ADS)

    Ye, J. T.; Zhang, Y. J.; Matsuhashi, Y.; Craciun, M. F.; Russo, S.; Kasahara, Y.; Morpurgo, A. F.; Iwasa, Y.

    2012-12-01

    High carrier density part of many materials could be accessed by a variation of the field effect transistor technique: electric double layer transistor. Carrier density regime of n~1014 cm-2 can be easily accessed electrostatically realizing effective doping without chemical modification. In this study, we utilized micro-cleavage on a number of interesting layered materials. And realized high carrier density state and high performance transport on atomically flat surfaces.

  10. High performance spiro ammonium electrolyte for Electric Double Layer Capacitors

    NASA Astrophysics Data System (ADS)

    DeRosa, Donald; Higashiya, Seiichiro; Schulz, Adam; Rane-Fondacaro, Manisha; Haldar, Pradeep

    2017-08-01

    The smallest spiro ammonium salt reported to date, 1 M 4-Axoniaspiro[3,4]octane tetrafluoroborate (APBF4), was successfully synthesized and investigated as the electrolyte with acetonitrile (AN) in an Electric Double Layer Capacitor (EDLC) for the first time. The electrochemical characteristics of EDLC devices containing 1 M APBF4/AN paired with commercial activated carbon electrodes were compared to devices containing popular EDLC electrolytes, 1 M 5-Azoniaspiro[4.4]nonane tetrafluoroborate (SBPBF4/AN) and 1 M tetraethyl ammonium tetrafluoroborate (TEABF4/AN), using cyclic voltammetry (CV), galvanostatic charge discharge (GCD), and electrochemical impedance spectroscopy (EIS). The average gravimetric capacitance of the 1 M APBF4 device (124.7 F g-1) was found to be greater than the values measured for both the 1 M SBPBF4 device (108.6 F g-1) and the 1 M TEABF4 device (99.2 F g-1). The direct current equivalent series resistance (ESR) of the 1 M APBF4 device (383.4 mΩ cm-2) was found to be substantially lower than the values measured for both the 1 M SBPBF4 device (501.0 mΩ cm-2) and the 1 M TEABF4 device (710.8 mΩ cm-2). These results demonstrate that APBF4, when compared to current commercial electrolytes, significantly enhances the energy storage properties of EDLC devices.

  11. Fast charging self-powered electric double layer capacitor

    NASA Astrophysics Data System (ADS)

    Parida, Kaushik; Bhavanasi, Venkateswarlu; Kumar, Vipin; Wang, Jiangxin; Lee, Pooi See

    2017-02-01

    Self-powered electrochemical energy storage devices, which store energy upon application of mechanical force, have emerged as a promising technology for the realization of autonomous systems for maintenance-free, independent and multifunctional operations. However, the existing state-of-the-art technology demonstrates slow self-charging due to slow Faradaic reactions and intercalation mechanism. Here, we report a fast self-charging, self-powered electrochemical energy storage device owing to the formation of an electric double layer with fast adsorption and desorption of ions at the carbon nanotube (CNT) electrode upon application of mechanical force. The device charges up to 70 mV from the open-circuit potential, storing a capacitance of 95 μFcm-2 upon application of a mechanical pressure of 70 N at a frequency of 5 Hz. More importantly, it takes less than 10 s to achieve 90% of the increment in the potential (60 mV), which is more than one order of magnitude faster than all of the previously reported self-powered energy storage devices.

  12. Weak localization in electric-double-layer gated few-layer graphene

    NASA Astrophysics Data System (ADS)

    Gonnelli, R. S.; Piatti, E.; Sola, A.; Tortello, M.; Dolcini, F.; Galasso, S.; Nair, J. R.; Gerbaldi, C.; Cappelluti, E.; Bruna, M.; Ferrari, A. C.

    2017-09-01

    We induce surface carrier densities up to  ˜7\\centerdot {{10}14} cm-2 in few-layer graphene devices by electric double layer gating with a polymeric electrolyte. In 3-, 4- and 5-layer graphene below 20-30 K we observe a logarithmic upturn of resistance that we attribute to weak localization in the diffusive regime. By studying this effect as a function of carrier density and with ab initio calculations we derive the dependence of transport, intervalley and phase coherence scattering lifetimes on total carrier density. We find that electron-electron scattering in the Nyquist regime is the main source of dephasing at temperatures lower than 30 K in the  ˜1013 cm-2 to  ˜7\\centerdot {{10}14} cm-2 range of carrier densities. With the increase of gate voltage, transport elastic scattering is dominated by the competing effects due to the increase in both carrier density and charged scattering centers at the surface. We also tune our devices into a crossover regime between weak and strong localization, indicating that simultaneous tunability of both carrier and defect density at the surface of electric double layer gated materials is possible.

  13. The polarization of a nanoparticle surrounded by a thick electric double layer.

    PubMed

    Zhao, Hui; Bau, Haim H

    2009-05-15

    The polarization of a charged, dielectric, nanoparticle enveloped by a thick electric double layer and subjected to a uniform, alternating electric field is studied theoretically with the standard model (the Poisson-Nernst-Planck PNP equations). The dipole coefficient (f) is calculated as a function of the electric field's frequency and the double layer's thickness (lambda(D)). For a weakly charged particle with a small zeta potential zeta, an approximate, analytic expression for the dipole moment coefficient, accurate within O(zeta(2)), is derived. Two processes contribute to the dipole moment: the ion transport in the electric double layer under the action of the electric field and the particle's electrophoretic motion. As the thickness of the electric double layer increases so does the importance of the latter. In contrast to the case of the thin electric double layer, the particle with the thick double layer exhibits only high-frequency dispersion. The theoretical predictions are compared and favorably agree with experimental data, leading one to conclude that the standard, PNP based-model adequately represents the behavior of nanoparticles subject to electric fields.

  14. Molecular physics of electrical double layers in electrochemical capacitors

    NASA Astrophysics Data System (ADS)

    Feng, Guang

    At present, electrochemical capacitors (ECs) are emerging as a novel type of energy storage devices and have attracted remarkable attention, due to their key characteristics, such as high power density and excellent durability. However, the moderate energy density of ECs restricts their widespread deployment in everyday technology. To surmount this limitation, four strategies are adopted: (1) to reduce the total system mass, (2) to increase the specific surface area of electrodes, (3) to enhance normalized capacitance, and (4) to expand the range of potentials applied on electrodes. The implementation of these approaches critically relies on the fundamental understanding of physical processes underlying the energy storage mechanisms hinging on the electrical double layers (EDLs) in ECs. In this dissertation, to gain the fundamentals of EDLs in ECs, based on the strategies described above, we studied the structure, capacitance, and dynamics of EDLs in different electrolytes near electrodes featuring different pores using atomistic simulations. The pores of electrodes are categorized into macropores, mesopores, and micropores, following the decreasing order of pore size. The chosen electrolytes fall into aqueous electrolytes, organic electrolytes, and ionic liquids (ILs), listed by the increasing order of their decomposition voltages. For the aqueous electrolytes, we explored the water and ion distributions inside electrified micropores (< 2nm) using molecular dynamics (MD) simulations. The results showed that the ion distribution differs qualitatively from that described by classical EDL theories. Based on such exceptional phenomenon, a new sandwich capacitance model was developed to describe the EDLs inside micropores, which is capable of predicting the sharp increase of capacitance that has been experimentally observed in micropores. For the organic electrolytes, we examined the ion solvation and the EDL structure, capacitance, and dynamics in the electrolyte of

  15. Electric double layer at the interface of ionic liquid-dielectric liquid under electric field.

    PubMed

    Lee, D W; Im, D J; Kang, I S

    2013-02-12

    The structure of the electric double layer (EDL) is analyzed in order to understand the electromechanical behavior of the interface of ionic liquid-dielectric liquid. The modified Poisson-Boltzmann equation proposed by Bazant et al. is solved to see the crowding and the overscreening effects that are the characteristics of an ionic liquid (Bazant, M. Z.; Storey, B. D.; Kornyshev, A. A. Double layer in ionic liquids: Overscreening versus crowding. Phys. Rev. Lett. 2011, 106, 046102.). From the simple one-dimensional (1-D) analysis, it is found that the changes of the composition and the material properties in the EDL are negligible except under some extreme conditions such as strong electric field over O(10(8)) V/m. From the electromechanical view points, an ionic liquid behaves like a pure conductor at the interface with a dielectric liquid. Based on these findings, three specific application problems are considered. In the first, a new method is suggested for measuring the interfacial tension of an ionic liquid-dielectric liquid system. The deformation of a charged ionic liquid droplet translating between two electrodes is used for this measurement. The second is for the Taylor cone problem, which includes an extreme electric field condition near the tip. The size of the critical region, where the EDL effect should be considered, is estimated by using the 1-D analysis result. Numerical computation is also performed to see the profiles of electric potential and the electric stress along the interface of the Taylor cone. Lastly, the electrowetting problem of the ionic liquid is considered. The discrepancies in the results of previous workers are interpreted by using the results of the present work. It is shown that all the results might be consistent if the leaking of the dielectric layer and/or the adsorption of ions is considered.

  16. Dynamical features and electric field strengths of double layers driven by currents. [in auroras

    NASA Technical Reports Server (NTRS)

    Singh, N.; Thiemann, H.; Schunk, R. W.

    1985-01-01

    In recent years, a number of papers have been concerned with 'ion-acoustic' double layers. In the present investigation, results from numerical simulations are presented to show that the shapes and forms of current-driven double layers evolve dynamically with the fluctuations in the current through the plasma. It is shown that double layers with a potential dip can form even without the excitation of ion-acoustic modes. Double layers in two-and one-half-dimensional simulations are discussed, taking into account the simulation technique, the spatial and temporal features of plasma, and the dynamical behavior of the parallel potential distribution. Attention is also given to double layers in one-dimensional simulations, and electrical field strengths predicted by two-and one-half-dimensional simulations.

  17. Electric potential calculation in molecular simulation of electric double layer capacitors

    NASA Astrophysics Data System (ADS)

    Wang, Zhenxing; Olmsted, David L.; Asta, Mark; Laird, Brian B.

    2016-11-01

    For the molecular simulation of electric double layer capacitors (EDLCs), a number of methods have been proposed and implemented to determine the one-dimensional electric potential profile between the two electrodes at a fixed potential difference. In this work, we compare several of these methods for a model LiClO4-acetonitrile/graphite EDLC simulated using both the traditional fixed-charged method (FCM), in which a fixed charge is assigned a priori to the electrode atoms, or the recently developed constant potential method (CPM) (2007 J. Chem. Phys. 126 084704), where the electrode charges are allowed to fluctuate to keep the potential fixed. Based on an analysis of the full three-dimensional electric potential field, we suggest a method for determining the averaged one-dimensional electric potential profile that can be applied to both the FCM and CPM simulations. Compared to traditional methods based on numerically solving the one-dimensional Poisson’s equation, this method yields better accuracy and no supplemental assumptions.

  18. Electric potential calculation in molecular simulation of electric double layer capacitors.

    PubMed

    Wang, Zhenxing; Olmsted, David L; Asta, Mark; Laird, Brian B

    2016-11-23

    For the molecular simulation of electric double layer capacitors (EDLCs), a number of methods have been proposed and implemented to determine the one-dimensional electric potential profile between the two electrodes at a fixed potential difference. In this work, we compare several of these methods for a model LiClO4-acetonitrile/graphite EDLC simulated using both the traditional fixed-charged method (FCM), in which a fixed charge is assigned a priori to the electrode atoms, or the recently developed constant potential method (CPM) (2007 J. Chem. Phys. 126 084704), where the electrode charges are allowed to fluctuate to keep the potential fixed. Based on an analysis of the full three-dimensional electric potential field, we suggest a method for determining the averaged one-dimensional electric potential profile that can be applied to both the FCM and CPM simulations. Compared to traditional methods based on numerically solving the one-dimensional Poisson's equation, this method yields better accuracy and no supplemental assumptions.

  19. Development of high energy density electrical double layer capacitors

    NASA Astrophysics Data System (ADS)

    Devarajan, Thamarai selvi

    Electrochemical Double Layer capacitors (EDLCs) have shown themselves as a viable energy storage alternative. EDLCs have high power density, faster charge/discharge, wide operating temperature and long cycle life compared to batteries since it stores charge by physical separation. Despites all their advantages, their low energy density stand as a bottleneck for capacitors. This research aims to increase the energy density of EDLC without compromising the power density. Energy is proportional to the square of cell voltage. Cell voltage is mainly dependent on electrolyte breakdown. Electrolytes also provide ions for charge separation and conduction. Therefore various electrolytes (Solutes and Solvents) which can give high concentration, solubility and decomposition potential were characterized in the first part of the research. In that study, a novel ionic liquid OPBF4 had higher capacitance and comparable voltage window compared to commercial TEABF4 in Acetonitrile. However, the increased polarity of the fixed ring O-atom and the ion-ion interaction in OPBF4 was responsible for lowering its conductivity. Oxygenated ionic compounds with alkyl groups had lower stability due to beta elimination between two electron withdrawing atoms. Volume based thermodynamics and quantum chemical calculations were used to calculate ion size, HOMO/LUMO energies, and free energy changes and establish relationship with capacitance, redox potential and melting points respectively. In addition free energy of fusion was used to predict the melting point. Ion size had correlation with capacitance due to compact double layer formation. Free energy changes did not explain the differences in melting point and predicted dielectric constant was inconsistent with the polarity. This is presumably due to using Van der Waals volume instead of crystal structure volume and insufficient incorporation of polarization term. The HOMO/LUMO energies gave direct relation between oxidation and reduction

  20. Topological defects in electric double layers of ionic liquids at carbon interfaces

    SciTech Connect

    Black, Jennifer M.; Okatan, Mahmut Baris; Feng, Guang; Cummings, Peter T.; Kalinin, Sergei V.; Balke, Nina

    2015-06-07

    The structure and properties of the electrical double layer in ionic liquids is of interest in a wide range of areas including energy storage, catalysis, lubrication, and many more. Theories describing the electrical double layer for ionic liquids have been proposed, however a full molecular level description of the double layer is lacking. To date, studies have been predominantly focused on ion distributions normal to the surface, however the 3D nature of the electrical double layer in ionic liquids requires a full picture of the double layer structure not only normal to the surface, but also in plane. Here we utilize 3D force mapping to probe the in plane structure of an ionic liquid at a graphite interface and report the direct observation of the structure and properties of topological defects. The observation of ion layering at structural defects such as step-edges, reinforced by molecular dynamics simulations, defines the spatial resolution of the method. Observation of defects allows for the establishment of the universality of ionic liquid behavior vs. separation from the carbon surface and to map internal defect structure. In conclusion, these studies offer a universal pathway for probing the internal structure of topological defects in soft condensed matter on the nanometer level in three dimensions.

  1. Topological defects in electric double layers of ionic liquids at carbon interfaces

    DOE PAGES

    Black, Jennifer M.; Okatan, Mahmut Baris; Feng, Guang; ...

    2015-06-07

    The structure and properties of the electrical double layer in ionic liquids is of interest in a wide range of areas including energy storage, catalysis, lubrication, and many more. Theories describing the electrical double layer for ionic liquids have been proposed, however a full molecular level description of the double layer is lacking. To date, studies have been predominantly focused on ion distributions normal to the surface, however the 3D nature of the electrical double layer in ionic liquids requires a full picture of the double layer structure not only normal to the surface, but also in plane. Here wemore » utilize 3D force mapping to probe the in plane structure of an ionic liquid at a graphite interface and report the direct observation of the structure and properties of topological defects. The observation of ion layering at structural defects such as step-edges, reinforced by molecular dynamics simulations, defines the spatial resolution of the method. Observation of defects allows for the establishment of the universality of ionic liquid behavior vs. separation from the carbon surface and to map internal defect structure. In conclusion, these studies offer a universal pathway for probing the internal structure of topological defects in soft condensed matter on the nanometer level in three dimensions.« less

  2. Toward the Theory of an Electric Double Layer in a Plasma

    NASA Astrophysics Data System (ADS)

    Gutsev, S. A.

    2017-07-01

    The conditions for the appearance of a double layer are considered. A theoretical description of the latter is given. Based on experimental data on probe diagnostics of oxygen and helium plasmas, a self-consistent theory of the volume charge layer is being constructed. Analysis of the phenomenon of screening the probe potential by charged particles is carried out. The procedure used for correcting the particle temperature determined by the logarithmic operation method is presented. The problem of application of Langmuir probes, the 3/2 law, and of the theory of electric double layer in a plasma is discussed.

  3. Formating double layer mechanism by electric charged particle stream in plasma

    NASA Astrophysics Data System (ADS)

    Shan-jun, Ma; Qian-li, Yang; Xiao-qing, Li

    1998-08-01

    In this paper, two-fluid equations have been solved after having considered magnetic field generated by charged particle stream. Finally, the distribution of electric field Ez(z, r) and its growth rate γ in plasma have been obtained. From the expression of Ez(z, r) it can be known that the double layer has been formed. With the increase of disturbance γ will be larger, and finally this will result in the interruption of electric current and occurrence of burst.

  4. Interaction between electrical double layers of soil colloids and Fe/Al oxides in suspensions.

    PubMed

    Hou, Tao; Xu, Renkou; Tiwari, Diwakar; Zhao, Anzhen

    2007-06-15

    Phyllosilicates with net negative surface charge and Fe/Al oxides with net positive surface charge coexist in variable-charge soils, and the interaction between these oppositely charged particles affects the stability of mixed colloids, aggregation, and even the surface chemical properties of variable-charge soils. The interaction of the diffuse layers of electrical double layers between the negatively charged soil colloidal particles and the positively charged particles of goethite or gamma-Al(2)O(3) was investigated in this article through the comparison of zeta potentials between single-soil colloidal systems and binary systems containing soil colloids and Fe/Al oxides. The results showed that the presence of goethite and gamma-Al(2)O(3) increased the zeta potential of the binary system containing soil colloids and Fe/Al oxides, which clearly suggests the overlapping of the diffuse layers in soil colloids and Fe/Al oxides. The overlapping of the diffuse layers leads to a decrease in the effective negative charge density on soil colloid and thus causes a shift of pH-zeta potential curves toward the more positive-value side. The interaction of the electrical double layers is also related to the charge characteristics on the Fe/Al oxides: the higher the positive charge density on Fe/Al oxides, the stronger the interaction of the electrical double layers between the soil colloid particles and the Fe/Al oxides.

  5. Skin electric explosion in double-layer conductors with a low-conductivity deposited layer

    NASA Astrophysics Data System (ADS)

    Datsko, I. M.; Labetskaya, N. A.; Chaikovsky, S. A.; Shugurov, V. V.

    2016-06-01

    The experiments on explosion of cylindrical conductors aimed at comparison of plasma formation during skin explosion of homogeneous and double-layer conductors with an external layer with a lower conductivity are carried out on a high-current MIG generator (current amplitude up to 2.5 MA and current rise time 100 ns). The generator is loaded with cylindrical copper conductors with a diameter of 3 mm on the cathode part of which a titanium layer of thickness 20, 50, and 80 μm is deposited in vacuum. This type of loading makes it possible to compare the behaviors of the homogeneous and double-layer conductors in identical conditions. It is shown that using the double-layer structure of the conductor with an external layer of thickness 20-80 μm with a lower conductivity, which is obtained by vacuum arc deposition, higher values of magnetic induction (as compared to homogeneous conductor) can be attained on its surface prior to plasma formation and spread.

  6. Spherical electric double layers containing mixed electrolytes: A case study for multivalent counterions

    NASA Astrophysics Data System (ADS)

    Patra, Chandra N.

    2017-10-01

    Spherical electric double layers containing mixed electrolytes with multivalent counterions, is studied using density functional theory and Monte Carlo simulation. The macroion and small ions are represented as uniformly charged hard spheres within a continuum solvent. The theory involves an weighted density approximation for the hard-sphere contribution, whereas the electrical part is evaluated through a functional expansion around the uniform fluid. The system includes a number of parameters, viz. ionic concentrations, macroion charge density, and the valence of the counterion. This study points towards the distinctive evidence of size and charge correlations manifested through layering and charge reversal phenomena.

  7. Role of the electric double layer in the ice nucleation of water droplets under an electric field

    NASA Astrophysics Data System (ADS)

    Zhang, Xiang-Xiong; Li, Xin-Hao; Chen, Min

    2016-09-01

    Figuring out the mechanism of ice nucleation on charged aerosols or in thunderstorms is of fundamental importance in atmospheric science. However, findings on whether the electric field promotes or suppresses heterogeneous ice nucleation are conflicting. In this work, we design an apparatus and test the influence of the electric field on ice nucleation by freezing a series of deionized water droplets resting on solid surfaces with an electric field perpendicular to the substrates. Results show that ice nucleation is obviously promoted under the electric field and is independent of the field direction. Theoretic analyses show that the promotion is due to the reduction of Gibbs free energy which can be partially rationalized by the electric field sustained in the electric double layer at the solid-water interface, with strength about two orders higher than that of the external electric field. Moreover, water-droplet deformation under the electric field is not expected to be the cause of the ice-nucleation promotion.

  8. Tunable surface electron spin splitting with electric double-layer transistors based on InN.

    PubMed

    Yin, Chunming; Yuan, Hongtao; Wang, Xinqiang; Liu, Shitao; Zhang, Shan; Tang, Ning; Xu, Fujun; Chen, Zhuoyu; Shimotani, Hidekazu; Iwasa, Yoshihiro; Chen, Yonghai; Ge, Weikun; Shen, Bo

    2013-05-08

    Electrically manipulating electron spins based on Rashba spin-orbit coupling (SOC) is a key pathway for applications of spintronics and spin-based quantum computation. Two-dimensional electron systems (2DESs) offer a particularly important SOC platform, where spin polarization can be tuned with an electric field perpendicular to the 2DES. Here, by measuring the tunable circular photogalvanic effect (CPGE), we present a room-temperature electric-field-modulated spin splitting of surface electrons on InN epitaxial thin films that is a good candidate to realize spin injection. The surface band bending and resulting CPGE current are successfully modulated by ionic liquid gating within an electric double-layer transistor configuration. The clear gate voltage dependence of CPGE current indicates that the spin splitting of the surface electron accumulation layer is effectively tuned, providing a way to modulate the injected spin polarization in potential spintronic devices.

  9. Study of Electrical Conduction Mechanism of Organic Double-Layer Diode Using Electric Field Induced Optical Second Harmonic Generation Measurement.

    PubMed

    Nishi, Shohei; Taguchi, Dai; Manaka, Takaaki; Iwamoto, Mitsumasa

    2016-04-01

    By using electric field induced optical second harmonic generation (EFISHG) and current voltage (I-V) measurements, we studied the electrical transport mechanism of organic double-layer diodes with a structure of Au/N, N'-di-[(1-naphthyl)-N, N'-diphenyl]-(1,1'-biphenyl)-4,4'-diamine (a-NPD)/poly(methyl methacrylate) (PMMA)/indium zinc oxide (IZO). Here the α-NPD is a carrier transport layer and the PMMA is an electrical insulating layer. The current level was very low, but the I-V characteristics showed a rectifying behavior. The EFISHG measurement selectively and directly probed the electric field across the α-NPD layer, and showed that the electric field across the a-NPD layer is completely relaxed owing to the charge accumulation at the a-NPD/PMMA interface in the region V > 0, whereas the carrier accumulation was not significant in the region V < 0. On the basis of these experimental results, we proposed a model of the rectification. Further, by coupling the I-V characteristics with the EFISHG measurement, the I-V characteristics of the diodes were well converted into the current-electric field (I-E) characteristics of the α-NPD layer and the PMMA layer. The I-E characteristics suggested the Schottky-type conduction governs the carrier transport. We conclude that the I-V measurement coupled with the EFISHG measurement is very useful to study carrier transport mechanism of the organic double-layer diodes.

  10. Electrical Double Layer Capacitance in a Graphene-embedded Al2O3 Gate Dielectric.

    PubMed

    Ki Min, Bok; Kim, Seong K; Jun Kim, Seong; Ho Kim, Sung; Kang, Min-A; Park, Chong-Yun; Song, Wooseok; Myung, Sung; Lim, Jongsun; An, Ki-Seok

    2015-11-04

    Graphene heterostructures are of considerable interest as a new class of electronic devices with exceptional performance in a broad range of applications has been realized. Here, we propose a graphene-embedded Al2O3 gate dielectric with a relatively high dielectric constant of 15.5, which is about 2 times that of Al2O3, having a low leakage current with insertion of tri-layer graphene. In this system, the enhanced capacitance of the hybrid structure can be understood by the formation of a space charge layer at the graphene/Al2O3 interface. The electrical properties of the interface can be further explained by the electrical double layer (EDL) model dominated by the diffuse layer.

  11. Electrical Double Layer Capacitance in a Graphene-embedded Al2O3 Gate Dielectric

    PubMed Central

    Ki Min, Bok; Kim, Seong K.; Jun Kim, Seong; Ho Kim, Sung; Kang, Min-A; Park, Chong-Yun; Song, Wooseok; Myung, Sung; Lim, Jongsun; An, Ki-Seok

    2015-01-01

    Graphene heterostructures are of considerable interest as a new class of electronic devices with exceptional performance in a broad range of applications has been realized. Here, we propose a graphene-embedded Al2O3 gate dielectric with a relatively high dielectric constant of 15.5, which is about 2 times that of Al2O3, having a low leakage current with insertion of tri-layer graphene. In this system, the enhanced capacitance of the hybrid structure can be understood by the formation of a space charge layer at the graphene/Al2O3 interface. The electrical properties of the interface can be further explained by the electrical double layer (EDL) model dominated by the diffuse layer. PMID:26530817

  12. External electric field dependence of the structure of the electric double layer at an ionic liquid/Au interface

    NASA Astrophysics Data System (ADS)

    Yamamoto, Ryosuke; Morisaki, Hazuki; Sakata, Osami; Shimotani, Hidekazu; Yuan, Hongtao; Iwasa, Yoshihiro; Kimura, Tsuyoshi; Wakabayashi, Yusuke

    2012-07-01

    In order to clarify its electric double layer (EDL) structure under external voltage, an interface between the ionic liquid N,N-diethyl-N-methyl-N-(2-methoxyethyl)ammonium bis(trifluoromethanesulfonyl)imide and a Au (111) surface was studied by x-ray reflectometry. A clear change in reflectivity was observed as a function of applied voltage. The electron density profile of the ionic liquid around the interface was calculated using liquid structure models. Switching of the external electric field reversed the polarity of the EDL, and the magnitude of the applied voltage controlled the magnitude of the layering structure as well as molecular position fluctuation.

  13. Molecular simulation of electric double-layer capacitors based on carbon nanotube forests.

    PubMed

    Yang, Lu; Fishbine, Brian H; Migliori, Albert; Pratt, Lawrence R

    2009-09-02

    Described here are the first simulations of electric double-layer capacitors based on carbon nanotube forests modeled fully at a molecular level. The computations determine single-electrode capacitances in the neighborhood of 80 F/g, in agreement with experimental capacitances of electric double-layer capacitors utilizing carbon nanotube forests or carbide-derived carbons as electrode material. The capacitance increases modestly with the decrease of the pore size through radii greater than 1 nm, which is consistent with recent experiments on carbide-derived carbon electrodes. Because the various factors included in these simulations are precisely defined, these simulation data will help to disentangle distinct physical chemical factors that contribute to the performance of these materials, e.g., pore geometry, variable filling of the pores, pseudocapacitance, and electronic characteristics of the nanotubes.

  14. Double-gate SnO{sub 2} nanowire electric-double-layer transistors with tunable threshold voltage

    SciTech Connect

    Liu, Huixuan

    2015-06-08

    Double-gate Sb-SnO{sub 2} nanowire electric-double-layer (EDL) transistors with in-plane gates were fabricated using only one shadow mask. The threshold voltage of such devices can be tuned in a wide range from −0.13 V to 0.72 V by the in-plane gate, which allows the device to switch from depletion-mode to enhancement-mode operation. The operation voltage of the double-gate device is 1 V because the EDL gate dielectric can lead to a high gate capacitance (>3.5 μF/cm{sup 2}). Moreover, all double-gate devices show good electrical characteristics with high field-effect mobility (>200 cm{sup 2}/V·s), high drain-current I{sub on/off} ratio (>7 × 10{sup 4}), and small subthreshold slope (<100 mV/dec). These double-gate nanowire EDL transistors can pave the way for an electrically working low-voltage nano-electronic process.

  15. Novel electric double-layer capacitor with a coaxial fiber structure.

    PubMed

    Chen, Xuli; Qiu, Longbin; Ren, Jing; Guan, Guozhen; Lin, Huijuan; Zhang, Zhitao; Chen, Peining; Wang, Yonggang; Peng, Huisheng

    2013-11-26

    A coaxial electric double-layer capacitor fiber is developed from the aligned carbon nanotube fiber and sheet, which functions as two electrodes with a polymer gel sandwiched between them. The unique coaxial structure enables a rapid transportation of ions between the two electrodes with a high electrochemical performance. These energy storage fibers are also flexible and stretchable, and can be woven into and widely used for electronic textiles.

  16. The electric double layer at a metal electrode in pure water

    NASA Astrophysics Data System (ADS)

    Brüesch, Peter; Christen, Thomas

    2004-03-01

    Pure water is a weak electrolyte that dissociates into hydronium ions and hydroxide ions. In contact with a charged electrode a double layer forms for which neither experimental nor theoretical studies exist, in contrast to electrolytes containing extrinsic ions like acids, bases, and solute salts. Starting from a self-consistent solution of the one-dimensional modified Poisson-Boltzmann equation, which takes into account activity coefficients of point-like ions, we explore the properties of the electric double layer by successive incorporation of various correction terms like finite ion size, polarization, image charge, and field dissociation. We also discuss the effect of the usual approximation of an average potential as required for the one-dimensional Poisson-Boltzmann equation, and conclude that the one-dimensional approximation underestimates the ion density. We calculate the electric potential, the ion distributions, the pH-values, the ion-size corrected activity coefficients, and the dissociation constants close to the electric double layer and compare the results for the various model corrections.

  17. The capacitance of ionic liquid electric double layer near nanostructured electrodes

    NASA Astrophysics Data System (ADS)

    Park, Yun Sung; Ahn, Myung Mo; Kang, In Seok

    2015-11-01

    The electric double layer capacitors (EDLC) with nanostructured electrodes have attracted much attention of researchers due to their high power density and long life time. Recently, the ionic liquids are used as an electrolyte of EDLC owing to their electrochemical stability. When ionic liquids are used as an electrolyte, the interrelations between the electric double layer of ionic liquids and the nanostructured electrode must be studied. In this study, the EDLC systems with nanostructured electrodes and ionic liquids are simulated by solving the modified Poisson-Boltzmann equation proposed by Bazant, Storey, and Kornyshev with COMSOL Multiphysics. Several electrode geometries including exohedral, endohedral and arrayed shapes with different length scales are simulated. The potential and charge distributions in the normal direction to the electrode surface are analyzed. The capacitance per unit area is obtained and compared to that of flat electrode. The structure determines the space for counter-ion packing and co-ion gathering, thus has crucial effects on electric double layer capacitance. The critical increase of capacitance with nanoscale confined space is observed with low electrode potential. This research was supported by Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Science, ICT and Future Planning (Grant Number: 2013R1A1A2011956).

  18. A new correlation effect in the Helmholtz and surface potentials of the electrical double layer.

    PubMed

    González-Tovar, Enrique; Jiménez-Angeles, Felipe; Messina, René; Lozada-Cassou, Marcelo

    2004-05-22

    The restricted primitive model of an electrical double layer around a spherical macroparticle is studied by using integral equation theories and Monte Carlo simulations. The resulting theoretical curves for the Helmholtz and surface potentials versus the macroparticle charge show an unexpected positive curvature when the ionic size of uni- and divalent electrolyte species is increased. This is a novel effect that is confirmed here by computer experiments. An explanation of this phenomenon is advanced in terms of the adsorption and layering of the electrolytic species and of the compactness of the diffuse double layer. It is claimed that the interplay between electrostatic and ionic size correlation effects, absent in the classical Poisson-Boltzmann view, is responsible for this singularity.

  19. Asymptotic theory of double layer and shielding of electric field at the edge of illuminated plasma

    SciTech Connect

    Benilov, M. S.; Thomas, D. M.

    2014-04-15

    The method of matched asymptotic expansions is applied to the problem of a collisionless plasma generated by UV illumination localized in a central part of the plasma in the limiting case of small Debye length λ{sub D}. A second-approximation asymptotic solution is found for the double layer positioned at the boundary of the illuminated region and for the un-illuminated plasma for the plane geometry. Numerical calculations for different values of λ{sub D} are reported and found to confirm the asymptotic results. The net integral space charge of the double layer is asymptotically small, although in the plane geometry it is just sufficient to shield the ambipolar electric field existing in the illuminated region and thus to prevent it from penetrating into the un-illuminated region. The double layer has the same mathematical nature as the intermediate transition layer separating an active plasma and a collisionless sheath, and the underlying physics is also the same. In essence, the two layers represent the same physical object: a transonic layer.

  20. Study of surface charge density on solid/liquid interfaces by modulating the electrical double layer

    NASA Astrophysics Data System (ADS)

    Pak, Hyuk Kyu; Moon, Jong Kyun

    2014-11-01

    A solid surface in contact with water or aqueous solution usually carries specific electric charges. These surface charges attract counter ions from the liquid side. Since the geometry of opposite charge distribution parallel to the solid/liquid interface is similar to that of a capacitor, it is called an electrical double layer capacitor (EDLC). Therefore, there is an electrical potential difference across an EDLC in equilibrium. When a liquid bridge is formed between two conducting plates, the system behaves as two serially connected EDLCs. In this work, we propose a new method for investigating the surface charge density on solid/liquid interfaces. By mechanically modulating the electrical double layers and simultaneously applying a DC bias voltage across the plates, an AC electric current can be generated. By measuring the voltage difference between the plates as a function of bias voltage, we can study the surface charge density on solid/liquid interfaces. Our experimental results agree very well with the simple equivalent circuit model proposed here. Furthermore, using this method, one can determine the polarity of the adsorbed state on the solid surface depending on the material used. This work was supported by Center for Soft and Living Matter through IBS program in Korea.

  1. Boosted output performance of triboelectric nanogenerator via electric double layer effect

    NASA Astrophysics Data System (ADS)

    Chun, Jinsung; Ye, Byeong Uk; Lee, Jae Won; Choi, Dukhyun; Kang, Chong-Yun; Kim, Sang-Woo; Wang, Zhong Lin; Baik, Jeong Min

    2016-10-01

    For existing triboelectric nanogenerators (TENGs), it is important to explore unique methods to further enhance the output power under realistic environments to speed up their commercialization. We report here a practical TENG composed of three layers, in which the key layer, an electric double layer, is inserted between a top layer, made of Al/polydimethylsiloxane, and a bottom layer, made of Al. The efficient charge separation in the middle layer, based on Volta's electrophorus, results from sequential contact configuration of the TENG and direct electrical connection of the middle layer to the earth. A sustainable and enhanced output performance of 1.22 mA and 46.8 mW cm-2 under low frequency of 3 Hz is produced, giving over 16-fold enhancement in output power and corresponding to energy conversion efficiency of 22.4%. Finally, a portable power-supplying system, which provides enough d.c. power for charging a smart watch or phone battery, is also successfully developed.

  2. Boosted output performance of triboelectric nanogenerator via electric double layer effect

    PubMed Central

    Chun, Jinsung; Ye, Byeong Uk; Lee, Jae Won; Choi, Dukhyun; Kang, Chong-Yun; Kim, Sang-Woo; Wang, Zhong Lin; Baik, Jeong Min

    2016-01-01

    For existing triboelectric nanogenerators (TENGs), it is important to explore unique methods to further enhance the output power under realistic environments to speed up their commercialization. We report here a practical TENG composed of three layers, in which the key layer, an electric double layer, is inserted between a top layer, made of Al/polydimethylsiloxane, and a bottom layer, made of Al. The efficient charge separation in the middle layer, based on Volta's electrophorus, results from sequential contact configuration of the TENG and direct electrical connection of the middle layer to the earth. A sustainable and enhanced output performance of 1.22 mA and 46.8 mW cm−2 under low frequency of 3 Hz is produced, giving over 16-fold enhancement in output power and corresponding to energy conversion efficiency of 22.4%. Finally, a portable power-supplying system, which provides enough d.c. power for charging a smart watch or phone battery, is also successfully developed. PMID:27703165

  3. Boosted output performance of triboelectric nanogenerator via electric double layer effect.

    PubMed

    Chun, Jinsung; Ye, Byeong Uk; Lee, Jae Won; Choi, Dukhyun; Kang, Chong-Yun; Kim, Sang-Woo; Wang, Zhong Lin; Baik, Jeong Min

    2016-10-05

    For existing triboelectric nanogenerators (TENGs), it is important to explore unique methods to further enhance the output power under realistic environments to speed up their commercialization. We report here a practical TENG composed of three layers, in which the key layer, an electric double layer, is inserted between a top layer, made of Al/polydimethylsiloxane, and a bottom layer, made of Al. The efficient charge separation in the middle layer, based on Volta's electrophorus, results from sequential contact configuration of the TENG and direct electrical connection of the middle layer to the earth. A sustainable and enhanced output performance of 1.22 mA and 46.8 mW cm(-2) under low frequency of 3 Hz is produced, giving over 16-fold enhancement in output power and corresponding to energy conversion efficiency of 22.4%. Finally, a portable power-supplying system, which provides enough d.c. power for charging a smart watch or phone battery, is also successfully developed.

  4. Bias-free, solar-charged electric double-layer capacitors

    NASA Astrophysics Data System (ADS)

    Wu, Hao; Geng, Jing; Wang, Yuhang; Wang, Yanli; Peng, Zheng; Zheng, Gengfeng

    2014-11-01

    The conversion of solar energy with simultaneous electric energy storage provides a promising means for optimizing energy utilization efficiency and reducing device volume. In this paper, a 3-dimensional mesoporous carbon coated branched TiO2 nanowire composite is rationally designed for direct conversion and storage of solar energy as electric double-layer capacitive energy. The 1-dimensional, crystalline TiO2 trunks serve as long light absorption and continuous charge transport pathways, and the high-density TiO2 branches can efficiently increase the contact area with the surface coated mesoporous carbon layers. In addition, the ordered and uniformed mesopores provide large pore sizes for electrolyte penetration, and a high surface area for charge absorption and storage. Under a 1-sun illumination and no external electric bias, this branched TiO2/mesoporous carbon composite exhibits specific capacitances of over 30 and 23.4 F g-1, at current densities of 0.1 and 0.5 A g-1, respectively. An excellent stability of >50 photocharging-electrical discharging cycles has also been demonstrated, suggesting the potential of further developing this hybrid material structure for simultaneous solar conversion and electric energy storage.The conversion of solar energy with simultaneous electric energy storage provides a promising means for optimizing energy utilization efficiency and reducing device volume. In this paper, a 3-dimensional mesoporous carbon coated branched TiO2 nanowire composite is rationally designed for direct conversion and storage of solar energy as electric double-layer capacitive energy. The 1-dimensional, crystalline TiO2 trunks serve as long light absorption and continuous charge transport pathways, and the high-density TiO2 branches can efficiently increase the contact area with the surface coated mesoporous carbon layers. In addition, the ordered and uniformed mesopores provide large pore sizes for electrolyte penetration, and a high surface area for

  5. Structure of an electric double layer containing a 2:2 valency dimer electrolyte

    DOE PAGES

    Silvestre-Alcantara, Whasington; Henderson, Douglas; Wu, Jianzhong; ...

    2014-12-05

    In this study, the structure of a planar electric double layer formed by a 2:2 valency dimer electrolyte in the vicinity of a uniformly charged planar hard electrode is investigated using density functional theory and Monte Carlo simulations. The dimer electrolyte consists of a mixture of charged divalent dimers and charged divalent monomers in a dielectric continuum. A dimer is constructed by two tangentially tethered rigid spheres, one of which is divalent and positively charged and the other neutral, whereas the monomer is a divalent and negatively charged rigid sphere. The density functional theory reproduces well the simulation results formore » (i) the singlet distributions of the various ion species with respect to the electrode, and (ii) the mean electrostatic potential. Lastly, comparison with earlier results for a 2:1/1:2 dimer electrolyte shows that the double layer structure is similar when the counterion has the same valency.« less

  6. Structure of an electric double layer containing a 2:2 valency dimer electrolyte

    SciTech Connect

    Silvestre-Alcantara, Whasington; Henderson, Douglas; Wu, Jianzhong; Kaja, Monika; Lamperski, Stanisław; Bhuiyan, Lutful Bari

    2014-12-05

    In this study, the structure of a planar electric double layer formed by a 2:2 valency dimer electrolyte in the vicinity of a uniformly charged planar hard electrode is investigated using density functional theory and Monte Carlo simulations. The dimer electrolyte consists of a mixture of charged divalent dimers and charged divalent monomers in a dielectric continuum. A dimer is constructed by two tangentially tethered rigid spheres, one of which is divalent and positively charged and the other neutral, whereas the monomer is a divalent and negatively charged rigid sphere. The density functional theory reproduces well the simulation results for (i) the singlet distributions of the various ion species with respect to the electrode, and (ii) the mean electrostatic potential. Lastly, comparison with earlier results for a 2:1/1:2 dimer electrolyte shows that the double layer structure is similar when the counterion has the same valency.

  7. Density functional study of the electric double layer formed by a high density electrolyte.

    PubMed

    Henderson, Douglas; Lamperski, Stanisław; Jin, Zhehui; Wu, Jianzhong

    2011-11-10

    We use a classical density functional theory (DFT) to study the electric double layer formed by charged hard spheres near a planar charged surface. The DFT predictions are found to be in good agreement with recent computer simulation results. We study the capacitance of the charged hard-sphere system at a range of densities and surface charges and find that the capacitance exhibits a local minimum at low ionic densities and small electrode charge. Although this charging behavior is typical for an aqueous electrolyte solution, the local minimum gradually turns into a maximum as the density of the hard spheres increases. Charged hard spheres at high density provide a reasonable first approximation for ionic liquids. In agreement with experiment, the capacitance of this model ionic liquid double layer has a maximum at small electrode charge density.

  8. Double layer electric fields aiding the production of superthermal electrons within magnetic reconnection exhausts

    NASA Astrophysics Data System (ADS)

    Egedal, Jan; Daughton, William; Le, Ari

    2015-11-01

    Using a kinetic simulation of magnetic reconnection it was recently shown that parallel electric fields (E∥) can be present over large spatial scales in reconnection exhausts. The largest values of E∥ are observed within double layers, which form through large parallel streaming of electrons into the reconnection region. The electron confinement, provided in part by the structure in E∥, allows sustained energization by perpendicular electric fields (E⊥). The energization is a consequence of the confined electrons' chaotic orbital motion that includes drifts aligned with the reconnection electric field. The mechanism is effective in an extended region of the reconnection exhaust allowing for the generation of superthermal electrons in reconnection scenarios, including those with only a single x-line. The numerical and analytical results agree with detailed spacecraft observations recorded during reconnection events in the Earth's magnetotail. Supported by NSF GEM award 1405166 and NASA grant NNX14AC68G.

  9. Electric double-layer capacitors based on highly graphitized nanoporous carbons derived from ZIF-67.

    PubMed

    Torad, Nagy L; Salunkhe, Rahul R; Li, Yunqi; Hamoudi, Hicham; Imura, Masataka; Sakka, Yoshio; Hu, Chi-Chang; Yamauchi, Yusuke

    2014-06-23

    Nanoporous carbons (NPCs) have large specific surface areas, good electrical and thermal conductivity, and both chemical and mechanical stability, which facilitate their use in energy storage device applications. In the present study, highly graphitized NPCs are synthesized by one-step direct carbonization of cobalt-containing zeolitic imidazolate framework-67 (ZIF-67). After chemical etching, the deposited Co content can be completely removed to prepare pure NPCs with high specific surface area, large pore volume, and intrinsic electrical conductivity (high content of sp(2) -bonded carbons). A detailed electrochemical study is performed using cyclic voltammetry and galvanostatic charge-discharge measurements. Our NPC is very promising for efficient electrodes for high-performance supercapacitor applications. A maximum specific capacitance of 238 F g(-1) is observed at a scan rate of 20 mV s(-1) . This value is very high compared to previous works on carbon-based electric double layer capacitors.

  10. Bias-free, solar-charged electric double-layer capacitors.

    PubMed

    Wu, Hao; Geng, Jing; Wang, Yuhang; Wang, Yanli; Peng, Zheng; Zheng, Gengfeng

    2014-12-21

    The conversion of solar energy with simultaneous electric energy storage provides a promising means for optimizing energy utilization efficiency and reducing device volume. In this paper, a 3-dimensional mesoporous carbon coated branched TiO2 nanowire composite is rationally designed for direct conversion and storage of solar energy as electric double-layer capacitive energy. The 1-dimensional, crystalline TiO2 trunks serve as long light absorption and continuous charge transport pathways, and the high-density TiO2 branches can efficiently increase the contact area with the surface coated mesoporous carbon layers. In addition, the ordered and uniformed mesopores provide large pore sizes for electrolyte penetration, and a high surface area for charge absorption and storage. Under a 1-sun illumination and no external electric bias, this branched TiO2/mesoporous carbon composite exhibits specific capacitances of over 30 and 23.4 F g(-1), at current densities of 0.1 and 0.5 A g(-1), respectively. An excellent stability of >50 photocharging-electrical discharging cycles has also been demonstrated, suggesting the potential of further developing this hybrid material structure for simultaneous solar conversion and electric energy storage.

  11. Structure and charging kinetics of electrical double layers at large electrode voltage

    SciTech Connect

    Cagle, Clint; Feng, Guang; Qiao, Rui; Huang, Jingsong; Sumpter, Bobby G; Meunier, Vincent

    2009-01-01

    The structure and charging kinetics of electrical double layers (EDLs) at interfaces of NaCl solutions and planar electrodes are studied by molecular dynamics (MD) and Poisson Nernst Planck (PNP) simulations. Based on the MD results and prior experimental data, we show that counterion packing in planar EDLs does not reach the steric limit at electrode voltages below 1 V. In addition, we demonstrate that a PNP model, when complemented with a Stern model, can be effectively used to capture the overall charging kinetics. However, the PNP/Stern model can only give a qualitative description of the fine features of the EDL.

  12. Effects of mixed discrete surface charges on the electrical double layer.

    PubMed

    Jiménez-Ángeles, Felipe

    2012-08-01

    Adsorption of surface coions and charge reversal are induced at the electrical double layer of a wall charged with positive and negative surface sites next to an electrolyte solution. While for the considered surface charge density these effects are found over a wide range of conditions, they are not observed for the typically employed surface models in equivalent conditions. Important consequences in electrophoresis experiments for different colloids with equal effective surface charge density are foreseen. This study is carried out by means of molecular dynamics simulations.

  13. Electric Double Layer Gate Field-Effect Transistors Based on Si

    NASA Astrophysics Data System (ADS)

    Takashi Yanase,; Toshihiro Shimada,; Tetsuya Hasegawa,

    2010-04-01

    Electric double layer field-effect transistors (EDL-FETs) were fabricated using single crystal Si wafer as the active semiconductor and various characteristics were studied including dynamic response against step-function gate bias. The static FET mobility was more than 100 cm2 V-1 s-1. The response time of the drain current was 20 μs for ionic liquid and 3 ms for poly(ethylene glycol) (PEG) solution of LiBF4. Unexpected fast response was observed at a certain “speed up bias” condition. This effect will be useful to switching circuits using EDL-FETs.

  14. Electric Double Layer Gate Field-Effect Transistors Based on Si

    NASA Astrophysics Data System (ADS)

    Yanase, Takashi; Shimada, Toshihiro; Hasegawa, Tetsuya

    2010-04-01

    Electric double layer field-effect transistors (EDL-FETs) were fabricated using single crystal Si wafer as the active semiconductor and various characteristics were studied including dynamic response against step-function gate bias. The static FET mobility was more than 100 cm2 V-1 s-1. The response time of the drain current was 20 µs for ionic liquid and 3 ms for poly(ethylene glycol) (PEG) solution of LiBF4. Unexpected fast response was observed at a certain “speed up bias” condition. This effect will be useful to switching circuits using EDL-FETs.

  15. A simple algorithm for calculating electrical double layer interactions in asymmetric electrolytes-Poisson-Boltzmann theory.

    PubMed

    Chan, Derek Y C

    2002-01-15

    A simple, general, and numerically robust algorithm is presented for calculating the disjoining pressure and interaction free energy per unit area between two identically charged flat plates due to electrical double layer interactions according to the nonlinear Poisson-Boltzmann theory. The result is applicable to electrolytes with any number of ionic species having any combination of valencies as well as to constant potential, constant charge, or charge regulation boundary conditions on the plates. The algorithm is very simple to implement on commonly available numerical software environments and is therefore particularly suitable for use in data analysis.

  16. Simulation of electric double-layer capacitors: evaluation of constant potential method

    NASA Astrophysics Data System (ADS)

    Wang, Zhenxing; Laird, Brian; Yang, Yang; Olmsted, David; Asta, Mark

    2014-03-01

    Atomistic simulations can play an important role in understanding electric double-layer capacitors (EDLCs) at a molecular level. In such simulations, typically the electrode surface is modeled using fixed surface charges, which ignores the charge fluctuation induced by local fluctuations in the electrolyte solution. In this work we evaluate an explicit treatment of charges, namely constant potential method (CPM)[1], in which the electrode charges are dynamically updated to maintain constant electrode potential. We employ a model system with a graphite electrode and a LiClO4/acetonitrile electrolyte, examined as a function of electrode potential differences. Using various molecular and macroscopic properties as metrics, we compare CPM simulations on this system to results using fixed surface charges. Specifically, results for predicted capacity, electric potential gradient and solvent density profile are identical between the two methods; However, ion density profiles and solvation structure yield significantly different results.

  17. Molecular Simulations of Graphene-Based Electric Double-Layer Capacitors

    NASA Astrophysics Data System (ADS)

    Kalluri, Raja K.; Konatham, Deepthi; Striolo, Alberto

    2011-03-01

    Towards deploying renewable energy sources it is crucial to develop efficient and cost-effective technologies to store electricity. Traditional batteries are plagued by a number of practical problems that at present limit their widespread applicability. One possible solution is represented by electric double-layer capacitors (EDLCs). To deploy EDLCs at the large scale it is necessary to better understand how electrolytes pack and diffuse within narrow charged pores. We present here simulation results for the concentrated aqueous solutions of NaCl, CsCl, and NaI confined within charged graphene-based porous materials. We discuss how the structure of confined water, the salt concentration, the ions size, and the surface charge density determine the accumulation of electrolytes within the porous network. Our results, compared to data available for bulk systems, are critical for relating macroscopic observations to molecular-level properties of the confined working fluids. Research supported by the Department of Energy.

  18. Sub-millimeter arbitrary arrangements of monolithically micro-scale electrical double layer capacitors

    NASA Astrophysics Data System (ADS)

    Laszczyk, Karolina U.; Kazufumi, Kobashi; Sakurai, Shunsuke; Sekiguchi, Atsuko; Futaba, Don N.; Yamada, Takeo; Hata, Kenji

    2015-12-01

    We report the investigation on the reproducibility of micro-scale electric double layer capacitors (micro-EDLCs). The micro-EDLC components were fabricated parallel using photolithography, wet and dry processing. Electrodes of the micro-EDLCs are highly dense packed Single Wall Carbon Nanotubes (SWCNTs) that form a mesh structure. The micro- EDLCs are connected 1-10 in series and in parallel being unified electrical circuits to tune the capacitance and the operational voltage. To confirm the reproducibility of the cells as well as the yield we performed electrochemical measurements in order to define the performance uniformity between cells strings and individual cells connected in a string. For 1-10 cells in series and in parallel the trends for the capacitance and operational voltage satisfied electrophysics rules governing cells addition. However, the measurements of the individual cells in a string revealed the significant performance discrepancy that might result in a shorten life cycling of a circuit.

  19. A Study on Equivalent Circuit Model of High-Power Density Electric Double Layer Capacitor

    NASA Astrophysics Data System (ADS)

    Yamada, Tetsu; Yamashiro, Susumu; Sasaki, Masakazu; Araki, Shuuichi

    Various models for the equivalent circuit of EDLC (Electric Double Layer Capacitor) have been presented so far. The multi-stage connection of RC circuit is a representative model to simulate the EDLC's charge-discharge characteristic. However, since high energy density type EDLC for electric power storage has the electrostatic capacity of thousands F, the phenomenon of being almost uninfluential for the case of conventional capacitor appears in an actual measurement notably. To overcome this difficulty, we develop an equivalent circuit model using a nonlinear model that considers the voltage dependency of the electrostatic capacity in this paper. After various simulations and comparison with experimental results, we confirmed the effectiveness of the proposed model.

  20. Electric double layer force between charged surfaces: Effect of solvent polarization

    NASA Astrophysics Data System (ADS)

    Prasanna Misra, Rahul; Das, Siddhartha; Mitra, Sushanta K.

    2013-03-01

    In this paper, we develop a theory to delineate the consequences of finite solvent polarization in electric double layer interaction or the osmotic pressure between two similar or oppositely charged surfaces. We use previously published Langevin-Bikerman equations to calculate this electric double layer interaction force or the osmotic pressure between the charged surfaces. The osmotic pressure between oppositely charged surfaces is found to be much larger than that between similarly charged surfaces, and for either case, the influence of solvent polarization ensures a larger pressure than that predicted by the Poisson-Boltzmann (PB) model. We derive distinct scaling relationships to explain the increase of the pressure as a function of the separation between the surfaces, the solvent polarizability, and the number density of water molecules. Most importantly, we demonstrate that our theory can successfully reproduce the experimental results of interaction force between similar and oppositely charged surfaces, by accounting for the large under-prediction made by the corresponding PB model.

  1. Poisson-Helmholtz-Boltzmann model of the electric double layer: analysis of monovalent ionic mixtures.

    PubMed

    Bohinc, Klemen; Shrestha, Ahis; Brumen, Milan; May, Sylvio

    2012-03-01

    In the classical mean-field description of the electric double layer, known as the Poisson-Boltzmann model, ions interact exclusively through their Coulomb potential. Ion specificity can arise through solvent-mediated, nonelectrostatic interactions between ions. We employ the Yukawa pair potential to model the presence of nonelectrostatic interactions. The combination of Yukawa and Coulomb potential on the mean-field level leads to the Poisson-Helmholtz-Boltzmann model, which employs two auxiliary potentials: one electrostatic and the other nonelectrostatic. In the present work we apply the Poisson-Helmholtz-Boltzmann model to ionic mixtures, consisting of monovalent cations and anions that exhibit different Yukawa interaction strengths. As a specific example we consider a single charged surface in contact with a symmetric monovalent electrolyte. From the minimization of the mean-field free energy we derive the Poisson-Boltzmann and Helmholtz-Boltzmann equations. These nonlinear equations can be solved analytically in the weak perturbation limit. This together with numerical solutions in the nonlinear regime suggests an intricate interplay between electrostatic and nonelectrostatic interactions. The structure and free energy of the electric double layer depends sensitively on the Yukawa interaction strengths between the different ion types and on the nonelectrostatic interactions of the mobile ions with the surface.

  2. Application of a site-binding, electrical, double-layer model to nuclear waste disposal

    SciTech Connect

    Relyea, J.F.; Silva, R.J.

    1981-09-01

    A site-binding, electrical, double-layer adsorption model has been applied to adsorption of Cs for both a montmorillonite clay and powdered SiO/sub 2/. Agreement between experimental and predicted results indicates that C/sub s//sup +/ is adsorbed by a simple cation-exchange mechanism. Further application of a combination equilibrium thermodynamic model and site-binding, electrical, double-layer adsorption model has been made to predict the behavior of U(VI) in solutions contacting either the montmorillonite clay or powdered SiO/sub 2/. Experimentally determined U solution concentrations have been used to select what is felt to be the best available thermodynamic data for U under oxidizing conditions. Given the existing information about the probable U solution species, it was possible to determine that UO/sub 2//sup +2/ is most likely adsorbed by cation-exchange at pH 5. At higher values (pH 7 and 9), it was shown that UO/sub 2/(OH)/sub 2//sup 0/ is probably the most strongly adsorbed U solution species. It was also found that high NaCl solution concentrations at higher pH values lowered U concentrations (either because of enhanced sorption or lowered solubility); however, the mechanism responsible for this behavior has not been determined.

  3. Electrical double layers and differential capacitance in molten salts from density functional theory

    DOE PAGES

    Frischknecht, Amalie L.; Halligan, Deaglan O.; Parks, Michael L.

    2014-08-05

    Classical density functional theory (DFT) is used to calculate the structure of the electrical double layer and the differential capacitance of model molten salts. The DFT is shown to give good qualitative agreement with Monte Carlo simulations in the molten salt regime. The DFT is then applied to three common molten salts, KCl, LiCl, and LiKCl, modeled as charged hard spheres near a planar charged surface. The DFT predicts strong layering of the ions near the surface, with the oscillatory density profiles extending to larger distances for larger electrostatic interactions resulting from either lower temperature or lower dielectric constant. Inmore » conclusion, overall the differential capacitance is found to be bell-shaped, in agreement with recent theories and simulations for ionic liquids and molten salts, but contrary to the results of the classical Gouy-Chapman theory.« less

  4. Electrical double layers and differential capacitance in molten salts from density functional theory

    SciTech Connect

    Frischknecht, Amalie L.; Halligan, Deaglan O.; Parks, Michael L.

    2014-08-05

    Classical density functional theory (DFT) is used to calculate the structure of the electrical double layer and the differential capacitance of model molten salts. The DFT is shown to give good qualitative agreement with Monte Carlo simulations in the molten salt regime. The DFT is then applied to three common molten salts, KCl, LiCl, and LiKCl, modeled as charged hard spheres near a planar charged surface. The DFT predicts strong layering of the ions near the surface, with the oscillatory density profiles extending to larger distances for larger electrostatic interactions resulting from either lower temperature or lower dielectric constant. In conclusion, overall the differential capacitance is found to be bell-shaped, in agreement with recent theories and simulations for ionic liquids and molten salts, but contrary to the results of the classical Gouy-Chapman theory.

  5. The Equivalent Electrokinetic Circuit Model of Ion Concentration Polarization Layer: Electrical Double Layer, Extended Space Charge and Electro-convection

    NASA Astrophysics Data System (ADS)

    Cho, Inhee; Huh, Keon; Kwak, Rhokyun; Lee, Hyomin; Kim, Sung Jae

    2016-11-01

    The first direct chronopotentiometric measurement was provided to distinguish the potential difference through the extended space charge (ESC) layer which is formed with the electrical double layer (EDL) near a perm-selective membrane. From this experimental result, the linear relationship was obtained between the resistance of ESC and the applied current density. Furthermore, we observed the step-wise distributions of relaxation time at the limiting current regime, confirming the existence of ESC capacitance other than EDL's. In addition, we proposed the equivalent electrokinetic circuit model inside ion concentration polarization (ICP) layer under rigorous consideration of EDL, ESC and electro-convection (EC). In order to elucidate the voltage configuration in chronopotentiometric measurement, the EC component was considered as the "dependent voltage source" which is serially connected to the ESC layer. This model successfully described the charging behavior of the ESC layer with or without EC, where both cases determined each relaxation time, respectively. Finally, we quantitatively verified their values utilizing the Poisson-Nernst-Planck equations. Therefore, this unified circuit model would provide a key insight of ICP system and potential energy-efficient applications.

  6. The Importance of Ion Size and Electrode Curvature on Electrical Double Layers in Ionic Liquids

    SciTech Connect

    Feng, Guang; Qiao, Rui; Huang, Jingsong; Dai, Sheng; Sumpter, Bobby G; Meunier, Vincent

    2010-01-01

    Room-temperature ionic liquids (ILs) are an emerging class of electrolytes for supercapacitors. We investigate the effects of ion size and electrode curvature on the electrical double layers (EDLs) in two ILs 1-butyl-3-methylimidazolium chloride [BMIM][Cl] and 1-butyl-3-methylimidazolium hexafluorophosphate [BMIM][PF(6)], using a combination of molecular dynamics (MD) and quantum density functional theory (DFT) simulations. The sizes of the counter-ion and co-ion affect the ion distribution and orientational structure of EDLs. The EDL capacitances near both planar and cylindrical electrodes were found to follow the order: [BMIM][Cl] (near the positive electrode) > [BMIM][PF(6)] (near the positive electrode) {approx} [BMIM][Cl] (near the negative electrode) {approx} [BMIM][PF(6)] (near the negative electrode). The EDL capacitance was also found to increase as the electrode curvature increases. These capacitance data can be fit to the Helmholtz model and the recently proposed exohedral electrical double-cylinder capacitor (xEDCC) model when the EDL thickness is properly parameterized, even though key features of the EDLs in ILs are not accounted for in these models. To remedy the shortcomings of existing models, we propose a 'Multiple Ion Layers with Overscreening' (MILO) model for the EDLs in ILs that takes into account two critical features of such EDLs, i.e., alternating layering of counter-ions and co-ions and charge overscreening. The capacitance computed from the MILO model agrees well with the MD prediction. Although some input parameters of the MILO model must be obtained from MD simulations, the MILO model may provide a new framework for understanding many important aspects of EDLs in ILs (e.g., the variation of EDL capacitance with the electrode potential) that are difficult to interpret using classical EDL models and experiments.

  7. The importance of ion size and electrode curvature on electrical double layers in ionic liquids

    SciTech Connect

    Feng, G.; Qiao, R.; Huang, J; Dai, S.; Sumpter, B. G.; Meunier, V.

    2011-01-01

    Room-temperature ionic liquids (ILs) are an emerging class of electrolytes for supercapacitors. We investigate the effects of ion size and electrode curvature on the electrical double layers (EDLs) in two ILs 1-butyl-3-methylimidazolium chloride [BMIM][Cl] and 1-butyl-3-methylimidazolium hexafluorophosphate [BMIM][PF{sub 6}], using a combination of molecular dynamics (MD) and quantum density functional theory (DFT) simulations. The sizes of the counter-ion and co-ion affect the ion distribution and orientational structure of EDLs. The EDL capacitances near both planar and cylindrical electrodes were found to follow the order: [BMIM][Cl] (near the positive electrode) > [BMIM][PF{sub 6}] (near the positive electrode) ≈ [BMIM][Cl] (near the negative electrode) ≈ [BMIM][PF{sub 6}] (near the negative electrode). The EDL capacitance was also found to increase as the electrode curvature increases. These capacitance data can be fit to the Helmholtz model and the recently proposed exohedral electrical double-cylinder capacitor (xEDCC) model when the EDL thickness is properly parameterized, even though key features of the EDLs in ILs are not accounted for in these models. To remedy the shortcomings of existing models, we propose a “Multiple Ion Layers with Overscreening” (MILO) model for the EDLs in ILs that takes into account two critical features of such EDLs, i.e., alternating layering of counter-ions and co-ions and charge overscreening. The capacitance computed from the MILO model agrees well with the MD prediction. Although some input parameters of the MILO model must be obtained from MD simulations, the MILO model may provide a new framework for understanding many important aspects of EDLs in ILs (e.g., the variation of EDL capacitance with the electrode potential) that are difficult to interpret using classical EDL models and experiments.

  8. Strong Deformation of the Thick Electric Double Layer around a Charged Particle during Sedimentation or Electrophoresis.

    PubMed

    Khair, Aditya S

    2017-08-15

    The deformation of the electric double layer around a charged colloidal particle during sedimentation or electrophoresis in a binary, symmetric electrolyte is studied. The surface potential of the particle is assumed to be small compared to the thermal voltage scale. Additionally, the Debye length is assumed to be large compared to the particle size. These assumptions enable a linearization of the electrokinetic equations. The particle appears as a point charge in this thick-double-layer limit; the distribution of charge in the diffuse cloud surrounding it is determined by a balance of advection due to the particle motion, Brownian diffusion of ions, and electrostatic screening of the particle by the cloud. The ability of advection to deform the charge cloud from its equilibrium state is parametrized by a Péclet number, Pe. For weak advection (Pe ≪ 1), the cloud is only slightly deformed. In contrast, the cloud can be completely stripped from the particle at Pe ≫ 1; consequently, electrokinetic effects on the particle motion vanish in this regime. Therefore, in sedimentation the drag limits to Stokes' law for an uncharged particle as Pe → ∞. Likewise, the particle velocity for electrophoresis approaches Huckel's result. The strongly deformed cloud at large Pe is predicted to generate a concomitant increase in the sedimentation field in a dilute settling suspension.

  9. Molecular Dynamics Study of the Electrical Double Layer at Silver Chloride Electrolyte Interfaces

    SciTech Connect

    Zarzycki, Piotr P.; Kerisit, Sebastien N.; Rosso, Kevin M.

    2010-05-20

    Molecular dynamics simulations of the electrical double layer at AgCl/aqueous electrolyte (KCl) interfaces are presented, accompanied by a new force field and properties of bulk AgCl computed using planewave density functional theory. Long dynamics simulations were performed to estimate ion adsorption free energies at the AgCl surface. The simulations demonstrate formation of a bilayer hydration sheet composed of two sublayers of water molecules interconnected by hydrogen bonds. Potassium ions prefer to form an inner-sphere complex, whereas chloride ions prefer outer-sphere complexes. The adsorbed ions/water layers form a relatively rigid structure within the range of ionic strength considered, which confirms the applicability of the Helmholtz model in a high concentration regime. Profiles of the charge density, electric field and electrostatic potential across the simulation cell revealed that oscillations of water molecules govern these quantities. The electrostatic potential generated only by the electrolyte ions was used to study the quasi-Nernstian response of the silver chloride surface to the variation in the ionic strength.

  10. "Squishy capacitor" model for electrical double layers and the stability of charged interfaces.

    PubMed

    Partenskii, Michael B; Jordan, Peter C

    2009-07-01

    Negative capacitance (NC), predicted by various electrical double layer (EDL) theories, is critically reviewed. Physically possible for individual components of the EDL, the compact or diffuse layer, it is strictly prohibited for the whole EDL or for an electrochemical cell with two electrodes. However, NC is allowed for the artificial conditions of sigma control, where an EDL is described by the equilibrium electric response of electrolyte to a field of fixed, and typically uniform, surface charge-density distributions, sigma. The contradiction is only apparent; in fact local sigma cannot be set independently, but is established by the equilibrium response to physically controllable variables, i.e., applied voltage phi (phi control) or total surface charge q (q control). NC predictions in studies based on sigma control signify potential instabilities and phase transitions for physically realizable conditions. Building on our previous study of phi control [M. B. Partenskii and P. C. Jordan, Phys. Rev. E 77, 061117 (2008)], here we analyze critical behavior under q control, clarifying the basic picture using an exactly solvable "squishy capacitor" toy model. We find that phi can change discontinuously in the presence of a lateral transition, specify stability conditions for an electrochemical cell, analyze the origin of the EDL's critical point in terms of compact and diffuse serial contributions, and discuss perspectives and challenges for theoretical studies not limited by sigma control.

  11. A molecular theory for optimal blue energy extraction by electrical double layer expansion

    SciTech Connect

    Kong, Xian; Gallegos, Alejandro; Lu, Diannan; Liu, Zheng; Wu, Jianzhong

    2015-08-19

    We proposed the electrical double layer expansion (CDLE) as a promising alternative to reverse electrodialysis (RED) and pressure retarded osmosis (PRO) processes for extracting osmotic power generated by the salinity difference between freshwater and seawater. The performance of the CDLE process is sensitive to the configuration of porous electrodes and operation parameters for ion extraction and release cycles. In our work, we use a classical density functional theory (CDFT) to examine how the electrode pore size and charging/discharging potentials influence the thermodynamic efficiency of the CDLE cycle. The existence of an optimal charging potential that maximizes the energy output for a given pore configuration is predicted, which varies substantially with the pore size, especially when it is smaller than 2 nm. Finally, the thermodynamic efficiency is maximized when the electrode has a pore size about twice the ion diameter.

  12. A molecular theory for optimal blue energy extraction by electrical double layer expansion

    DOE PAGES

    Kong, Xian; Gallegos, Alejandro; Lu, Diannan; ...

    2015-08-19

    We proposed the electrical double layer expansion (CDLE) as a promising alternative to reverse electrodialysis (RED) and pressure retarded osmosis (PRO) processes for extracting osmotic power generated by the salinity difference between freshwater and seawater. The performance of the CDLE process is sensitive to the configuration of porous electrodes and operation parameters for ion extraction and release cycles. In our work, we use a classical density functional theory (CDFT) to examine how the electrode pore size and charging/discharging potentials influence the thermodynamic efficiency of the CDLE cycle. The existence of an optimal charging potential that maximizes the energy output formore » a given pore configuration is predicted, which varies substantially with the pore size, especially when it is smaller than 2 nm. Finally, the thermodynamic efficiency is maximized when the electrode has a pore size about twice the ion diameter.« less

  13. Spreading of Electrolyte Drops on Charged Surfaces: Electric Double Layer Effects on Drop Dynamics

    NASA Astrophysics Data System (ADS)

    Bae, Kyeong; Sinha, Shayandev; Chen, Guang; Das, Siddhartha

    2015-11-01

    Drop spreading is one of the most fundamental topics of wetting. Here we study the spreading of electrolyte drops on charged surfaces. The electrolyte solution in contact with the charged solid triggers the formation of an electric double layer (EDL). We develop a theory to analyze how the EDL affects the drop spreading. The drop dynamics is studied by probing the EDL effects on the temporal evolution of the contact angle and the base radius (r). The EDL effects are found to hasten the spreading behaviour - this is commensurate to the EDL effects causing a ``philic'' tendency in the drops (i.e., drops attaining a contact angle smaller than its equilibrium value), as revealed by some of our recent papers. We also develop scaling laws to illustrate the manner in which the EDL effects make the r versus time (t) variation deviate from the well known r ~tn variation, thereby pinpointing the attainment of different EDL-mediated spreading regimes.

  14. Simulation of diffuse-charge capacitance in electric double layer capacitors

    NASA Astrophysics Data System (ADS)

    Sun, Ning; Gersappe, Dilip

    2017-01-01

    We use a Lattice Boltzmann Model (LBM) in order to simulate diffuse-charge dynamics in Electric Double Layer Capacitors (EDLCs). Simulations are carried out for both the charge and the discharge processes on 2D systems of complex random electrode geometries (pure random, random spheres and random fibers). The steric effect of concentrated solutions is considered by using a Modified Poisson-Nernst-Planck (MPNP) equations and compared with regular Poisson-Nernst-Planck (PNP) systems. The effects of electrode microstructures (electrode density, electrode filler morphology, filler size, etc.) on the net charge distribution and charge/discharge time are studied in detail. The influence of applied potential during discharging process is also discussed. Our studies show how electrode morphology can be used to tailor the properties of supercapacitors.

  15. Up and down translocation events and electric double-layer formation inside solid-state nanopores

    NASA Astrophysics Data System (ADS)

    Zanjani, Mehdi B.; Engelke, Rebecca E.; Lukes, Jennifer R.; Meunier, Vincent; Drndić, Marija

    2015-08-01

    We present a theoretical study of nanorod translocation events through solid-state nanopores of different sizes which result in positive or negative ion conductance changes. Using theoretical models, we show that positive conductance changes or up events happen for nanopore diameters smaller than a transition diameter dt, and negative conductance changes or down events occur for nanopore diameters larger than dt. We investigate the underlying physics of such translocation phenomena and describe the significance of the electric double-layer effects for nanopores with small diameters. Furthermore, for nanopores with large diameters, it is shown that a geometric model, formulated based on the nanoparticle blockade inside the nanopore, provides a straightforward and reasonably accurate prediction of ion conductance change. Based on this concept, we also implement a method to distinguish and detect nanorods of different sizes by focusing solely on the sign and not the exact value of the conductance change.

  16. Free energy of electrical double layers: Entropy of adsorbed ions and the binding polynomial

    SciTech Connect

    Stigter, D.; Dill, K.A. )

    1989-09-07

    The authors adapt the method of binding polynomials to general problems of binding equilibria of ions to polybases, polyacids, and mixed polyelectrolytes, such as proteins and other colloids. For spherical particles with a smeared charge the interaction effects are taken into account using the Poisson-Boltzmann equation, which is shown to differ little from the Debye-Hueckel approximation under conditions met in most protein solutions. Examples are given of the salt dependence of pH titration equilibria. Binding polynomials produce an extra term in the free energy of the electrical double layer, which arises from the entropy of the adsorbed ions. The maximum term method applied to the binding polynominal yields an expression which is similar to that derived by the charging process of Chan and Mitchell. Applications to monolayers and to polyelectrolyte gels are also discussed.

  17. Enhancement of electric double layer capacitance of carbon nanotubes by gallium ion irradiation

    SciTech Connect

    Rai, Padmnabh; Pandey, Srikrishna; Menemparabath, Minimol; Sug Kim, Young; Nikolaev, Pavel; Arepalli, Sivaram; Lee, Il Ha

    2011-02-15

    Irradiation by 30 keV Ga{sup +} ions was used to create defects in multiwalled carbon nanotubes. Damage to the graphitic structure of the nanotube wall resulting from ion irradiation was observed by a transmission electron microscope which was accompanied by corresponding changes in Raman spectra. It was found that ion irradiation at 2 x 10{sup 13} ions/cm{sup 2} cumulative dose increases the electric double layer capacitance of a multiwalled carbon nanotube electrode by a factor of 2.3, followed by a decrease and saturation at higher (2 x 10{sup 14} and 4 x 10{sup 14} ions/cm{sup 2}) doses. This might be a trade-off between the enhancement caused by the tip opening and lowering of the capacitance due to amorphization of carbon nanotubes.

  18. Kinetic-Dominated Charging Mechanism within Representative Aqueous Electrolyte-based Electric Double-Layer Capacitors.

    PubMed

    Yang, Huachao; Yang, Jinyuan; Bo, Zheng; Chen, Xia; Shuai, Xiaorui; Kong, Jing; Yan, Jianhua; Cen, Kefa

    2017-08-03

    The chemical nature of electrolytes has been demonstrated to play a pivotal role in the charge storage of electric double-layer capacitors (EDLCs), whereas primary mechanisms are still partially resolved but controversial. In this work, a systematic exploration into EDL structures and kinetics of representative aqueous electrolytes is performed with numerical simulation and experimental research. Unusually, a novel charging mechanism exclusively predominated by kinetics is recognized, going beyond traditional views of manipulating capacitances preferentially via interfacial structural variations. Specifically, strikingly distinctive EDL structures stimulated by diverse ion sizes, valences, and mixtures manifest a virtually identical EDL capacitance, where the dielectric nature of solvents attenuates ionic effects on electrolyte redistributions, in stark contradiction with solvent-free counterpart and traditional Helmholtz theory. Meanwhile, corresponding kinetics evolve conspicuously with ionic species, intimately correlated with ion-solvent interactions. The achieved mechanisms are subsequently illuminated by electrochemical measurements, highlighting the crucial interplay between ions and solvents in regulating EDLC performances.

  19. Up and down translocation events and electric double-layer formation inside solid-state nanopores.

    PubMed

    Zanjani, Mehdi B; Engelke, Rebecca E; Lukes, Jennifer R; Meunier, Vincent; Drndić, Marija

    2015-08-01

    We present a theoretical study of nanorod translocation events through solid-state nanopores of different sizes which result in positive or negative ion conductance changes. Using theoretical models, we show that positive conductance changes or up events happen for nanopore diameters smaller than a transition diameter dt, and negative conductance changes or down events occur for nanopore diameters larger than dt. We investigate the underlying physics of such translocation phenomena and describe the significance of the electric double-layer effects for nanopores with small diameters. Furthermore, for nanopores with large diameters, it is shown that a geometric model, formulated based on the nanoparticle blockade inside the nanopore, provides a straightforward and reasonably accurate prediction of ion conductance change. Based on this concept, we also implement a method to distinguish and detect nanorods of different sizes by focusing solely on the sign and not the exact value of the conductance change.

  20. Investigation of Interface between Ge Electrodes and Ionic Liquid Electrolytes for Electric Double Layer Capacitors

    NASA Astrophysics Data System (ADS)

    Abeysinghe, R. M.; Oguchi, H.; Kuwano, H.

    2016-11-01

    This study discusses novel way of use of ionic liquids to develop Ge-based electrodes for electric double layer capacitors (EDLC). We found that ionic liquids change their electrochemical properties depending on the amount of the absorbed water. Wet ionic liquids work as solvents to dissolve Ge and make porous structures, whereas dry ones work as electrolytes of the EDLCs. The former property was used to increase surface area of the electrodes which is desired to increase the capacity of EDLCs. This method showed another advantage in contrast to the dry ionic liquids; wet ones could fill the complex Ge pores in parallel to porous structure formation. Finally, after porous formation, we dried the ionic liquid at 100 °C and prepared the EDLCs composed of Ge porous electrodes. Cyclic voltammetry and impedance measurements indicated that the obtained devices can work as EDLCs.

  1. High-surface-area nitrogen-doped reduced graphene oxide for electric double-layer capacitors

    DOE PAGES

    Youn, Hee-Chang; Bak, Seong-Min; Kim, Myeong-Seong; ...

    2015-06-08

    A two-step method consisting of solid-state microwave irradiation and heat treatment under NH₃ gas was used to prepare nitrogen-doped reduced graphene oxide (N-RGO) with a high specific surface area (1007m²g⁻¹), high electrical conductivity (1532S m⁻¹), and low oxygen content (1.5 wt%) for electric double-layer capacitor applications. The specific capacitance of N-RGO was 291 Fg⁻¹ at a current density of 1 A g⁻¹, and a capacitance of 261 F g⁻¹ was retained at 50 A g⁻¹, indicating a very good rate capability. N-RGO also showed excellent cycling stability, preserving 96% of the initial specific capacitance after 100,000 cycles. Near-edge X-ray absorptionmore » fine-structure spectroscopy evidenced the recover of π-conjugation in the carbon networks with the removal of oxygenated groups and revealed the chemical bonding of the nitrogen atoms in N-RGO. The good electrochemical performance of N-RGO is attributed to its high surface area, high electrical conductivity, and low oxygen content.« less

  2. High-surface-area nitrogen-doped reduced graphene oxide for electric double-layer capacitors

    SciTech Connect

    Youn, Hee-Chang; Bak, Seong-Min; Kim, Myeong-Seong; Jaye, Cherno; Fischer, Daniel A.; Lee, Chang-Wook; Yang, Xiao-Qing; Roh, Kwang Chul; Kim, Kwang-Bum

    2015-06-08

    A two-step method consisting of solid-state microwave irradiation and heat treatment under NH₃ gas was used to prepare nitrogen-doped reduced graphene oxide (N-RGO) with a high specific surface area (1007m²g⁻¹), high electrical conductivity (1532S m⁻¹), and low oxygen content (1.5 wt%) for electric double-layer capacitor applications. The specific capacitance of N-RGO was 291 Fg⁻¹ at a current density of 1 A g⁻¹, and a capacitance of 261 F g⁻¹ was retained at 50 A g⁻¹, indicating a very good rate capability. N-RGO also showed excellent cycling stability, preserving 96% of the initial specific capacitance after 100,000 cycles. Near-edge X-ray absorption fine-structure spectroscopy evidenced the recover of π-conjugation in the carbon networks with the removal of oxygenated groups and revealed the chemical bonding of the nitrogen atoms in N-RGO. The good electrochemical performance of N-RGO is attributed to its high surface area, high electrical conductivity, and low oxygen content.

  3. High-Surface-Area Nitrogen-Doped Reduced Graphene Oxide for Electric Double-Layer Capacitors.

    PubMed

    Youn, Hee-Chang; Bak, Seong-Min; Kim, Myeong-Seong; Jaye, Cherno; Fischer, Daniel A; Lee, Chang-Wook; Yang, Xiao-Qing; Roh, Kwang Chul; Kim, Kwang-Bum

    2015-06-08

    A two-step method consisting of solid-state microwave irradiation and heat treatment under NH3 gas was used to prepare nitrogen-doped reduced graphene oxide (N-RGO) with a high specific surface area (1007 m(2)  g(-1) ), high electrical conductivity (1532 S m(-1) ), and low oxygen content (1.5 wt %) for electrical double-layer capacitor applications. The specific capacitance of N-RGO was 291 F g(-1) at a current density of 1 A g(-1) , and a capacitance of 261 F g(-1) was retained at 50 A g(-1) , which indicated a very good rate capability. N-RGO also showed excellent cycling stability and preserved 96 % of the initial specific capacitance after 100 000 cycles. Near-edge X-ray absorption fine-structure spectroscopy results provided evidenced for the recovery of π conjugation in the carbon networks with the removal of oxygenated groups and revealed chemical bonding of the nitrogen atoms in N-RGO. The good electrochemical performance of N-RGO is attributed to its high surface area, high electrical conductivity, and low oxygen content.

  4. Electroosmosis over charge-modulated surfaces with finite electrical double layer thicknesses: Asymptotic and numerical investigations

    NASA Astrophysics Data System (ADS)

    Ghosh, Uddipta; Mandal, Shubhadeep; Chakraborty, Suman

    2017-06-01

    Here we attempt to solve the fully coupled Poisson-Nernst-Planck-Navier-Stokes equations, to ascertain the influence of finite electric double layer (EDL) thickness on coupled charge and fluid dynamics over patterned charged surfaces. We go beyond the well-studied "weak-field" limit and obtain numerical solutions for a wide range of EDL thicknesses, applied electric field strengths, and the surface potentials. Asymptotic solutions to the coupled system are also derived using a combination of singular and regular perturbation, for thin EDLs and low surface potential, and good agreement between the two solutions is observed. Counterintuitively to common arguments, our analysis reveals that finite EDL thickness may either increase or decrease the "free-stream velocity" (equivalent to net throughput), depending on the strength of the applied electric field. We also unveil a critical EDL thickness for which the effect of finite EDL thickness on the free-stream velocity is the most prominent. Finally, we demonstrate that increasing the surface potential and the applied field tends to influence the overall flow patterns in the contrasting manners. These results may be of profound importance in developing a comprehensive theoretical basis for designing electro-osmotically actuated microfluidic mixtures.

  5. Water Density in the Electric Double Layer at the Insulator/Electrolyte Solution Interface

    SciTech Connect

    Tikhonov,A.

    2006-01-01

    I studied the spatial structure of the thick transition region between n-hexane and a colloidal solution of 7-nm silica particles by X-ray reflectivity and grazing incidence small-angle scattering. The interfacial structure is discussed in terms of a semiquantitative interface model wherein the potential gradient at the n-hexane/sol interface reflects the difference in the potentials of 'image forces' between the cationic Na{sup +} and anions (nanoparticles) and the specific adsorption of surface charge at the interface between the adsorbed layer and the solution, as well as at the interface between the adsorbed layer and n-hexane. The X-ray scattering data revealed that the average density of water in the field {approx}10{sup 9}-10{sup 10} V/m of the electrical double layer at the hexane/silica sol interface is the same as, or only few percent higher (1-7%) than, its density under normal conditions.

  6. Evaluation of the constant potential method in simulating electric double-layer capacitors

    NASA Astrophysics Data System (ADS)

    Wang, Zhenxing; Yang, Yang; Olmsted, David L.; Asta, Mark; Laird, Brian B.

    2014-11-01

    A major challenge in the molecular simulation of electric double layer capacitors (EDLCs) is the choice of an appropriate model for the electrode. Typically, in such simulations the electrode surface is modeled using a uniform fixed charge on each of the electrode atoms, which ignores the electrode response to local charge fluctuations in the electrolyte solution. In this work, we evaluate and compare this Fixed Charge Method (FCM) with the more realistic Constant Potential Method (CPM), [S. K. Reed et al., J. Chem. Phys. 126, 084704 (2007)], in which the electrode charges fluctuate in order to maintain constant electric potential in each electrode. For this comparison, we utilize a simplified LiClO4-acetonitrile/graphite EDLC. At low potential difference (ΔΨ ⩽ 2 V), the two methods yield essentially identical results for ion and solvent density profiles; however, significant differences appear at higher ΔΨ. At ΔΨ ⩾ 4 V, the CPM ion density profiles show significant enhancement (over FCM) of "inner-sphere adsorbed" Li+ ions very close to the electrode surface. The ability of the CPM electrode to respond to local charge fluctuations in the electrolyte is seen to significantly lower the energy (and barrier) for the approach of Li+ ions to the electrode surface.

  7. Evaluation of the constant potential method in simulating electric double-layer capacitors

    SciTech Connect

    Wang, Zhenxing; Laird, Brian B.; Yang, Yang; Olmsted, David L.; Asta, Mark

    2014-11-14

    A major challenge in the molecular simulation of electric double layer capacitors (EDLCs) is the choice of an appropriate model for the electrode. Typically, in such simulations the electrode surface is modeled using a uniform fixed charge on each of the electrode atoms, which ignores the electrode response to local charge fluctuations in the electrolyte solution. In this work, we evaluate and compare this Fixed Charge Method (FCM) with the more realistic Constant Potential Method (CPM), [S. K. Reed et al., J. Chem. Phys. 126, 084704 (2007)], in which the electrode charges fluctuate in order to maintain constant electric potential in each electrode. For this comparison, we utilize a simplified LiClO{sub 4}-acetonitrile/graphite EDLC. At low potential difference (ΔΨ ⩽ 2 V), the two methods yield essentially identical results for ion and solvent density profiles; however, significant differences appear at higher ΔΨ. At ΔΨ ⩾ 4 V, the CPM ion density profiles show significant enhancement (over FCM) of “inner-sphere adsorbed” Li{sup +} ions very close to the electrode surface. The ability of the CPM electrode to respond to local charge fluctuations in the electrolyte is seen to significantly lower the energy (and barrier) for the approach of Li{sup +} ions to the electrode surface.

  8. Evolution of electronic states in n-type copper oxide superconductor via electric double layer gating.

    PubMed

    Jin, Kui; Hu, Wei; Zhu, Beiyi; Kim, Dohun; Yuan, Jie; Sun, Yujie; Xiang, Tao; Fuhrer, Michael S; Takeuchi, Ichiro; Greene, Richard L

    2016-05-25

    The occurrence of electrons and holes in n-type copper oxides has been achieved by chemical doping, pressure, and/or deoxygenation. However, the observed electronic properties are blurred by the concomitant effects such as change of lattice structure, disorder, etc. Here, we report on successful tuning the electronic band structure of n-type Pr2-xCexCuO4 (x = 0.15) ultrathin films, via the electric double layer transistor technique. Abnormal transport properties, such as multiple sign reversals of Hall resistivity in normal and mixed states, have been revealed within an electrostatic field in range of -2 V to + 2 V, as well as varying the temperature and magnetic field. In the mixed state, the intrinsic anomalous Hall conductivity invokes the contribution of both electron and hole-bands as well as the energy dependent density of states near the Fermi level. The two-band model can also describe the normal state transport properties well, whereas the carrier concentrations of electrons and holes are always enhanced or depressed simultaneously in electric fields. This is in contrast to the scenario of Fermi surface reconstruction by antiferromagnetism, where an anti-correlation is commonly expected.

  9. Evaluation of the constant potential method in simulating electric double-layer capacitors.

    PubMed

    Wang, Zhenxing; Yang, Yang; Olmsted, David L; Asta, Mark; Laird, Brian B

    2014-11-14

    A major challenge in the molecular simulation of electric double layer capacitors (EDLCs) is the choice of an appropriate model for the electrode. Typically, in such simulations the electrode surface is modeled using a uniform fixed charge on each of the electrode atoms, which ignores the electrode response to local charge fluctuations in the electrolyte solution. In this work, we evaluate and compare this Fixed Charge Method (FCM) with the more realistic Constant Potential Method (CPM), [S. K. Reed et al., J. Chem. Phys. 126, 084704 (2007)], in which the electrode charges fluctuate in order to maintain constant electric potential in each electrode. For this comparison, we utilize a simplified LiClO4-acetonitrile/graphite EDLC. At low potential difference (ΔΨ ⩽ 2 V), the two methods yield essentially identical results for ion and solvent density profiles; however, significant differences appear at higher ΔΨ. At ΔΨ ⩾ 4 V, the CPM ion density profiles show significant enhancement (over FCM) of "inner-sphere adsorbed" Li(+) ions very close to the electrode surface. The ability of the CPM electrode to respond to local charge fluctuations in the electrolyte is seen to significantly lower the energy (and barrier) for the approach of Li(+) ions to the electrode surface.

  10. Evolution of electronic states in n-type copper oxide superconductor via electric double layer gating

    NASA Astrophysics Data System (ADS)

    Jin, Kui; Hu, Wei; Zhu, Beiyi; Kim, Dohun; Yuan, Jie; Sun, Yujie; Xiang, Tao; Fuhrer, Michael S.; Takeuchi, Ichiro; Greene, Richard. L.

    2016-05-01

    The occurrence of electrons and holes in n-type copper oxides has been achieved by chemical doping, pressure, and/or deoxygenation. However, the observed electronic properties are blurred by the concomitant effects such as change of lattice structure, disorder, etc. Here, we report on successful tuning the electronic band structure of n-type Pr2‑xCexCuO4 (x = 0.15) ultrathin films, via the electric double layer transistor technique. Abnormal transport properties, such as multiple sign reversals of Hall resistivity in normal and mixed states, have been revealed within an electrostatic field in range of ‑2 V to + 2 V, as well as varying the temperature and magnetic field. In the mixed state, the intrinsic anomalous Hall conductivity invokes the contribution of both electron and hole-bands as well as the energy dependent density of states near the Fermi level. The two-band model can also describe the normal state transport properties well, whereas the carrier concentrations of electrons and holes are always enhanced or depressed simultaneously in electric fields. This is in contrast to the scenario of Fermi surface reconstruction by antiferromagnetism, where an anti-correlation is commonly expected.

  11. Electric-double-layer field-effect transistors with ionic liquids.

    PubMed

    Fujimoto, Takuya; Awaga, Kunio

    2013-06-21

    Charge carrier control is a key issue in the development of electronic functions of semiconductive materials. Beyond the simple enhancement of conductivity, high charge carrier accumulation can realize various phenomena, such as chemical reaction, phase transition, magnetic ordering, and superconductivity. Electric double layers (EDLs), formed at solid-electrolyte interfaces, induce extremely large electric fields. This results in a high charge carrier accumulation in the solid, much more effectively than solid dielectric materials. In the present review, we describe recent developments in the field-effect transistors (FETs) with gate dielectrics of ionic liquids, which have attracted much attention due to their wide electrochemical windows, low vapor pressures, and high chemical and physical stability. We explain the capacitance effects of ionic liquids, and describe the various combinations of ionic liquids and organic and inorganic semiconductors that are used to achieve such effects as high transistor performance, insulator-metal transitions, superconductivity, and ferromagnetism, in addition to the applications of the ionic-liquid EDL-FETs in logic devices. We discuss the factors controlling the mobility and threshold voltage in these types of FETs, and show the ionic liquid dependence of the transistor performance.

  12. Evolution of electronic states in n-type copper oxide superconductor via electric double layer gating

    PubMed Central

    Jin, Kui; Hu, Wei; Zhu, Beiyi; Kim, Dohun; Yuan, Jie; Sun, Yujie; Xiang, Tao; Fuhrer, Michael S.; Takeuchi, Ichiro; Greene, Richard. L.

    2016-01-01

    The occurrence of electrons and holes in n-type copper oxides has been achieved by chemical doping, pressure, and/or deoxygenation. However, the observed electronic properties are blurred by the concomitant effects such as change of lattice structure, disorder, etc. Here, we report on successful tuning the electronic band structure of n-type Pr2−xCexCuO4 (x = 0.15) ultrathin films, via the electric double layer transistor technique. Abnormal transport properties, such as multiple sign reversals of Hall resistivity in normal and mixed states, have been revealed within an electrostatic field in range of −2 V to + 2 V, as well as varying the temperature and magnetic field. In the mixed state, the intrinsic anomalous Hall conductivity invokes the contribution of both electron and hole-bands as well as the energy dependent density of states near the Fermi level. The two-band model can also describe the normal state transport properties well, whereas the carrier concentrations of electrons and holes are always enhanced or depressed simultaneously in electric fields. This is in contrast to the scenario of Fermi surface reconstruction by antiferromagnetism, where an anti-correlation is commonly expected. PMID:27221198

  13. Theory of the formation of the electric double layer at the ion exchange membrane-solution interface.

    PubMed

    Moya, A A

    2015-02-21

    This work aims to extend the study of the formation of the electric double layer at the interface defined by a solution and an ion-exchange membrane on the basis of the Nernst-Planck and Poisson equations, including different values of the counter-ion diffusion coefficient and the dielectric constant in the solution and membrane phases. The network simulation method is used to obtain the time evolution of the electric potential, the displacement electric vector, the electric charge density and the ionic concentrations at the interface between a binary electrolyte solution and a cation-exchange membrane with total co-ion exclusion. The numerical results for the temporal evolution of the interfacial electric potential and the surface electric charge are compared with analytical solutions derived in the limit of the shortest times by considering the Poisson equation for a simple cationic diffusion process. The steady-state results are justified from the Gouy-Chapman theory for the diffuse double layer in the limits of similar and high bathing ionic concentrations with respect to the fixed-charge concentration inside the membrane. Interesting new physical insights arise from the interpretation of the process of the formation of the electric double layer at the ion exchange membrane-solution interface on the basis of a membrane model with total co-ion exclusion.

  14. Formation of the Electric Double Layer and its Effects on Moving Bodies in a Space Plasma Environment

    NASA Technical Reports Server (NTRS)

    Yang, Qianli; Wu, S. T.; Stone, N. H.; Li, Xiaoquing

    1996-01-01

    In this paper we solve the self-consistent Vlasov and Poisson equations by a numerical method to determine the local distribution function of the ion and the electron, within a thin layer near the moving body, respectively. Using these ion and electron distributions, the number density for the ions and electrons are determined, such that, the electric potential is obtained within this thin layer (i.e., measured by Debye length). Numerical results are presented for temporal evolution of the electron and ion density and its corresponding electric potential within the layer which shows the formation of electric double layer and its structures. From these numerical results, we are able to determine the maximum conditions of the electric potential, it may create satellite anomaly.

  15. Electric double-layer transistor using layered iron selenide Mott insulator TlFe1.6Se2

    PubMed Central

    Katase, Takayoshi; Hiramatsu, Hidenori; Kamiya, Toshio; Hosono, Hideo

    2014-01-01

    A1–xFe2–ySe2 (A = K, Cs, Rb, Tl) are recently discovered iron-based superconductors with critical temperatures (Tc) ranging up to 32 K. Their parent phases have unique properties compared with other iron-based superconductors; e.g., their crystal structures include ordered Fe vacancies, their normal states are antiferromagnetic (AFM) insulating phases, and they have extremely high Néel transition temperatures. However, control of carrier doping into the parent AFM insulators has been difficult due to their intrinsic phase separation. Here, we fabricated an Fe-vacancy-ordered TlFe1.6Se2 insulating epitaxial film with an atomically flat surface and examined its electrostatic carrier doping using an electric double-layer transistor (EDLT) structure with an ionic liquid gate. The positive gate voltage gave a conductance modulation of three orders of magnitude at 25 K, and further induced and manipulated a phase transition; i.e., delocalized carrier generation by electrostatic doping is the origin of the phase transition. This is the first demonstration, to the authors' knowledge, of an EDLT using a Mott insulator iron selenide channel and opens a way to explore high Tc superconductivity in iron-based layered materials, where carrier doping by conventional chemical means is difficult. PMID:24591598

  16. A thin layer including a carbon material improves the rate capability of an electric double layer capacitor

    NASA Astrophysics Data System (ADS)

    Sato, Takaya; Marukane, Shoko; Morinaga, Takashi; Uemura, Taichi; Fukumoto, Kunihiro; Yamazaki, Satoshi

    2011-03-01

    We present a new method to improve the rate capability of an electric double layer capacitor (EDLC) using a thin polymer layer having a high concentration of carbon material on a current collector (CLC). A novel thermocuring coating composed of a glycol-chitosan, a pyromellitic acid and a conductive carbon powder can form stable CLC on a metal foil current collector simply by spreading and curing at 160 °C for a couple of minutes. We compared the performance of some demonstration EDLC cells using three kinds of current collector: a conventional aluminum oxide foil for EDLC, an aluminum foil and an aluminum foil with CLC. The cell with the CLC had a much higher rate capability than the cell without CLC. Only the CLC cell was able to discharge at a current density of 500C. This cell shows a slight deterioration in capacity in a high temperature, continuous charging, life test, and the CLC has a suppressing effect on the internal resistance increase of EDLCs. The use of a CLC film current collector is one of the most effective and simple methods for the improvement of EDLC rate performance. In particular, a current collector consisting of aluminum foil coupled with a CLC promises to be a low cost alternative to the aluminum oxide foil commonly used in EDLCs.

  17. A counter-charge layer in generalized solvents framework for electrical double layers in neat and hybrid ionic liquid electrolytes

    SciTech Connect

    Huang, Jingsong; Feng, Guang; Sumpter, Bobby G; Qiao, Rui; Meunier, Vincent

    2011-01-01

    Room-temperature ionic liquids (RTILs) have received significant attention as electrolytes due to a number of attractive properties such as their wide electrochemical windows. Since electrical double layers (EDLs) are the cornerstone for the applications of RTILs in electrochemical systems such as supercapacitors, it is important to develop an understanding of the structure capacitance relationships for these systems. Here we present a theoretical framework termed counter-charge layer in generalized solvents (CGS) for describing the structure and capacitance of the EDLs in neat RTILs and in RTILs mixed with different mass fractions of organic solvents. Within this framework, an EDL is made up of a counter-charge layer exactly balancing the electrode charge, and of polarized generalized solvents (in the form of layers of ion pairs, each of which has a zero net charge but has a dipole moment the ion pairs thus can be considered as a generalized solvent) consisting of all RTILs inside the system except the counter-ions in the counter-charge layer, together with solvent molecules if present. Several key features of the EDLs that originate from the strong ion ion correlation in RTILs, e.g., overscreening of electrode charge and alternating layering of counter-ions and co-ions, are explicitly incorporated into this framework. We show that the dielectric screening in EDLs is governed predominately by the polarization of generalized solvents (or ion pairs) in the EDL, and the capacitance of an EDL can be related to its microstructure with few a priori assumptions or simplifications. We use this framework to understand two interesting phenomena observed in molecular dynamics simulations of EDLs in a neat IL of 1-butyl-3- methylimidazolium tetrafluoroborate ([BMIM][BF4]) and in a mixture of [BMIM][BF4] and acetonitrile (ACN): (1) the capacitance of the EDLs in the [BMIM][BF4]/ACN mixture increases only slightly when the mass fraction of ACN in the mixture increases from zero

  18. Preparation of porous carbon sphere from waste sugar solution for electric double-layer capacitor

    NASA Astrophysics Data System (ADS)

    Hao, Zhi-Qiang; Cao, Jing-Pei; Wu, Yan; Zhao, Xiao-Yan; Zhuang, Qi-Qi; Wang, Xing-Yong; Wei, Xian-Yong

    2017-09-01

    Waste sugar solution (WSS), which contains abundant 2-keto-L-gulonic acid, is harmful to the environment if discharged directly. For value-added utilization of the waste resource, a novel process is developed for preparation of porous carbon spheres by hydrothermal carbonization (HTC) of WSS followed by KOH activation. Additionally, the possible preparation mechanism of carbon spheres is proposed. The effects of hydrothermal and activation parameters on the properties of the carbon sphere are also investigated. The carbon sphere is applied to electric double-layer capacitor and its electrochemical performance is studied. These results show that the carbon sphere obtained by HTC at 180 °C for 12 h with the WSS/deionized water volume ratio of 2/3 possess the highest specific capacitance under identical activation conditions. The specific capacitance of the carbon spheres can reach 296.1 F g-1 at a current density of 40 mA g-1. Besides, excellent cycle life and good capacitance retention (89.6%) are observed at 1.5 A g-1 after 5000 cycles. This study not only provides a facile and potential method for the WSS treatment, but also achieves the high value-added recycling of WSS for the preparation of porous carbon spheres with superior electrochemical properties.

  19. Edge effects in vertically-oriented graphene based electric double-layer capacitors

    NASA Astrophysics Data System (ADS)

    Yang, Huachao; Yang, Jinyuan; Bo, Zheng; Zhang, Shuo; Yan, Jianhua; Cen, Kefa

    2016-08-01

    Vertically-oriented graphenes (VGs) have been demonstrated as a promising active material for electric double-layer capacitors (EDLCs), partially due to their edge-enriched structure. In this work, the 'edge effects', i.e., edges as the promoters of high capacitance, in VG based EDLCs are investigated with experimental research and numerical simulations. VGs with diverse heights (i.e., edge-to-basal ratios) and edge densities are prepared with varying the plasma-enabled growth time and employing different plasma sources. Electrochemical measurements show that the edges play a predominant role on the charge storage behavior of VGs. A simulation is further conducted to unveil the roles of the edges on the separation and adsorption of ions within VG channels. The initial charge distribution of a VG plane is obtained with density functional theory (DFT) calculations, which is subsequently applied to a molecular dynamics (MD) simulation system to gain the insights into the microscope EDLC structures. Compared with the basal planes, the edges present higher initial charge density (by 4.2 times), higher ion packing density (by 2.6 times), closer ion packing location (by 0.8 Å), and larger ion separation degree (by 14%). The as-obtained findings will be instructive in designing the morphology and structure of VGs for enhanced capacitive performances.

  20. Electrochemical cell studies based on non-aqueous magnesium electrolyte for electric double layer capacitor applications

    NASA Astrophysics Data System (ADS)

    Chandrasekaran, Ramasamy; Koh, Meiten; Yamauchi, Akiyoshi; Ishikawa, Masashi

    Performances of electric double layer capacitors (EDLCs) based on an activated carbon electrode with acetonitrile (ACN), propylene carbonate (PC), or a ternary electrolyte, i.e., PC:ethylene carbonate (EC):diethyl carbonate (DEC), at 1 mol dm -3 of magnesium perchlorate [Mg(ClO 4) 2] salt have been investigated. The electrochemical responses were studied by impedance spectroscopy, cyclic voltammetry, and galvanostatic charge-discharge experiments at 25 °C in a three-electrode configuration. For a comparative evaluation, lithium perchlorate (LiClO 4) salt-based systems were also evaluated. All the observed results showed typical EDLC characteristics within the potential range between 0 and 1 V vs. an Ag/Ag + reference electrode. The Mg-based systems exhibited similar or rather better performances than the corresponding Li-based electrolytes; in particular, the rate capability of Mg-based ACN and PC electrolytes was much better than the corresponding Li-based electrolytes, indicating the high accessibility and utility of activated carbon pores by solvated Mg ions.

  1. Enhancing the Capacitive Performance of Electric Double-Layer Capacitors with Ionic Liquid Mixtures

    DOE PAGES

    Lian, C.; Liu, K.; Van Aken, Katherine L.; ...

    2016-04-18

    Formulating room-temperature ionic liquid (RTIL) mixed electrolytes was recently proposed as an effective and convenient strategy to increase the capacitive performance of electrochemical capacitors. In this paper, we investigate the electrical double-layer (EDL) structure and the capacitance of two RTILs, 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (EMI-TFSI) and 1-ethyl-3-methylimidazolium tetrafluoroborate (EMI-BF4), and their mixtures with onion-like carbon electrodes using experiment and classical density functional theory. The principal difference between these ionic liquids is the smaller diameter of the BF4– anion relative to the TFSI– anion and the EMI+ cation. A volcano-shaped trend is identified for the capacitance versus the composition of the RTIL mixture.more » The mixture effect, which makes more counterions pack on and more co-ions leave from the electrode surface, leads to an increase of the counterion density within the EDL and thus a larger capacitance. Finally, these theoretical predictions are in good agreement with our experimental observations and offer guidance for designing RTIL mixtures for EDL supercapacitors.« less

  2. Enhancing the Capacitive Performance of Electric Double-Layer Capacitors with Ionic Liquid Mixtures

    SciTech Connect

    Lian, C.; Liu, K.; Van Aken, Katherine L.; Gogotsi, Yury G.; Wesolowski, David J.; Liu, Honglai; Jiang, D. E.; Wu, Jianzhong

    2016-04-18

    Formulating room-temperature ionic liquid (RTIL) mixed electrolytes was recently proposed as an effective and convenient strategy to increase the capacitive performance of electrochemical capacitors. In this paper, we investigate the electrical double-layer (EDL) structure and the capacitance of two RTILs, 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (EMI-TFSI) and 1-ethyl-3-methylimidazolium tetrafluoroborate (EMI-BF4), and their mixtures with onion-like carbon electrodes using experiment and classical density functional theory. The principal difference between these ionic liquids is the smaller diameter of the BF4 anion relative to the TFSI anion and the EMI+ cation. A volcano-shaped trend is identified for the capacitance versus the composition of the RTIL mixture. The mixture effect, which makes more counterions pack on and more co-ions leave from the electrode surface, leads to an increase of the counterion density within the EDL and thus a larger capacitance. Finally, these theoretical predictions are in good agreement with our experimental observations and offer guidance for designing RTIL mixtures for EDL supercapacitors.

  3. Heterogeneous electron transfer at nanoscopic electrodes: importance of electronic structures and electric double layers.

    PubMed

    Chen, Shengli; Liu, Yuwen; Chen, Junxiang

    2014-08-07

    Heterogeneous electron-transfer (ET) processes at solid electrodes play key roles in molecular electronics and electrochemical energy conversion and sensing. Electrode nanosization and/or nanostructurization are among the major current strategies for performance promotion in these fields. Besides, nano-sized/structured electrodes offer great opportunities to characterize electrochemical structures and processes with high spatial and temporal resolution. This review presents recent insights into the nanoscopic size and structure effects of electrodes and electrode materials on heterogeneous ET kinetics, by emphasizing the importance of the electric double-layer (EDL) at the electrode/electrolyte interface and the electronic structure of electrode materials. It is shown, by general conceptual analysis and recent example demonstrations of representative electrode systems including electrodes of nanometer sizes and gaps and of nanomaterials such as sp(2) hybridized nanocarbons and semiconductor quantum dots, how the heterogeneous ET kinetics, the electronic structures of electrodes, the EDL structures at the electrode/electrolyte interface and the nanoscopic electrode sizes and structures may be related.

  4. Enhancing the Capacitive Performance of Electric Double-Layer Capacitors with Ionic Liquid Mixtures

    SciTech Connect

    Lian, C.; Liu, K.; Van Aken, Katherine L.; Gogotsi, Yury G.; Wesolowski, David J.; Liu, Honglai; Jiang, D. E.; Wu, Jianzhong

    2016-04-18

    Formulating room-temperature ionic liquid (RTIL) mixed electrolytes was recently proposed as an effective and convenient strategy to increase the capacitive performance of electrochemical capacitors. In this paper, we investigate the electrical double-layer (EDL) structure and the capacitance of two RTILs, 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (EMI-TFSI) and 1-ethyl-3-methylimidazolium tetrafluoroborate (EMI-BF4), and their mixtures with onion-like carbon electrodes using experiment and classical density functional theory. The principal difference between these ionic liquids is the smaller diameter of the BF4 anion relative to the TFSI anion and the EMI+ cation. A volcano-shaped trend is identified for the capacitance versus the composition of the RTIL mixture. The mixture effect, which makes more counterions pack on and more co-ions leave from the electrode surface, leads to an increase of the counterion density within the EDL and thus a larger capacitance. Finally, these theoretical predictions are in good agreement with our experimental observations and offer guidance for designing RTIL mixtures for EDL supercapacitors.

  5. Theory of volumetric capacitance of an electric double-layer supercapacitor.

    PubMed

    Skinner, Brian; Chen, Tianran; Loth, M S; Shklovskii, B I

    2011-05-01

    Electric double-layer supercapacitors are a fast-rising class of high-power energy storage devices based on porous electrodes immersed in a concentrated electrolyte or ionic liquid. As yet there is no microscopic theory to describe their surprisingly large capacitance per unit volume (volumetric capacitance) of ~100 F/cm(3), nor is there a good understanding of the fundamental limits on volumetric capacitance. In this paper we present a non-mean-field theory of the volumetric capacitance of a supercapacitor that captures the discrete nature of the ions and the exponential screening of their repulsive interaction by the electrode. We consider analytically and via Monte Carlo simulations the case of an electrode made from a good metal and show that in this case the volumetric capacitance can reach the record values. We also study how the capacitance is reduced when the electrode is an imperfect metal characterized by some finite screening radius. Finally, we argue that a carbon electrode, despite its relatively large linear screening radius, can be approximated as a perfect metal because of its strong nonlinear screening. In this way the experimentally measured capacitance values of ~100 F/cm(3) may be understood.

  6. PWM Inverter with Voltage Boosters with Regenerating Capability Augmented by Electric Double-Layer Capacitor

    NASA Astrophysics Data System (ADS)

    Yamamoto, Kichiro; Imakiire, Akihiro; Iimori, Kenichi

    An interior permanent magnet (IPM) motor drive system which has regenerating capability augmented by electric double-layer capacitors (EDLCs) is proposed. In the proposed system, EDLCs are arranged in series with batteries so that a lesser number of the EDLCs and batteries will be required. The proposed system has two bi-directional voltage boosters: one is for both the batteries and EDLCs to control the dc-link voltage of a PWM inverter and the other is for only the EDLCs and is used to control the energy flow from and to the EDLCs. In this paper, a strategy to control the energy flow to and from the EDLCs is explained and its effectiveness is confirmed by simulation and experimental results. Furthermore, the efficiencies of the voltage booster, inverter, PM motor, and whole system are measured for the system with the basic configuration, i.e., which consists of only one bi-directional voltage booster and PWM inverter. Then, the steady-state characteristics are determined. Finally, the efficiency of the voltage boosters in the proposed system is determined, and the advantage of the proposed PM motor drive system is discussed.

  7. One-step synthesis of hierarchically porous carbons for high-performance electric double layer supercapacitors

    NASA Astrophysics Data System (ADS)

    Zhang, Haitao; Zhang, Lei; Chen, Jun; Su, Hai; Liu, Fangyan; Yang, Weiqing

    2016-05-01

    With plenty of unique porous structure at micro-/nano scale, hierarchically porous carbons (HPCs) are promising for usage in advanced electric double layer supercapacitors (EDLCs) as the electrode materials. However, wide-range adoption of HPC for practical application is largely shadowed by its extremely complex synthesis process with considerably low production efficiency. Herein we reported a simple template-free, one-step sintering method, to massively produce the HPCs for high-performance EDLCs. Resorting to the 3D structure modification of the wide pore size distribution, high surface area of HPCs (up to 3000 m2 g-1) was achieved. By using 1 M Na2SO4 as electrolyte, the as-fabricated HPCs based EDLCs can be operated reversibly over a wide voltage window of 1.6 V with superior specific capacitance of 240 F g-1 under a current density of 0.5 A g-1. In the meanwhile, the EDLCs exhibit excellent rate capability (high power density of 16 kW kg-1 at 10.2 Wh kg-1) and long-term cycling stability with 9% loss of its initial capacitance after 2000 cycles. This output performance distinguished itself among most of the carbon-based EDLCs with neutral aqueous electrolyte. Thus, the template-free one-step sintering method produced HPCs for EDLCs represents a new approach for high-performance energy storage.

  8. Langevin-Poisson-EQT: A dipolar solvent based quasi-continuum approach for electric double layers

    NASA Astrophysics Data System (ADS)

    Mashayak, S. Y.; Aluru, N. R.

    2017-01-01

    Water is a highly polar solvent. As a result, electrostatic interactions of interfacial water molecules play a dominant role in determining the distribution of ions in electric double layers (EDLs). Near a surface, an inhomogeneous and anisotropic arrangement of water molecules gives rise to pronounced variations in the electrostatic and hydration energies of ions. Therefore, a detailed description of the structural and dielectric properties of water is important to study EDLs. However, most theoretical models ignore the molecular effects of water and treat water as a background continuum with a uniform dielectric permittivity. Explicit consideration of water polarization and hydration of ions is both theoretically and numerically challenging. In this work, we present an empirical potential-based quasi-continuum theory (EQT) for EDL, which incorporates the polarization and hydration effects of water explicitly. In EQT, water molecules are modeled as Langevin point dipoles and a point dipole based coarse-grained model for water is developed systematically. The space dependence of the dielectric permittivity of water is included in the Poisson equation to compute the electrostatic potential. In addition, to reproduce hydration of ions, ion-water coarse-grained potentials are developed. We demonstrate the EQT framework for EDL by simulating NaCl aqueous electrolyte confined inside slit-like capacitor channels at various ion concentrations and surface charge densities. We show that the ion and water density predictions from EQT agree well with the reference molecular dynamics simulations.

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

    PubMed Central

    Tsai, Sing-Jyun; Yang, Ruey-Jen

    2016-01-01

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

  10. Electrolyte dependence of transport properties of SrTiO3 electric double layer transistors

    NASA Astrophysics Data System (ADS)

    Sato, Yohei; Doi, Kiyomasa; Katayama, Yumiko; Ueno, Kazunori

    2017-05-01

    We report the electrolyte dependence of the transport properties of SrTiO3 electric double layer transistors (EDLTs). Ionic liquids such as 1-ethyl-3-methylimidazolium (EMIM) bis(trifluoromethylsulfonyl)imide (TFSI), EMIM dicyanamide (DCA), N,N-diethyl-N-methyl-N-(2-methoxyethyl) ammonium (DEME) TFSI, and DEME tetrafluoroborate (BF4), and polymer electrolytes such as poly(ethylene oxide) (PEO):CsClO4, were used as the electrolytes. All the devices showed metal-insulator transition with a threshold carrier density of 1 × 1013 cm-2. The maximum carrier density was also limited to below 1.6 × 1014 cm-2 for all the devices. On the other hand, the electron mobility at low temperature varied with the cation of the electrolyte and the gating temperature. The EDLT with the ionic liquid EMIM-DCA, which gated at room temperature, showed the highest mobility of 2,600 cm2 V-1 s-1 at 2 K. The observed electrolyte dependence of the SrTiO3 channel mobility is attributed to the change in the surface scattering rate by the adsorbed cations and spatial homogeneity of the cations in the electrolyte.

  11. Elucidating the DEP phenomena using a volumetric polarization approach with consideration of the electric double layer.

    PubMed

    Zhao, Yu; Brcka, Jozef; Faguet, Jacques; Zhang, Guigen

    2017-03-01

    Dielectrophoretic (DEP) phenomena have been explored to great success for various applications like particle sorting and separation. To elucidate the underlying mechanism and quantify the DEP force experienced by particles, the point-dipole and Maxwell Stress Tensor (MST) methods are commonly used. However, both methods exhibit their own limitations. For example, the point-dipole method is unable to fully capture the essence of particle-particle interactions and the MST method is not suitable for particles of non-homogeneous property. Moreover, both methods fare poorly when it comes to explaining DEP phenomena such as the dependence of crossover frequency on medium conductivity. To address these limitations, the authors have developed a new method, termed volumetric-integration method, with the aid of computational implementation, to reexamine the DEP phenomena, elucidate the governing mechanism, and quantify the DEP force. The effect of an electric double layer (EDL) on particles' crossover behavior is dealt with through consideration of the EDL structure along with surface ionic/molecular adsorption, unlike in other methods, where the EDL is accounted for through simply assigning a surface conductance value to the particles. For validation, by comparing with literature experimental data, the authors show that the new method can quantify the DEP force on not only homogeneous particles but also non-homogeneous ones, and predict particle-particle interactions fairly accurately. Moreover, the authors also show that the predicted dependence of crossover frequency on medium conductivity and particle size agrees very well with experimental measurements.

  12. Electric Double-Layer Capacitor Module with Series-Parallel Reconfigurable Cell Voltage Equalizers

    NASA Astrophysics Data System (ADS)

    Uno, Masatoshi; Kukita, Akio; Tanaka, Koji

    When electric double-layer capacitors (EDLCs) are connected in series, cell voltage imbalance that results due to non-uniform cell properties is observed. Cell voltage imbalance should be minimized to prolong cycle lives and maximize the available energy of cells. In this study, we propose a series-parallel reconfigurable cell voltage equalizer that is considered suitable for energy-storage systems using EDLCs instead of traditional secondary batteries as main energy-storage sources. The proposed equalizer requires only EDLCs and switches as its main circuit elements, and it utilizes EDLCs not only for energy storage but also for equalization. An equivalent circuit model using equivalent resistors that can be regarded as an index of equalization speed is developed. Current distribution and cell voltage imbalance during operation are quantitatively generalized. Experimental charge-discharge tests were performed for EDLC modules to demonstrate the performance of the cell voltage equalizer. All the cells in the modules could be charged/discharged uniformly even when a degradation-mimicking cell was intentionally included in the module. The resultant cell voltage imbalances and current distributions were in good agreement with those predicted by mathematical analyses.

  13. Electric Double-Layer Capacitor Based on an Ionic Clathrate Hydrate

    SciTech Connect

    Lee, Wonhee; Kwon, Minchul; Park, Seongmin; Lim, Dongwook; Cha, Jong-Ho; Lee, Huen

    2013-05-13

    Herein, we suggest a new approach to an electric double-layer capacitor (EDLC) that is based on a proton-conducting ionic clathrate hydrate (ICH). The ice-like structures of clathrate hydrates, which are comprised of host water molecules and guest ions, make them suitable for applications in EDLC electrolytes, owing to their high proton conductivities and thermal stabilities. The carbon materials in the ICH Me{sub 4}NOH[DOT OPERATOR]5H{sub 2}O show a high specific capacitance, reversible charge–discharge behavior, and a long cycle life. The ionic-hydrate complex provides the following advantages in comparison with conventional aqueous and polymer electrolytes: 1)The ICH does not cause leakage problems under normal EDLC operating conditions. 2)The hydrate material can be utilized itself, without requiring any pre-treatments or activation for proton conduction, thus shortening the preparation procedure of the EDLC. 3)The crystallization of the ICH makes it possible to tailor practical EDLC dimensions because of its fluidity as a liquid hydrate. 4)The hydrate solid electrolyte exhibits more-favorable electrochemical stability than aqueous and polymer electrolytes. Therefore, ICH materials are expected to find practical applications in versatile energy devices that incorporate electrochemical systems.

  14. Fast Response, vertically oriented graphene nanosheet electric double layer capacitors synthesized from C(2)H(2).

    PubMed

    Cai, Minzhen; Outlaw, Ronald A; Quinlan, Ronald A; Premathilake, Dilshan; Butler, Sue M; Miller, John R

    2014-06-24

    The growth and electrical characteristics of vertically oriented graphene nanosheets grown by radio frequency plasma-enhanced chemical vapor deposition from C2H2 feedstock on nickel substrates and used as electrodes in symmetric electric double layer capacitors (EDLC) are presented. The nanosheets exhibited 2.7 times faster growth rate and much greater specific capacitance for a given growth time than CH4 synthesized films. Raman spectra showed that the intensity ratio of the D band to G band versus temperature initially decreased to a minimum value of 0.45 at a growth temperature of 750 °C, but increased rapidly with further temperature increase (1.15 at 850 °C). The AC specific capacitance at 120 Hz of these EDLC devices increased in a linear fashion with growth temperature, up to 265 μF/cm(2) (2 μm high film, 850 °C with 10 min growth). These devices exhibited ultrafast frequency response: the frequency response at -45° phase angle reached over 20 kHz. Consistent with the increase in D band to G band ratio, the morphology of the films became less vertical, less crystalline, and disordered at substrate temperatures of 800 °C and above. This deterioration in morphology resulted in an increase in graphene surface area and defect density, which, in turn, contributed to the increased capacitance, as well as a slight decrease in frequency response. The low equivalent series resistance varied from 0.07 to 0.08 Ω and was attributed to the significant carbon incorporation into the Ni substrate.

  15. The effect of an electrical double layer on the voltammetric performance of nanoscale interdigitated electrodes: a simulation study.

    PubMed

    Yang, Xiaoling; Zhang, Guigen

    2008-11-19

    Finite-element based computational simulation is performed to investigate the effect of an electrical double layer (EDL) on the electrochemical processes of nanometer-scale interdigitated electrodes (nano-IDEs). Results show that the EDL structure will alter the voltammetric current response of nano-IDEs due to the expansion of the diffuse layer into the diffusion layer at the electrode surfaces and the overlap of the electrical fields of the neighboring electrodes. The EDL induced change in the voltammetric current response is more severe for nano-IDEs with a smaller electrode size and gap spacing, and the EDL effect is influenced by the compact layer thickness, the charge valence of the redox species, the electron transfer rate, and the absence of the supporting electrolyte.

  16. Electrokinetic flow in a nanochannel with an overlapped electrical double layer

    NASA Astrophysics Data System (ADS)

    Song, Zhuorui

    Electrokinetic flows within an overlapped Electrical Double Layer (EDL), which are not well-understood, were theoretically investigated in this study with the particular attention on the consideration of hydronium ions in the EDL. Theoretical models for fully-developed steady pressure-driven flow for salt-free water or a binary salt solution in a slit-like nanochannel connecting to two reservoirs were developed. The transient flow in such a domain was also simulated from static state to the final steady state. In these models, the Poisson equation and the Nernst-Planck equation were solved either by analytic methods or by the finite element method. Surface adsorption-desorption equilibrium and water equilibrium were considered to account for the proton exchange at the surface and in the fluid. These models were the first to include those comprehensive processes that are uniquely important for overlapped EDL scenarios. This study improves the understanding of electrokinetic flows within an overlapped EDL by demonstrating the profound impact of hydronium ions on the EDL structure. In the steady flow of potassium chloride solutions, hydronium ions are more enriched than potassium ions by up to 2~3 orders of magnitude, making the electrokinetic effects greatly depressed. The unequal enrichment effects of counterions were omitted in the traditional theory partially because the transient is extremely slow. The simulation results show that a concentration hump of hydronium ions initially forming at the channel entrance gradually expands over the whole channel in a way similar to the concentration plug flow moving downstream. The time required for the flow to reach the steady state could be as long as thousands of times the hydraulic retention time, dependent on the degree of the EDL overlap. This study improves the fundamental understanding for nanofluidic flows.

  17. Ionic Asymmetry and Solvent Excluded Volume Effects on Spherical Electric Double Layers: A Density Functional Approach

    SciTech Connect

    Medasani, Bharat; Ovanesyan, Zaven; Thomas, Dennis G.; Sushko, Maria L.; Marucho, Marcelo

    2014-05-29

    In this article we present a classical density functional theory for electrical double layers of spherical macroions that extends the capabilities of conventional approaches by accounting for electrostatic ion correlations, size asymmetry and excluded volume effects. The approach is based on a recent approximation introduced by Hansen-Goos and Roth for the hard sphere excess free energy of inhomogeneous fluids (J. Chem. Phys. 124, 154506). It accounts for the proper and efficient description of the effects of ionic asymmetry and solvent excluded volume, especially at high ion concentrations and size asymmetry ratios including those observed in experimental studies. Additionally, we utilize a leading functional Taylor expansion approximation of the ion density profiles. In addition, we use the Mean Spherical Approximation for multi-component charged hard sphere fluids to account for the electrostatic ion correlation effects. These approximations are implemented in our theoretical formulation into a suitable decomposition of the excess free energy which plays a key role in capturing the complex interplay between charge correlations and excluded volume effects. We perform Monte Carlo simulations in various scenarios to validate the proposed approach, obtaining a good compromise between accuracy and computational cost. We use the proposed computational approach to study the effects of ion size, ion size asymmetry and solvent excluded volume on the ion profiles, integrated charge, mean electrostatic potential, and ionic coordination number around spherical macroions in various electrolyte mixtures. Our results show that both solvent hard sphere diameter and density play a dominant role in the distribution of ions around spherical macroions, mainly for experimental water molarity and size values where the counterion distribution is characterized by a tight binding to the macroion, similar to that predicted by the Stern model.

  18. Electrocapillarity of an electrolyte solution in a nanoslit with overlapped electric double layer: continuum approach.

    PubMed

    Lee, Jung A; Kang, In Seok

    2014-09-01

    A nanoslit is a long narrow opening between two parallel plates that are nanometers apart from each other. When an electrolyte solution is present inside a nanoslit, an overlapped electrical double layer (EDL) is formed and there exist distributions of the osmotic pressure and the Maxwell stress across the nanoslit. It is well known that the total normal stress (osmotic pressure contribution + Maxwell stress contribution) in the direction normal to the nanoslit surface is uniform and the value is the same as the osmotic pressure at the centerline. On the other hand, it is not well known that the total normal stress in the direction parallel to the slit surface is not uniform. When there is an electrolyte-gas interface inside a nanoslit, this total normal stress in the direction parallel to the slit surface generates the electrocapillarity effect. In the present work, the electromechanical approach is adopted to estimate the electrocapillarity effect in terms of the slit surface potential (or the surface charge density), the gap size, and the bulk ion concentrations. In order to handle the problem analyically, it is assumed that the nanoslit problem is in the continuum range and the interface is initially flat. The deformation of the interface due to the nonuniform total normal stress along the interface is also obtained by using the first order perturbation method. The significance of the present work can be manifested by the fact that external voltage is frequently used in nanoscaled systems and the electrocapillarity effect should be considered in addition to the intrinsic capillarity due to surface tension.

  19. Rate of Bubble Coalescence following Quasi-Static Approach: Screening and Neutralization of the Electric Double Layer

    PubMed Central

    Katsir, Yael; Marmur, Abraham

    2014-01-01

    Air-bubble coalescence in aqueous electrolytic solutions, following quasi-static approach, was studied in order to understand its slow rate in purified water and high rate in electrolytic solutions. The former is found to be due to surface charges, originating from the speciation of dissolved CO2, which sustain the electric double layer repulsion. Rapid coalescence in electrolytic solutions is shown to occur via two different mechanisms: (1) neutralization of the carbonaceous, charged species by acids; or (2) screening of the repulsive charge effects by salts and bases. The results do not indicate any ion specificity. They can be explained within the DLVO theory for the van der Waals and electric double layer interactions between particles, in contrast to observations of coalescence following dynamic approach. The present conclusions should serve as a reference point to understanding the dynamic behavior. PMID:24589528

  20. A systematic comparison of different approaches of density functional theory for the study of electrical double layers

    SciTech Connect

    Yang, Guomin; Liu, Longcheng

    2015-05-21

    Based on the best available knowledge of density functional theory (DFT), the reference-fluid perturbation method is here extended to yield different approaches that well account for the cross correlations between the Columbic interaction and the hard-sphere exclusion in an inhomogeneous ionic hard-sphere fluid. In order to quantitatively evaluate the advantage and disadvantage of different approaches in describing the interfacial properties of electrical double layers, this study makes a systematic comparison against Monte Carlo simulations over a wide range of conditions. The results suggest that the accuracy of the DFT approaches is well correlated to a coupling parameter that describes the coupling strength of electrical double layers by accounting for the steric effect and that can be used to classify the systems into two regimes. In the weak-coupling regime, the approaches based on the bulk-fluid perturbation method are shown to be more accurate than the counterparts based on the reference-fluid perturbation method, whereas they exhibit the opposite behavior in the strong-coupling regime. More importantly, the analysis indicates that, with a suitable choice of the reference fluid, the weighted correlation approximation (WCA) to DFT gives the best account of the coupling effect of the electrostatic-excluded volume correlations. As a result, a piecewise WCA approach can be developed that is robust enough to describe the structural and thermodynamic properties of electrical double layers over both weak- and strong-coupling regimes.

  1. Electrochemical and structural properties of the electrical double layer of two-component electrolytes in response to varied electrode potential

    NASA Astrophysics Data System (ADS)

    Kiyohara, Kenji; Yamagata, Masaki; Ishikawa, Masashi

    2016-04-01

    The electrochemical and structural properties of the electrical double layers for two-component electrolytes were studied by Monte Carlo simulations using simple models. When the electrolyte contains two species of cations that have different diameters, the capacitance on the cathode dramatically increases as a large negative potential is applied. This behavior is qualitatively similar to the one reported in an experimental work that has used Li-containing ionic liquid as the electrolyte [M. Yamagata et al., Electrochim. Acta 110, 181-190 (2013)], in which it has also been reported that addition of Li ions to the electrolyte enhances the potential window to the negative side. The analysis of the ionic structure showed that the electrical double layer on the cathode is dominantly formed by the larger cations under small negative potentials, while they are replaced by the smaller cations under large negative potentials. This transition of the ionic structure with electrode potential is also consistent with the enhancement of the potential window that was found in the experimental work, which suggests that the organic cations are expelled from the electrical double layer under large negative potentials and the chance of decomposition is reduced.

  2. Suppression of ion conductance by electro-osmotic flow in nano-channels with weakly overlapping electrical double layers

    NASA Astrophysics Data System (ADS)

    Liu, Yang; Guo, Lingzi; Zhu, Xin; Ran, Qiushi; Dutton, Robert

    2016-08-01

    This theoretical study investigates the nonlinear ionic current-voltage characteristics of nano-channels that have weakly overlapping electrical double layers. Numerical simulations as well as a 1-D mathematical model are developed to reveal that the electro-osmotic flow (EOF) interplays with the concentration-polarization process and depletes the ion concentration inside the channels, thus significantly suppressing the channel conductance. The conductance may be restored at high electrical biases in the presence of recirculating vortices within the channels. As a result of the EOF-driven ion depletion, a limiting-conductance behavior is identified, which is intrinsically different from the classical limiting-current behavior.

  3. Electrical double layers at shock fronts in glow discharges and afterglows

    SciTech Connect

    Siefert, Nicholas S.

    2010-12-15

    This paper examines the propagation of spark-generated shockwaves (1.0double layer, at the shock front. The double layer balances the flux of charged particles on both sides of the shock front. The double layer voltage drop was measured in the current-carrying discharge using floating probes and compared with previous models. As well, we measured argon 1s{sup 5} metastable-state density and demonstrate that metastable-state neutral species can be compressed across a shock front and approximately predicted using the Rankine-Hugoniot relationship.

  4. Electric Double Layer Composed of an Antagonistic Salt in an Aqueous Mixture: Local Charge Separation and Surface Phase Transition

    NASA Astrophysics Data System (ADS)

    Yabunaka, Shunsuke; Onuki, Akira

    2017-09-01

    We examine an electric double layer containing an antagonistic salt in an aqueous mixture, where the cations are small and hydrophilic but the anions are large and hydrophobic. In this situation, a strong coupling arises between the charge density and the solvent composition. As a result, the anions are trapped in an oil-rich adsorption layer on a hydrophobic wall. We then vary the surface charge density σ on the wall. For σ >0 the anions remain accumulated, but for σ <0 the cations are attracted to the wall with increasing |σ |. Furthermore, the electric potential drop Ψ (σ ) is nonmonotonic when the solvent interaction parameter χ (T ) exceeds a critical value χc determined by the composition and the ion density in the bulk. This leads to a first-order phase transition between two kinds of electric double layers with different σ and common Ψ . In equilibrium such two-layer regions can coexist. The steric effect due to finite ion sizes is crucial in these phenomena.

  5. Electric Double Layer Composed of an Antagonistic Salt in an Aqueous Mixture: Local Charge Separation and Surface Phase Transition.

    PubMed

    Yabunaka, Shunsuke; Onuki, Akira

    2017-09-15

    We examine an electric double layer containing an antagonistic salt in an aqueous mixture, where the cations are small and hydrophilic but the anions are large and hydrophobic. In this situation, a strong coupling arises between the charge density and the solvent composition. As a result, the anions are trapped in an oil-rich adsorption layer on a hydrophobic wall. We then vary the surface charge density σ on the wall. For σ>0 the anions remain accumulated, but for σ<0 the cations are attracted to the wall with increasing |σ|. Furthermore, the electric potential drop Ψ(σ) is nonmonotonic when the solvent interaction parameter χ(T) exceeds a critical value χ_{c} determined by the composition and the ion density in the bulk. This leads to a first-order phase transition between two kinds of electric double layers with different σ and common Ψ. In equilibrium such two-layer regions can coexist. The steric effect due to finite ion sizes is crucial in these phenomena.

  6. An analysis of electric double layers near comb electrodes using the linearized Poisson-Nernst-Planck theory

    NASA Astrophysics Data System (ADS)

    Zhang, Chunli; Lu, Shuting; Mao, Renwei; Chen, Weiqiu; Tan, Li; Zhou, Qin; Yang, Jiashi

    2017-01-01

    A theoretical analysis on electric double layers formed near corners and neighboring branches of a comb electrode with a prescribed electric potential in an ionic conductor was performed using the linearized Poisson-Nernst-Planck theory which is closely related to the linearized Gouy-Chapman theory in static (time-independent) problems. Analytical solutions were obtained for two problems relevant to ionic capacitance applications defined over rectangular domains. The electric potential and ion distributions were calculated which are new, useful, and fundamental to the understanding and design of devices with comb electrodes. The basic behaviors of the distributions are presented and examined. For a positively charged electrode, the distribution of the negative ions was found to be qualitatively similar to that of the electric potential, and the behavior of the positive ions is the opposite. At an electrode corner, the electric double layer is relatively thicker than along a line electrode. When the distance between two positively charged parallel electrode branches is about twice the Debye length, the region between the two electrode branches is nearly uniformly filled by negative ions.

  7. Increasing the Room-Temperature Electric Double Layer Retention Time in Two-Dimensional Crystal FETs.

    PubMed

    Kinder, Erich W; Fuller, Ashley; Lin, Yu-Chuan; Robinson, Joshua A; Fullerton-Shirey, Susan K

    2017-07-26

    Poly(vinyl alcohol) (PVA) and LiClO4, a solid polymer electrolyte with a glass transition temperature (Tg) of 80 °C, is used to electrostatically gate graphene field-effect transistors. The ions in PVA:LiClO4 are drifted into place by field-effect at T > Tg, providing n- or p-type doping, and when the device is cooled to room temperature, the polymer mobility and, hence ion mobility are arrested and the electric double layer (EDL) is "locked" into place in the absence of a gate bias. Unlike other electrolytes used to gate two-dimensional devices for which the Tg, and therefore the "locking" temperature, is well below room temperature, the electrolyte demonstrated in this work provides a route to achieve room-temperature EDL stability. Specifically, a 6 orders of magnitude increase in the room temperature EDL retention time is demonstrated over the commonly used electrolyte, poly(ethylene oxide) (PEO) and LiClO4. Hall measurements confirm that large sheet carrier densities can be achieved with PVA:LiClO4 at top gate programming voltages of ±2 V (-6.3 ± 0.03 × 10(13) cm(-2) for electrons and 1.6 ± 0.3 × 10(14) cm(-2) for holes). Transient drain current measurements show that at least 75% of the EDL is retained after more than 4 h at room temperature. Unlike PEO-based electrolytes, PVA:LiClO4 is compatible with the chemicals used in standard photolithographic processes enabling the direct deposition of patterned, metal contacts on the surface of the electrolyte. A thermal instability in the electrolyte is detected by both I-V measurements and differential scanning calorimetry, and FTIR measurements suggest that thermally catalyzed cross-linking may be driving phase separation between the polymer and the salt. Nevertheless, this work highlights how the relationship between polymer and ion mobility can be exploited to tune the state retention time and the charge carrier density of a 2D crystal transistor.

  8. Overcharging and charge reversal in the electrical double layer around the point of zero charge.

    PubMed

    Guerrero-García, G Iván; González-Tovar, Enrique; Chávez-Páez, Martín; Lozada-Cassou, Marcelo

    2010-02-07

    The ionic adsorption around a weakly charged spherical colloid, immersed in size-asymmetric 1:1 and 2:2 salts, is studied. We use the primitive model (PM) of an electrolyte to perform Monte Carlo simulations as well as theoretical calculations by means of the hypernetted chain/mean spherical approximation (HNC/MSA) and the unequal-radius modified Gouy-Chapman (URMGC) integral equations. Structural quantities such as the radial distribution functions, the integrated charge, and the mean electrostatic potential are reported. Our Monte Carlo "experiments" evidence that near the point of zero charge, the smallest ionic species is preferentially adsorbed onto the macroparticle, independently of the sign of the charge carried by this tiniest electrolytic component, giving rise to the appearance of the phenomena of charge reversal (CR) and overcharging (OC). Accordingly, colloidal CR, due to an excessive attachment of counterions, is observed when the macroion is slightly charged and the coions are larger than the counterions. In the opposite situation, i.e., if the counterions are larger than the coions, the central macroion acquires additional like-charge (coions) and hence becomes "overcharged," a feature theoretically predicted in the past [F. Jiménez-Angeles and M. Lozada-Cassou, J. Phys. Chem. B 108, 7286 (2004)]. In other words, here we present the first simulation data on OC in the PM electrical double layer, showing that close to the point of zero charge, this novel effect surges as a consequence of the ionic size asymmetry. We also find that the HNC/MSA theory captures well the CR and OC phenomena exhibited by the computer experiments, especially as the macroion's charge increases. On the contrary, even if URMGC also displays CR and OC, its predictions do not compare favorably with the Monte Carlo data, evidencing that the inclusion of hard-core correlations in Monte Carlo and HNC/MSA enhances and extends those effects. We explain our findings in terms of the

  9. X-ray Study of the Electric Double Layer at the n-Hexane/Nanocolloidal Silica Interface

    SciTech Connect

    Tikhonov,A.

    2006-01-01

    The spatial structure of the transition region between an insulator and an electrolyte solution was studied with x-ray scattering. The electron-density profile across the n-hexane/silica sol interface (solutions with 5, 7, and 12 nm colloidal particles) agrees with the theory of the electrical double layer and shows separation of positive and negative charges. The interface consists of three layers, i.e., a compact layer of Na{sup +}, a loose monolayer of nanocolloidal particles as part of a thick diffuse layer, and a low-density layer sandwiched between them. Its structure is described by a model in which the potential gradient at the interface reflects the difference in the potentials of 'image forces' between the cationic Na{sup +} and anionic nanoparticles and the specific adsorption of surface charge. The density of water in the large electric field ({approx}10{sup 9}-10{sup 10} V/m) of the transition region and the layering of silica in the diffuse layer is discussed.

  10. Comparison of Molecular Dynamics with Classical Density Functional and Poisson–Boltzmann Theories of the Electric Double Layer in Nanochannels

    PubMed Central

    2012-01-01

    Comparisons are made among Molecular Dynamics (MD), Classical Density Functional Theory (c-DFT), and Poisson–Boltzmann (PB) modeling of the electric double layer (EDL) for the nonprimitive three component model (3CM) in which the two ion species and solvent molecules are all of finite size. Unlike previous comparisons between c-DFT and Monte Carlo (MC), the present 3CM incorporates Lennard-Jones interactions rather than hard-sphere and hard-wall repulsions. c-DFT and MD results are compared over normalized surface charges ranging from 0.2 to 1.75 and bulk ion concentrations from 10 mM to 1 M. Agreement between the two, assessed by electric surface potential and ion density profiles, is found to be quite good. Wall potentials predicted by PB begin to depart significantly from c-DFT and MD for charge densities exceeding 0.3. Successive layers are observed to charge in a sequential manner such that the solvent becomes fully excluded from each layer before the onset of the next layer. Ultimately, this layer filling phenomenon results in fluid structures, Debye lengths, and electric surface potentials vastly different from the classical PB predictions. PMID:23316120

  11. Effect of conductivity variations within the electric double layer on the streaming potential estimation in narrow fluidic confinements.

    PubMed

    Das, Siddhartha; Chakraborty, Suman

    2010-07-06

    In this article, we investigate the implications of ionic conductivity variations within the electrical double layer (EDL) on the streaming potential estimation in pressure-driven fluidic transport through narrow confinements. Unlike the traditional considerations, we do not affix the ionic conductivities apriori by employing preset values of dimensionless parameters (such as the Dukhin number) to estimate the streaming potential. Rather, utilizing the Gouy-Chapman-Grahame model for estimating the electric potential and charge density distribution within the Stern layer, we first quantify the Stern layer electrical conductivity as a function of the zeta potential and other pertinent parameters quantifying the interaction of the ionic species with the charged surface. Next, by invoking the Boltzmann model for cationic and anionic distribution within the diffuse layer, we obtain the diffuse layer electrical conductivity. On the basis of these two different conductivities pertaining to the two different portions of the EDL as well as the bulk conductivity, we define two separate Dukhin numbers that turn out to be functions of the dimensionless zeta potential and the channel height to Debye length ratio. We derive analytical expressions for the streaming potential as a function of the fundamental governing parameters, considering the above. The results reveal interesting and significant deviations between the streaming potential predictions from the present considerations against the corresponding predictions from the classical considerations in which electrochemically consistent estimates of variable EDL conductivity are not traditionally accounted for. In particular, it is revealed that the variations of streaming potential with zeta potential are primarily determined by the competing effects of EDL electromigration and ionic advection. Over low and high zeta potential regimes, the Stern layer and diffuse layer conductivities predominantly dictate the streaming

  12. Relation between the ion size and pore size for an electric double-layer capacitor.

    PubMed

    Largeot, Celine; Portet, Cristelle; Chmiola, John; Taberna, Pierre-Louis; Gogotsi, Yury; Simon, Patrice

    2008-03-05

    The research on electrochemical double layer capacitors (EDLC), also known as supercapacitors or ultracapacitors, is quickly expanding because their power delivery performance fills the gap between dielectric capacitors and traditional batteries. However, many fundamental questions, such as the relations between the pore size of carbon electrodes, ion size of the electrolyte, and the capacitance have not yet been fully answered. We show that the pore size leading to the maximum double-layer capacitance of a TiC-derived carbon electrode in a solvent-free ethyl-methylimmidazolium-bis(trifluoro-methane-sulfonyl)imide (EMI-TFSI) ionic liquid is roughly equal to the ion size (approximately 0.7 nm). The capacitance values of TiC-CDC produced at 500 degrees C are more than 160 F/g and 85 F/cm(3) at 60 degrees C, while standard activated carbons with larger pores and a broader pore size distribution present capacitance values lower than 100 F/g and 50 F/cm(3) in ionic liquids. A significant drop in capacitance has been observed in pores that were larger or smaller than the ion size by just an angstrom, suggesting that the pore size must be tuned with sub-angstrom accuracy when selecting a carbon/ion couple. This work suggests a general approach to EDLC design leading to the maximum energy density, which has been now proved for both solvated organic salts and solvent-free liquid electrolytes.

  13. Effect of double-stranded DNA on electrical double layer structure at oxide/electrolyte interface in classical molecular dynamics simulation

    NASA Astrophysics Data System (ADS)

    Maekawa, Yuki; Shibuta, Yasushi; Sakata, Toshiya

    2015-01-01

    The elucidation of the electrical double layer (EDL) structure including biomolecules is helpful in controlling biointerfacial functions in biosensing devices. In this study, the effect of double-stranded DNA (ds-DNA) on the EDL structure at the SiO2/NaClaq interface in a concentrated solution was investigated by classical molecular dynamics (MD) simulation. In 1.0 M NaClaq, negatively charged ds-DNA shielded electrically by cations did not affect the potential profile of the EDL structure. This finding indicates that the simulated bio-interfacial structure allows the detection of ionic charges adsorbed directly onto substrates in a concentrated solution regardless of the presence of shielded biomolecular charges.

  14. Electric field effect on a double MgO CoFeB-based free layer

    NASA Astrophysics Data System (ADS)

    Huang, Jiancheng; Sim, Cheow Hin; Naik, Vinayak Bharat; Tran, Michael; Lim, Sze Ter; Huang, Aihong; Yap, Qi Jia; Han, Guchang

    2016-03-01

    We study the electric field (EF) effect on MgO/CoFeB/Ta/CoFeB/MgO free layers by varying the thickness of the top MgO layer. The two CoFeB/MgO interfaces oppose the change in magnetic anisotropy from each other and this can be understood by considering the voltage drop as well as the efficiency of the anisotropy modulation from both interfaces. These results are proven by monitoring both coercivity and anisotropy field as a function of the applied EF. From the fit to the model, we show that the bottom CoFeB/MgO interface has a higher EF efficiency than the top interface.

  15. Double layer electric fields aiding the production of energetic flat-top distributions and superthermal electrons within magnetic reconnection exhausts

    NASA Astrophysics Data System (ADS)

    Egedal, J.; Daughton, W.; Le, A.; Borg, A. L.

    2015-10-01

    Using a kinetic simulation of magnetic reconnection, it was recently shown that magnetic-field-aligned electric fields (E∥) can be present over large spatial scales in reconnection exhausts. The largest values of E∥ are observed within double layers. The existence of double layers in the Earth's magnetosphere is well documented. In our simulation, their formation is triggered by large parallel streaming of electrons into the reconnection region. These parallel electron fluxes are required for maintaining quasi-neutrality of the reconnection region and increase with decreasing values of the normalized electron pressure upstream of the reconnection region, βe∞=2 μ0ne ∞Te ∞/B∞2 . A threshold (βe∞ < 0.02) is derived for strong double layers to develop. We also document how the electron confinement, provided in part by the structure in E∥, allows sustained energization by perpendicular electric fields (E⊥). The energization is a consequence of the confined electrons' chaotic orbital motion that includes drifts aligned with the reconnection electric field. The level of energization is proportional to the initial particle energy and therefore is enhanced by the initial energy boost of the acceleration potential, e Φ∥=e ∫x∞∥ d l , acquired by electrons entering the region. The mechanism is effective in an extended region of the reconnection exhaust allowing for the generation of superthermal electrons in reconnection scenarios, including those with only a single x-line. An expression for the phase-space distribution of the superthermal electrons is derived, providing an accurate match to the kinetic simulation results. The numerical and analytical results agree with detailed spacecraft observations recorded during reconnection events in the Earth's magnetotail.

  16. Development of effective power supply using electric double layer capacitor for static magnetic field coils in fusion plasma experiments.

    PubMed

    Inomoto, M; Abe, K; Yamada, T; Kuwahata, A; Kamio, S; Cao, Q H; Sakumura, M; Suzuki, N; Watanabe, T; Ono, Y

    2011-02-01

    A cost-effective power supply for static magnetic field coils used in fusion plasma experiments has been developed by application of an electric double layer capacitor (EDLC). A prototype EDLC power supply system was constructed in the form of a series LCR circuit. Coil current of 100 A with flat-top longer than 1 s was successfully supplied to an equilibrium field coil of a fusion plasma experimental apparatus by a single EDLC module with capacitance of 30 F. The present EDLC power supply has revealed sufficient performance for plasma confinement experiments whose discharge duration times are an order of several seconds.

  17. A modified Poisson-Boltzmann analysis of the capacitance behavior of the electric double layer at low temperatures.

    PubMed

    Bhuiyan, L B; Outhwaite, C W; Henderson, D

    2005-07-15

    The modified Poisson-Boltzmann theory is used to analyze the anomalous behavior of the electric double layer capacitance for small surface charge at low temperatures and densities. Good agreement is found with simulation and recent density-functional theory results. Negative adsorption is also found in line with theory and simulation. An unsatisfactory feature is the relatively poor structure in this region due to the inherent approximations in the theory. This feature is unimportant in relation to the capacitance results but has implications when calculating adsorption properties.

  18. Potential dependent structure of electric double layer faced to solid electrode surfaces analyzed by electrochemical frequency modulation atomic force microscopy

    NASA Astrophysics Data System (ADS)

    Fukui, Ken-ichi; Utsunomiya, Toru; Yokota, Yasuyuki

    2017-08-01

    This progress review summarizes recent achievements on the analyses of electric double layer (EDL) formed at electrolyte/electrode interfaces by using electrochemical frequency modulation atomic force microscopy (EC-FM-AFM), which enables to obtain the liquid side information on the liquid molecules’ structuring as well as the atomic scale resolution of the solid side at low loading forces. Potential and electrolyte dependent EDL structures at aqueous solution/graphite interfaces and strong substrate dependency on the structuring of interfacial ionic liquid are mainly discussed.

  19. New design of electric double layer capacitors with aqueous LiOH electrolyte as alternative to capacitor with KOH solution

    NASA Astrophysics Data System (ADS)

    Stepniak, Izabela; Ciszewski, Aleksander

    Activated carbon (AC) fiber cloths and a hydrophobic microporous polypropylene (PP) membrane, both modified with lithiated acetone oligomers, were used as electrodes and a separator in electric double layer capacitors (EDLCs) with aqueous lithium hydroxide (LiOH) as the electrolyte. Electrochemical characteristics of EDLCs were investigated by cyclic voltammetry (CV), galvanostatic charge-discharge cycle tests and impedance spectroscopy (EIS), compared with a case of the capacitor with aqueous potassium hydroxide (KOH) as an electrolyte. As a result, the capacitor with LiOH aqueous solution and a modified separator and electrodes was found to exhibit higher specific capacitance, maximum energy stored and maximum power than that with KOH aqueous solution.

  20. All solid-state electric double-layer capacitors based on alkaline polyvinyl alcohol polymer electrolytes

    NASA Astrophysics Data System (ADS)

    Yang, Chun-Chen; Hsu, Sung-Ting; Chien, Wen-Chen

    Solid-state electrochemical double-layer capacitors (ELDCs) based on alkaline polyvinyl alcohol (PVA) solid polymer electrolytes (SPEs) are prepared. Electrochemical capacitance performance of these capacitors is studied by cyclic voltammetry, galvanostatic charge-discharge testing, and ac impedance spectroscopy. For comparison, two types of EDLC cells are constructed and tested. It is found that an EDLC with a PVA polymer electrolyte exhibits much higher capacitance and longer cycle-life than one with the PP/PE separator. The specific capacitance for the EDLC with the PVA-based SPE is in the range of 100-112 F g -1, and depends on the scan rate or the charge-discharge current rates. The results also indicate that the solid-state EDLC shows a relatively stable specific capacitance of 100 F g -1 after 1000 cycles. The findings suggest that the PVA-based SPE is a promising material for use in EDLCs.

  1. Magnetic and electrical properties of spin valve with single and double specular oxide layers

    NASA Astrophysics Data System (ADS)

    Hong, Jongill; Noma, Kenji; Kanai, Hitoshi; Kane, Junichi

    2001-06-01

    Appropriate oxide capping on a spin valve significantly improved electrical and magnetic properties. The interlayer exchange coupling oscillated in the thickness range of a Cu spacer (between 20 and 30 Å). The coupling was antiferromagnetic and it allowed us to reduce the Cu spacer down to 20 Å without sacrificing the good properties of the spin valve. The improvement is due to enhanced specular reflection at the interface between the magnetic and the oxide layer and to less current shunting through the Cu spacer. In particular, the Cu in the capping acts as a filter controlling the diffusion of oxygen, which has led to the soft magnetic properties. Embedding an additional thin oxide layer into the pinned layer further improved the magnetoresistance response of the spin valve. Confinement of electrons between two oxides helps increase the occurrence of spin-dependent scattering. As a result, high giant magnetoresistance values resulted. The coupling oscillated from ferromagnetic to antiferromagnetic as a function of thickness of the Cu spacer. No significant bias in the coupling was observed and this lack of bias can be attributed to the smoothness of the interfaces. The oscillations were observable due to amplified Ruderman-Kittel-Kasuya-Yoshida-like coupling by strong reflection at the interfaces of the oxides.

  2. Current driven weak double layers

    NASA Technical Reports Server (NTRS)

    Chanteur, Gerard

    1987-01-01

    Double layers in plasmas can be created by different means. For example, a potential difference forms between two plasmas with different temperatures, in a plasma jet flowing along a converging magnetic field, in a quiescent plasma submitted to an external difference of potential, or in a turbulent plasma carrying an electric charge. The first three cases can be current-free, but not necessarily, although the numerical simulations were made under such conditions for the first two points. Apart from the third case, which is mainly of interest for laboratory experiments, these double layers are good candidates for accelerating the auroral electrons to the few kiloelectron volts observed.

  3. Electric double-layer capacitor composed of activated carbon fiber cloth electrodes and solid polymer electrolytes containing alkylammonium salts

    SciTech Connect

    Ishikawa, Masashi; Morita, Masayuki; Ihara, Mitsuo; Matsuda, Yoshiharu . Dept. of Applied Chemistry and Chemical Engineering)

    1994-07-01

    Solid polymer electrolytes consisting of complexes of poly(ethylene oxide)-grafted poly(methyl)-methacrylate (PEO-PMMA) and tetraalkylammonium salts [tetrabutylammonium perchlorate, tetraethylammonium perchlorate, and tetraethylammonium tetrafluoroborate (TEABF[sub 4])] have been investigated for electric double-layer capacitors with activated carbon fiber cloth electrodes. The PEO-PMMA and tetraalkylammonium composites obtained showed high ionic conductivity (>10[sup [minus]4] S cm[sup [minus]1] at 298 K). The ionic conductivity depended on both the concentration and the size of each ion. The composites had good stability over a wide potential range (ca. 5.0 V). When the PEO-PMMA and TEABF[sub 4] composites were used in solid-state electric double-layer capacitors with activated carbon fiber cloths as polarizable electrodes, the capacitors showed charge/discharge behavior with large values of capacitance and high coulombic efficiency. The long voltage retention was observed in the self-discharge test of the capacitor with TEABF[sub 4].

  4. Effect of UV-light illumination on oxide-based electric-double-layer thin-film transistors

    NASA Astrophysics Data System (ADS)

    Zhou, Jumei; Hu, Yunping

    2017-01-01

    Indium-tin-oxide (ITO)-based thin-film transistors (TFTs) were fabricated using porous SiO2 deposited by plasma-enhanced chemical vapor deposition and Al2O3 deposited by atomic layer deposition as dielectrics. The results showed that the porous SiO2 film exhibited a high electric-double-layer (EDL) capacitance. Devices gated by the EDL dielectric exhibited a high drain current on/off ratio of >106 and a low operation voltage of <2.0 V in the dark. When illuminated by 254 nm UV light, ITO-based EDL TFTs gated by a single SiO2 dielectric displayed weak photo-responses. However, devices gated by a stacked Al2O3/EDL dielectric displayed a high photo responsivity of more than 104 with a gate bias of -0.5 V (depletion state).

  5. Spark plasma sintered carbon electrodes for electrical double layer capacitor applications

    NASA Astrophysics Data System (ADS)

    Daffos, B.; Chevallier, G.; Estournès, C.; Simon, P.

    The spark plasma sintering (SPS) is an emerging process for shaping any type of materials (metals, ceramic, polymers and their composites). The advantage of such a process is to prepare densified ceramic materials in a very short time, while keeping the materials internal porosity. In the present work, we have used the SPS technique to prepare activated carbon-based electrodes for Electrochemical Double Layer Capacitor applications (EDLC). Self-supported 600 and 300 μm-thick electrodes were prepared and characterized using of Electrochemical Impedance Spectroscopy and galvanostatic cycling in a non-aqueous 1.5 M NEt 4BF 4 in acetonitrile electrolyte. Electrochemical performance of these sintered electrodes were found to be in the same range - or even slightly better - than the conventional tape-casted activated carbon electrodes. Although organic liquid electrolyte was used to characterize the electrochemical performance of the sintered electrodes, these results demonstrate that the SPS technique could be worth of interest in the ultimate goal of designing solid-state supercapacitors.

  6. Simulation of plasma double-layer structures

    NASA Technical Reports Server (NTRS)

    Borovsky, J. E.; Joyce, G.

    1982-01-01

    Electrostatic plasma double layers are numerically simulated by means of a magnetized 2 1/2 dimensional particle in cell method. The investigation of planar double layers indicates that these one dimensional potential structures are susceptible to periodic disruption by instabilities in the low potential plasmas. Only a slight increase in the double layer thickness with an increase in its obliqueness to the magnetic field is observed. Weak magnetization results in the double layer electric field alignment of accelerated particles and strong magnetization results in their magnetic field alignment. The numerical simulations of spatially periodic two dimensional double layers also exhibit cyclical instability. A morphological invariance in two dimensional double layers with respect to the degree of magnetization implies that the potential structures scale with Debye lengths rather than with gyroradii. Electron beam excited electrostatic electron cyclotron waves and (ion beam driven) solitary waves are present in the plasmas adjacent to the double layers.

  7. The effect of the electrical double layer on hydrodynamic lubrication: a non-monotonic trend with increasing zeta potential

    PubMed Central

    Jing, Dalei

    2017-01-01

    In the present study, a modified Reynolds equation including the electrical double layer (EDL)-induced electroviscous effect of lubricant is established to investigate the effect of the EDL on the hydrodynamic lubrication of a 1D slider bearing. The theoretical model is based on the nonlinear Poisson–Boltzmann equation without the use of the Debye–Hückel approximation. Furthermore, the variation in the bulk electrical conductivity of the lubricant under the influence of the EDL is also considered during the theoretical analysis of hydrodynamic lubrication. The results show that the EDL can increase the hydrodynamic load capacity of the lubricant in a 1D slider bearing. More importantly, the hydrodynamic load capacity of the lubricant under the influence of the EDL shows a non-monotonic trend, changing from enhancement to attenuation with a gradual increase in the absolute value of the zeta potential. This non-monotonic hydrodynamic lubrication is dependent on the non-monotonic electroviscous effect of the lubricant generated by the EDL, which is dominated by the non-monotonic electrical field strength and non-monotonic electrical body force on the lubricant. The subject of the paper is the theoretical modeling and the corresponding analysis. PMID:28884056

  8. The effect of the electrical double layer on hydrodynamic lubrication: a non-monotonic trend with increasing zeta potential.

    PubMed

    Jing, Dalei; Pan, Yunlu; Wang, Xiaoming

    2017-01-01

    In the present study, a modified Reynolds equation including the electrical double layer (EDL)-induced electroviscous effect of lubricant is established to investigate the effect of the EDL on the hydrodynamic lubrication of a 1D slider bearing. The theoretical model is based on the nonlinear Poisson-Boltzmann equation without the use of the Debye-Hückel approximation. Furthermore, the variation in the bulk electrical conductivity of the lubricant under the influence of the EDL is also considered during the theoretical analysis of hydrodynamic lubrication. The results show that the EDL can increase the hydrodynamic load capacity of the lubricant in a 1D slider bearing. More importantly, the hydrodynamic load capacity of the lubricant under the influence of the EDL shows a non-monotonic trend, changing from enhancement to attenuation with a gradual increase in the absolute value of the zeta potential. This non-monotonic hydrodynamic lubrication is dependent on the non-monotonic electroviscous effect of the lubricant generated by the EDL, which is dominated by the non-monotonic electrical field strength and non-monotonic electrical body force on the lubricant. The subject of the paper is the theoretical modeling and the corresponding analysis.

  9. Vibrational Stark Effect to Probe the Electric-Double Layer of the Ionic Liquid-Metal Electrodes

    NASA Astrophysics Data System (ADS)

    Garcia Rey, Natalia; Moore, Alexander Knight; Toyouchi, Shuichi; Dlott, Dana

    2017-06-01

    Vibrational sum frequency generation (VSFG) spectroscopy is used to study the effect of room temperature ionic liquids (RTILs) in situ at the electrical double layer (EDL). RTILs have been recognized as electrolytes without solvent for applications in batteries, supercapacitors and electrodeposition^{1}. The molecular response of the RTIL in the EDL affects the performance of these devices. We use the vibrational Stark effect on CO as a probe to detect the changes in the electric field affected by the RTIL across the EDL on metal electrodes. The Stark effect is a shift in the frequency in response to an externally applied electric field and also influenced by the surrounding electrolyte and electrode^{2}. The CO Stark shift is monitored by the CO-VSFG spectra on Pt or Ag in a range of different imidazolium-based RTILs electrolytes, where their composition is tuned by exchanging the anion, the cation or the imidazolium functional group. We study the free induction decay (FID)^{3} of the CO to monitor how the RTIL structure and composition affect the vibrational relaxation of the CO. Combining the CO vibrational Stark effect and the FID allow us to understand how the RTIL electrochemical response, molecular orientation response and collective relaxation affect the potential drop of the electric field across the EDL, and, in turn, how determines the electrical capacitance or reactivity of the electrolyte/electrode interface. ^{1}Fedorov, M. V.; Kornyshev, A. A., Ionic Liquids at Electrified Interfaces. Chem. Rev. 2014, 114, 2978-3036. ^{2} (a) Lambert, D. K., Vibrational Stark Effect of Adsorbates at Electrochemical Interfaces. Electrochim. Acta 1996, 41, 623-630. (b) Oklejas, V.; Sjostrom, C.; Harris, J. M., SERS Detection of the Vibrational Stark Effect from Nitrile-Terminated SAMs to Probe Electric Fields in the Diffuse Double-Layer. J. Am. Chem. Soc. 2002, 124, 2408-2409. ^{3}Symonds, J. P. R.; Arnolds, H.; Zhang, V. L.; Fukutani, K.; King, D. A

  10. The interaction of electric field and hydrostatic pressure in an electrical double layer: A simple "first principle" model that accounts for the finite sizes of counterions.

    PubMed

    Shapovalov, Vladimir L

    2015-09-15

    A simple model describing the influence of ion size in the electrical double layer (EDL) near a highly charged plane is proposed here. This model is based on the Poisson-Boltzmann equation with a single additional term representing the mechanical response of bulky ions to hydrostatic pressure. This pressure is produced by Coulomb forces, and increases to several kilobars in the vicinity of a highly charged plane. Numerical simulations demonstrate close packing as a limit for counterion concentrations. Differential capacity reaches maximum at 0.1-0.3V and remains reasonably small in wide range of potentials.

  11. Tests on Double Layer Metalization

    NASA Technical Reports Server (NTRS)

    Woo, D. S.

    1983-01-01

    28 page report describes experiments in fabrication of integrated circuits with double-layer metalization. Double-layer metalization requires much less silicon "real estate" and allows more flexibility in placement of circuit elements than does single-layer metalization.

  12. Teaching the Double Layer.

    ERIC Educational Resources Information Center

    Bockris, J. O'M.

    1983-01-01

    Suggests various methods for teaching the double layer in electrochemistry courses. Topics addressed include measuring change in absolute potential difference (PD) at interphase, conventional electrode potential scale, analyzing absolute PD, metal-metal and overlap electron PDs, accumulation of material at interphase, thermodynamics of electrified…

  13. The surface chemical properties of multi-walled carbon nanotubes modified by thermal fluorination for electric double-layer capacitor

    NASA Astrophysics Data System (ADS)

    Jung, Min-Jung; Jeong, Euigyung; Lee, Young-Seak

    2015-08-01

    The surfaces of multi-walled carbon nanotubes (MWCNTs) were thermally fluorinated at various temperatures to enhance the electrochemical properties of the MWCNTs for use as electric double-layer capacitor (EDLC) electrodes. The fluorine functional groups were added to the surfaces of the MWCNTs via thermal fluorination. The thermal fluorination exposed the Fe catalyst on MWCNTs, and the specific surface area increased due to etching during the fluorination. The specific capacitances of the thermally fluorinated at 100 °C, MWCNT based electrode increased from 57 to 94 F/g at current densities of 0.2 A/g, respectively. This enhancement in capacitance can be attributed to increased polarization of the thermally fluorinated MWCNT surface, which increased the affinity between the electrode surface and the electrolyte ions.

  14. Capacitance of the double electrical layer on the copper-group metals in molten alkali metal halides

    NASA Astrophysics Data System (ADS)

    Kirillova, E. V.; Stepanov, V. P.

    2016-08-01

    The electrochemical impedance is measured to study the capacitance of the double electrical layer of metallic Au, Ag, and Cu as a function of potential and temperature in nine molten salts, namely, the chlorides, bromides, and iodides of sodium, potassium, and cesium. The C- E curve of a gold electrode has an additional minimum in the anodic branch. This minimum for silver is less pronounced and is only observed at low ac signal frequencies in cesium halides. The additional minimum is not detected for copper in any salt under study. This phenomenon is explained on the assumption that the adsorption of halide anions on a positively charged electrode surface has a predominantly chemical rather than an electrostatic character. The specific adsorption in this case is accompanied by charge transfer through the interface and the formation of an adsorbent-adsorbate covalent bond.

  15. Curvature Effect on the Capacitance of Electric Double Layers at Ionic Liquid/Onion-Like Carbon Interfaces

    SciTech Connect

    Feng, Guang; Jiang, Deen; Cummings, Peter T

    2012-01-01

    Recent experiments have revealed that onion-like carbons (OLCs) offer high energy density and charging/discharging rates when used as the electrodes in supercapacitors. To understand the physical origin of this phenomenon, molecular dynamics simulations were performed for a room-temperature ionic liquid near idealized spherical OLCs with radii ranging from 0.356 to 1.223 nm. We find that the surface charge density increases almost linearly with the potential applied on electric double layers (EDLs) near OLCs. This leads to a nearly flat shape of the differential capacitance versus the potential, unlike the bell or camel shape observed on planar electrodes. Moreover, our simulations reveal that the capacitance of EDLs on OLCs increases with the curvature or as the OLC size decreases, in agreement with experimental observations. The curvature effect is explained by dominance of charge overscreening over a wide potential range and increased ion density per unit area of electrode surface as the OLC becomes smaller.

  16. Time-dependent density functional theory for the charging kinetics of electric double layer containing room-temperature ionic liquids

    SciTech Connect

    Lian, Cheng; Zhao, Shuangliang; Liu, Honglai; Wu, Jianzhong

    2016-11-29

    Understanding the charging kinetics of electric double layers is of fundamental importance for the design and development of novel electrochemical devices such as supercapacitors and field-effect transistors. In this paper, we study the dynamic behavior of room-temperature ionic liquids using a classical time-dependent density functional theory that accounts for the molecular excluded volume effects, the electrostatic correlations, and the dispersion forces. While the conventional models predict a monotonic increase of the surface charge with time upon application of an electrode voltage, our results show that dispersion between ions results in a non-monotonic increase of the surface charge with the duration of charging. Finally and furthermore, we investigate the effects of van der Waals attraction between electrode/ionic-liquid interactions on the charging processes.

  17. Time-dependent density functional theory for the charging kinetics of electric double layer containing room-temperature ionic liquids

    DOE PAGES

    Lian, Cheng; Univ. of California, Riverside, CA; Zhao, Shuangliang; ...

    2016-11-29

    Understanding the charging kinetics of electric double layers is of fundamental importance for the design and development of novel electrochemical devices such as supercapacitors and field-effect transistors. In this paper, we study the dynamic behavior of room-temperature ionic liquids using a classical time-dependent density functional theory that accounts for the molecular excluded volume effects, the electrostatic correlations, and the dispersion forces. While the conventional models predict a monotonic increase of the surface charge with time upon application of an electrode voltage, our results show that dispersion between ions results in a non-monotonic increase of the surface charge with the durationmore » of charging. Finally and furthermore, we investigate the effects of van der Waals attraction between electrode/ionic-liquid interactions on the charging processes.« less

  18. Exploring new scaling regimes for streaming potential and electroviscous effects in a nanocapillary with overlapping electric double layers.

    PubMed

    Das, Siddhartha; Guha, Arnab; Mitra, Sushanta K

    2013-12-04

    In this paper, we unravel new scaling regimes for streaming potential and electroviscous effects in a nanocapillary with thick overlapping Electric Double Layers (EDLs). We observe that the streaming potential, for a given value of the capillary zeta (ζ) potential, varies with the EDL thickness and a dimensionless parameter R, quantifying the conduction current. Depending on the value of R, variation of the streaming potential with the EDL thickness demonstrates distinct scaling regimes: one can witness a Quadratic Regime where the streaming potential varies as the square of the EDL thickness, a Weak Regime where the streaming potential shows a weaker variation with the EDL thickness, and a Saturation Regime where the streaming potential ceases to vary with the EDL thickness. Effective viscosity, characterizing the electroviscous effect, obeys the variation of the streaming potential for smaller EDL thickness values; however, for larger EDL thickness the electroosmotic flow profile dictates the electroviscous effect, with insignificant contribution of the streaming potential.

  19. Fuel Cell/Electric Double Layer Capacitor Hybrid Power Source Using a Multi-port Bidirectional DC-DC Converter

    NASA Astrophysics Data System (ADS)

    Katayama, Noboru; Kogoshi, Sumio

    A fuel cell/electric double layer capacitor hybrid power source using a multi-port bidirectional DC-DC converter has been developed to reduce load variations for the purpose of extending fuel cell life. The proposed converter operates to maintain the fuel cell current, load voltage and bus voltage at constant values with a digital signal processor. The effect of the proposed converter is evaluated. The charging or discharging current of the EDLC rapidly changes along with step loading, and the voltage and current of the fuel cell are maintained at the constant values. Short-time transient responses show that the fuel cell current ripples 0.35 A at 1 A load change in 6 ms.

  20. Polarization-insensitive wide-angle multiband metamaterial absorber with a double-layer modified electric ring resonator array

    NASA Astrophysics Data System (ADS)

    Li, Wangchang; Zhou, Xiang; Ying, Yao; Qiao, Xiaojing; Qin, Faxiang; Li, Qian; Che, Shenglei

    2015-06-01

    In this letter, we report the design, demonstration and discussion of a multi- and broad- band metamaterial absorber (MMA) with wide angle polarization insensitive at microwave region. The MMA consisting of double layered electric ring resonator (ERR) with four fold rotational symmetry structure is used to realize a desirable absorption. Strong triple absorption peaks in 2˜8 GHz and broadband microwave absorption in 10˜18 GHz are demonstrated. The absorption can be reached as high as 0.73, 0.73 and 0.94 at 4.41, 5.15, 6.37 GHz, respectively. The multiband absorbing features originate from the synergetic effects of dipole resonance and Fabry-Pérot interference between two or three metasurfaces. This design is of high practical for constructing broad band and multiband absorber for electromagnetic intereference/compatibility (EMI/EMC) applications.

  1. Short-Term Synaptic Plasticity Regulation in Solution-Gated Indium-Gallium-Zinc-Oxide Electric-Double-Layer Transistors.

    PubMed

    Wan, Chang Jin; Liu, Yang Hui; Zhu, Li Qiang; Feng, Ping; Shi, Yi; Wan, Qing

    2016-04-20

    In the biological nervous system, synaptic plasticity regulation is based on the modulation of ionic fluxes, and such regulation was regarded as the fundamental mechanism underlying memory and learning. Inspired by such biological strategies, indium-gallium-zinc-oxide (IGZO) electric-double-layer (EDL) transistors gated by aqueous solutions were proposed for synaptic behavior emulations. Short-term synaptic plasticity, such as paired-pulse facilitation, high-pass filtering, and orientation tuning, was experimentally emulated in these EDL transistors. Most importantly, we found that such short-term synaptic plasticity can be effectively regulated by alcohol (ethyl alcohol) and salt (potassium chloride) additives. Our results suggest that solution gated oxide-based EDL transistors could act as the platforms for short-term synaptic plasticity emulation.

  2. A Gibbs-ensemble based technique for Monte Carlo simulation of electric double layer capacitors (EDLC) at constant voltage.

    PubMed

    Punnathanam, Sudeep N

    2014-05-07

    Current methods for molecular simulations of Electric Double Layer Capacitors (EDLC) have both the electrodes and the electrolyte region in a single simulation box. This necessitates simulation of the electrode-electrolyte region interface. Typical capacitors have macroscopic dimensions where the fraction of the molecules at the electrode-electrolyte region interface is very low. Hence, large systems sizes are needed to minimize the electrode-electrolyte region interfacial effects. To overcome these problems, a new technique based on the Gibbs Ensemble is proposed for simulation of an EDLC. In the proposed technique, each electrode is simulated in a separate simulation box. Application of periodic boundary conditions eliminates the interfacial effects. This in addition to the use of constant voltage ensemble allows for a more convenient comparison of simulation results with experimental measurements on typical EDLCs.

  3. Electric double layer capacitors employing nitrogen and sulfur co-doped, hierarchically porous graphene electrodes with synergistically enhanced performance

    NASA Astrophysics Data System (ADS)

    Kannan, Aravindaraj G.; Samuthirapandian, Amaresh; Kim, Dong-Won

    2017-01-01

    Hierarchically porous graphene nanosheets co-doped with nitrogen and sulfur are synthesized via a simple hydrothermal method, followed by a pore activation step. Pore architectures are controlled by varying the ratio of chemical activation agents to graphene, and its influence on the capacitive performance is evaluated. The electric double layer capacitor (EDLC) assembled with optimized dual-doped graphene delivers a high specific capacitance of 146.6 F g-1 at a current density of 0.8 A g-1, which is higher than that of cells with un-doped and single-heteroatom doped graphene. The EDLC with dual-doped graphene electrodes exhibits stable cycling performance with a capacitance retention of 94.5% after 25,000 cycles at a current density of 3.2 A g-1. Such a good performance can be attributed to synergistic effects due to co-doping of the graphene nanosheets and the presence of hierarchical porous structures.

  4. Performance of electrical double layer capacitors fabricated with gel polymer electrolytes containing Li+ and K+-salts: A comparison

    NASA Astrophysics Data System (ADS)

    Singh, Manoj K.; Hashmi, S. A.

    2015-06-01

    The comparative performance of the solid-state electrical double layer capacitors (EDLCs) based on the multiwalled carbon nanotube (MWCNT) electrodes and poly (vinaylidinefluoride-co-hexafluoropropyline) (PVdF-HFP) based gel polymer electrolytes (GPEs) containing potassium and lithium salts have been studied. The room temperature ionic conductivity of the GPEs have been found to be ˜3.8×10-3 and 5.9×10-3 S cm-1 for lithium and potassium based systems. The performance of EDLC cells studied by impedance spectroscopy, cyclic voltammetry and constant current charge-discharge techniques, indicate that the EDLC with potassium salt containing GPE shows excellent performance almost equivalent to the EDLC with Li-salt-based GPE.

  5. Enhancing the pH sensitivity by laterally synergic modulation in dual-gate electric-double-layer transistors

    SciTech Connect

    Liu, Ning; Hui Liu, Yang; Qiang Zhu, Li; Feng, Ping Shi, Yi; Wan, Qing

    2015-02-16

    The sensitivity of a standard ion-sensitive field-effect transistor is limited to be 59.2 mV/pH (Nernst limit) at room temperature. Here, a concept based on laterally synergic electric-double-layer (EDL) modulation is proposed in order to overcome the Nernst limit. Indium-zinc-oxide EDL transistors with two laterally coupled gates are fabricated, and the synergic modulation behaviors of the two asymmetric gates are investigated. A high sensitivity of ∼168 mV/pH is realized in the dual-gate operation mode. Laterally synergic modulation in oxide-based EDL transistors is interesting for high-performance bio-chemical sensors.

  6. Electric-double-layer doping of WSe2 field-effect transistors using polyethylene-oxide cesium perchlorate

    NASA Astrophysics Data System (ADS)

    Fathipour, Sara; Pandey, Pratyush; Fullerton-Shirey, Susan; Seabaugh, Alan

    2016-12-01

    Electric double layers (EDLs) formed between polyethylene oxide cesium perchlorate and multilayer WSe2 field-effect transistors (FETs) are explored as a means for contact and access region doping. In this application, the electric double layer is formed using a top field plate or a side gate and then locked into place by cooling of the device below the glass transition temperature of the polymer. A dual work-function Ti/Pd contact is used to form the Schottky contacts with Ti as the n-contact and Pd as the p-contact and these are evaporated in a single evaporation. Using the EDL doping technique, sheet carrier density and current density are as high as (4.9 ± 1.9) × 1013 cm-2 and 58 μA/μm for n-doping and (3.5 ± 1.9) × 1013 cm-2 and 50 μA/μm for p-doping for the highest channel conductivities. The weak temperature dependence of the transfer characteristics at high doping levels reveals that the current in the Schottky contacts is dominated by tunneling with a contact resistance of 1 kΩ μm for the p-branch and 3.4 kΩ μm for the n-branch, comparable to the best WSe2 FET reports. At the highest carrier densities, the temperature coefficient of the conductance becomes negative as the mobility of the channel controls the temperature dependence. Using EDL doping, n-FET and p-FET configurations are demonstrated.

  7. Properties of a planar electric double layer under extreme conditions investigated by classical density functional theory and Monte Carlo simulations.

    PubMed

    Zhou, Shiqi; Lamperski, Stanisław; Zydorczak, Maria

    2014-08-14

    Monte Carlo (MC) simulation and classical density functional theory (DFT) results are reported for the structural and electrostatic properties of a planar electric double layer containing ions having highly asymmetric diameters or valencies under extreme concentration condition. In the applied DFT, for the excess free energy contribution due to the hard sphere repulsion, a recently elaborated extended form of the fundamental measure functional is used, and coupling of Coulombic and short range hard-sphere repulsion is described by a traditional second-order functional perturbation expansion approximation. Comparison between the MC and DFT results indicates that validity interval of the traditional DFT approximation expands to high ion valences running up to 3 and size asymmetry high up to diameter ratio of 4 whether the high valence ions or the large size ion are co- or counter-ions; and to a high bulk electrolyte concentration being close to the upper limit of the electrolyte mole concentration the MC simulation can deal with well. The DFT accuracy dependence on the ion parameters can be self-consistently explained using arguments of liquid state theory, and new EDL phenomena such as overscreening effect due to monovalent counter-ions, extreme layering effect of counter-ions, and appearance of a depletion layer with almost no counter- and co-ions are observed.

  8. A two-step etching route to ultrathin carbon nanosheets for high performance electrical double layer capacitors.

    PubMed

    Ding, Bing; Wang, Jie; Wang, Ya; Chang, Zhi; Pang, Gang; Dou, Hui; Zhang, Xiaogang

    2016-06-07

    Two-dimensional (2D) carbon materials have attracted intense research interest for electrical double layer capacitors (EDLCs) due to their high aspect ratio and large surface area. Herein, we propose an exfoliation-chlorination route for preparing ultrathin carbon nanosheets by using ternary layered carbide Ti3AlC2 as the precursor. Due to the large intersheet space of exfoliated layered carbide (MXene), the as-prepared carbon nanosheets exhibit a thickness of 3-4 nm and a large specific surface area of 1766 m(2) g(-1) with hierarchical porosity. These features significantly improve the ion-accessible surface area for charge storage and shorten the ion transport length in the thin dimension. As a result, the carbon nanosheets show a high specific capacitance (220 F g(-1) at 0.5 A g(-1)), remarkable high power capability (79% capacitance retention at 20 A g(-1)) when measured in a symmetrical two-electrode configuration in an aqueous electrolyte. The method described in this work provides a new route to prepare 2D electrode materials from a bulk precursor, thus exploiting their full potential for EDLCs.

  9. Reevaluation of Performance of Electric Double-layer Capacitors from Constant-current Charge/Discharge and Cyclic Voltammetry

    NASA Astrophysics Data System (ADS)

    Allagui, Anis; Freeborn, Todd J.; Elwakil, Ahmed S.; Maundy, Brent J.

    2016-12-01

    The electric characteristics of electric-double layer capacitors (EDLCs) are determined by their capacitance which is usually measured in the time domain from constant-current charging/discharging and cyclic voltammetry tests, and from the frequency domain using nonlinear least-squares fitting of spectral impedance. The time-voltage and current-voltage profiles from the first two techniques are commonly treated by assuming ideal SsC behavior in spite of the nonlinear response of the device, which in turn provides inaccurate values for its characteristic metrics. In this paper we revisit the calculation of capacitance, power and energy of EDLCs from the time domain constant-current step response and linear voltage waveform, under the assumption that the device behaves as an equivalent fractional-order circuit consisting of a resistance Rs in series with a constant phase element (CPE(Q, α), with Q being a pseudocapacitance and α a dispersion coefficient). In particular, we show with the derived (Rs, Q, α)-based expressions, that the corresponding nonlinear effects in voltage-time and current-voltage can be encompassed through nonlinear terms function of the coefficient α, which is not possible with the classical RsC model. We validate our formulae with the experimental measurements of different EDLCs.

  10. Estimation of Bidirectional Buck/boost DC/DC Converters with Electric Double-Layer Capacitors for Energy Storage Systems

    NASA Astrophysics Data System (ADS)

    Funabiki, Shigeyuki; Yamamoto, Masayoshi

    Renewable energy such as wind force and solar light has collected the attention as alternative energy sources of fossil fuel. An energy storage system with an electric double-layer capacitor (EDLC), which balances the demand and supply power, is required in order to introduce the electric power generating system that utilizes renewable energy. Currently, the research and development of these energy storage systems are actively carried out. In the energy storage system with an EDLC, the DC/DC converter having the function of the bidirectional power flow and the buck/boost performance is essential as an interface and power control circuit. There are two types of the bidirectional buck/boost DC/DC converters. One type consists of two buck/boost DC/DC converters with one reactor. The other type consists of two sets of two-quadrant DC/DC converters with one reactor. This paper discusses the comparison of these types of DC/DC converters with bidirectional power flow and buck/boost performance. The two types of DC/DC converters are estimated for their application to the energy storage system with the EDLC. As the voltage endurance of the device is lower and the mean current is smaller in the latter type of converter despite of having twice the number of devices compared to the former, the latter type of converter has the advantage of a smaller reactor, i.e., core volume and loss, and lower loss in the converter.

  11. Extended-gate-type IGZO electric-double-layer TFT immunosensor with high sensitivity and low operation voltage

    NASA Astrophysics Data System (ADS)

    Liang, Lingyan; Zhang, Shengnan; Wu, Weihua; Zhu, Liqiang; Xiao, Hui; Liu, Yanghui; Zhang, Hongliang; Javaid, Kashif; Cao, Hongtao

    2016-10-01

    An immunosensor is proposed based on the indium-gallium-zinc-oxide (IGZO) electric-double-layer thin-film transistor (EDL TFT) with a separating extended gate. The IGZO EDL TFT has a field-effect mobility of 24.5 cm2 V-1 s-1 and an operation voltage less than 1.5 V. The sensors exhibit the linear current response to label-free target immune molecule in the concentrations ranging from 1.6 to 368 × 10-15 g/ml with a detection limit of 1.6 × 10-15 g/ml (0.01 fM) under an ultralow operation voltage of 0.5 V. The IGZO TFT component demonstrates a consecutive assay stability and recyclability due to the unique structure with the separating extended gate. With the excellent electrical properties and the potential for plug-in-card-type multifunctional sensing, extended-gate-type IGZO EDL TFTs can be promising candidates for the development of a label-free biosensor for public health applications.

  12. Reevaluation of Performance of Electric Double-layer Capacitors from Constant-current Charge/Discharge and Cyclic Voltammetry.

    PubMed

    Allagui, Anis; Freeborn, Todd J; Elwakil, Ahmed S; Maundy, Brent J

    2016-12-09

    The electric characteristics of electric-double layer capacitors (EDLCs) are determined by their capacitance which is usually measured in the time domain from constant-current charging/discharging and cyclic voltammetry tests, and from the frequency domain using nonlinear least-squares fitting of spectral impedance. The time-voltage and current-voltage profiles from the first two techniques are commonly treated by assuming ideal SsC behavior in spite of the nonlinear response of the device, which in turn provides inaccurate values for its characteristic metrics. In this paper we revisit the calculation of capacitance, power and energy of EDLCs from the time domain constant-current step response and linear voltage waveform, under the assumption that the device behaves as an equivalent fractional-order circuit consisting of a resistance Rs in series with a constant phase element (CPE(Q, α), with Q being a pseudocapacitance and α a dispersion coefficient). In particular, we show with the derived (Rs, Q, α)-based expressions, that the corresponding nonlinear effects in voltage-time and current-voltage can be encompassed through nonlinear terms function of the coefficient α, which is not possible with the classical RsC model. We validate our formulae with the experimental measurements of different EDLCs.

  13. Reevaluation of Performance of Electric Double-layer Capacitors from Constant-current Charge/Discharge and Cyclic Voltammetry

    PubMed Central

    Allagui, Anis; Freeborn, Todd J.; Elwakil, Ahmed S.; Maundy, Brent J.

    2016-01-01

    The electric characteristics of electric-double layer capacitors (EDLCs) are determined by their capacitance which is usually measured in the time domain from constant-current charging/discharging and cyclic voltammetry tests, and from the frequency domain using nonlinear least-squares fitting of spectral impedance. The time-voltage and current-voltage profiles from the first two techniques are commonly treated by assuming ideal SsC behavior in spite of the nonlinear response of the device, which in turn provides inaccurate values for its characteristic metrics. In this paper we revisit the calculation of capacitance, power and energy of EDLCs from the time domain constant-current step response and linear voltage waveform, under the assumption that the device behaves as an equivalent fractional-order circuit consisting of a resistance Rs in series with a constant phase element (CPE(Q, α), with Q being a pseudocapacitance and α a dispersion coefficient). In particular, we show with the derived (Rs, Q, α)-based expressions, that the corresponding nonlinear effects in voltage-time and current-voltage can be encompassed through nonlinear terms function of the coefficient α, which is not possible with the classical RsC model. We validate our formulae with the experimental measurements of different EDLCs. PMID:27934904

  14. Modulation of superconducting critical temperature in niobium film by using all-solid-state electric-double-layer transistor

    SciTech Connect

    Tsuchiya, Takashi E-mail: TERABE.Kazuya@nims.go.jp; Moriyama, Satoshi; Terabe, Kazuya E-mail: TERABE.Kazuya@nims.go.jp; Aono, Masakazu

    2015-07-06

    An all-solid-state electric-double-layer transistor (EDLT) was fabricated for electrical modulation of the superconducting critical temperature (T{sub c}) of Nb film epitaxially grown on α-Al{sub 2}O{sub 3} (0001) single crystal. In an experiment, T{sub c} was modulated from 8.33 to 8.39 K while the gate voltage (V{sub G}) was varied from 2.5 to −2.5 V. The specific difference of T{sub c} for the applied V{sub G} was 12 mK/V, which is larger than that of an EDLT composed of ionic liquid. A T{sub c} enhancement of 300 mK was found at the Li{sub 4}SiO{sub 4}/Nb film interface and is attributed to an increase in density of states near the Fermi level due to lattice constant modulation. This solid electrolyte gating method should enable development of practical superconducting devices highly compatible with other electronic devices.

  15. Ion size effects on the electric double layer of a spherical particle in a realistic salt-free concentrated suspension.

    PubMed

    Roa, Rafael; Carrique, Félix; Ruiz-Reina, Emilio

    2011-05-28

    A new modified Poisson-Boltzmann equation accounting for the finite size of the ions valid for realistic salt-free concentrated suspensions has been derived, extending the formalism developed for pure salt-free suspensions [Roa et al., Phys. Chem. Chem. Phys., 2011, 13, 3960-3968] to real experimental conditions. These realistic suspensions include water dissociation ions and those generated by atmospheric carbon dioxide contamination, in addition to the added counterions released by the particles to the solution. The electric potential at the particle surface will be calculated for different ion sizes and compared with classical Poisson-Boltzmann predictions for point-like ions, as a function of particle charge and volume fraction. The realistic predictions turn out to be essential to achieve a closer picture of real salt-free suspensions, and even more important when ionic size effects are incorporated to the electric double layer description. We think that both corrections have to be taken into account when developing new realistic electrokinetic models, and surely will help in the comparison with experiments for low-salt or realistic salt-free systems. This journal is © the Owner Societies 2011

  16. Insights into the effects of solvent properties in graphene based electric double-layer capacitors with organic electrolytes

    NASA Astrophysics Data System (ADS)

    Zhang, Shuo; Bo, Zheng; Yang, Huachao; Yang, Jinyuan; Duan, Liangping; Yan, Jianhua; Cen, Kefa

    2016-12-01

    Organic electrolytes are widely used in electric double-layer capacitors (EDLCs). In this work, the microstructure of planar graphene-based EDLCs with different organic solvents are investigated with molecular dynamics simulations. Results show that an increase of solvent polarity could weaken the accumulation of counter-ions nearby the electrode surface, due to the screen of electrode charges and relatively lower ionic desolvation. It thus suggests that solvents with low polarity could be preferable to yield high EDL capacitance. Meanwhile, the significant effects of the size and structure of solvent molecules are reflected by non-electrostatic molecule-electrode interactions, further influencing the adsorption of solvent molecules on electrode surface. Compared with dimethyl carbonate, γ-butyrolactone, and propylene carbonate, acetonitrile with relatively small-size and linear structure owns weak non-electrostatic interactions, which favors the easy re-orientation of solvent molecules. Moreover, the shift of solvent orientation in surface layer, from parallel orientation to perpendicular orientation relative to the electrode surface, deciphers the solvent twin-peak behavior near negative electrode. The as-obtained insights into the roles of solvent properties on the interplays among particles and electrodes elucidate the solvent influences on the microstructure and capacitive behavior of EDLCs using organic electrolytes.

  17. Dynamics of electrical double layer formation in room-temperature ionic liquids under constant-current charging conditions.

    PubMed

    Jiang, Xikai; Huang, Jingsong; Zhao, Hui; Sumpter, Bobby G; Qiao, Rui

    2014-07-16

    We report detailed simulation results on the formation dynamics of an electrical double layer (EDL) inside an electrochemical cell featuring room-temperature ionic liquids (RTILs) enclosed between two planar electrodes. Under relatively small charging currents, the evolution of cell potential from molecular dynamics (MD) simulations during charging can be suitably predicted by the Landau-Ginzburg-type continuum model proposed recently (Bazant et al 2011 Phys. Rev. Lett. 106 046102). Under very large charging currents, the cell potential from MD simulations shows pronounced oscillation during the initial stage of charging, a feature not captured by the continuum model. Such oscillation originates from the sequential growth of the ionic space charge layers near the electrode surface. This allows the evolution of EDLs in RTILs with time, an atomistic process difficult to visualize experimentally, to be studied by analyzing the cell potential under constant-current charging conditions. While the continuum model cannot predict the potential oscillation under such far-from-equilibrium charging conditions, it can nevertheless qualitatively capture the growth of cell potential during the later stage of charging. Improving the continuum model by introducing frequency-dependent dielectric constant and density-dependent ion diffusion coefficients may help to further extend the applicability of the model. The evolution of ion density profiles is also compared between the MD and the continuum model, showing good agreement.

  18. Towards understanding the effects of van der Waals strengths on the electric double-layer structures and capacitive behaviors

    NASA Astrophysics Data System (ADS)

    Yang, Huachao; Bo, Zheng; Yang, Jinyuan; Yan, Jianhua; Cen, Kefa

    2017-10-01

    Solid-liquid interactions are considered to play a crucial role in charge storage capability of electric double-layer capacitors (EDLCs). In this work, effects of van der Waals (VDW) strengths on the EDL structures and capacitive performances within two representative electrolytes of solvated aqueous solutions and solvent-free ionic liquids are illuminated by molecular dynamics simulations. Single crystalline metals with similar lattice constant but diverse VDW potentials are employed as electrodes. Upon enhancing VDW strengths, capacitance of aqueous electrolytes first increases conspicuously by ∼34.0% and then descends, manifesting a non-monotonic trend, which goes beyond traditional perspectives. Such unusual observation is interpreted by the excluded-volume effects stemmed from ion-solvent competitions. Stimulated by predominant coulombic interactions, more ions are aggregated at the interface despite of the increasing VDW potentials, facilitating superior screening efficiency and capacitance. However, further enhancing strengths preferentially attracts more solvents instead of ions to the electrified surface, which in turn strikingly repels ions from Helmholtz layers, deteriorating electrode capacitance. An essentially similar feather is also recognized for ionic liquids, while the corresponding mechanisms are prominently ascribed to the suppressed ionic separations issued from cation-anion competitions. We highlight that constructing electrode materials with a moderate-hydrophilicity could further advance the performances of EDLCs.

  19. Dynamics of electrical double layer formation in room-temperature ionic liquids under constant-current charging conditions

    SciTech Connect

    Jiang, Xikai; Huang, Jingsong; Zhao, Hui; Sumpter, Bobby G; Qiao, Rui

    2014-01-01

    We report detailed simulation results on the formation dynamics of an electrical double layer (EDL) inside an electrochemical cell featuring room-temperature ionic liquids (RTILs) enclosed between two planar electrodes. Under relatively small charging currents, the evolution of cell potential during charging can be suitably predicted by the Landau-Ginzburg-type continuum model proposed recently (M. Z. Bazant, B. D. Storey, and A. A. Kornyshev, Phys. Rev. Lett., 106, 046102, 2011). Under very large charging currents, the cell potential shows pronounced oscillation during the initial stage of charging, a feature not captured by the continuum model. Such oscillation originates from the sequential growth of the ionic space charge layers near the electrode surface, allowing the evolution of EDLs in RTILs with time, an atomistic process difficult to visualize experimentally, to be studied by analyzing the cell potential under constant current charging conditions. While the continuum model cannot predict the potential oscillation under such far-from-equilibrium charging conditions, it can nevertheless qualitatively capture the growth of cell potential during the later stage of charging. Improving the continuum model by introducing frequency-dependent dielectric constant and density-dependent ion diffusion coefficients may help to further extend the applicability of the model. Keywords: ionic

  20. Macroscopic fibres of CNTs as electrodes for multifunctional electric double layer capacitors: from quantum capacitance to device performance

    NASA Astrophysics Data System (ADS)

    Senokos, E.; Reguero, V.; Palma, J.; Vilatela, J. J.; Marcilla, Rebeca

    2016-02-01

    In this work we present a combined electrochemical and mechanical study of mesoporous electrodes based on CNT fibres in the context of electric double layer capacitors. We show that through control of the synthetic and assembly processes of the fibres, it is possible to obtain an active material that combines a surface area of 250 m2 g-1, high electrical conductivity (3.5 × 105 S m-1) and mechanical properties in the high-performance range including toughness (35 J g-1) comparable to that of aramid fibre (e.g. Kevlar). These properties are a consequence of the predominant orientation of the CNTs, observed by wide- and small-angle X-ray diffraction, and to the exceptionally long CNT length on the millimetre scale. Cyclic voltammetry measurements in a three-electrode configuration and using 1-butyl-3-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide (PYR14TFSI) ionic liquid electrolyte, show that the CNT fibres have a large quantum capacitance, evidenced by the near linear dependence of geometric capacitance (and conductivity) on potential bias. This reflects the low dimensionality of the CNT building blocks, which were purposely synthesised to have 1-5 layers and a high degree of graphitization. From the charge-discharge measurements of supercapacitor devices with symmetric CNT fibre electrodes we obtain power and energy densities as high as 58 kW kg-1 and 14 Wh kg-1, respectively. These record-high values for CNT fibre-based supercapacitors, are a consequence of the low equivalent series resistance due to the high conductivity of the fibres, the large contribution from quantum capacitance, and the wide stability window of the ionic liquid (3.5 V). Cycle life experiments demonstrate stable capacitance and energy retention over 10 000 cycles of charge-discharge at 3.5 V.In this work we present a combined electrochemical and mechanical study of mesoporous electrodes based on CNT fibres in the context of electric double layer capacitors. We show that through

  1. Macroscopic fibres of CNTs as electrodes for multifunctional electric double layer capacitors: from quantum capacitance to device performance.

    PubMed

    Senokos, E; Reguero, V; Palma, J; Vilatela, J J; Marcilla, Rebeca

    2016-02-14

    In this work we present a combined electrochemical and mechanical study of mesoporous electrodes based on CNT fibres in the context of electric double layer capacitors. We show that through control of the synthetic and assembly processes of the fibres, it is possible to obtain an active material that combines a surface area of 250 m(2) g(-1), high electrical conductivity (3.5 × 10(5) S m(-1)) and mechanical properties in the high-performance range including toughness (35 J g(-1)) comparable to that of aramid fibre (e.g. Kevlar). These properties are a consequence of the predominant orientation of the CNTs, observed by wide- and small-angle X-ray diffraction, and to the exceptionally long CNT length on the millimetre scale. Cyclic voltammetry measurements in a three-electrode configuration and using 1-butyl-3-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide (PYR14TFSI) ionic liquid electrolyte, show that the CNT fibres have a large quantum capacitance, evidenced by the near linear dependence of geometric capacitance (and conductivity) on potential bias. This reflects the low dimensionality of the CNT building blocks, which were purposely synthesised to have 1-5 layers and a high degree of graphitization. From the charge-discharge measurements of supercapacitor devices with symmetric CNT fibre electrodes we obtain power and energy densities as high as 58 kW kg(-1) and 14 Wh kg(-1), respectively. These record-high values for CNT fibre-based supercapacitors, are a consequence of the low equivalent series resistance due to the high conductivity of the fibres, the large contribution from quantum capacitance, and the wide stability window of the ionic liquid (3.5 V). Cycle life experiments demonstrate stable capacitance and energy retention over 10,000 cycles of charge-discharge at 3.5 V.

  2. Plasma sheets, plasma currents and electric field double layers in the equatorial ionosphere

    SciTech Connect

    Gupta, S.P.

    1981-01-01

    Plasma measurements carried out in the equatorial ionosphere at altitudes of 80-200 km are discussed. It is found that within this region the ion collision frequency exceeds the gyro-frequency. For electrons, however, the collision frequency is much lower than their gyro-frequency. It is pointed out that the earth's magnetic field is horizontal in the equatorial ionosphere, particularly at altitudes of approximately 100 km, where the curvature of the magnetic field can be neglected. The results obtained from rocket-borne probes in the equatorial ionosphere over Thumba (India) are presented. Localized regions illustrating the polarity of the vertical electric field are shown, as are current density profiles obtained at different times of the day. It is found that as expected, the vertical electric field becomes very small during a weak magnetic storm.

  3. Influence of electric-double-layer structure on the transient response of nanochannels

    NASA Astrophysics Data System (ADS)

    Schiffbauer, Jarrod; Yossifon, Gilad

    2014-05-01

    A fundamental Poisson-Nernst-Planck-Stokes model is presented for the impedance response of a long nanochannel under zero bias, capturing the effects of surface conduction and the coupling between transverse momentum and axial ion distribution in a manner reminiscent of Taylor dispersion. This is shown to result in a shift of the impedance frequency spectrum with bulk concentration similar to previous experimental observation [Schiffbauer, Liel, and Yossifon, Phys. Rev. E 89, 033017 (2014), 10.1103/PhysRevE.89.033017]. It further predicts an additional downward shift in frequency with increasing viscosity. Finally, the introduction of a phenomenological model for the impedance response of a dynamic Stern layer in parallel with the diffuse layer transport model is shown to yield good agreement between theory and experiment. As a result, we are able to obtain an equivalent circuit model based on the fundamental model and proposed corrections.

  4. Classical density functional theory and Monte Carlo simulation study of electric double layer in the vicinity of a cylindrical electrode

    NASA Astrophysics Data System (ADS)

    Zhou, Shiqi; Lamperski, Stanisław; Sokołowska, Marta

    2017-07-01

    We have performed extensive Monte-Carlo simulations and classical density functional theory (DFT) calculations of the electrical double layer (EDL) near a cylindrical electrode in a primitive model (PM) modified by incorporating interionic dispersion interactions. It is concluded that (i) in general, an unsophisticated use of the mean field (MF) approximation for the interionic dispersion interactions does not distinctly worsen the classical DFT performance, even if the salt ions considered are highly asymmetrical in size (3:1) and charge (5:1), the bulk molar concentration considered is high up to a total bulk ion packing fraction of 0.314, and the surface charge density of up to 0.5 C m-2. (ii) More specifically, considering the possible noises in the simulation, the local volume charge density profiles are the most accurately predicted by the classical DFT in all situations, and the co- and counter-ion singlet distributions are also rather accurately predicted; whereas the mean electrostatic potential profile is relatively less accurately predicted due to an integral amplification of minor inaccuracy of the singlet distributions. (iii) It is found that the layered structure of the co-ion distribution is abnormally possible only if the surface charge density is high enough (for example 0.5 C m-2) moreover, the co-ion valence abnormally influences the peak height of the first counter-ion layer, which decreases with the former. (iv) Even if both the simulation and DFT indicate an insignificant contribution of the interionic dispersion interaction to the above three ‘local’ quantities, it is clearly shown by the classical DFT that the interionic dispersion interaction does significantly influence a ‘global’ quantity like the cylinder surface-aqueous electrolyte interfacial tension, and this may imply the role of the interionic dispersion interaction in explaining the specific Hofmeister effects. We elucidate all of the above observations based on the

  5. Atomistic and molecular effects in electric double layers at high surface charges

    SciTech Connect

    Templeton, Jeremy Alan; Lee, Jonathan; Mani, Ali

    2015-06-16

    Here, the Poisson–Boltzmann theory for electrolytes near a charged surface is known to be invalid due to unaccounted physics associated with high ion concentration regimes. In order to investigate this regime, fluids density functional theory (f-DFT) and molecular dynamics (MD) simulations were used to determine electric surface potential as a function of surface charge. Based on these detailed computations, for electrolytes with nonpolar solvent, the surface potential is shown to depend quadratically on the surface charge in the high charge limit. We demonstrate that modified Poisson–Boltzmann theories can model this limit if they are augmented with atomic packing densities provided by MD. However, when the solvent is a highly polar molecule water an intermediate regime is identified in which a constant capacitance is realized. Simulation results demonstrate the mechanism underlying this regime, and for the salt water system studied here, it persists throughout the range of physically realistic surface charge densities so the potential’s quadratic surface charge dependence is not obtained.

  6. Atomistic and molecular effects in electric double layers at high surface charges

    DOE PAGES

    Templeton, Jeremy Alan; Lee, Jonathan; Mani, Ali

    2015-06-16

    Here, the Poisson–Boltzmann theory for electrolytes near a charged surface is known to be invalid due to unaccounted physics associated with high ion concentration regimes. In order to investigate this regime, fluids density functional theory (f-DFT) and molecular dynamics (MD) simulations were used to determine electric surface potential as a function of surface charge. Based on these detailed computations, for electrolytes with nonpolar solvent, the surface potential is shown to depend quadratically on the surface charge in the high charge limit. We demonstrate that modified Poisson–Boltzmann theories can model this limit if they are augmented with atomic packing densities providedmore » by MD. However, when the solvent is a highly polar molecule water an intermediate regime is identified in which a constant capacitance is realized. Simulation results demonstrate the mechanism underlying this regime, and for the salt water system studied here, it persists throughout the range of physically realistic surface charge densities so the potential’s quadratic surface charge dependence is not obtained.« less

  7. Can ionophobic nanopores enhance the energy storage capacity of electric-double-layer capacitors containing nonaqueous electrolytes?

    SciTech Connect

    Lian, Cheng; Liu, Honglai; Henderson, Douglas; Wu, Jianzhong

    2016-08-22

    The ionophobicity effect of nanoporous electrodes on the capacitance and the energy storage capacity of nonaqueous-electrolyte supercapacitors is studied by means of the classical density functional theory (DFT). It has been hypothesized that ionophobic nanopores may create obstacles in charging, but they store energy much more efficiently than ionophilic pores. In this paper, we find that, for both ionic liquids and organic electrolytes, an ionophobic pore exhibits a charging behavior different from that of an ionophilic pore, and that the capacitance–voltage curve changes from a bell shape to a two-hump camel shape when the pore ionophobicity increases. For electric-double-layer capacitors containing organic electrolytes, an increase in the ionophobicity of the nanopores leads to a higher capacity for energy storage. Without taking into account the effects of background screening, the DFT predicts that an ionophobic pore containing an ionic liquid does not enhance the supercapacitor performance within the practical voltage ranges. However, by using an effective dielectric constant to account for ion polarizability, the DFT predicts that, like an organic electrolyte, an ionophobic pore with an ionic liquid is also able to increase the energy stored when the electrode voltage is beyond a certain value. We find that the critical voltage for an enhanced capacitance in an ionic liquid is larger than that in an organic electrolyte. Finally, our theoretical predictions provide further understanding of how chemical modification of porous electrodes affects the performance of supercapacitors.

  8. Can ionophobic nanopores enhance the energy storage capacity of electric-double-layer capacitors containing nonaqueous electrolytes?

    DOE PAGES

    Lian, Cheng; Univ. of California, Riverside, CA; Liu, Honglai; ...

    2016-08-22

    The ionophobicity effect of nanoporous electrodes on the capacitance and the energy storage capacity of nonaqueous-electrolyte supercapacitors is studied by means of the classical density functional theory (DFT). It has been hypothesized that ionophobic nanopores may create obstacles in charging, but they store energy much more efficiently than ionophilic pores. In this paper, we find that, for both ionic liquids and organic electrolytes, an ionophobic pore exhibits a charging behavior different from that of an ionophilic pore, and that the capacitance–voltage curve changes from a bell shape to a two-hump camel shape when the pore ionophobicity increases. For electric-double-layer capacitorsmore » containing organic electrolytes, an increase in the ionophobicity of the nanopores leads to a higher capacity for energy storage. Without taking into account the effects of background screening, the DFT predicts that an ionophobic pore containing an ionic liquid does not enhance the supercapacitor performance within the practical voltage ranges. However, by using an effective dielectric constant to account for ion polarizability, the DFT predicts that, like an organic electrolyte, an ionophobic pore with an ionic liquid is also able to increase the energy stored when the electrode voltage is beyond a certain value. We find that the critical voltage for an enhanced capacitance in an ionic liquid is larger than that in an organic electrolyte. Finally, our theoretical predictions provide further understanding of how chemical modification of porous electrodes affects the performance of supercapacitors.« less

  9. Influences of internal resistance and specific surface area of electrode materials on characteristics of electric double layer capacitors

    NASA Astrophysics Data System (ADS)

    Suda, Yoshiyuki; Mizutani, Akitaka; Harigai, Toru; Takikawa, Hirofumi; Ue, Hitoshi; Umeda, Yoshito

    2017-01-01

    We fabricated electric double layer capacitors (EDLCs) using particulate and fibrous types of carbon nanomaterials with a wide range of specific surface areas and resistivity as an active material. The carbon nanomaterials used in this study are carbon nanoballoons (CNBs), onion-like carbon (OLC), and carbon nanocoils (CNCs). A commercially used activated carbon (AC) combined with a conductive agent was used as a comparison. We compared the EDLC performance using cyclic voltammetry (CV), galvanostatic charge/discharge testing, and electrochemical impedance spectroscopy (EIS). OLC showed a poor EDLC performance, although it has the lowest resistivity among the carbon nanomaterials. CNB, which has a 1/16 lower specific surface area than AC but higher specific surface area than CNC and OLC, had a higher specific capacitance than CNC and OLC. Moreover, at current densities of 1.5 Ag-1 and larger, the specific capacitance of the EDLC using CNB was almost the same as that using AC. Electrochemical impedance spectroscopy of the EDLCs revealed that the CNB and CNC electrodes had a much lower internal resistance than the AC electrode, which correlated with a low capacitance maintenance factor as the current density increased.

  10. Can ionophobic nanopores enhance the energy storage capacity of electric-double-layer capacitors containing nonaqueous electrolytes?

    SciTech Connect

    Lian, Cheng; Liu, Honglai; Henderson, Douglas; Wu, Jianzhong

    2016-08-22

    The ionophobicity effect of nanoporous electrodes on the capacitance and the energy storage capacity of nonaqueous-electrolyte supercapacitors is studied by means of the classical density functional theory (DFT). It has been hypothesized that ionophobic nanopores may create obstacles in charging, but they store energy much more efficiently than ionophilic pores. In this paper, we find that, for both ionic liquids and organic electrolytes, an ionophobic pore exhibits a charging behavior different from that of an ionophilic pore, and that the capacitance–voltage curve changes from a bell shape to a two-hump camel shape when the pore ionophobicity increases. For electric-double-layer capacitors containing organic electrolytes, an increase in the ionophobicity of the nanopores leads to a higher capacity for energy storage. Without taking into account the effects of background screening, the DFT predicts that an ionophobic pore containing an ionic liquid does not enhance the supercapacitor performance within the practical voltage ranges. However, by using an effective dielectric constant to account for ion polarizability, the DFT predicts that, like an organic electrolyte, an ionophobic pore with an ionic liquid is also able to increase the energy stored when the electrode voltage is beyond a certain value. We find that the critical voltage for an enhanced capacitance in an ionic liquid is larger than that in an organic electrolyte. Finally, our theoretical predictions provide further understanding of how chemical modification of porous electrodes affects the performance of supercapacitors.

  11. Spiro-(1,1‧)-bipyrrolidinium tetrafluoroborate salt as high voltage electrolyte for electric double layer capacitors

    NASA Astrophysics Data System (ADS)

    Yu, Xuewen; Ruan, Dianbo; Wu, Changcheng; Wang, Jing; Shi, Zhiqiang

    2014-11-01

    A novel quaternary ammonium salt based on spiro-(1,1‧)-bipyrolidinium tetrafluoroborate (SBP-BF4) has been synthesized and dissolved in propylene carbonate (PC) with 1.5 mol L-1 (M) concentration for electric double-layer capacitors (EDLCs). The physic-chemical properties and electrochemical performance of SBP-BF4/PC electrolyte are investigated. Compared with the standard electrolyte 1.5 M TEMA-BF4 in PC, the novel SBP-BF4/PC electrolyte exhibited much better electrochemical performance due to its smaller cation size, lower viscosity and higher conductivity. The specific discharge capacitance of activated carbon electrode based EDLCs using SBP-BF4/PC electrolyte is 120 F g-1, the energy density and power density can reach 31 kW kg-1 and 6938 W kg-1, respectively, when the working voltage is 2.7 V and current density is 50 mA g-1. The withstand voltage of activated carbon based EDLCs with SBP-BF4/PC electrolyte can reach to 3.2 V, where the stable discharge capacitance and energy density are 121 F g-1 and 43 Wh kg-1, respectively.

  12. Electric double-layer capacitors with tea waste derived activated carbon electrodes and plastic crystal based flexible gel polymer electrolytes

    NASA Astrophysics Data System (ADS)

    Suleman, M.; Deraman, M.; Othman, M. A. R.; Omar, R.; Hashim, M. A.; Basri, N. H.; Nor, N. S. M.; Dolah, B. N. M.; Hanappi, M. F. Y. M.; Hamdan, E.; Sazali, N. E. S.; Tajuddin, N. S. M.; Jasni, M. R. M.

    2016-08-01

    We report a novel configuration of symmetrical electric double-layer capacitors (EDLCs) comprising a plastic crystalline succinonitrile (SN) based flexible polymer gel electrolyte, incorporated with sodium trifluoromethane sulfonate (NaTf) immobilised in a host polymer poly (vinylidine fluoride-co-hexafluoropropylene) (PVdF-HFP). The cost-effective activated carbon powder possessing a specific surface area (SSA) of ~ 1700 m2g-1 containing a large proportion of meso-porosity has been derived from tea waste to use as supercapacitor electrodes. The high ionic conductivity (~3.6×10-3 S cm-1 at room temperature) and good electrochemical stability render the gel polymer electrolyte film a suitable candidate for the fabrication of EDLCs. The performance of the EDLCs has been tested by electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV), and galvanostatic charge-discharge studies. The performance of the EDLC cell is found to be promising in terms of high values of specific capacitance (~270 F g-1), specific energy (~ 36 Wh kg-1), and power density (~ 33 kW kg-1).

  13. Frequency-selective electrokinetic enrichment of biomolecules in physiological media based on electrical double-layer polarization.

    PubMed

    Rohani, Ali; Sanghavi, Bankim J; Salahi, Armita; Liao, Kuo-Tang; Chou, Chia-Fu; Swami, Nathan S

    2017-08-24

    Proteomic biomarkers of interest to the early diagnosis of diseases and infections are present at trace levels versus interfering species. Hence, their selective enrichment is needed within bio-assays for speeding binding kinetics with receptors and for reducing signal interferences. While DC fields can separate biomolecules based on their electrokinetic mobilities, they are unable to selectively enrich biomarkers versus interfering species, which may possess like-charges. We present the utilization of AC electrokinetics to enable frequency-selective enrichment of nanocolloidal biomolecules, based on the characteristic time constant for polarization of their electrical double-layer, since surface conduction in their ion cloud depends on colloidal size, shape and surface charge. In this manner, using DC-offset AC fields, differences in frequency dispersion for negative dielectrophoresis are balanced against electrophoresis in a nanoslit channel to enable the selective enrichment of prostate specific antigen (PSA) versus anti-mouse immunoglobulin antibodies that cause signal interferences to immunoassays. Through coupling enrichment to capture by receptors on graphene-modified surfaces, we demonstrate the elimination of false positives caused by anti-mouse immunoglobulin antibodies to the PSA immunoassay.

  14. Structure of electric double layers in capacitive systems and to what extent (classical) density functional theory describes it

    NASA Astrophysics Data System (ADS)

    Härtel, Andreas

    2017-10-01

    Ongoing scientific interest is aimed at the properties and structure of electric double layers (EDLs), which are crucial for capacitive energy storage, water treatment, and energy harvesting technologies like supercapacitors, desalination devices, blue engines, and thermocapacitive heat-to-current converters. A promising tool to describe their physics on a microscopic level is (classical) density functional theory (DFT), which can be applied in order to analyze pair correlations and charge ordering in the primitive model of charged hard spheres. This simple model captures the main properties of ionic liquids and solutions and it predicts many of the phenomena that occur in EDLs. The latter often lead to anomalous response in the differential capacitance of EDLs. This work constructively reviews the powerful theoretical framework of DFT and its recent developments regarding the description of EDLs. It explains to what extent current approaches in DFT describe structural ordering and in-plane transitions in EDLs, which occur when the corresponding electrodes are charged. Further, the review briefly summarizes the history of modeling EDLs, presents applications, and points out limitations and strengths in present theoretical approaches. It concludes that DFT as a sophisticated microscopic theory for ionic systems is expecting a challenging but promising future in both fundamental research and applications in supercapacitive technologies.

  15. Fundamental measure theory for the electric double layer: implications for blue-energy harvesting and water desalination

    NASA Astrophysics Data System (ADS)

    Härtel, Andreas; Janssen, Mathijs; Samin, Sela; van Roij, René

    2015-05-01

    Capacitive mixing (CAPMIX) and capacitive deionization (CDI) are promising candidates for harvesting clean, renewable energy and for the energy efficient production of potable water, respectively. Both CAPMIX and CDI involve water-immersed porous carbon (supercapacitors) electrodes at voltages of the order of hundreds of millivolts, such that counter-ionic packing is important for the electric double layer (EDL) which forms near the surfaces of these porous materials. Thus, we propose a density functional theory (DFT) to model the EDL, where the White-Bear mark II fundamental measure theory functional is combined with a mean-field Coulombic and a mean spherical approximation-type correction to describe the interplay between dense packing and electrostatics, in good agreement with molecular dynamics simulations. We discuss the concentration-dependent potential rise due to changes in the chemical potential in capacitors in the context of an over-ideal theoretical description and its impact on energy harvesting and water desalination. Compared to less elaborate mean-field models our DFT calculations reveal a higher work output for blue-energy cycles and a higher energy demand for desalination cycles.

  16. Structure of electric double layers in capacitive systems and to what extent (classical) density functional theory describes it.

    PubMed

    Härtel, Andreas

    2017-09-12

    Ongoing scientific interest is aimed at the properties and structure of electric double layers (EDLs), which are crucial for capacitive energy storage, water treatment, and energy harvesting technologies like supercapacitors, desalination devices, blue engines, and thermocapacitive heat-to-current converters. A promising tool to describe their physics on a microscopic level is (classical) density functional theory (DFT), which can be applied in order to analyze pair correlations and charge ordering in the primitive model of charged hard spheres. This simple model captures the main properties of ionic liquids and solutions and it predicts many of the phenomena that occur in EDLs. The latter often lead to anomalous response in the differential capacitance of EDLs. This work constructively reviews the powerful theoretical framework of DFT and its recent developments regarding the description of EDLs. It explains to what extent current approaches in DFT describe structural ordering and in-plane transitions in EDLs, which occur when the corresponding electrodes are charged. Further, the review briefly summarizes the history of modeling EDLs, presents applications, and points out limitations and strengths in present theoretical approaches. It concludes that DFT as a sophisticated microscopic theory for ionic systems is expecting a challenging but promising future in both fundamental research and applications in supercapacitive technologies.

  17. In situ NMR and electrochemical quartz crystal microbalance techniques reveal the structure of the electrical double layer in supercapacitors.

    PubMed

    Griffin, John M; Forse, Alexander C; Tsai, Wan-Yu; Taberna, Pierre-Louis; Simon, Patrice; Grey, Clare P

    2015-08-01

    Supercapacitors store charge through the electrosorption of ions on microporous electrodes. Despite major efforts to understand this phenomenon, a molecular-level picture of the electrical double layer in working devices is still lacking as few techniques can selectively observe the ionic species at the electrode/electrolyte interface. Here, we use in situ NMR to directly quantify the populations of anionic and cationic species within a working microporous carbon supercapacitor electrode. Our results show that charge storage mechanisms are different for positively and negatively polarized electrodes for the electrolyte tetraethylphosphonium tetrafluoroborate in acetonitrile; for positive polarization charging proceeds by exchange of the cations for anions, whereas for negative polarization, cation adsorption dominates. In situ electrochemical quartz crystal microbalance measurements support the NMR results and indicate that adsorbed ions are only partially solvated. These results provide new molecular-level insight, with the methodology offering exciting possibilities for the study of pore/ion size, desolvation and other effects on charge storage in supercapacitors.

  18. Grafting effect on the wetting and electrochemical performance of carbon cloth electrode and polypropylene separator in electric double layer capacitor

    NASA Astrophysics Data System (ADS)

    Stepniak, Izabela; Ciszewski, Aleksander

    Activated carbon (AC) fiber cloths and hydrophobic microporous polypropylene (PP) membrane, both modified by plasma-induced graft polymerization of acrylic acid (AAc) under UV irradiation, and filled with saturated lithium hydroxide solution were used as electrodes, a separator and electrolyte in electric double layer capacitors (EDLCs). The modification process changed the hydrophobic character of AC and PP materials to hydrophilic, made them wettable and serviceable as components of an electrochemical capacitor. The presence of poly(acrylic acid) on the AC and PP surface was confirmed by SEM and XPS methods. Electrochemical characteristics of EDLCs were investigated by cyclic voltammetry and galvanostatic charge-discharge cycle tests and also by impedance spectroscopy. At the 1000th cycle of potential cycling (1 A g -1) the specific capacitance of 110 F g -1 was obtained with a specific energy of 11 Wh kg -1 at power density of 1 kW kg -1. The above results provide valuable information which may be used when developing novel compositions of EDLCs.

  19. Electric Double Layer Capacitor (EDLC) based Mismatching Losses Reduction under Fast-Shaded Conditions of PV Modules

    NASA Astrophysics Data System (ADS)

    Syafaruddin; Tanaka, Yasuyuki; Karatepe, Engin; Hiyama, Takashi

    Fast-moving irradiance condition is one of problems that need to be solved in the non-stationary conventional maximum power point (MPP) trackers of PV system. Under sudden irradiance changes, the output power is changed drastically that leads to the shifting in MPP voltage. Conventional MPP algorithms may start continuously to search for finding the optimum point. However, suddenly another shadow can occur prior to complete removing of previous shadow. Continuing the tracking process under this condition will cause to lose energy. This paper presents the electric double layer capacitor (EDLC) as the power compensation method for improving the maximum power transfer of PV system under short-term period of shading. Several scenarios are tested in this work by measurement the percentage of power compensation, for instance the effect of capacitor size to the period of shading, the effects of shading period to the level shading intensity and cell temperature. This paper is directly purposed to reduce the power losses for moving objects powered by solar energy, such as solar car and solar boat systems.

  20. Electrode Mass Balancing as an Inexpensive and Simple Method to Increase the Capacitance of Electric Double-Layer Capacitors.

    PubMed

    Andres, Britta; Engström, Ann-Christine; Blomquist, Nicklas; Forsberg, Sven; Dahlström, Christina; Olin, Håkan

    Symmetric electric double-layer capacitors (EDLCs) have equal masses of the same active material in both electrodes. However, having equal electrode masses may prevent the EDLC to have the largest possible specific capacitance if the sizes of the hydrated anions and cations in the electrolyte differ because the electrodes and the electrolyte may not be completely utilized. Here we demonstrate how this issue can be resolved by mass balancing. If the electrode masses are adjusted according to the size of the ions, one can easily increase an EDLC's specific capacitance. To that end, we performed galvanostatic cycling to measure the capacitances of symmetric EDLCs with different electrode mass ratios using four aqueous electrolytes- Na2SO4, H2SO4, NaOH, and KOH (all with a concentration of 1 M)-and compared these to the theoretical optimal electrode mass ratio that we calculated using the sizes of the hydrated ions. Both the theoretical and experimental values revealed lower-than-1 optimal electrode ratios for all electrolytes except KOH. The largest increase in capacitance was obtained for EDLCs with NaOH as electrolyte. Specifically, we demonstrate an increase of the specific capacitance by 8.6% by adjusting the electrode mass ratio from 1 to 0.86. Our findings demonstrate that electrode mass balancing is a simple and inexpensive method to increase the capacitance of EDLCs. Furthermore, our results imply that one can reduce the amount of unused material in EDLCs and thus decrease their weight, volume and cost.

  1. Can ionophobic nanopores enhance the energy storage capacity of electric-double-layer capacitors containing nonaqueous electrolytes?

    PubMed

    Lian, Cheng; Liu, Honglai; Henderson, Douglas; Wu, Jianzhong

    2016-10-19

    The ionophobicity effect of nanoporous electrodes on the capacitance and the energy storage capacity of nonaqueous-electrolyte supercapacitors is studied by means of the classical density functional theory (DFT). It has been hypothesized that ionophobic nanopores may create obstacles in charging, but they store energy much more efficiently than ionophilic pores. In this study, we find that, for both ionic liquids and organic electrolytes, an ionophobic pore exhibits a charging behavior different from that of an ionophilic pore, and that the capacitance-voltage curve changes from a bell shape to a two-hump camel shape when the pore ionophobicity increases. For electric-double-layer capacitors containing organic electrolytes, an increase in the ionophobicity of the nanopores leads to a higher capacity for energy storage. Without taking into account the effects of background screening, the DFT predicts that an ionophobic pore containing an ionic liquid does not enhance the supercapacitor performance within the practical voltage ranges. However, by using an effective dielectric constant to account for ion polarizability, the DFT predicts that, like an organic electrolyte, an ionophobic pore with an ionic liquid is also able to increase the energy stored when the electrode voltage is beyond a certain value. We find that the critical voltage for an enhanced capacitance in an ionic liquid is larger than that in an organic electrolyte. Our theoretical predictions provide further understanding of how chemical modification of porous electrodes affects the performance of supercapacitors.

  2. Monolayer Solid-State Electrolyte for Electric Double Layer Gating of Graphene Field-Effect Transistors.

    PubMed

    Xu, Ke; Lu, Hao; Kinder, Erich W; Seabaugh, Alan; Fullerton-Shirey, Susan K

    2017-06-27

    The electrostatic gating of graphene field-effect transistors is demonstrated using a monolayer electrolyte. The electrolyte, cobalt crown ether phthalocyanine (CoCrPc) and LiClO4, is deposited as a monolayer on the graphene channel, essentially creating an additional two-dimensional layer on top of graphene. The crown ethers on the CoCrPc solvate lithium ions and the ion location is modulated by a backgate without requiring liquid solvent. Ions dope the channel by inducing image charges; the doping level (i.e., induced charge density) can be modulated by the backgate bias with the extent of the surface potential change being controlled by the magnitude and polarity of the backgate bias. With a crown ether to Li(+) ratio of 5:1, programming tests for which the backgate is held at -VBG shift the Dirac point by ∼15 V, corresponding to a sheet carrier density on the order of 10(12) cm(-2). This charge carrier density agrees with the packing density of monolayer CoCrPc on graphene that would be expected with one Li(+) for every five crown ethers (at the maximum possible Li(+) concentration, 10(13) cm(-2) is predicted). The crown ethers provide two stable states for the Li(+): one near the graphene channel (low-resistance state) and one ∼5 Å away from the channel (high-resistance state). Initial state retention measurements indicate that the two states can be maintained for at least 30 min (maximum time monitored), which is 10(6) times longer than polymer-based electrolytes at room temperature, with at least a 250 Ω μm difference between the channel resistance in the high- and low-resistance states.

  3. Transient finite element analysis of electric double layer using Nernst-Planck-Poisson equations with a modified Stern layer.

    PubMed

    Lim, Jongil; Whitcomb, John; Boyd, James; Varghese, Julian

    2007-01-01

    A finite element implementation of the transient nonlinear Nernst-Planck-Poisson (NPP) and Nernst-Planck-Poisson-modified Stern (NPPMS) models is presented. The NPPMS model uses multipoint constraints to account for finite ion size, resulting in realistic ion concentrations even at high surface potential. The Poisson-Boltzmann equation is used to provide a limited check of the transient models for low surface potential and dilute bulk solutions. The effects of the surface potential and bulk molarity on the electric potential and ion concentrations as functions of space and time are studied. The ability of the models to predict realistic energy storage capacity is investigated. The predicted energy is much more sensitive to surface potential than to bulk solution molarity.

  4. Electric double layer at metal oxide surfaces:static properties of the cassiterite-water interface.

    SciTech Connect

    Vlcek, L.; Zhang, Z.; Machesky, M .L.; Fenter, P.; Rosenqvist, J.; Wesolowski, D. J.; Anovitz, L. M.; Predota, M.; Cummings, P. T.; Vanderbilt Univ.; ORNL; Univ. of South Bohimia; Illinois State Water Survey

    2007-03-24

    The structure of water at the (110) surface of cassiterite ({alpha}-SnO{sub 2}) at ambient conditions was studied by means of molecular dynamics simulations and X-ray crystal truncation rod experiments and interpreted with the help of the revised MUSIC model of surface protonation. The interactions of the metal oxide in the simulations were described by a recently developed classical force field based on the SPC/E model of water. Two extreme cases of completely hydroxylated and nonhydroxylated surfaces were considered along with a mixed surface with 50% dissociation. To study the dependence of the surface properties on pH, neutral and negatively charged variants of the surfaces were constructed. Axial and lateral density distributions of water for different types of surfaces were compared to each other and to experimental axial density distributions found by X-ray experiments. Although significant differences were found between the structures of the studied interfaces, the axial distances between Sn and O atoms are very similar and therefore could not be clearly distinguished by the diffraction technique. The explanation of structures observed in the density distributions was provided by a detailed analysis of hydrogen bonding in the interfacial region. It revealed qualitatively different hydrating patterns formed at neutral hydroxylated and nonhydroxylated surfaces and suggested a preference for the dissociative adsorption of water. At negatively charged surfaces, however, the situation can be reversed by the electric field stabilizing a hydrogen bond network similar to that found at the neutral nonhydroxylated surface. Comparison with previously studied rutile ({alpha}-TiO{sub 2}) surfaces provided insight into the differences between the hydration of these two metal oxides, and an important role was ascribed to their different lattice parameters. A link to macroscopic properties was provided by the revised MUSIC surface protonation model. Explicit use of the Sn

  5. Electric double layer at metal oxide surfaces: Static properties of the cassiterite - Water Interface

    SciTech Connect

    Vlcek, Lukas; Zhang, Zhan; Machesky, Michael L.; Wesolowski, David J

    2007-04-01

    The structure of water at the (110) surface of cassiterite ({alpha}-SnO{sub 2}) at ambient conditions was studied by means of molecular dynamics simulations and X-ray crystal truncation rod experiments and interpreted with the help of the revised MUSIC model of surface protonation. The interactions of the metal oxide in the simulations were described by a recently developed classical force field based on the SPC/E model of water. Two extreme cases of completely hydroxylated and nonhydroxylated surfaces were considered along with a mixed surface with 50% dissociation. To study the dependence of the surface properties on pH, neutral and negatively charged variants of the surfaces were constructed. Axial and lateral density distributions of water for different types of surfaces were compared to each other and to experimental axial density distributions found by X-ray experiments. Although significant differences were found between the structures of the studied interfaces, the axial distances between Sn and O atoms are very similar and therefore could not be clearly distinguished by the diffraction technique. The explanation of structures observed in the density distributions was provided by a detailed analysis of hydrogen bonding in the interfacial region. It revealed qualitatively different hydrating patterns formed at neutral hydroxylated and nonhydroxylated surfaces and suggested a preference for the dissociative adsorption of water. At negatively charged surfaces, however, the situation can be reversed by the electric field stabilizing a hydrogen bond network similar to that found at the neutral nonhydroxylated surface. Comparison with previously studied rutile ({alpha}-TiO{sub 2}) surfaces provided insight into the differences between the hydration of these two metal oxides, and an important role was ascribed to their different lattice parameters. A link to macroscopic properties was provided by the revised MUSIC surface protonation model. Explicit use of the Sn

  6. Electric double layer at metal oxide surfaces: static properties of the cassiterite-water interface.

    PubMed

    Vlcek, Lukas; Zhang, Zhan; Machesky, Mike L; Fenter, Paul; Rosenqvist, Jorgen; Wesolowski, David J; Anovitz, Larry M; Predota, Milan; Cummings, Peter T

    2007-04-24

    The structure of water at the (110) surface of cassiterite (alpha-SnO2) at ambient conditions was studied by means of molecular dynamics simulations and X-ray crystal truncation rod experiments and interpreted with the help of the revised MUSIC model of surface protonation. The interactions of the metal oxide in the simulations were described by a recently developed classical force field based on the SPC/E model of water. Two extreme cases of completely hydroxylated and nonhydroxylated surfaces were considered along with a mixed surface with 50% dissociation. To study the dependence of the surface properties on pH, neutral and negatively charged variants of the surfaces were constructed. Axial and lateral density distributions of water for different types of surfaces were compared to each other and to experimental axial density distributions found by X-ray experiments. Although significant differences were found between the structures of the studied interfaces, the axial distances between Sn and O atoms are very similar and therefore could not be clearly distinguished by the diffraction technique. The explanation of structures observed in the density distributions was provided by a detailed analysis of hydrogen bonding in the interfacial region. It revealed qualitatively different hydrating patterns formed at neutral hydroxylated and nonhydroxylated surfaces and suggested a preference for the dissociative adsorption of water. At negatively charged surfaces, however, the situation can be reversed by the electric field stabilizing a hydrogen bond network similar to that found at the neutral nonhydroxylated surface. Comparison with previously studied rutile (alpha-TiO2) surfaces provided insight into the differences between the hydration of these two metal oxides, and an important role was ascribed to their different lattice parameters. A link to macroscopic properties was provided by the revised MUSIC surface protonation model. Explicit use of the Sn-O bond lengths

  7. Instability limits for spontaneous double layer formation

    SciTech Connect

    Carr, J. Jr.; Galante, M. E.; McCarren, D.; Scime, E. E.; Sears, S.; VanDervort, R. W.; Magee, R. M.; Reynolds, E.

    2013-11-15

    We present time-resolved measurements that demonstrate that large amplitude electrostatic instabilities appear in pulsed, expanding helicon plasmas at the same time as particularly strong double layers appear in the expansion region. A significant cross-correlation between the electrostatic fluctuations and fluctuations in the number of ions accelerated by the double layer electric field is observed. No correlation is observed between the electrostatic fluctuations and ions that have not passed through the double layer. These measurements confirm that the simultaneous appearance of the electrostatic fluctuations and the double layer is not simple coincidence. In fact, the accelerated ion population is responsible for the growth of the instability. The double layer strength, and therefore, the velocity of the accelerated ions, is limited by the appearance of the electrostatic instability.

  8. A new hydrodynamic analysis of double layers

    NASA Technical Reports Server (NTRS)

    Hora, Heinrich

    1987-01-01

    A genuine two-fluid model of plasmas with collisions permits the calculation of dynamic (not necessarily static) electric fields and double layers inside of plasmas including oscillations and damping. For the first time a macroscopic model for coupling of electromagnetic and Langmuir waves was achieved with realistic damping. Starting points were laser-produced plasmas showing very high dynamic electric fields in nonlinear force-produced cavitous and inverted double layers in agreement with experiments. Applications for any inhomogeneous plasma as in laboratory or in astrophysical plasmas can then be followed up by a transparent hydrodynamic description. Results are the rotation of plasmas in magnetic fields and a new second harmonic resonance, explanation of the measured inverted double layers, explanation of the observed density-independent, second harmonics emission from laser-produced plasmas, and a laser acceleration scheme by the very high fields of the double layers.

  9. New Approach for High-Voltage Electrical Double-Layer Capacitors Using Vertical Graphene Nanowalls with and without Nitrogen Doping.

    PubMed

    Chi, Yu-Wen; Hu, Chi-Chang; Shen, Hsiao-Hsuan; Huang, Kun-Ping

    2016-09-14

    Integrating various devices to achieve high-performance energy storage systems to satisfy various demands in modern societies become more and more important. Electrical double-layer capacitors (EDLCs), one kind of the electrochemical capacitors, generally provide the merits of high charge-discharge rates, extremely long cycle life, and high efficiency in electricity capture/storage, leading to a desirable device of electricity management from portable electronics to hybrid vehicles or even smart grid application. However, the low cell voltage (2.5-2.7 V in organic liquid electrolytes) of EDLCs lacks the direct combination of Li-ion batteries (LIBs) and EDLCs for creating new functions in future applications without considering the issue of a relatively low energy density. Here we propose a guideline, "choosing a matching pair of electrode materials and electrolytes", to effectively extend the cell voltage of EDLCs according to three general strategies. Based on the new strategy proposed in this work, materials with an inert surface enable to tolerate a wider potential window in commercially available organic electrolytes in comparison with activated carbons (ACs). The binder-free, vertically grown graphene nanowalls (GNW) and nitrogen-doped GNW (NGNW) electrodes respectively provide good examples for extending the upper potential limit of a positive electrode of EDLCs from 0.1 to 1.5 V (vs Ag/AgNO3) as well as the lower potential limit of a negative electrode of EDLCs from -2.0 V to ca. -2.5 V in 1 M TEABF4/PC (propylene carbonate) compared to ACs. This newly designed asymmetric EDLC exhibits a cell voltage of 4 V, specific energy of 52 Wh kg(-1) (ca. a device energy density of 13 Wh kg(-1)), and specific power of 8 kW kg(-1) and ca. 100% retention after 10,000 cycles charge-discharge, reducing the series number of EDLCs to enlarge the module voltage and opening the possibility for directly combining EDLCs and LIBs in advanced applications.

  10. Double layers on auroral field lines

    NASA Technical Reports Server (NTRS)

    Hudson, M. K.; Lotko, W.; Witt, E.

    1982-01-01

    Time-stationary solutions to the Vlasov-Poisson equation for ion holes and double layers were examined along with particle simulations which pertain to recent observations of small amplitude (e phi)/t sub e approx. 1 electric field structures on auroral field lines. Both the time-stationary analysis and the simulations suggest that double layers evolve from holes in ion phase space when their amplitude reaches (e phi)/t sub e approx. 1. Multiple small amplitude double layers which are seen in long simulation systems and are seen to propagate past spacecraft may account for the acceleration of plasma sheet electrons to produce the discrete aurora.

  11. Electrode Mass Balancing as an Inexpensive and Simple Method to Increase the Capacitance of Electric Double-Layer Capacitors

    PubMed Central

    Andres, Britta; Engström, Ann-Christine; Blomquist, Nicklas; Forsberg, Sven; Dahlström, Christina; Olin, Håkan

    2016-01-01

    Symmetric electric double-layer capacitors (EDLCs) have equal masses of the same active material in both electrodes. However, having equal electrode masses may prevent the EDLC to have the largest possible specific capacitance if the sizes of the hydrated anions and cations in the electrolyte differ because the electrodes and the electrolyte may not be completely utilized. Here we demonstrate how this issue can be resolved by mass balancing. If the electrode masses are adjusted according to the size of the ions, one can easily increase an EDLC’s specific capacitance. To that end, we performed galvanostatic cycling to measure the capacitances of symmetric EDLCs with different electrode mass ratios using four aqueous electrolytes— Na2SO4, H2SO4, NaOH, and KOH (all with a concentration of 1 M)—and compared these to the theoretical optimal electrode mass ratio that we calculated using the sizes of the hydrated ions. Both the theoretical and experimental values revealed lower-than-1 optimal electrode ratios for all electrolytes except KOH. The largest increase in capacitance was obtained for EDLCs with NaOH as electrolyte. Specifically, we demonstrate an increase of the specific capacitance by 8.6% by adjusting the electrode mass ratio from 1 to 0.86. Our findings demonstrate that electrode mass balancing is a simple and inexpensive method to increase the capacitance of EDLCs. Furthermore, our results imply that one can reduce the amount of unused material in EDLCs and thus decrease their weight, volume and cost. PMID:27658253

  12. Can ionophobic nanopores enhance the energy storage capacity of electric-double-layer capacitors containing nonaqueous electrolytes?

    NASA Astrophysics Data System (ADS)

    Lian, Cheng; Liu, Honglai; Henderson, Douglas; Wu, Jianzhong

    2016-10-01

    The ionophobicity effect of nanoporous electrodes on the capacitance and the energy storage capacity of nonaqueous-electrolyte supercapacitors is studied by means of the classical density functional theory (DFT). It has been hypothesized that ionophobic nanopores may create obstacles in charging, but they store energy much more efficiently than ionophilic pores. In this study, we find that, for both ionic liquids and organic electrolytes, an ionophobic pore exhibits a charging behavior different from that of an ionophilic pore, and that the capacitance-voltage curve changes from a bell shape to a two-hump camel shape when the pore ionophobicity increases. For electric-double-layer capacitors containing organic electrolytes, an increase in the ionophobicity of the nanopores leads to a higher capacity for energy storage. Without taking into account the effects of background screening, the DFT predicts that an ionophobic pore containing an ionic liquid does not enhance the supercapacitor performance within the practical voltage ranges. However, by using an effective dielectric constant to account for ion polarizability, the DFT predicts that, like an organic electrolyte, an ionophobic pore with an ionic liquid is also able to increase the energy stored when the electrode voltage is beyond a certain value. We find that the critical voltage for an enhanced capacitance in an ionic liquid is larger than that in an organic electrolyte. Our theoretical predictions provide further understanding of how chemical modification of porous electrodes affects the performance of supercapacitors. The authors are saddened by the passing of George Stell but are pleased to contribute this article in his memory. Some years ago, DH gave a talk at a Gordon Conference that contained an approximation that George had demonstrated previously to be in error in one of his publications. Rather than making this point loudly in the discussion, George politely, quietly, and privately pointed this out

  13. High Power Electric Double-Layer Capacitors based on Room-Temperature Ionic Liquids and Nanostructured Carbons

    NASA Astrophysics Data System (ADS)

    Perez, Carlos R.

    The efficient storage of electrical energy constitutes both a fundamental challenge for 21st century science and an urgent requirement for the sustainability of our technological civilization. The push for cleaner renewable forms of energy production, such as solar and wind power, strongly depends on a concomitant development of suitable storage methods to pair with these intermittent sources, as well as for mobile applications, such as vehicles and personal electronics. In this regard, Electrochemical Double-Layer Capacitors (supercapacitors) represent a vibrant area of research due to their environmental friendliness, long lifetimes, high power capability, and relative underdevelopment when compared to electrochemical batteries. Currently supercapacitors have gravimetric energies one order of magnitude lower than similarly advanced batteries, while conversly enjoying a similar advantage over them in terms of power. The challenge is to increase the gravimentric energies and conserve the high power. On the material side, research focuses on highly porous supports and electrolytes, the critical components of supercapacitors. Through the use of electrolyte systems with a wider electrochemical stability window, as well as properly tailored carbon nanomaterials as electrodes, significant improvements in performance are possible. Room Temperature Ionic Liquids and Carbide-Derived Carbons are promising electrolytes and electrodes, respectively. RTILs have been shown to be stable at up to twice the voltage of organic solvent-salt systems currently employed in supercapacitors, and CDCs are tunable in pore structure, show good electrical conductivity, and superior demonstrated capability as electrode material. This work aims to better understand the interplay of electrode and electrolyte parameters, such as pore structure and ion size, in the ultimate performance of RTIL-based supercapacitors in terms of power, energy, and temperature of operation. For this purpose, carbon

  14. Electric Potential (psi(delta) and psi(d)) at Outer Helmholtz Plane and Midplane on the Clay Colloid Surface with Overlapping Flat Double Layers.

    PubMed

    Xin; Jian-Min; Guo-Liang; Tian-Ren

    2000-07-15

    An anion negative adsorption equation in the condensed colloidal suspension with overlapping flat double layers was derived according to Gouy-Chapman theory. The electric potential at the outer Helmholtz plane (OHP), psi(delta), and the electric potential at the midplane, psi(d), were numerically solved by computer using the anion negative adsorption equation on the basis of experiments. The results showed that psi(delta) and psi(d) increase with the decrease of the distance between two clay plates, lambda, at first in the given electrolyte concentration. When lambda is smaller than 50-70 Å, psi(d) remains almost unchanged while psi(delta) declines remarkably with the further decrease of lambda. The change of psi(d)/psi(delta) with lambda can explain and manifest overlapping degree of flat double layers more appropriately than psi(d) in previous works. Due to compression of the flat double layer on the clay colloid surface at increasing electrolyte concentration, the magnitude of the electrical potentials at OHP and midplane is considerably reduced at a given lambda. Copyright 2000 Academic Press.

  15. Electrically detected electron spin resonance (EDESR) in thiophene thin films and a thiophene/C 60 double layer

    NASA Astrophysics Data System (ADS)

    Maier, A.; Grupp, A.; Mehring, M.

    1996-09-01

    We report on the investigation of EDESR signals under light illumination in thin films of an end-capped oligothiophen with four thiophene rings (EC4T) and a molecular photodiode made of a double layer of EC4T/C 60 between gold electrodes. The different EDESR signals are interpreted in terms of photogenerated positive (P +) and negative (P -) polarons which undergo spin-dependent recombination.

  16. Advanced double layer capacitors

    NASA Technical Reports Server (NTRS)

    Sarangapani, S.; Lessner, P.; Forchione, J.; Laconti, A. B.

    1989-01-01

    There is a need for large amounts of power to be delivered rapidly in a number of airborne and space systems. Conventional, portable power sources, such as batteries, are not suited to delivering high peak power pulses. The charge stored at the electrode-electrolyte double layer is, however, much more assessible on a short time scale. Devices exploiting this concept were fabricated using carbon and metal oxides (Pinnacle Research) as the electrodes and sulfuric acid as the electrolyte. The approach reported, replaces the liquid sulfuric acid electrolyte with a solid ionomer electrolyte. The challenge is to form a solid electrode-solid ionomer electrolyte composite which has a high capacitance per geometric area. The approach to maximize contact between the electrode particles and the ionomer was to impregnate the electrode particles using a liquid ionomer solution and to bond the solvent-free structure to a solid ionomer membrane. Ruthenium dioxide is the electrode material used. Three strategies are being pursued to provide for a high area electrode-ionomer contact: mixing of the RuOx with a small volume of ionomer solution followed by filtration to remove the solvent, and impregnation of the ionomer into an already formed RuOx electrode. RuOx powder and electrodes were examined by non-electrochemical techniques. X-ray diffraction has shown that the material is almost pure RuO2. The electrode structure depends on the processing technique used to introduce the Nafion. Impregnated electrodes have Nafion concentrated near the surface. Electrodes prepared by the evaporation method show large aggregates of crystals surrounded by Nafion.

  17. Theory of nonmonotonic double layers

    SciTech Connect

    Kim, K.Y.

    1987-12-01

    A simple graphic method of solving the Vlasov--Poisson system associated with nonlinear eigenvalue conditions for arbitrary potential structures is presented. A general analytic formulation for nonmonotonic double layers is presented and illustrated with some particular closed form solutions. This class of double layers satisfies the time stationary Vlasov--Poisson system while requiring a Sagdeev potential, which is a double-valued function of the physical potential. It follows that any distribution function having a density representation as any integer or noninteger power series of potential can never satisfy the nonmonotonic double-layer boundary conditions. A Korteweg--de Vries-like equation is found showing a relationship among the speed of the nonmonotonic double layer, its scale length, and its degree of asymmetry.

  18. Electron acceleration in stochastic double layers

    NASA Technical Reports Server (NTRS)

    Lotko, William

    1987-01-01

    Transversely localized double layers evolve randomly in turbulent regions of strongly magnetized plasma carrying current along the magnetic field. Results from numerical simulations and spacecraft observations in the auroral plasma indicate that the parallel electric field in such regions is microscopically intermittent or stochastic. The implications of stochastic double layer fields on electron acceleration will be discussed in terms of a statistical process involving ensemble averages over test particle motion. A Fokker-Planck equation can be derived for the electron phase space density, which depends on the mean and rms amplitudes of the double layers, the mean double layer density, and the initial electron velocity distribution. It is shown that the resulting electron acceleration is very sensitive to the ratio of the initial electron energy to the rms double layer amplitude. When this ratio is large, the acceleration process differs little from that expected in a dc electric field. When it is small, stochastic heating competes with directed acceleration. Evidence for both cases can be found in the auroral ionosphere in association with so-called inverted-V precipitation and collimated edge precipitation.

  19. Generalization of the Gouy-Chapman-Stern model of an electric double layer for a morphologically complex electrode: deterministic and stochastic morphologies.

    PubMed

    Kant, Rama; Singh, Maibam Birla

    2013-11-01

    We generalize the linearized Gouy-Chapman-Stern theory of an electric double layer for morphologically complex and disordered electrodes. An equation for capacitance is obtained using a linear Gouy-Chapman or Debye-Hückel equation for the potential near the complex-geometry electrode-electrolyte interface. The effect of the surface morphology of an electrode on an electric double layer is obtained using multiple scattering formalism in surface curvature. The result for capacitance is expressed in terms of the ratio of Gouy screening length to the local principal radii of curvatures of the surface. We also include a contribution of a compact layer, which is significant in the overall prediction of capacitance. Our general results are analyzed in detail for two special morphologies of electrodes, i.e., a nanoporous membrane and a forest of nanopillars. Variations of local shapes and global size variations due to residual randomness in morphology are accounted for as curvature fluctuations over a reference shape element. In particular, the theory shows that the presence of geometrical fluctuations in porous systems causes an enhanced dependence of capacitance on mean pore sizes and suppresses the magnitude of capacitance. This theory is further extended to include contributions to capacitance from adsorption of ions and electrode material due to electronic screening. Our predictions are in reasonable agreement with recent experimental measurements on supercapacitive microporous and mesoporous systems.

  20. Unit Cell Level Thickness Control of Single-Crystalline Zinc Oxide Nanosheets Enabled by Electrical Double-Layer Confinement.

    PubMed

    Yin, Xin; Shi, Yeqi; Wei, Yanbing; Joo, Yongho; Gopalan, Padma; Szlufarska, Izabela; Wang, Xudong

    2017-08-08

    Ionic layer epitaxy (ILE) has recently been developed as an effective strategy to synthesize nanometer thick 2D materials with a nonlayered crystal structure, such as ZnO. The packing density of the amphiphilic monolayer is believed to be a key parameter that controls the nanosheet nucleation and growth. In this work, we systematically investigated the growth behavior of single-crystalline ZnO nanosheets templated at the water-air interface by an anionic oleylsulfate monolayer with different packing densities. The thicknesses of ZnO nanosheets were tuned from one unit cell to four unit cells and exhibited good correlation with the width of Zn(2+) ion concentration zone (the Stern layer) underneath the ionized surfactant monolayer. Further analysis of the nanosheet sizes and density revealed that the nanosheet growth was dominated by the steric hindrance from the surfactant monolayer at lower surface pressure, while the nucleation density became the dominating factor at higher surface pressure. The ZnO nanosheets exhibited a decreasing work function as the thickness reduced to a few unit cells. This research validated a critical hypothesis that the nanosheet growth is self-limited by the formation of a double layer of ionic precursors. This work will open up a new way toward controlled synthesis of novel 2D nanosheets from nonlayered materials with a thickness down to one unit cell.

  1. A Model for the Interaction of Two Electric Double Layers in Two Dimensions: The Metal Electrolyte Interface, and the Donnan Membrane.

    DTIC Science & Technology

    1983-06-09

    2he Donnan equilibrium is established between two media containing different concentra- ions of 3roteins, and which are seoarated by a membrane that...N00014-81-C-0776 TASK No. NR 051-775 TECHNICAL REPORT #7 vow A MODEL FOR THE INTERACTION OF TWO ELECTRIC DOUBLE LAYERS r-- IN TWO DIMENSIONS: THE METAL ...CIS-.RINUT ION STATEMENT (at &he abstratt ente in BkOCA 20, If Wi1.rentIrmo R*Poet) :4. SU1WLfMCN-,ARV NOTIES P-zepared for Publication in THE

  2. A mini review of designed mesoporous materials for energy-storage applications: from electric double-layer capacitors to hybrid supercapacitors.

    PubMed

    Lim, Eunho; Jo, Changshin; Lee, Jinwoo

    2016-04-21

    In recent years, porous materials have attracted significant attention in various research fields because of their structural merits. In particular, well-designed mesoporous structures with two- or three-dimensionally interconnected pores have been recognized as electrode materials of particular interest for achieving high-performance electrochemical capacitors (ECs). In this mini review, recent progress in the design of mesoporous electrode materials for ECs, from electric double-layer capacitors (EDLCs) and pseudocapacitors (PCs) to hybrid supercapacitors (HSCs), and research challenges for the development of new mesoporous electrode materials has been discussed.

  3. Double layers acting as particles accelerators

    SciTech Connect

    Sanduloviciu, M.; Lozneanu, E.

    1995-12-31

    It is shown that self-consistent stable and unstable double layers generated in plasma after a self-organisation process are able to accelerate charged particles. The implication of cosmic double layers (Dls) in the acceleration of electrical charged particles long been advocated by Alfven and his Stockholm school is today disputed by argument that static electric fields associated with Dls are conservative and consequently the line integral of the electric field outside the DL balances the line integral inside it. Related with this dispute we will evidence some, so far not considered, facts which are in our opinion arguments that aurora Dls are able to energize particles. For justifying this assertion we start from recent experimental results concerning the phenomenology of self-consistent Dls whose generation involve beside ionisations the neutrals excitations which are at tile origin of the light phenomena as those observed in auroras.

  4. Structure of cylindrical electric double layers: A systematic study by Monte Carlo simulations and density functional theory

    NASA Astrophysics Data System (ADS)

    Goel, Teena; Patra, Chandra N.; Ghosh, Swapan K.; Mukherjee, Tulsi

    2008-10-01

    We present a systematic study of the structure of cylindrical double layers to envisage the distribution of small ions around a cylindrical polyion through canonical Monte Carlo simulation and density functional theory. The polyion is modeled as an infinite, rigid, and impenetrable charged cylinder surrounded by charged hard spheres of equal diameter modeled for small ions of the electrolyte. The solvent is considered as dielectric continuum. The theory is partially perturbative where the hard sphere contribution to the total excess free energy is evaluated using weighted density approximation, and the ionic interactions are calculated using quadratic Taylor expansion with respect to a uniform fluid. The system is studied over a wide range of parameters, viz., ionic concentrations, valences, and ionic sizes as well as for varying axial charge densities of the polyion. The theoretical predictions are observed to be in good agreement with that of simulation results. Some interesting phenomena relating to the width of the diffuse layer, mean electrostatic potential, and charge inversion have been observed to be dependent on different parametric conditions.

  5. Ultralow-Voltage Electric-Double-Layer Oxide-Based Thin-Film Transistors with Faster Switching Response on Flexible Substrates

    NASA Astrophysics Data System (ADS)

    Zhang, Jin; Wu, Guo-Dong

    2014-07-01

    Phosphosilicate glass (PSG) electrolyte films are deposited by improving the content of phosphorus doping during plasma-enhanced chemical vapor deposition, and a fast electric-double-layer (EDL) polarization response of 100 kHz is measured. The mechanism of the fast polarization response and EDL formation are investigated in detail. By using PSG electrolyte films as gate dielectrics, indium-zinc-oxide (IZO) thin-film transistors (TFTs) are fabricated on flexible plastic substrates. Due to the huge EDL gate capacitance, such TFTs show only 0.8 V operation and excellent electrical performances with a large current on/off ratio of 107, low subthreshold swing of 72 mV/decade and high field-effect mobility of 16.76 cm2/V·s. More importantly, the devices exhibit a fast switching response above 100 Hz. Our results demonstrate that such PSG gated TFTs take a great step for low-power flexible oxide electronics application.

  6. Catalytic Graphitization for Preparation of Porous Carbon Material Derived from Bamboo Precursor and Performance as Electrode of Electrical Double-Layer Capacitor

    NASA Astrophysics Data System (ADS)

    Tsubota, Toshiki; Maguchi, Yuta; Kamimura, Sunao; Ohno, Teruhisa; Yasuoka, Takehiro; Nishida, Haruo

    2015-12-01

    The combination of addition of Fe (as a catalyst for graphitization) and CO2 activation (a kind of gaseous activation) was applied to prepare a porous carbon material from bamboo powder (a waste product of superheated steam treatment). Regardless of the heat treatment temperature, many macropores were successfully formed after the heating process by removal of Fe compounds. A turbostratic carbon structure was generated in the Fe-added sample heated at 850°C. It was confirmed that the added Fe acted as a template for pore formation. Moreover, it was confirmed that the added Fe acted as a catalyst for graphitization. The resulting electrochemical performance as the electrode of an electrical double-layer capacitor, as demonstrated by cyclic voltammetry, electrochemical impedance spectroscopy, and charge-discharge testing, could be explained based on the graphitization and activation effects. Addition of Fe could affect the electrical properties of carbon material derived from bamboo.

  7. Effect of ion charges on the electric double layer capacitance of activated carbon in aqueous electrolyte systems

    NASA Astrophysics Data System (ADS)

    Icaza, Juan C.; Guduru, Ramesh K.

    2016-12-01

    Carbon based electrochemical double layer capacitors (EDLCs) are known for high power density, but their energy density is limited due to surface characteristics of the electrode materials as well as the size and charge of the ions used in the electrolyte. Therefore, considering the current demand for enhanced energy density devices, we investigated the use of multivalent electrolytes to increase the capacitance of activated carbon (AC) based EDLCs. As part of these studies, we examined the effect of the charge of the multivalent ions on the capacitive behavior of microporous AC electrodes and compared with the univalent Li+ system. We performed impedance and cyclic voltammetry measurements on AC electrodes in a symmetric two electrode configuration to determine the impedance and capacitance with respect to varying charge and concentration of the ions in the aqueous nitrate electrolytes. These studies clearly demonstrated an increased capacitance with Mg2+ and Al3+ implying the possible effects of ion mobility and electrolyte conductivity in addition to the multivalent charge. These preliminary observations clearly point to the importance of selection of electrolyte ions with more charge, conductivity, and suitable size with respect to the pore size of the electrodes in order to increase the capacitance of EDLCs.

  8. Preparation of hierarchical porous carbon from waste printed circuit boards for high performance electric double-layer capacitors

    NASA Astrophysics Data System (ADS)

    Du, Xuan; Wang, Li; Zhao, Wei; Wang, Yi; Qi, Tao; Li, Chang Ming

    2016-08-01

    Renewable clean energy and resources recycling have become inevitable choices to solve worldwide energy shortages and environmental pollution problems. It is a great challenge to recycle tons of waste printed circuit boards (PCB) produced every year for clean environment while creating values. In this work, low cost, high quality activated carbons (ACs) were synthesized from non-metallic fractions (NMF) of waste PCB to offer a great potential for applications of electrochemical double-layer capacitors (EDLCs). After recovering metal from waste PCB, hierarchical porous carbons were produced from NMF by carbonization and activation processes. The experimental results exhibit that some pores were formed after carbonization due to the escape of impurity atoms introduced by additives in NMF. Then the pore structure was further tailored by adjusting the activation parameters. Roles of micropores and non-micropores in charge storage were investigated when the hierarchical porous carbons were applied as electrode of EDLCs. The highest specific capacitance of 210 F g-1 (at 50 mA g-1) and excellent rate capability were achieved when the ACs possessing a proper micropores/non-micropores ratio. This work not only provides a promising method to recycle PCB, but also investigates the structure tailoring arts for a rational hierarchical porous structure in energy storage/conversion.

  9. Electric double layer capacitance of restricted primitive model for an ionic fluid in slit-like nanopores: A density functional approach

    NASA Astrophysics Data System (ADS)

    Pizio, O.; Sokołowski, S.; Sokołowska, Z.

    2012-12-01

    We apply recently developed version of a density functional theory [Z. Wang, L. Liu, and I. Neretnieks, J. Phys.: Condens. Matter 23, 175002 (2011)], 10.1088/0953-8984/23/17/175002 to study adsorption of a restricted primitive model for an ionic fluid in slit-like pores in the absence of interactions induced by electrostatic images. At present this approach is one of the most accurate theories for such model electric double layers. The dependencies of the differential double layer capacitance on the pore width, on the electrostatic potential at the wall, bulk fluid density, and temperature are obtained. We show that the differential capacitance can oscillate as a function of the pore width dependent on the values of the above parameters. The number of oscillations and their magnitude decrease for high values of the electrostatic potential. For very narrow pores, close to the ion diameter, the differential capacitance tends to a minimum. The dependence of differential capacitance on temperature exhibits maximum at different values of bulk fluid density and applied electrostatic potential.

  10. The electric double layer at a rutile TiO₂ water interface modelled using density functional theory based molecular dynamics simulation.

    PubMed

    Cheng, J; Sprik, M

    2014-06-18

    A fully atomistic model of a compact electric double layer at the rutile TiO2(1 1 0)-water interface is constructed by adding protons to bridging oxygens or removing them from H2O molecules adsorbed on terminal metal cation sites. The surface charge is compensated by F(-) or Na(+) counter ions in outer as well as inner sphere coordination. For each of the protonation states the energy of the TiO2 conduction band minimum is determined relative to the standard hydrogen electrode by computing the free energy for the combined insertion of an electron in the solid and a proton in solution away from the double layer using density functional theory based molecular dynamics methods. Interpreted as electrode potentials, this gives an estimate of the capacitance which is compared to the capacitance obtained from the difference in the average electrostatic potentials in the solid and aqueous phase. When aligned at the point of zero charge these two methods lead to almost identical potential-charge profiles. We find that inner sphere complexes have a slightly larger capacitance (0.4 F m(-2)) compared to outer sphere complexes (0.3 F m(-2)).

  11. Electric double layer capacitance of restricted primitive model for an ionic fluid in slit-like nanopores: A density functional approach.

    PubMed

    Pizio, O; Sokołowski, S; Sokołowska, Z

    2012-12-21

    We apply recently developed version of a density functional theory [Z. Wang, L. Liu, and I. Neretnieks, J. Phys.: Condens. Matter 23, 175002 (2011)] to study adsorption of a restricted primitive model for an ionic fluid in slit-like pores in the absence of interactions induced by electrostatic images. At present this approach is one of the most accurate theories for such model electric double layers. The dependencies of the differential double layer capacitance on the pore width, on the electrostatic potential at the wall, bulk fluid density, and temperature are obtained. We show that the differential capacitance can oscillate as a function of the pore width dependent on the values of the above parameters. The number of oscillations and their magnitude decrease for high values of the electrostatic potential. For very narrow pores, close to the ion diameter, the differential capacitance tends to a minimum. The dependence of differential capacitance on temperature exhibits maximum at different values of bulk fluid density and applied electrostatic potential.

  12. A laboratory investigation of potential double layers

    NASA Technical Reports Server (NTRS)

    Leung, Philip

    1987-01-01

    In a triple plasma device, the injection of electron current from the source chamber to the target chamber causes the formation of a potential double layer. At a low current density, the space charge of the injected current produces a virtual cathode-type potential double layer. This double layer is stable, and various wave instabilities are observed to associate with this double layer. As the current density is increased, the double layer becomes unstable, and a moving double layer results. As the current density is increased further, the enhanced ionization causes the neutralization of the space charge of the electron beam, and the beam plasma discharge is ignited.

  13. A laboratory investigation of potential double layers

    NASA Technical Reports Server (NTRS)

    Leung, Philip

    1987-01-01

    In a triple plasma device, the injection of electron current from the source chamber to the target chamber causes the formation of a potential double layer. At a low current density, the space charge of the injected current produces a virtual cathode-type potential double layer. This double layer is stable and various wave instabilities are observed to associate with this double layer. As the current density is increased, the double layer becomes unstable and a moving double layer results. As the current density is increased further, the enhanced ionization causes the neutralization of the space charge of the electron beam and the 'beam plasma discharge' is ignited.

  14. A laboratory investigation of potential double layers

    NASA Technical Reports Server (NTRS)

    Leung, Philip

    1987-01-01

    In a triple plasma device, the injection of electron current from the source chamber to the target chamber causes the formation of a potential double layer. At a low current density, the space charge of the injected current produces a virtual cathode-type potential double layer. This double layer is stable and various wave instabilities are observed to associate with this double layer. As the current density is increased, the double layer becomes unstable and a moving double layer results. As the current density is increased further, the enhanced ionization causes the neutralization of the space charge of the electron beam and the 'beam plasma discharge' is ignited.

  15. Performance of electrical double layer capacitors fabricated with gel polymer electrolytes containing Li{sup +} and K{sup +}-salts: A comparison

    SciTech Connect

    Singh, Manoj K. Hashmi, S. A.

    2015-06-24

    The comparative performance of the solid-state electrical double layer capacitors (EDLCs) based on the multiwalled carbon nanotube (MWCNT) electrodes and poly (vinaylidinefluoride-co-hexafluoropropyline) (PVdF-HFP) based gel polymer electrolytes (GPEs) containing potassium and lithium salts have been studied. The room temperature ionic conductivity of the GPEs have been found to be ∼3.8×10{sup −3} and 5.9×10{sup −3} S cm{sup −1} for lithium and potassium based systems. The performance of EDLC cells studied by impedance spectroscopy, cyclic voltammetry and constant current charge-discharge techniques, indicate that the EDLC with potassium salt containing GPE shows excellent performance almost equivalent to the EDLC with Li-salt-based GPE.

  16. Study of Method for Designing the Power and the Capacitance of Fuel Cells and Electric Double-Layer Capacitors of Hybrid Railway Vehicle

    NASA Astrophysics Data System (ADS)

    Takizawa, Kenji; Kondo, Keiichiro

    A hybrid railway traction system with fuel cells (FCs) and electric double layer-capacitors (EDLCs) is discussed in this paper. This system can save FC costs and absorb the regenerative energy. A method for designing FCs and EDLCs on the basis of the output power and capacitance, respectively, has not been reported, even though their design is one of the most important technical issues encountered in the design of hybrid railway vehicles. Such design method is presented along with a train load profile and an energy management strategy. The design results obtained using the proposed method are verified by performing numerical simulations of a running train. These results reveal that the proposed method for designing the EDLCs and FCs on the basis of the capacitance and power, respectively, and by using a method for controlling the EDLC voltage is sufficiently effective in designing efficient EDLCs and FCs of hybrid railway traction systems.

  17. Conductivity Modulation of Gold Thin Film at Room Temperature via All-Solid-State Electric-Double-Layer Gating Accelerated by Nonlinear Ionic Transport.

    PubMed

    Asano, Tetsuya; Kaneko, Yukihiro; Omote, Atsushi; Adachi, Hideaki; Fujii, Eiji

    2017-02-15

    We demonstrated the field-effect conductivity modulation of a gold thin film by all-solid-state electric-double-layer (EDL) gating at room temperature using an epitaxially grown oxide fast lithium conductor, La2/3-xLi3xTiO3 (LLT), as a solid electrolyte. The linearly increasing gold conductivity with increasing gate bias demonstrates that the conductivity modulation is indeed due to carrier injection by EDL gating. The response time becomes exponentially faster with increasing gate bias, a result of the onset of nonlinear ionic transportation. This nonlinear dynamic response indicates that the ionic motion-driven device can be much faster than would be estimated from a linear ionic transport model.

  18. The Effects of Self-Discharge on the Performance of Symmetric Electric Double-Layer Capacitors and Active Electrolyte-Enhanced Supercapacitors: Insights from Modeling and Simulation

    NASA Astrophysics Data System (ADS)

    Ike, Innocent S.; Sigalas, Iakovos; Iyuke, Sunny E.

    2017-02-01

    The effects of self-discharge on the performance of symmetric electric double-layer capacitors (EDLCs) and active electrolyte-enhanced supercapacitors were examined by incorporating self-discharge into electrochemical capacitor models during charging and discharging. The sources of self-discharge in capacitors were side reactions or redox reactions and several impurities and electric double-layer (EDL) instability. The effects of self-discharge during capacitor storage was negligible since it took a fully charged capacitor a minimum of 14.0 days to be entirely discharged by self-discharge in all conditions studied, hence self-discharge in storage condition can be ignored. The first and second charge-discharge cycle energy efficiencies η_{{{{E}}1}} and η_{{{{E}}2}} of a capacitor of electrode effective conductivity α1 = 0.05 S/cm with only EDL instability self-discharge with current density J_{{VR}} = 1.25 × 10-3 A/cm2 were 72.33% and 72.34%, respectively. Also, energy efficiencies η_{{{{E}}1}} and η_{{{{E}}2}} of a similar capacitor with both side reactions and redox reactions and EDL instability self-discharges with current densities J_{{VR}} = 0.00125 A/cm2 and J_{{{{VR}}1}} = 0.0032 A/cm2 were 38.13% and 38.14% respectively, compared with 84.24% and 84.25% in a similar capacitor without self-discharge. A capacitor with only EDL instability self-discharge and that with both side reactions and redox reactions and EDL instability self-discharge lost 9.73 Wh and 28.38 Wh of energy, respectively, through self-discharge during charging and discharging. Hence, EDLCs charging and discharging time is significantly dependent on the self-discharge rate which are too large to be ignored.

  19. Effect of A-Site Cation Ordering on Chemical Stability, Oxygen Stoichiometry and Electrical Conductivity in Layered LaBaCo2O5+δ Double Perovskite

    PubMed Central

    Bernuy-Lopez, Carlos; Høydalsvik, Kristin; Einarsrud, Mari-Ann; Grande, Tor

    2016-01-01

    The effect of the A-site cation ordering on the chemical stability, oxygen stoichiometry and electrical conductivity in layered LaBaCo2O5+δ double perovskite was studied as a function of temperature and partial pressure of oxygen. Tetragonal A-site cation ordered layered LaBaCo2O5+δ double perovskite was obtained by annealing cubic A-site cation disordered La0.5Ba0.5CoO3-δ perovskite at 1100 °C in N2. High temperature X-ray diffraction between room temperature (RT) and 800 °C revealed that LaBaCo2O5+δ remains tetragonal during heating in oxidizing atmosphere, but goes through two phase transitions in N2 and between 450 °C and 675 °C from tetragonal P4/mmm to orthorhombic Pmmm and back to P4/mmm due to oxygen vacancy ordering followed by disordering of the oxygen vacancies. An anisotropic chemical and thermal expansion of LaBaCo2O5+δ was demonstrated. La0.5Ba0.5CoO3-δ remained cubic at the studied temperature irrespective of partial pressure of oxygen. LaBaCo2O5+δ is metastable with respect to La0.5Ba0.5CoO3-δ at oxidizing conditions inferred from the thermal evolution of the oxygen deficiency and oxidation state of Co in the two materials. The oxidation state of Co is higher in La0.5Ba0.5CoO3-δ resulting in a higher electrical conductivity relative to LaBaCo2O5+δ. The conductivity in both materials was reduced with decreasing partial pressure of oxygen pointing to a p-type semiconducting behavior. PMID:28773279

  20. Double-diffusive layer formation

    NASA Astrophysics Data System (ADS)

    Zaussinger, Florian; Kupka, Friedrich; Hücker, Sebastian; Egbers, Christoph

    2015-04-01

    Double-diffusive convection plays an important role in geo- and astrophysical applications. The special case, where a destabilising temperature gradient counteracts a stabilising solute gradient leads to layering phenomena under certain conditions. Convectively mixed layers sandwiched in diffusive interfaces form a so-called stack. Well-known double-diffusive systems are observed in rift lakes in Africa and even from the coffee drink Latte Macciatto. Stacks of layers are also predicted to occur inside massive stars and inside giant planets. Their dynamics depend on the thermal, the solute and the momentum diffusivities, as well on the ratio of the gradients of the opposing stratifications. Since the layering process cannot be derived from linear stability analysis, the full nonlinear set of equations has to be investigated. Numerical simulations have become feasible for this task, despite the physical processes operate on a vast range of length and time scales, which is challenging for numerical hydrodynamical modelling. The oceanographically relevant case of fresh and salty water is investigated here in further details. The heat and mass transfer is compared with theoretical results and experimental measurements. Additionally, the initial dynamic of layering, the transient behaviour of a stack and the long time evolution are presented using the example of Lake Kivu and the interior of a giant planet.

  1. The dominance of small ions in the electric double layer of size- and charge-asymmetric electrolytes: a mean-field study on the charge reversal and surface charge amplification

    NASA Astrophysics Data System (ADS)

    Angélica Barrios-Contreras, Evelyn; González-Tovar, Enrique; Iván Guerrero-García, Guillermo

    2015-05-01

    The dominance of counterions in the electric double layer of size-asymmetric semi-punctual ions was proposed more than 30 years ago by Valleau and Torrie. According to their theoretical prescription, at large colloidal surface charges, the double layer properties of a fully asymmetric binary electrolyte become similar to those of a completely symmetric electrolyte if the properties of counterions are the same in both instances. In the same theoretical framework, we propose here that, for a fixed concentration of the smallest ionic species and weakly/moderate colloidal surface charges, the valence of small ions rules or mainly determines the structural and thermodynamic properties of the electric double layer regardless of the colloidal polarity. In other words, we show that the characteristics of the small ions dominate the double layer structure of non-highly charged colloids, independently if the small ions are coions or counterions. This is illustrated by a comprehensive analysis of the ionic and integrated charge profiles around a spherical macroion immersed in a fully size- and charge-asymmetric semi-punctual electrolyte. Charge reversal and surface charge amplification are observed in the regime of low/medium colloidal surface charge densities. The origin of these counterintuitive phenomena, and their corresponding localisation properties in the Helmholtz zone, are explained in terms of the electric double layer structure.

  2. Electrostatic interaction between an enzyme and electrodes in the electric double layer examined in a view of direct electron transfer-type bioelectrocatalysis.

    PubMed

    Sugimoto, Yu; Kitazumi, Yuki; Tsujimura, Seiya; Shirai, Osamu; Yamamoto, Masahiro; Kano, Kenji

    2015-01-15

    Effects of the electrode poential on the activity of an adsorbed enzyme has been examined by using copper efflux oxidase (CueO) as a model enzyme and by monitoring direct electron transfer (DET)-type bioelectrocatalysis of oxygen reduction. CueO adsorbed on bare Au electrodes at around the point of zero charge (E(pzc)) shows the highest DET activity, and the activity decreases as the adsorption potential (E(ad); at which the enzyme adsorbs) is far from E(pzc). We propose a model to explain the phenomena in which the electrostatic interaction between the enzyme and electrodes in the electric double layer affects the orientation and the stability of the adsorbed enzyme. The self-assembled monolayer of butanethiol on Au electrodes decreases the electric field in the outside of the inner Helmholtz plane and drastically diminishes the E(ad) dependence of the DET activity of CueO. When CueO is adsorbed on bare Au electrodes under open circuit potential and then is held at hold potentials (E(ho)) more positive than E(pzc), the DET activity of the CueO rapidly decreases with the hold time. The strong electric field with positive surface charge density on the metallic electrode (σ(M)) leads to fatal denaturation of the adsorbed CueO. Such denaturation effect is not so serious at E(ho)electric field with negative σ(M) induces an orientation inconvenient for the DET reaction during the adsorption process. A positively charged neomycin shows a promoter ability to CueO adsorbed at E(ad)

  3. Heat generation in double layer capacitors

    NASA Astrophysics Data System (ADS)

    Schiffer, Julia; Linzen, Dirk; Sauer, Dirk Uwe

    Thermal management is a key issue concerning lifetime and performance of double layer capacitors and battery technologies. Double layer capacitor modules for hybrid vehicles are subject to heavy duty cycling conditions and therefore significant heat generation occurs. High temperature causes accelerated aging of the double layer capacitors and hence reduced lifetime. To investigate the thermal behavior of double layer capacitors, thermal measurements during charge/discharge cycles were performed. These measurements show that heat generation in double layer capacitors is the superposition of an irreversible Joule heat generation and a reversible heat generation caused by a change in entropy. A mathematical representation of both parts is provided.

  4. Fundamental aspects of electric double layer force-distance measurements at liquid-solid interfaces using atomic force microscopy

    SciTech Connect

    Black, Jennifer M.; Zhu, Mengyang; Zhang, Pengfei; Unocic, Raymond R.; Guo, Daqiang; Okatan, M. Baris; Dai, Sheng; Cummings, Peter T.; Kalinin, Sergei V.; Feng, Guang; Balke, Nina

    2016-09-02

    In this paper, atomic force microscopy (AFM) force-distance measurements are used to investigate the layered ion structure of Ionic Liquids (ILs) at the mica surface. The effects of various tip properties on the measured force profiles are examined and reveal that the measured ion position is independent of tip properties, while the tip radius affects the forces required to break through the ion layers as well as the adhesion force. Force data is collected for different ILs and directly compared with interfacial ion density profiles predicted by molecular dynamics. Through this comparison it is concluded that AFM force measurements are sensitive to the position of the ion with the larger volume and mass, suggesting that ion selectivity in force-distance measurements are related to excluded volume effects and not to electrostatic or chemical interactions between ions and AFM tip. Finally, the comparison also revealed that at distances greater than 1 nm the system maintains overall electroneutrality between the AFM tip and sample, while at smaller distances other forces (e.g., van der waals interactions) dominate and electroneutrality is no longer maintained.

  5. Fundamental aspects of electric double layer force-distance measurements at liquid-solid interfaces using atomic force microscopy

    DOE PAGES

    Black, Jennifer M.; Zhu, Mengyang; Zhang, Pengfei; ...

    2016-09-02

    In this paper, atomic force microscopy (AFM) force-distance measurements are used to investigate the layered ion structure of Ionic Liquids (ILs) at the mica surface. The effects of various tip properties on the measured force profiles are examined and reveal that the measured ion position is independent of tip properties, while the tip radius affects the forces required to break through the ion layers as well as the adhesion force. Force data is collected for different ILs and directly compared with interfacial ion density profiles predicted by molecular dynamics. Through this comparison it is concluded that AFM force measurements aremore » sensitive to the position of the ion with the larger volume and mass, suggesting that ion selectivity in force-distance measurements are related to excluded volume effects and not to electrostatic or chemical interactions between ions and AFM tip. Finally, the comparison also revealed that at distances greater than 1 nm the system maintains overall electroneutrality between the AFM tip and sample, while at smaller distances other forces (e.g., van der waals interactions) dominate and electroneutrality is no longer maintained.« less

  6. Fundamental aspects of electric double layer force-distance measurements at liquid-solid interfaces using atomic force microscopy.

    PubMed

    Black, Jennifer M; Zhu, Mengyang; Zhang, Pengfei; Unocic, Raymond R; Guo, Daqiang; Okatan, M Baris; Dai, Sheng; Cummings, Peter T; Kalinin, Sergei V; Feng, Guang; Balke, Nina

    2016-09-02

    Atomic force microscopy (AFM) force-distance measurements are used to investigate the layered ion structure of Ionic Liquids (ILs) at the mica surface. The effects of various tip properties on the measured force profiles are examined and reveal that the measured ion position is independent of tip properties, while the tip radius affects the forces required to break through the ion layers as well as the adhesion force. Force data is collected for different ILs and directly compared with interfacial ion density profiles predicted by molecular dynamics. Through this comparison it is concluded that AFM force measurements are sensitive to the position of the ion with the larger volume and mass, suggesting that ion selectivity in force-distance measurements are related to excluded volume effects and not to electrostatic or chemical interactions between ions and AFM tip. The comparison also revealed that at distances greater than 1 nm the system maintains overall electroneutrality between the AFM tip and sample, while at smaller distances other forces (e.g., van der waals interactions) dominate and electroneutrality is no longer maintained.

  7. Fundamental aspects of electric double layer force-distance measurements at liquid-solid interfaces using atomic force microscopy

    PubMed Central

    Black, Jennifer M.; Zhu, Mengyang; Zhang, Pengfei; Unocic, Raymond R.; Guo, Daqiang; Okatan, M. Baris; Dai, Sheng; Cummings, Peter T.; Kalinin, Sergei V.; Feng, Guang; Balke, Nina

    2016-01-01

    Atomic force microscopy (AFM) force-distance measurements are used to investigate the layered ion structure of Ionic Liquids (ILs) at the mica surface. The effects of various tip properties on the measured force profiles are examined and reveal that the measured ion position is independent of tip properties, while the tip radius affects the forces required to break through the ion layers as well as the adhesion force. Force data is collected for different ILs and directly compared with interfacial ion density profiles predicted by molecular dynamics. Through this comparison it is concluded that AFM force measurements are sensitive to the position of the ion with the larger volume and mass, suggesting that ion selectivity in force-distance measurements are related to excluded volume effects and not to electrostatic or chemical interactions between ions and AFM tip. The comparison also revealed that at distances greater than 1 nm the system maintains overall electroneutrality between the AFM tip and sample, while at smaller distances other forces (e.g., van der waals interactions) dominate and electroneutrality is no longer maintained. PMID:27587276

  8. Fundamental aspects of electric double layer force-distance measurements at liquid-solid interfaces using atomic force microscopy

    NASA Astrophysics Data System (ADS)

    Black, Jennifer M.; Zhu, Mengyang; Zhang, Pengfei; Unocic, Raymond R.; Guo, Daqiang; Okatan, M. Baris; Dai, Sheng; Cummings, Peter T.; Kalinin, Sergei V.; Feng, Guang; Balke, Nina

    2016-09-01

    Atomic force microscopy (AFM) force-distance measurements are used to investigate the layered ion structure of Ionic Liquids (ILs) at the mica surface. The effects of various tip properties on the measured force profiles are examined and reveal that the measured ion position is independent of tip properties, while the tip radius affects the forces required to break through the ion layers as well as the adhesion force. Force data is collected for different ILs and directly compared with interfacial ion density profiles predicted by molecular dynamics. Through this comparison it is concluded that AFM force measurements are sensitive to the position of the ion with the larger volume and mass, suggesting that ion selectivity in force-distance measurements are related to excluded volume effects and not to electrostatic or chemical interactions between ions and AFM tip. The comparison also revealed that at distances greater than 1 nm the system maintains overall electroneutrality between the AFM tip and sample, while at smaller distances other forces (e.g., van der waals interactions) dominate and electroneutrality is no longer maintained.

  9. Using Molecular Dynamics to quantify the electrical double layer and examine the potential for its direct observation in the in-situ TEM

    DOE PAGES

    Welch, David A.; Mehdi, Beata L.; Hatchell, Hanna J.; ...

    2015-03-25

    Understanding the fundamental processes taking place at the electrode-electrolyte interface in batteries will play a key role in the development of next generation energy storage technologies. One of the most fundamental aspects of the electrode-electrolyte interface is the electrical double layer (EDL). Given the recent development of high spatial resolution in-situ electrochemical cells for scanning transmission electron microscopy (STEM), there now exists the possibility that we can directly observe the formation and dynamics of the EDL. In this paper we predict electrolyte structure within the EDL using classical models and atomistic Molecular Dynamics (MD) simulations. The MD simulations show thatmore » the classical models fail to accurately reproduce concentration profiles that exist within the electrolyte. It is thus suggested that MD must be used in order to accurately predict STEM images of the electrode-electrolyte interface. Using MD and image simulations together for a high contrast electrolyte (the high atomic number CsCl electrolyte), it is determined that, for a smooth interface, concentration profiles within the EDL should be visible experimentally. When normal experimental parameters such as rough interfaces and low-Z electrolytes (like those used in Li-ion batteries) are considered, observation of the EDL appears to be more difficult.« less

  10. Molecular dynamics simulations of the electrical double layer on smectite surfaces contacting concentrated mixed electrolyte (NaCl-CaCl2)

    SciTech Connect

    Bourg, I.C.; Sposito, G.

    2011-04-01

    We report new molecular dynamics results elucidating the structure of the electrical double layer (EDL) on smectite surfaces contacting mixed NaCl-CaCl{sup 2} electrolyte solutions in the range of concentrations relevant to pore waters in geologic repositories for CO{sub 2} or high-level radioactive waste (0.34-1.83 mol{sub c} dm{sup -3}). Our results confirm the existence of three distinct ion adsorption planes (0-, {beta}-, and d-planes), often assumed in EDL models, but with two important qualifications: (1) the location of the {beta}- and d-planes are independent of ionic strength or ion type and (2) 'indifferent electrolyte' ions can occupy all three planes. Charge inversion occurred in the diffuse ion swarm because of the affinity of the clay surface for CaCl{sup +} ion pairs. Therefore, at concentrations 0.34 mol{sub c} dm{sup -3}, properties arising from long-range electrostatics at interfaces (electrophoresis, electro-osmosis, co-ion exclusion, colloidal aggregation) will not be correctly predicted by most EDL models. Co-ion exclusion, typically neglected by surface speciation models, balanced a large part of the clay mineral structural charge in the more concentrated solutions. Water molecules and ions diffused relatively rapidly even in the first statistical water monolayer, contradicting reports of rigid 'ice-like' structures for water on clay mineral surfaces.

  11. Molecular dynamics simulations of the electrical double layer on smectite surfaces contacting concentrated mixed electrolyte (NaCl-CaCl₂) solutions

    SciTech Connect

    Bourg, Ian C.; Sposito, Garrison

    2011-01-01

    We report new molecular dynamics results elucidating the structure of the electrical double layer (EDL) on smectite surfaces contacting mixed NaCl–CaCl2 electrolyte solutions in the range of concentrations relevant to pore waters in geologic repositories for CO2 or high-level radioactive waste (0.34–1.83 molc dm-3). Our results confirm the existence of three distinct ion adsorption planes (0-, β-, and d-planes), often assumed in EDL models, but with two important qualifications: (1) the location of the β- and d-planes are independent of ionic strength or ion type and (2) “indifferent electrolyte” ions can occupy all three planes. Charge inversion occurred in the diffuse ion swarm because of the affinity of the clay surface for CaCl+ ion pairs. Therefore, at concentrations {>=0.34 molc dm-3}, properties arising from long-range electrostatics at interfaces (electrophoresis, electro-osmosis, co-ion exclusion, colloidal aggregation) will not be correctly predicted by most EDL models. Co-ion exclusion, typically neglected by surface speciation models, balanced a large part of the clay mineral structural charge in the more concentrated solutions. Water molecules and ions diffused relatively rapidly even in the first statistical water monolayer, contradicting reports of rigid “ice-like” structures for water on clay mineral surfaces.

  12. Using Molecular Dynamics to quantify the electrical double layer and examine the potential for its direct observation in the in-situ TEM

    SciTech Connect

    Welch, David A.; Mehdi, Beata L.; Hatchell, Hanna J.; Faller, Roland; Evans, James E.; Browning, Nigel D.

    2015-03-25

    Understanding the fundamental processes taking place at the electrode-electrolyte interface in batteries will play a key role in the development of next generation energy storage technologies. One of the most fundamental aspects of the electrode-electrolyte interface is the electrical double layer (EDL). Given the recent development of high spatial resolution in-situ electrochemical cells for scanning transmission electron microscopy (STEM), there now exists the possibility that we can directly observe the formation and dynamics of the EDL. In this paper we predict electrolyte structure within the EDL using classical models and atomistic Molecular Dynamics (MD) simulations. The MD simulations show that the classical models fail to accurately reproduce concentration profiles that exist within the electrolyte. It is thus suggested that MD must be used in order to accurately predict STEM images of the electrode-electrolyte interface. Using MD and image simulations together for a high contrast electrolyte (the high atomic number CsCl electrolyte), it is determined that, for a smooth interface, concentration profiles within the EDL should be visible experimentally. When normal experimental parameters such as rough interfaces and low-Z electrolytes (like those used in Li-ion batteries) are considered, observation of the EDL appears to be more difficult.

  13. Simulational and theoretical study of the spherical electrical double layer for a size-asymmetric electrolyte: the case of big coions.

    PubMed

    Guerrero-García, G Iván; González-Tovar, Enrique; Chávez-Páez, Martín

    2009-08-01

    Monte Carlo simulations of a spherical macroion, surrounded by a size-asymmetric electrolyte in the primitive model, were performed. We considered 1:1 and 2:2 salts with a size ratio of 2 (i.e., with coions twice the size of counterions), for several surface charge densities of the macrosphere. The radial distribution functions, electrostatic potential in all the space and at the Helmholtz surfaces, and integrated charge are reported. We compare these simulational data with original results obtained from the Ornstein-Zernike integral equation, supplemented by the hypernetted chain-hypernetted chain (HNC-HNC) and hypernetted chain-mean spherical approximation (HNC-MSA) closures, and with the corresponding calculations using the modified Gouy-Chapman and unequal-radius modified Gouy-Chapman theories. The HNC-HNC and HNC-MSA integral equations formalisms show good concordance with Monte Carlo "experiments," whereas the notable limitations of point-ion approaches are evidenced. Most importantly, the simulations confirm our previous theoretical predictions of the nondominance of the counterions in the size-asymmetric spherical electrical double layer [J. Chem. Phys. 123, 034703 (2005)], the appearance of anomalous curvatures at the outer Helmholtz plane, and the enhancement of the charge reversal and screening at high colloidal surface charge densities due to the ionic size asymmetry.

  14. Molecular simulations of the electric double layer structure, differential capacitance, and charging kinetics for N-methyl-N-propylpyrrolidinium bis(fluorosulfonyl)imide at graphite electrodes.

    PubMed

    Vatamanu, Jenel; Borodin, Oleg; Smith, Grant D

    2011-03-31

    Molecular dynamics simulations were performed on N-methyl-N-propylpyrrolidinium bis(fluorosulfonyl)imide (pyr(13)FSI) room temperature ionic liquid (RTIL) confined between graphite electrodes as a function of applied potential at 393 and 453 K using an accurate force field developed in this work. The electric double layer (EDL) structure and differential capacitance (DC) of pyr(13)FSI was compared with the results of the previous study of a similar RTIL pyr(13)bis(trifluoromethanesulfonyl)imide (pyr(13)TFSI) with a significantly larger anion [ Vatamanu, J.; Borodin, O.; Smith, G. D. J. Am. Chem. Soc. 2010, 132, 14825]. Intriguingly, the smaller size of the FSI anion compared to TFSI did not result in a significant increase of the DC on the positive electrode. Instead, a 30% higher DC was observed on the negative electrode for pyr(13)FSI compared to pyr(13)TFSI. The larger DC observed on the negative electrode for pyr(13)FSI compared to pyr(13)TFSI was associated with two structural features of the EDL: (a) a closer approach of FSI compared to TFSI to the electrode surface and (b) a faster rate (vs potential decrease) of anion desorption from the electrode surface for FSI compared to TFSI. Additionally, the limiting behavior of DC at large applied potentials was investigated. Finally, we show that constant potential simulations indicate time scales of hundreds of picoseconds required for electrode charge/discharge and EDL formation.

  15. High performance thin film transistor (flex-TFT) with textured nanostructure ZnO film channel fabricated by exploiting electric double layer gate insulator

    NASA Astrophysics Data System (ADS)

    Ghimire, Rishi Ram; Raychaudhuri, A. K.

    2017-01-01

    We report a flexible thin film transistor (flex-TFT) fabricated on a commonly available polyimide (Kapton®) tape with a channel of highly textured nanocrystalline ZnO film grown by pulsed laser deposition. The flex-TFT with an electric double layer (EDL) gate insulator shows a low threshold for operation (Vth ≤ 1 V), an ON/OFF ratio reaching ≈107 and a subthreshold swing ≈75 mV/dec. The superior performance is enabled by a high saturation mobility (μs ≈ 70 cm2/V s) of the highly textured nanocrystalline channel. The low Vth arises from large charge density (≈1014/cm2) induced into the channel by EDL gate insulator. The large charge density induced by the EDL gate dielectric also enhances the Hall mobility in the film and brings down the sheet resistance by nearly 2 orders, which leads to large ON/OFF ratio. The flex-TFT operation can be sustained with reproducibility when the TFT is bent down to a radius of curvature ≈2 cm.

  16. The Influence of Anion Shape on the Electrical Double Layer Microstructure and Capacitance of Ionic Liquids-Based Supercapacitors by Molecular Simulations.

    PubMed

    Chen, Ming; Li, Song; Feng, Guang

    2017-02-16

    Room-temperature ionic liquids (RTILs) are an emerging class of electrolytes for supercapacitors. In this work, we investigate the effects of different supercapacitor models and anion shape on the electrical double layers (EDLs) of two different RTILs: 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide ([Emim][Tf₂N]) and 1-ethyl-3-methylimidazolium 2-(cyano)pyrrolide ([Emim][CNPyr]) by molecular dynamics (MD) simulation. The EDL microstructure is represented by number densities of cations and anions, and the potential drop near neutral and charged electrodes reveal that the supercapacitor model with a single electrode has the same EDL structure as the model with two opposite electrodes. Nevertheless, the employment of the one-electrode model without tuning the bulk density of RTILs is more time-saving in contrast to the two-electrode one. With the one-electrode model, our simulation demonstrated that the shapes of anions significantly imposed effects on the microstructure of EDLs. The EDL differential capacitance vs. potential (C-V) curves of [Emim][CNPyr] electrolyte exhibit higher differential capacitance at positive potentials. The modeling study provides microscopic insight into the EDLs structure of RTILs with different anion shapes.

  17. Direct detection of fibrinogen in human plasma using electric-double-layer gated AlGaN/GaN high electron mobility transistors

    NASA Astrophysics Data System (ADS)

    Regmi, Abiral; Sarangadharan, Indu; Chen, Yen-Wen; Hsu, Chen-Pin; Lee, Geng-Yen; Chyi, Jen-Inn; Shiesh, Shu-Chu; Lee, Gwo-Bin; Wang, Yu-Lin

    2017-08-01

    Fibrinogen found in blood plasma is an important protein biomarker for potentially fatal diseases such as cardiovascular diseases. This study focuses on the development of an assay to detect plasmatic fibrinogen using electrical double layer gated AlGaN/GaN high electron mobility transistor biosensors without complex sample pre-treatment methods used in the traditional assays. The test results in buffer solution and clinical plasma samples show high sensitivity, specificity, and dynamic range. The sensor exhibits an ultra-low detection limit of 0.5 g/l and a detection range of 0.5-4.5 g/l in 1× PBS with 1% BSA. The concentration dependent sensor signal in human serum samples demonstrates the specificity to fibrinogen in a highly dense matrix of background proteins. The sensor does not require complicated automation, and quantitative results are obtained in 5 min with <5 μl sample volume. This sensing technique is ideal for speedy blood based diagnostics such as POC (point of care) tests, homecare tests, or personalized healthcare.

  18. An Approach to Solid-State Electrical Double Layer Capacitors Fabricated with Graphene Oxide-Doped, Ionic Liquid-Based Solid Copolymer Electrolytes.

    PubMed

    Fattah, N F A; Ng, H M; Mahipal, Y K; Numan, Arshid; Ramesh, S; Ramesh, K

    2016-06-06

    Solid polymer electrolyte (SPE) composed of semi-crystalline poly (vinylidene fluoride-hexafluoropropylene) [P(VdF-HFP)] copolymer, 1-ethyl-3-methylimidazolium bis (trifluoromethyl sulphonyl) imide [EMI-BTI] and graphene oxide (GO) was prepared and its performance evaluated. The effects of GO nano-filler were investigated in terms of enhancement in ionic conductivity along with the electrochemical properties of its electrical double layer capacitors (EDLC). The GO-doped SPE shows improvement in ionic conductivity compared to the P(VdF-HFP)-[EMI-BTI] SPE system due to the existence of the abundant oxygen-containing functional group in GO that assists in the improvement of the ion mobility in the polymer matrix. The complexation of the materials in the SPE is confirmed in X-ray diffraction (XRD) and thermogravimetric analysis (TGA) studies. The electrochemical performance of EDLC fabricated with GO-doped SPE is examined using cyclic voltammetry and charge-discharge techniques. The maximum specific capacitance obtained is 29.6 F∙g(-1), which is observed at a scan rate of 3 mV/s in 6 wt % GO-doped, SPE-based EDLC. It also has excellent cyclic retention as it is able keep the performance of the EDLC at 94% even after 3000 cycles. These results suggest GO doped SPE plays a significant role in energy storage application.

  19. An Approach to Solid-State Electrical Double Layer Capacitors Fabricated with Graphene Oxide-Doped, Ionic Liquid-Based Solid Copolymer Electrolytes

    PubMed Central

    Fattah, N. F. A.; Ng, H. M.; Mahipal, Y. K.; Numan, Arshid; Ramesh, S.; Ramesh, K.

    2016-01-01

    Solid polymer electrolyte (SPE) composed of semi-crystalline poly (vinylidene fluoride-hexafluoropropylene) [P(VdF-HFP)] copolymer, 1-ethyl-3-methylimidazolium bis (trifluoromethyl sulphonyl) imide [EMI-BTI] and graphene oxide (GO) was prepared and its performance evaluated. The effects of GO nano-filler were investigated in terms of enhancement in ionic conductivity along with the electrochemical properties of its electrical double layer capacitors (EDLC). The GO-doped SPE shows improvement in ionic conductivity compared to the P(VdF-HFP)-[EMI-BTI] SPE system due to the existence of the abundant oxygen-containing functional group in GO that assists in the improvement of the ion mobility in the polymer matrix. The complexation of the materials in the SPE is confirmed in X-ray diffraction (XRD) and thermogravimetric analysis (TGA) studies. The electrochemical performance of EDLC fabricated with GO-doped SPE is examined using cyclic voltammetry and charge–discharge techniques. The maximum specific capacitance obtained is 29.6 F∙g−1, which is observed at a scan rate of 3 mV/s in 6 wt % GO-doped, SPE-based EDLC. It also has excellent cyclic retention as it is able keep the performance of the EDLC at 94% even after 3000 cycles. These results suggest GO doped SPE plays a significant role in energy storage application. PMID:28773573

  20. Effect of Ionic Conductivity on Response Speed of SrTiO3-Based All-Solid-State Electric-Double-Layer Transistor.

    PubMed

    Tsuchiya, Takashi; Ochi, Masanori; Higuchi, Tohru; Terabe, Kazuya; Aono, Masakazu

    2015-06-10

    An all-solid-state electric-double-layer transistor (EDLT) with a Y-stabilized ZrO₂ (YSZ) proton conductor/SrTiO₃ (STO) single crystal has been fabricated to investigate ionic conductivity effect on the response speed, which should be a key parameter for development of next-generation EDLTs. The drain current exhibited a 4-order-of-magnitude increment by electrostatic carrier doping at the YSZ/STO interface due to ion migration, and the behavior strongly depended on the operation temperature. An Arrhenius-type plot of the ionic conductivity (σ(i)) in the YSZ and t(c)⁻¹, which is a current-rise time needed for charge accumulation at the YSZ/STO interface, shows a synchronized variation, indicating a proportional relationship between the two parameters. Analysis of the σ(i)-t(c) diagram shows that, in contrast to conventional EDLTs, the response speed should reach picosecond order at room temperature by using extreme miniaturization and superionic conductors. Furthermore, the diagram indicates that plenty of solid electrolytes, which have not been used due to the lack of criteria for evaluation, can be a candidate for all-solid-state EDLTs exceeding the carrier density of conventional EDLTs, even though the response speed becomes comparably lower than those of FETs.

  1. Novel computational approach for studying ph effects, excluded volume and ion-ion correlations in electrical double layers around polyelectrolytes and nanoparticles

    NASA Astrophysics Data System (ADS)

    Ovanesyan, Zaven

    Highly charged cylindrical and spherical objects (macroions) are probably the simplest structures for modeling nucleic acids, proteins and nanoparticles. Their ubiquitous presence within biophysical systems ensures that Coulomb forces are among the most important interactions that regulate the behavior of these systems. In these systems, ions position themselves in a strongly correlated manner near the surface of a macroion and form electrical double layers (EDLs). These EDLs play an important role in many biophysical and biochemical processes. For instance, the macroion's net charge can change due to the binding of many multivalent ions to its surface. Thus, proper description of EDLs near the surface of a macroion may reveal a counter-intuitive charge inversion behavior, which can generate attraction between like-charged objects. This is relevant for the variety of fields such as self-assembly of DNA and RNA folding, as well as for protein aggregation and neurodegenerative diseases. Certainly, the key factors that contribute to these phenomena cannot be properly understood without an accurate solvation model. With recent advancements in computer technologies, the possibility to use computational tools for fundamental understanding of the role of EDLs around biomolecules and nanoparticles on their physical and chemical properties is becoming more feasible. Establishing the impact of the excluded volume and ion-ion correlations, ionic strength and pH of the electrolyte on the EDL around biomolecules and nanoparticles, and how changes in these properties consequently affect the Zeta potential and surface charge density are still not well understood. Thus, modeling and understanding the role of these properties on EDLs will provide more insights on the stability, adsorption, binding and function of biomolecules and nanoparticles. Existing mean-field theories such as Poisson Boltzmann (PB) often neglect the ion-ion correlations, solvent and ion excluded volume effects

  2. SISGR: Improved Electrical Energy Storage with Electrochemical Double Layer Capacitance Based on Novel Carbon Electrodes, New Electrolytes, and Thorough Development of a Strong Science Base

    SciTech Connect

    Ruoff, Rodney S.; Alam, Todd M.; Bielawski, Christopher W.; Chabal, Yves; Hwang, Gyeong; Ishii, Yoshitaka; Rogers, Robin

    2014-07-23

    The broad objective of the SISGR program is to advance the fundamental scientific understanding of electrochemical double layer capacitance (EDLC) and thus of ultracapacitor systems composed of a new type of electrode based on chemically modified graphene (CMG) and (primarily) with ionic liquids (ILs) as the electrolyte. Our team has studied the interplay between graphene-based and graphene-derived carbons as the electrode materials in electrochemical double layer capacitors (EDLC) systems on the one hand, and electrolytes including novel ionic liquids (ILs), on the other, based on prior work on the subject.

  3. Double layers and circuits in astrophysics

    NASA Technical Reports Server (NTRS)

    Alfven, Hannes

    1986-01-01

    As the rate of energy release in a double layer with voltage delta V is P approx I delta V, a double layer must be treated as a part of a circuit which delivers the current I. As neither double layer nor circuit can be derived from magnetofluid models of a plasma, such models are useless for treating energy transfer by means of double layers. They must be replaced by particle models and circuit theory. A simple circuit is suggested which is applied to the energizing of auroral particles, to solar flares, and to intergalactic double radio sources. Application to the heliospheric current systems leads to the prediction of two double layers on the Sun's axis which may give radiations detectable from Earth. Double layers in space should be classified as a new type of celestial object (one example is the double radio sources). It is tentatively suggested in X-ray and Gamma-ray bursts may be due to exploding double layers (although annihilation is an alternative energy source). A study of how a number of the most used textbooks in astrophysics treat important concepts like double layers, critical velocity, pinch effects and circuits is made.

  4. The theory of Maxwell-Boltzmann-Helmholtz-Gouy about the double electric layer in disperse systems and its application to soil science (on the 100th anniversary of the paper published by Gouy)

    NASA Astrophysics Data System (ADS)

    Sudnitsyn, I. I.; Smagin, A. V.; Shvarov, A. P.

    2012-04-01

    Numerous experimental data obtained by different methods confirm the theoretical ideas about the electric nature of the interaction between the solid and liquid soil phases, which were first suggested by the Maxwell-Boltzmann-Helmholtz-Gouy and Deryagin-Landau-Verwey-Overbeek theories about the double electric layer in two-phase disperse systems. The interaction between the solid phase and water in the diffuse part of this layer may be described by the theoretically derived equation ln P w = A - BW, where P w is the soil moisture pressure, W is the ratio between the masses of the water and the solid phase in the soil, and A and B are physically grounded parameters. The exponential form of this equation first predicted by the out-standing researcher Gouy 100 years ago results from the exponential distribution of ions in the diffuse layer near the electrically charged surface of the solid soil phase.

  5. Cation diffusion in the electrical double layer enhances the mass transfer rates for Sr2+, Co2+ and Zn2+ in compacted illite

    NASA Astrophysics Data System (ADS)

    Glaus, M. A.; Aertsens, M.; Appelo, C. A. J.; Kupcik, T.; Maes, N.; Van Laer, L.; Van Loon, L. R.

    2015-09-01

    Enhanced mass transfer rates have been frequently observed in diffusion studies with alkaline and earth alkaline elements in compacted clay minerals and clay rocks. Whether this phenomenon - often termed surface diffusion - is also relevant for more strongly sorbing species is an open question. We therefore investigated the diffusion of Sr2+, Co2+ and Zn2+ in compacted illite with respect to variations of the concentration of the background electrolyte, pH and carbonate. New experimental techniques were developed in order to avoid artefacts stemming from the confinement of the clay sample. A distinct dependence of the effective diffusion coefficients on the concentration of the background electrolyte was observed for all three elements. A similar correlation was found for the sorption distribution ratio (Rd) derived from tracer breakthrough in the case of Sr2+, while this dependence was much weaker for Co2+ and Zn2+. Model calculations using Phreeqc resulted in a good agreement with the experimental data when it was assumed that the cationic species, present in the electrical double layer (EDL) of the charged clay surface, are mobile. Species bound to the specific surface complexation sites at the clay edges were assumed to be immobile. An assessment of the mobility of the type of cationic elements studied here in argillaceous media thus requires an analysis of their distribution among specifically sorbed surface species and species in the EDL. The normal approach of deriving unknown effective diffusion coefficients from reference values of an uncharged water tracer may significantly underestimate the mobility of metal cations in argillaceous media.

  6. Characterization and organic electric-double-layer-capacitor application of KOH activated coal-tar-pitch-based carbons: Effect of carbonization temperature

    NASA Astrophysics Data System (ADS)

    Choi, Poo Reum; Lee, Eunji; Kwon, Soon Hyung; Jung, Ji Chul; Kim, Myung-Soo

    2015-12-01

    The present study reports the influence of pre-carbonization on the properties of KOH-activated coal tar pitch (CTP). The change of crystallinity and pore structure of pre-carbonized CTPs as well as their activated carbons (ACs) as function of pre-carbonization temperature are investigated. The crystallinity of pre-carbonized CTPs increases with increasing the carbonization temperature up to 600 °C, but a disorder occurs during the carbonization around 700 °C and an order happens gradually with increasing the carbonization temperatures in range of 800-1000 °C. The CTPs pre-carbonized at high temperatures are more difficult to be activated with KOH than those pre-carbonized at low temperatures due to the increase of micro-crystalline size and the decrease of surface functional groups. The micro-pores and meso-pores are well developed at around 1.0 nm and 2.4 nm, respectively, as the ACs are pre-carbonized at temperatures of 500-600 °C, exhibiting high specific capacitances as electrode materials for electric double layer capacitor (EDLC). Although the specific surface area (SSA) and pore volume of ACs pre-carbonized at temperatures of 900-1000 °C are extraordinary low (non-porous) as compared to those of AC pre-carbonized at 600 °C, their specific capacitances are comparable to each other. The large specific capacitances with low SSA ACs can be attributed to the structural change resulting from the electrochemical activation during the 1st charge above 2.0 V.

  7. Electron temperature differences and double layers

    NASA Technical Reports Server (NTRS)

    Chan, C.; Hershkowitz, N.; Lonngren, K. E.

    1983-01-01

    Electron temperature differences across plasma double layers are studied experimentally. It is shown that the temperature differences across a double layer can be varied and are not a result of thermalization of the bump-on-tail distribution. The implications of these results for electron thermal energy transport in laser-pellet and tandem-mirror experiments are also discussed.

  8. A fluid description of plasma double-layers

    NASA Technical Reports Server (NTRS)

    Levine, J. S.; Crawford, F. W.

    1979-01-01

    The space-charge double-layer that forms between two plasmas with different densities and thermal energies was investigated using three progressively realistic models which are treated by fluid theory, and take into account four species of particles: electrons and ions reflected by the double-layer, and electrons and ions transmitted through it. The two plasmas are assumed to be cold, and the self-consistent potential, electric field and space-charge distributions within the double-layer are determined. The effects of thermal velocities are taken into account for the reflected particles, and the modifications to the cold plasma solutions are established. Further modifications due to thermal velocities of the transmitted particles are examined. The applicability of a one dimensional fluid description, rather than plasma kinetic theory, is discussed. Theoretical predictions are compared with double layer potentials and lengths deduced from laboratory and space plasma experiments.

  9. Analysis of carrier behavior in C60/P(VDF-TrFE) double-layer capacitor by using electric-field-induced optical second-harmonic generation measurement

    SciTech Connect

    Cui, Xiaojin; Taguchi, Dai; Manaka, Takaaki; Iwamoto, Mitsumasa

    2013-12-21

    By using displacement current measurement (DCM) and electric-field-induced optical second-harmonic generation (EFISHG) measurement, we studied the carrier behavior in the indium-tin oxide (ITO)/Poly(vinylidene fluoride-trifluoroethylene) (P(VDF-TrFE))/C60/Au(or Al) capacitors. Two DCM peaks appeared asymmetrically at around −35.5 V and +30.0 V in the dark. Correspondingly, the EFISHG response from the C60 layer was observed, but the peak positions were different with respect to DCM ones. The results show that the spontaneous polarization of the ferroelectric P(VDF-TrFE) polymeric layer directly affects the electric field in the C60 layer, and thus governs the carrier motion in this layer. As a result, the C60 layer serves like an insulator in the dark, while electrons and holes are captured and released at the interface in response to the turn-over of spontaneous polarization of ferroelectric layer. On the other hand, under white light illumination, C60 layer serves like a conductor due to the increase of photogenerated mobile carriers, and these carriers dominate the carrier motions therein. Our findings here will be helpful for analyzing carrier behaviors in organic electronic devices using ferroelectric polymers.

  10. Double layers and circuits in astrophysics

    NASA Technical Reports Server (NTRS)

    Alfven, H.

    1986-01-01

    A simple circuit is applied to the energizing of auroral particles, to solar flares, and to intergalactic double radio sources. Application to the heliospheric current systems leads to the prediction of two double layers on the Sun's axis which may give radiations detectable from Earth. Double layers in space should be classified as a new type of celestial object. It is suggested that X-ray and gamma-ray bursts may be due to exploding double layers (although annihilation is an alternative energy source). The way the most used textbooks in astrophysics treat concepts like double layers, critical velocity, pinch effects and circuits was studied. It is found that students using these textbooks remain essentially ignorant of even the existence of these, although some of the phenomena were discovered 50 yr ago.

  11. Double layers and circuits in astrophysics

    NASA Technical Reports Server (NTRS)

    Alfven, Hannes

    1986-01-01

    A simple circuit is applied to the energizing of auroral particles, to solar flares, and to intergalactic double radio sources. Application to the heliospheric current systems leads to the prediction of two double layers on the Sun's axis which may give radiations detectable from earth. Double layers in space should be classified as a new type of celestial object. It is suggested that X-ray and gamma-ray bursts may be due to exploding double layers (although annihilation is an alternative energy source). The way the most used textbooks in astrophysics treat concepts like double layers, critical velocity, pinch effects and circuits was studied. It is found that students using these textbooks remain essentially ignorant of even the existence of these, although some of the phenomena were discovered 50 yr ago.

  12. A Potential Role of Double Layers on Solar Wind Acceleration

    NASA Astrophysics Data System (ADS)

    Parks, G. K.; McCarthy, M.; Lee, E.; Hong, J.

    2012-12-01

    The distribution function of solar wind (SW) is non-Maxwellian and often includes field-aligned beams. Recently, electrostatic solitary waves (ESW) have been observed in the SW and they have been interpreted as double layers. Taking a cue from Earth's auroral observations that large-scale electric field parallel to magnetic field may be due to many double layers distributed along the geomagnetic field, we have looked at the potential role double layers could play in SW acceleration. This picture would suggest that the halo component of the SW represents a beam that has been accelerated by parallel electric field. The core electrons come from secondaries produced by the beam going through the solar coronal atmosphere. The source of the super-halo component is not known and we speculate that it could represent the field-aligned non-thermal high-energy halo electrons that have been accelerated to ``runaway" energies.

  13. Effects of image charges on double layer structure and forces.

    PubMed

    Wang, Rui; Wang, Zhen-Gang

    2013-09-28

    The study of the electrical double layer lies at the heart of soft matter physics and biophysics. Here, we address the effects of the image charges on the double layer structure and forces. For electrolyte solutions between two neutral plates, we show that depletion of the salt ions by the image charge repulsion results in short-range attractive and long-range repulsive forces. If cations and anions are of different valency, the asymmetric depletion leads to the formation of an induced electrical double layer. In comparison to a 1:1 electrolyte solution, both the attractive and the repulsive parts of the interaction are stronger for the 2:1 electrolyte solution. For two charged plates, the competition between the surface charge and the image charge effect can give rise to like-charge attraction and charge inversion. These results are in stark contrast with predictions from the Poisson-Boltzmann theory.

  14. Reactivity and applications of layered silicates and layered double hydroxides.

    PubMed

    Selvam, Thangaraj; Inayat, Alexandra; Schwieger, Wilhelm

    2014-07-21

    Layered materials, such as layered sodium silicates and layered double hydroxides (LDHs), are well-known for their remarkable adsorption, intercalation and swelling properties. Their tunable interlayers offer an interesting avenue for the fabrication of pillared nanoporous materials, organic-inorganic hybrid materials and catalysts or catalyst supports. This perspective article provides a summary of the reactivity and applications of layered materials including aluminium-free layered sodium silicates (kanemite, ilerite (RUB-18 or octosilicate) and magadiite) and layered double hydroxides (LDHs). Recent developments in the use of layered sodium silicates as precursors for the preparation of various porous, functional and catalytic materials including zeolites, mesoporous materials, pillared layered silicates, organic-inorganic nanocomposites and synthesis of highly dispersed nanoparticles supported on silica are reviewed in detail. Along this perspective, we have attempted to illustrate the reactivity and transformational potential of LDHs in order to deduce the main differences and similarities between these two types of layered materials.

  15. Magnetic steering of a helicon double layer thruster

    SciTech Connect

    Charles, C.; Boswell, R. W.; Cox, W.; Laine, R.; MacLellan, P.

    2008-11-17

    The ion beam generated by a helicon double layer has been electrically steered up to 20 deg. off axis by using a solenoid placed normal to the two axial solenoids of the helicon plasma source without significantly changing the beam exhaust velocity.

  16. Numerical simulations on ion acoustic double layers

    SciTech Connect

    Sato, T.; Okuda, H.

    1980-07-01

    A comprehensive numerical study of ion acoustic double layers has been performed for both periodic as well as for nonperiodic systems by means of one-dimensional particle simulations. For a nonperiodic system, an external battery and a resistance are used to model the magnetospheric convection potential and the ionospheric Pedersen resistance. It is found that the number of double layers and the associated potential buildup across the system increases with the system length.

  17. Organic doping of rotated double layer graphene

    SciTech Connect

    George, Lijin; Jaiswal, Manu

    2016-05-06

    Charge transfer techniques have been extensively used as knobs to tune electronic properties of two- dimensional systems, such as, for the modulation of conductivity \\ mobility of single layer graphene and for opening the bandgap in bilayer graphene. The charge injected into the graphene layer shifts the Fermi level away from the minimum density of states point (Dirac point). In this work, we study charge transfer in rotated double-layer graphene achieved by the use of organic dopant, Tetracyanoquinodimethane. Naturally occurring bilayer graphene has a well-defined A-B stacking whereas in rotated double-layer the two graphene layers are randomly stacked with different rotational angles. This rotation is expected to significantly alter the interlayer interaction. Double-layer samples are prepared using layer-by-layer assembly of chemical vapor deposited single-layer graphene and they are identified by characteristic resonance in the Raman spectrum. The charge transfer and distribution of charges between the two graphene layers is studied using Raman spectroscopy and the results are compared with that for single-layer and A-B stacked bilayer graphene doped under identical conditions.

  18. Electric Field Induced Superconductivity in Layered Materials

    NASA Astrophysics Data System (ADS)

    Ye, J. T.; Craciun, M. F.; Russo, S.; Morpurgo, M. F.; Kasahara, Y.; Yuan, H. T.; Shimotani, H.; Iwasa, Y.

    2011-03-01

    Using electric double layer (EDL) gating, large amount of carriers can be accumulated on a broad range of materials, which provides new opportunities in effectively manipulating their electronic properties in complementary with the chemical doping. In searching for novel transport phenomena, layered materials are advantageous because atomically flat surface can be easily fabricated using the graphene techniques. We used layered material: ZrNCl and graphite to act as the channel of EDL transistors. For both ZrNCl and graphene, we achieved high carrier density up to 1014 cm-2 , electrostatically. For graphene, we studied the high carrier density transport for graphene of 1-3 layers. Transport properties at the high carrier density exhibit clear layer dependence governed by the intrinsic band structures of graphene and its multi-layers. For ZrNCl EDL transistor, we observed metallic states at gate voltage higher than 3.5 V followed by gate-induced superconductivity after metal-insulator transition when the transistor was cooled down to about 15 K.

  19. A MODIFIED POISSON–BOLTZMANN STUDY OF THE SINGLET ION DISTRIBUTION AT CONTACT WITH THE ELECTRODE FOR A PLANAR ELECTRIC DOUBLE LAYER

    PubMed Central

    Silvestre-Alcantara, Whasington; Bhuiyan, Lutful B.; Outhwaite, Christopher W.; Henderson, Douglas

    2010-01-01

    The properties of the singlet ion distributions at and around contact in a restricted primitive model double layer are characterized in the modified Poisson–Boltzmann theory. Comparisons are made with the corresponding exact Monte Carlo simulation data, the results from the Gouy–Chapman–Stern theory coupled to an exclusion volume term, and the mean spherical approximation. Particular emphasis is given to the behaviour of the theoretical predictions in relation to the contact value theorem involving the charge profile. The simultaneous behaviour of the coion and counterion contact values is also examined. The performance of the modified Poisson–Boltzmann theory in regard to the contact value theorems is very reasonable with the contact characteristics showing semi-quantitative or better agreement overall with the simulation results. The exclusion-volume-treated Gouy–Chapman–Stern theory reveals a fortuitous cancellation of errors, while the mean spherical approximation is poor. PMID:20664814

  20. Propagating double layers in electronegative plasmas

    SciTech Connect

    Meige, A.; Plihon, N.; Hagelaar, G. J. M.; Boeuf, J.-P.; Chabert, P.; Boswell, R. W.

    2007-05-15

    Double layers have been observed to propagate from the source region to the diffusion chamber of a helicon-type reactor filled up with a low-pressure mixture of Ar/SF{sub 6} [N. Plihon et al., J. Appl. Phys. 98, 023306 (2005)]. In the present paper the most significant and new experimental results are reported. A fully self-consistent hybrid model in which the electron energy distribution function, the electron temperature, and the various source terms are calculated is developed to investigate these propagating double layers. The spontaneous formation of propagating double layers is only observed in the simulation for system in which the localized inductive heating is combined with small diameter chambers. The conditions of formation and the properties of the propagating double layers observed in the simulation are in good agreement with that of the experiment. By correlating the results of the experiment and the simulation, a formation mechanism compatible with ion two-stream instability is proposed.

  1. Influence of electrical double-layer dispersion forces and size dependency on pull-in instability of clamped microplate immersed in ionic liquid electrolytes

    NASA Astrophysics Data System (ADS)

    Karimipour, I.; Beni, Yaghoub Tadi; Taheri, N.

    2017-10-01

    Plate-type clamped microplate is of the most common constructive elements for developing in-liquid-operating devices. While the electromechanical behavior of clamped microplate in non-liquid environments has exclusively been addressed in the literature, no theoretical studies have yet been conducted on precise modeling of the clamped microplate in electrolyte liquid. Herein, the electromechanical response and instability of the clamped microplate immersed in ionic electrolyte media are investigated. The electrochemical force field is determined using double layer theory and linearized Poisson-Boltzmann equation. The presence of dispersion forces, i.e., Casimir and van der Waals attractions, are included in the theoretical model considering the correction due to the presence of liquid media between the interacting surfaces (three-layer model). To this end, a kind of microplate has been designed, i.e., a square microplate with all edges clamped supported. The strain gradient elasticity is employed to model the size-dependent structural behavior of the clamped microplate. To solve the nonlinear constitutive equation of the system, Extended Kantorovich Method, is employed and the pull-in parameter of the microplate are extracted. Impacts of the dispersion forces and size effect on the instability characteristics are discussed as well as the effect of ion concentration and potential ratio. It is found that the significant difference between the pull-in instability parameters in the modified strain gradient theory and the classical theory for thin microplates is merely due to the consideration of size effect parameter in the modified strain gradient theory. To confirm the validity of formulations, the numerical values of the results are compared. The results predicted via the aforementioned approach are in excellent agreement with those in the literature. Some new examples are solved to demonstrate the applicability of the procedure.

  2. Nonlinear Surface Transport in the Thin Double-Layer Limit

    NASA Astrophysics Data System (ADS)

    Chu, Kevin; Bazant, Martin

    2006-03-01

    At high applied electric fields, ionic transport within the double layer plays a significant role in the overall response of electrokinetic systems. It is well-known that surface transport processes, including surface electromigration, surface diffusion and surface advection, may impact the strength of electrokinetic phenomena by affecting both the zeta-potential and the magnitude of the tangential electric field. Therefore, it is important to include these effects when formulating the effective boundary conditions for the equations that govern electrokinetic flow outside of the double layer. In this talk, we discuss the application of a general formulation of ``surface conservation laws'' for diffuse boundary layers to derive effective boundary conditions that capture the physics of electrokinetic surface transport. Previous analyses (e.g. Deryagin & Dukhin 1969) are only valid for weak applied fields and are based on a linearization of the concentration and potential about a reference solution, but our results are fully nonlinear and hold at large applied fields as long as the double layer is sufficiently thin. We compare our nonlinear surface transport theory with existing linear analogues and apply it to the canonical problem of induced-charge electro-osmosis around a metal sphere or cylinder in a strong DC field.

  3. Double layer in ionic liquids: overscreening versus crowding.

    PubMed

    Bazant, Martin Z; Storey, Brian D; Kornyshev, Alexei A

    2011-01-28

    We develop a simple Landau-Ginzburg-type continuum theory of solvent-free ionic liquids and use it to predict the structure of the electrical double layer. The model captures overscreening from short-range correlations, dominant at small voltages, and steric constraints of finite ion sizes, which prevail at large voltages. Increasing the voltage gradually suppresses overscreening in favor of the crowding of counterions in a condensed inner layer near the electrode. This prediction, the ion profiles, and the capacitance-voltage dependence are consistent with recent computer simulations and experiments on room-temperature ionic liquids, using a correlation length of order the ion size.

  4. Observations of double layers in earth's plasma sheet.

    PubMed

    Ergun, R E; Andersson, L; Tao, J; Angelopoulos, V; Bonnell, J; McFadden, J P; Larson, D E; Eriksson, S; Johansson, T; Cully, C M; Newman, D N; Goldman, M V; Roux, A; LeContel, O; Glassmeier, K-H; Baumjohann, W

    2009-04-17

    We report the first direct observations of parallel electric fields (E_{ parallel}) carried by double layers (DLs) in the plasma sheet of Earth's magnetosphere. The DL observations, made by the THEMIS spacecraft, have E_{ parallel} signals that are analogous to those reported in the auroral region. DLs are observed during bursty bulk flow events, in the current sheet, and in plasma sheet boundary layer, all during periods of strong magnetic fluctuations. These observations imply that DLs are a universal process and that strongly nonlinear and kinetic behavior is intrinsic to Earth's plasma sheet.

  5. Interaction Effects in Double Layer Systems

    NASA Astrophysics Data System (ADS)

    Zheng, Lian

    A number of properties of two dimensional electron systems are investigated in this thesis. In the absence of a magnetic field, interaction effects for a double layer system are studied by employing the self-consistent STLS approximation. Results from using the RPA and the STLS are contrasted. An attempt to use standard finite-temperature perturbation theory to study the strongly-correlated system of electrons in a partially filled Landau level is discussed. The perturbative calculation for the grand potential of up to the third order is obtained. We also evaluate the sum of particle-particle ladder diagrams and show that, at zero temperature, it leads to a ground state energy with a cusp at v = 1/2. We study effects of disorder and the correlation of disorder potentials on the tunneling features of a double layer system and suggest that the electron lifetimes can be determined from the tunneling experiment. We derive an expression for the interlayer frictional drag in a double layer system, which can incorporate the effects of disorder and magnetic field. The disorder enhancement to the interlayer scattering is studied. We discuss the possibility of using the drag experiment to probe the properties of a single layer FQHE system.

  6. Double sodium layers observation over Beijing, China

    NASA Astrophysics Data System (ADS)

    Wang, Jihong; Yang, Yong; Cheng, Xuewu; Yang, Guotao; Song, Shalei; Gong, Shunsheng

    2012-08-01

    The altitude of the sodium layer in the mesosphere and lower thermosphere is usually from 80 km to 105 km. In this paper, we report a set of double sodium layer (DSL) events observed by sodium lidar over Beijing, China. In these DSL events, the normal sodium layer and secondary sodium layer (SeSL) present separately. There were about 17 DSL events occurred in 319 observation nights during 2009˜2011. All DSL events were observed in spring and summer. The SeSL appeared independently within the altitude range from 105 km to 130 km. The density of the SeSL is very high. The maximum ratio of peak density and the ratio of column density for the SeSL to the normal sodium layer are up to ˜60% and ˜47%, respectively. The SeSL lasted several hours, and then merged into the normal sodium layer. After the SeSL, a sporadic sodium layer occurred in the normal sodium layer.

  7. Single-particle thermal diffusion of charged colloids: double-layer theory in a temperature gradient.

    PubMed

    Dhont, J K G; Briels, W J

    2008-01-01

    The double-layer contribution to the single-particle thermal diffusion coefficient of charged, spherical colloids with arbitrary double-layer thickness is calculated and compared to experiments. The calculation is based on an extension of the Debye-Hückel theory for the double-layer structure that includes a small temperature gradient. There are three forces that constitute the total thermophoretic force on a charged colloidal sphere due to the presence of its double layer: i) the force F W that results from the temperature dependence of the internal electrostatic energy W of the double layer, ii) the electric force Fel with which the temperature-induced non-spherically symmetric double-layer potential acts on the surface charges of the colloidal sphere and iii) the solvent-friction force Fsol on the surface of the colloidal sphere due to the solvent flow that is induced in the double layer because of its asymmetry. The force F W will be shown to reproduce predictions based on irreversible-thermodynamics considerations. The other two forces Fel and Fsol depend on the details of the temperature-gradient-induced asymmetry of the double-layer structure which cannot be included in an irreversible-thermodynamics treatment. Explicit expressions for the thermal diffusion coefficient are derived for arbitrary double-layer thickness, which complement the irreversible-thermodynamics result through the inclusion of the thermophoretic velocity resulting from the electric- and solvent-friction force.

  8. High performance solid-state electric double layer capacitor from redox mediated gel polymer electrolyte and renewable tamarind fruit shell derived porous carbon.

    PubMed

    Senthilkumar, S T; Selvan, R Kalai; Melo, J S; Sanjeeviraja, C

    2013-11-13

    The activated carbon was derived from tamarind fruit shell and utilized as electrodes in a solid state electrochemical double layer capacitor (SSEDLC). The fabricated SSEDLC with PVA (polyvinyl alcohol)/H2SO4 gel electrolyte delivered high specific capacitance and energy density of 412 F g(-1) and 9.166 W h kg(-1), respectively, at 1.56 A g(-1). Subsequently, Na2MoO4 (sodium molybdate) added PVA/H2SO4 gel electrolyte was also prepared and applied for SSEDLC, to improve the performance. Surprisingly, 57.2% of specific capacitance (648 F g(-1)) and of energy density (14.4 Wh kg(-1)) was increased while introducing Na2MoO4 as the redox mediator in PVA/H2SO4 gel electrolyte. This improved performance is owed to the redox reaction between Mo(VI)/Mo(V) and Mo(VI)/Mo(IV) redox couples in Na2MoO4/PVA/H2SO4 gel electrolyte. Similarly, the fabricated device shows the excellent capacitance retention of 93% for over 3000 cycles. The present work suggests that the Na2MoO4 added PVA/H2SO4 gel is a potential electrolyte to improve the performance instead of pristine PVA/H2SO4 gel electrolyte. Based on the overall performance, it is strongly believed that the combination of tamarind fruit shell derived activated carbon and Na2MoO4/PVA/H2SO4 gel electrolyte is more attractive in the near future for high performance SSEDLCs.

  9. Double layered tailorable advanced blanket insulation

    NASA Technical Reports Server (NTRS)

    Falstrup, D.

    1983-01-01

    An advanced flexible reusable surface insulation material for future space shuttle flights was investigated. A conventional fly shuttle loom with special modifications to weave an integral double layer triangular core fabric from quartz yarn was used. Two types of insulating material were inserted into the cells of the fabric, and a procedure to accomplish this was developed. The program is follow up of a program in which single layer rectangular cell core fabrics are woven and a single type of insulating material was inserted into the cells.

  10. Double layer capacitance of carbon foam electrodes

    SciTech Connect

    Delnick, F.M.; Ingersoll, D.; Firsich, D.

    1993-11-01

    We have evaluated a wide variety of microcellular carbon foams prepared by the controlled pyrolysis and carbonization of several polymers including: polyacrylonitrile (PAN), polymethacrylonitrile (PMAN), resorcinol/formaldehyde (RF), divinylbenzene/methacrylonitrile (DVB), phenolics (furfuryl/alcohol), and cellulose polymers such as Rayon. The porosity may be established by several processes including: Gelation (1-5), phase separation (1-3,5-8), emulsion (1,9,10), aerogel/xerogel formation (1,11,12,13), replication (14) and activation. In this report we present the complex impedance analysis and double layer charging characteristics of electrodes prepared from one of these materials for double layer capacitor applications, namely activated cellulose derived microcellular carbon foam.

  11. Double layer capacitance of carbon foam electrodes

    NASA Astrophysics Data System (ADS)

    Delnick, F. M.; Ingersoll, D.; Firsich, D.

    We have evaluated a wide variety of microcellular carbon foams prepared by the controlled pyrolysis and carbonization of several polymers including: polyacrylonitrile (PAN), polymethacrylonitrile (PMAN), resorcinol/formaldehyde (RF), divinylbenzene/methacrylonitrile (DVB), phenolics (furfuryl/alcohol), and cellulose polymers such as Rayon. The porosity may be established by several processes including: gelation (1-5), phase separation (1-3,5-8), emulsion (1,9,10), aerogel/xerogel formation (1,11,12,13), replication (14), and activation. In this report we present the complex impedance analysis and double layer charging characteristics of electrodes prepared from one of these materials for double layer capacitor applications, namely activated cellulose derived microcellular carbon foam.

  12. Double layers and double wells in arbitrary degenerate plasmas

    NASA Astrophysics Data System (ADS)

    Akbari-Moghanjoughi, M.

    2016-06-01

    Using the generalized hydrodynamic model, the possibility of variety of large amplitude nonlinear excitations is examined in electron-ion plasma with arbitrary electron degeneracy considering also the ion temperature effect. A new energy-density relation is proposed for plasmas with arbitrary electron degeneracy which reduces to the classical Boltzmann and quantum Thomas-Fermi counterparts in the extreme limits. The pseudopotential method is employed to find the criteria for existence of nonlinear structures such as solitons, periodic nonlinear structures, and double-layers for different cases of adiabatic and isothermal ion fluids for a whole range of normalized electron chemical potential, η0, ranging from dilute classical to completely degenerate electron fluids. It is observed that there is a Mach-speed gap in which no large amplitude localized or periodic nonlinear excitations can propagate in the plasma under consideration. It is further revealed that the plasma under investigation supports propagation of double-wells and double-layers the chemical potential and Mach number ranges of which are studied in terms of other plasma parameters. The Mach number criteria for nonlinear waves are shown to significantly differ for cases of classical with η0 < 0 and quantum with η0 > 0 regimes. It is also shown that the localized structure propagation criteria possess significant dissimilarities for plasmas with adiabatic and isothermal ions. Current research may be generalized to study the nonlinear structures in plasma containing positrons, multiple ions with different charge states, and charged dust grains.

  13. Double layers and double wells in arbitrary degenerate plasmas

    SciTech Connect

    Akbari-Moghanjoughi, M.

    2016-06-15

    Using the generalized hydrodynamic model, the possibility of variety of large amplitude nonlinear excitations is examined in electron-ion plasma with arbitrary electron degeneracy considering also the ion temperature effect. A new energy-density relation is proposed for plasmas with arbitrary electron degeneracy which reduces to the classical Boltzmann and quantum Thomas-Fermi counterparts in the extreme limits. The pseudopotential method is employed to find the criteria for existence of nonlinear structures such as solitons, periodic nonlinear structures, and double-layers for different cases of adiabatic and isothermal ion fluids for a whole range of normalized electron chemical potential, η{sub 0}, ranging from dilute classical to completely degenerate electron fluids. It is observed that there is a Mach-speed gap in which no large amplitude localized or periodic nonlinear excitations can propagate in the plasma under consideration. It is further revealed that the plasma under investigation supports propagation of double-wells and double-layers the chemical potential and Mach number ranges of which are studied in terms of other plasma parameters. The Mach number criteria for nonlinear waves are shown to significantly differ for cases of classical with η{sub 0} < 0 and quantum with η{sub 0} > 0 regimes. It is also shown that the localized structure propagation criteria possess significant dissimilarities for plasmas with adiabatic and isothermal ions. Current research may be generalized to study the nonlinear structures in plasma containing positrons, multiple ions with different charge states, and charged dust grains.

  14. Some dynamical properties of very strong double layers in a triple plasma device

    NASA Technical Reports Server (NTRS)

    Carpenter, T.; Torven, S.

    1987-01-01

    Dynamical properties of very strong double layers seen in a differentially pumped triple plasma device are reported. These double layers are V-shaped. The following findings are discussed: (1) Disruptions in the double layer potential and in the plasma current occur when an inductance is placed in series with the bias supply between the sources in the external circuit. These disruptions, which can be highly periodic, are the result of a negative resistance region. (2) When reactances in the circuit are minimized, the double layer exhibits a jitter motion in position approximately equal to the double layer thickness. (3) When the bias between the sources is rapidly turned on, the initial phase in the double layer formation is the occurrence of a constant electric field for the first few microseconds. First the apparatus used in all of the work is discussed and then each of the three phenomena are considered.

  15. On The Physical Mechanism At The Origin Of Multiple Double Layers Appearance In Plasma

    SciTech Connect

    Dimitriu, D. G.; Gurlui, S.; Aflori, M.; Ivan, L. M.

    2006-01-15

    Double layer in plasma are nonlinear potential structures consisting of two adjacent layers of positive and negative space charges, respectively. Between these layers a potential jump exists, creating an electric field. A common way to obtain a double layer structure is to positively bias an electrode immersed into stable plasma. Under certain experimental conditions, a more complex structure in form of two or more subsequent double layers was observed, which was called multiple double layers. It appears as several bright and concentric plasma shells attached to the electrode. The successive double layers are located at the abrupt changes of luminosity between two adjacent plasma shells. However, if the electrode is large, the multiple double layers structure appears non-concentrically, as a network of plasma spots, near each other, almost equally distributed on the electrode surface. Each of the plasma spots is confined by an electrical double layer. Here, we will present experimental results on the appearance and dynamics of concentric, as well as non-concentric multiple double layers. The results prove that the same physical mechanism is at the origin of their appearance in plasma. In this mechanism, the electron-neutral impact excitations and ionizations play the key role.

  16. Two-dimensional potential double layers and discrete auroras

    NASA Technical Reports Server (NTRS)

    Kan, J. R.; Lee, L. C.; Akasofu, S.-I.

    1979-01-01

    This paper is concerned with the formation of the acceleration region for electrons which produce the visible auroral arc and with the formation of the inverted V precipitation region. The former is embedded in the latter, and both are associated with field-aligned current sheets carried by plasma sheet electrons. It is shown that an electron current sheet driven from the plasma sheet into the ionosphere leads to the formation of a two-dimensional potential double layer. For a current sheet of a thickness less than the proton gyrodiameter solutions are obtained in which the field-aligned potential drop is distributed over a length much greater than the Debye length. For a current sheet of a thickness much greater than the proton gyrodiameter solutions are obtained in which the potential drop is confined to a distance on the order of the Debye length. The electric field in the two-dimensional double-layer model is the zeroth-order field inherent to the current sheet configuration, in contrast to those models in which the electric field is attributed to the first-order field due to current instabilities or turbulences. The maximum potential in the two-dimensional double-layer models is on the order of the thermal energy of plasma sheet protons, which ranges from 1 to 10 keV.

  17. Effects of double-layer polarization on ion transport.

    PubMed

    Hainsworth, A H; Hladky, S B

    1987-01-01

    It has been proposed that changes in ionic strength will alter the shape of current-voltage relations for ion transport across a lipid membrane. To investigate this effect, we measured currents across glyceryl monooleate membranes at applied potentials between 10 and 300 mV using either gramicidin and 1 mM NaCl or valinomycin and 1 mM KCl. A bridge circuit with an integrator as null detector was used to separate the capacitative and ionic components of the current. The changes in the current-voltage relations when ionic strength is varied between 1 and 100 mM are compared with predictions of Gouy-Chapman theory for the effects of these variations on polarization of the electrical diffuse double-layer. Double-layer polarization accounts adequately for the changes observed using membranes made permeable by either gramicidin or valinomycin.

  18. Effects of double-layer polarization on ion transport.

    PubMed Central

    Hainsworth, A H; Hladky, S B

    1987-01-01

    It has been proposed that changes in ionic strength will alter the shape of current-voltage relations for ion transport across a lipid membrane. To investigate this effect, we measured currents across glyceryl monooleate membranes at applied potentials between 10 and 300 mV using either gramicidin and 1 mM NaCl or valinomycin and 1 mM KCl. A bridge circuit with an integrator as null detector was used to separate the capacitative and ionic components of the current. The changes in the current-voltage relations when ionic strength is varied between 1 and 100 mM are compared with predictions of Gouy-Chapman theory for the effects of these variations on polarization of the electrical diffuse double-layer. Double-layer polarization accounts adequately for the changes observed using membranes made permeable by either gramicidin or valinomycin. PMID:2432953

  19. Electromechanics and Electrical Breakdown of Particulate Layers

    NASA Astrophysics Data System (ADS)

    Moslehi, Bizhan G. R.

    A comprehensive theory of the electromechanics and electrical breakdown of a current-carrying particulate layer is developed, which takes into account its inhomogeneous nature and mode of compaction. The theory treates the general case of combined surface and volume conduction and takes account of self-compression of the layer due to electrical forces. The electromechanical theory predicts the existence of a remarkably large electrical cohesive stress in the layer due to a strong field enhancement in and around the contact regions. Furthermore, it shows a decrease in the apparent resistivity of the layer with increasing electric field as a result of self-compression. The analysis of electrical breakdown of current -carrying particulate layer predicts the onset of breakdown of the layer in the form of intermittent microsparks in the gap between the contacting particles when the electric field at the contact or in the surrounding gap exceeds the threshold breakdown value. An analysis of the behavior of the layer after breakdown in terms of a simplified equivalent lumped circuit predicts increases of sparking frequency and average current as the applied average field exceeds the threshold average field for the onset of breakdown. The results of measurements on layers of glass beads and fly-ash in a standard resistivity cell are in good agreement with the theoretical predictions for the field-dependent resistivity characteristics. The work has particular significance for electrostatic precipitation and addresses the phenomenon of backdischarge and the questions of the retention, rapping, and reentrainment of precipitation ash layers.

  20. Intercalation of Layered Silicates, Layered Double Hydroxides, and Lead Iodide: Synthesis, Characterization and Properties.

    NASA Astrophysics Data System (ADS)

    Mehrotra, Vivek

    Layered silicates, layered double hydroxides, and lead iodide are lamellar solids that can incorporate guest species into the galleries between their layers. Various intercalated forms of these layered materials have been synthesized and their properties studied. The dielectric behavior of pristine fluorohectorite, a typical layered silicate, and Zn-Al layered double hydroxide is explained by considering the structural ordering and mobility of the intercalated water molecules, as well as models invoking fractal time processes and fractal structure. Intercalative polymerization of aniline and pyrrole into fluorohectorite leads to a multilayered structure consisting of single polymer chains alternately stacked with the 9.6 A thick silicate layers. The polymer chains are confined to the quasi two-dimensional interlayer space between the rigid host layers. The hybrid films exhibit highly anisotropic properties. The optical, electrical and mechanical behavior is discussed in terms of the molecular confinement of the polymer chains. Ethylenediamine functionalized C _{60} clusters have also been intercalated into fluorohectorite via an ion-exchange procedure. Intercalation results in an improved thermal stability of the functionalized C_{60} clusters. Rutherford backscattering spectrometry has been used to elucidate the mechanism of intercalative ion exchange of silver in muscovite mica, a layered silicate with a layer charge density of 2e per unit cell. It is proposed that ion-exchange progresses by intercalating successive galleries through the edges of the mica layers. Guest-host interactions have been studied in the system aniline-PbI_2. The optical and structural effects of aniline intercalation in lead iodide thin films is discussed. Intercalation leads to a large shift in the optical band gap of PbI_2. The observed change in band gap is not only due to the increased separation between the PbI_2 layers but also because of an electrostatic interaction between the

  1. Improving Breakdown Behavior by Substrate Bias in a Novel Double Epi-layer Lateral Double Diffused MOS Transistor

    NASA Astrophysics Data System (ADS)

    Li, Qi; Wang, Wei-Dong; Liu, Yun; Wei, Xue-Ming

    2012-02-01

    A new lateral double diffused MOS (LDMOS) transistor with a double epitaxial layer formed by an n-type substrate and a p-type epitaxial layer is reported (DEL LDMOS). The mechanism of the improved breakdown characteristic is that the high electric field around the drain is reduced by substrate reverse bias, which causes the redistribution of the bulk electric field in the drift region, and the vertical blocking voltage is shared by the drain side and the source side. The numerical results indicate that the trade-off between breakdown voltage and on-resistance of the proposed device is improved greatly in comparison to that of the conventional LDMOS.

  2. Tunable magnetic resonance in double layered metallic structures.

    PubMed

    Zhou, L; Zhu, Y Y

    2011-12-01

    Double layered metallic gratings have been investigated both theoretically and experimentally. The authors have reported that tunable magnetic resonance (MR) can be achieved by modulating the vertical chirped width dh which could be controlled conveniently in the common electron and/or ion beam microfabrications. The linear relationship between MR wavelength and dh has been reported. By introducing the difference of electric and magnetic penetration depth, an analytic formula deduced from a modified LC model has shown good agreement with the simulation results, and an effective width for trapezoidal sandwiched microstructures has been presented. Our results may provide an alternative choice for tunable MR and broad bandwidth of magnetic metamaterials.

  3. Electrostatic supersolitons and double layers at the acoustic speed

    SciTech Connect

    Verheest, Frank; Hellberg, Manfred A.

    2015-01-15

    Supersolitons are characterized by subsidiary extrema on the sides of a typical bipolar electric field signature or by association with a root beyond double layers in the fully nonlinear Sagdeev pseudopotential description. It has been proven that supersolitons may exist in several plasmas having at least three constituent species, but they cannot be found in weakly nonlinear theory. Another recent aspect of pseudopotential theory is that in certain plasma models and parameter regimes solitons and/or double layers can exist at the acoustic speed, having no reductive perturbation counterparts. Importantly, they signal coexistence between solitons having positive and negative polarity, in that one solution can be realized at a time, depending on infinitesimal perturbations from the equilibrium state. Weaving the two strands together, we demonstrate here that one can even find supersolitons and double layers at the acoustic speed, as illustrated using the model of cold positive and negative ions, in the presence of nonthermal electrons following a Cairns distribution. This model has been discussed before, but the existence and properties of supersolitons at the acoustic speed were not established at the time of publication.

  4. Double-Diffusive Layers and Phase Transitions

    NASA Astrophysics Data System (ADS)

    Dude, Sabine; Hansen, Ulrich

    2015-04-01

    Researching the thermal evolution of the Earth's mantle on numerical base is very challenging. During the last decade different approaches are put forward in oder to understand the picture of the today's Earth's mantle. One way is to incorporate all the known features and physics (plate tectonics, phase transitions, CMB-topography, ...) into numerical models and make them as complex (or 'complete') as possible to capture Earth's mantle processes and surface signals. Another way is, to take a step back and look at less complex models which account for single processes and their interaction and evolution. With these 'simpler' models one is able look in detail into the physical processes and dependencies on certain parameters. Since the knowledge of slab stagnation in the transitions zone of the Earth's mantle the question whether the mantle is or at least has been layered to some degree is still under debate. On this basis we address two important features that lead to layered mantle convection and may affect each other and with this the thermal evolution of the mantle. It is commonly known the main mantle mineral olivine pass through various phase changes with depth [1]. Detailed numerical studies had been carried out to ascertain the influence on convective motion and planetary evolution [2]. It is still heavily discussed whether the endothermic phase change at 660km depth can lead an isolated lower mantle. Most of the numerical studies favour a model which has phases of layering that are disrupted by catastrophic events. In the last years double-diffusive convection has also been intensively studied with regard to planetary mantle evolution such as pile formation and core-mantle boundary topography [3]. However, another striking feature still posing open questions are evolving layers self-organised from a previous non layered state. Considering a chemical component that influences the density of a fluid in addition to the temperature leads to dynamical phenomena

  5. On the threshold energization of radiation belt electrons by double layers.

    NASA Astrophysics Data System (ADS)

    Dimmock, A. P.; Osmane, A.; Pulkkinen, T. I.

    2014-12-01

    Recent in situ electric field measurements by the Van Allen Probes in the radiation belts have revealed the existence and ubiquitous presence of double layers [Mozer et al. Phys. Rev. Lett., 2013]. Encounters with double layers during 1 minute burst mode intervals were both common and indicative of large cumulative potential drops. With electric fields averaging 20 mV/m, and sometimes reaching as high as 100 mV/m, observed double layers have been suggested as possible accelerators of radiation belt electrons and generators of a seed population of 100 keV. Using a Hamiltonian approach we quantify the energization threshold of electrons interacting with radiation belts' double layers analytically and numerically. We find that double layers with electric field amplitude δE ranging between 10-100 mV/m and spatial scales of the order of few Debye lengths are very efficient in energizing electrons with initial velocities v ≤ vthermal≈3000 km/s to 1 keV levels, but are unable to energize electrons with energies E ≥ 10 keV. Our results therefore indicate that the localized electric field associated with the double layers are unlikely to generate a seed population of 100 keV necessary for a plethora of relativistic acceleration mechanisms and additional transport to higher energetic levels.

  6. Unravelling the electrochemical double layer by direct probing of the solid/liquid interface

    SciTech Connect

    Favaro, Marco; Jeong, Beomgyun; Ross, Philip N.; Yano, Junko; Hussain, Zahid; Liu, Zhi; Crumlin, Ethan J.

    2016-08-31

    The electrochemical double layer plays a critical role in electrochemical processes. Whilst there have been many theoretical models predicting structural and electrical organization of the electrochemical double layer, the experimental verification of these models has been challenging due to the limitations of available experimental techniques. The induced potential drop in the electrolyte has never been directly observed and verified experimentally, to the best of our knowledge. In this study, we report the direct probing of the potential drop as well as the potential of zero charge by means of ambient pressure X-ray photoelectron spectroscopy performed under polarization conditions. By analyzing the spectra of the solvent (water) and a spectator neutral molecule with numerical simulations of the electric field, we discern the shape of the electrochemical double layer profile. In addition, we determine how the electrochemical double layer changes as a function of both the electrolyte concentration and applied potential.

  7. Unravelling the electrochemical double layer by direct probing of the solid/liquid interface

    PubMed Central

    Favaro, Marco; Jeong, Beomgyun; Ross, Philip N.; Yano, Junko; Hussain, Zahid; Liu, Zhi; Crumlin, Ethan J.

    2016-01-01

    The electrochemical double layer plays a critical role in electrochemical processes. Whilst there have been many theoretical models predicting structural and electrical organization of the electrochemical double layer, the experimental verification of these models has been challenging due to the limitations of available experimental techniques. The induced potential drop in the electrolyte has never been directly observed and verified experimentally, to the best of our knowledge. In this study, we report the direct probing of the potential drop as well as the potential of zero charge by means of ambient pressure X-ray photoelectron spectroscopy performed under polarization conditions. By analyzing the spectra of the solvent (water) and a spectator neutral molecule with numerical simulations of the electric field, we discern the shape of the electrochemical double layer profile. In addition, we determine how the electrochemical double layer changes as a function of both the electrolyte concentration and applied potential. PMID:27576762

  8. Double Layers Throughout the Magnetosphere and Their Relation to Magnetic Reconnection

    NASA Astrophysics Data System (ADS)

    Goodrich, Katherine; Ergun, Robert; Wilder, Frederick; Ahmadi, Narges; Khotyaintsev, Yuri; Lindqvist, Per-Arne; Torbert, Roy; Argall, Matthew; Le Contel, Olivier; Russell, Christopher; Strangeway, Robert; Giles, Barbara; Burch, James

    2017-04-01

    Observations throughout the terrestrial magnetosphere have shown large-amplitude parallel electric field signatures in regions of strong magnetic turbulence. Debye-length, unipolar parallel electric fields identified as double layers have consistently been observed in regions such as the auroral acceleration region, near-Earth plasmasheet, and in the terrestrial bow shock. Double layers have been theorized to be a dissipation mechanism for magnetic turbulence. Recent observations from MMS have suggested that double layers can act as a signature of secondary magnetic reconnection, particularly in the Earth's magnetopause. We present a comparative study of double layer signatures in various regions of the Earth's magnetosphere to determine the relationship between secondary magnetic reconnection and turbulent dissipation.

  9. Unravelling the electrochemical double layer by direct probing of the solid/liquid interface

    DOE PAGES

    Favaro, Marco; Jeong, Beomgyun; Ross, Philip N.; ...

    2016-08-31

    The electrochemical double layer plays a critical role in electrochemical processes. Whilst there have been many theoretical models predicting structural and electrical organization of the electrochemical double layer, the experimental verification of these models has been challenging due to the limitations of available experimental techniques. The induced potential drop in the electrolyte has never been directly observed and verified experimentally, to the best of our knowledge. In this study, we report the direct probing of the potential drop as well as the potential of zero charge by means of ambient pressure X-ray photoelectron spectroscopy performed under polarization conditions. By analyzingmore » the spectra of the solvent (water) and a spectator neutral molecule with numerical simulations of the electric field, we discern the shape of the electrochemical double layer profile. In addition, we determine how the electrochemical double layer changes as a function of both the electrolyte concentration and applied potential.« less

  10. Unravelling the electrochemical double layer by direct probing of the solid/liquid interface

    NASA Astrophysics Data System (ADS)

    Favaro, Marco; Jeong, Beomgyun; Ross, Philip N.; Yano, Junko; Hussain, Zahid; Liu, Zhi; Crumlin, Ethan J.

    2016-08-01

    The electrochemical double layer plays a critical role in electrochemical processes. Whilst there have been many theoretical models predicting structural and electrical organization of the electrochemical double layer, the experimental verification of these models has been challenging due to the limitations of available experimental techniques. The induced potential drop in the electrolyte has never been directly observed and verified experimentally, to the best of our knowledge. In this study, we report the direct probing of the potential drop as well as the potential of zero charge by means of ambient pressure X-ray photoelectron spectroscopy performed under polarization conditions. By analyzing the spectra of the solvent (water) and a spectator neutral molecule with numerical simulations of the electric field, we discern the shape of the electrochemical double layer profile. In addition, we determine how the electrochemical double layer changes as a function of both the electrolyte concentration and applied potential.

  11. Limiting factors for carbon based chemical double layer capacitors

    NASA Technical Reports Server (NTRS)

    Rose, M. Frank; Johnson, C.; Owens, T.; Stevens, B.

    1993-01-01

    The Chemical Double Layer (CDL) capacitor improves energy storage density dramatically when compared with conventional electrolytic capacitors. When compared to batteries, the CDL Capacitor is much less energy dense; however, the power density is orders of magnitude better. As a result, CDL-battery combinations present an interesting pulse power system with many potential applications. Due to the nature of the CDL it is inherently a low voltage device. The applications of the CDL can be tailored to auxiliary energy and burst mode storages which require fast charge/discharge cycles. Typical of the applications envisioned are power system backup, directed energy weapons concepts, electric automobiles, and electric actuators. In this paper, we will discuss some of the general characteristics of carbon-based CDL technology describing the structure, performance parameters, and methods of construction. Further, analytical and experimental results which define the state of the art are presented and described in terms of impact on applications.

  12. Effect of double layers on magnetosphere-ionosphere coupling

    NASA Technical Reports Server (NTRS)

    Lysak, Robert L.; Hudson, Mary K.

    1987-01-01

    The Earth's auroral zone contains dynamic processes occurring on scales from the length of an auroral zone field line which characterizes Alfven wave propagation to the scale of microscopic processes which occur over a few Debye lengths. These processes interact in a time-dependent fashion since the current carried by the Alfven waves can excite microscopic turbulence which can in turn provide dissipation of the Alfven wave energy. This review will first describe the dynamic aspects of auroral current structures with emphasis on consequences for models of microscopic turbulence. A number of models of microscopic turbulence will be introduced into a large-scale model of Alfven wave propagation to determine the effect of various models on the overall structure of auroral currents. In particular, the effects of a double layer electric field which scales with the plasma temperature and Debye length is compared with the effect of anomalous resistivity due to electrostatic ion cyclotron turbulence in which the electric field scales with the magnetic field strength. It is found that the double layer model is less diffusive than in the resistive model leading to the possibility of narrow, intense current structures.

  13. Polysulfide intercalated layered double hydroxides for metal capture applications

    DOEpatents

    Kanatzidis, Mercouri G.; Ma, Shulan

    2017-04-04

    Polysulfide intercalated layered double hydroxides and methods for their use in vapor and liquid-phase metal capture applications are provided. The layered double hydroxides comprise a plurality of positively charged host layers of mixed metal hydroxides separated by interlayer spaces. Polysulfide anions are intercalated in the interlayer spaces.

  14. Low temperature double-layer capacitors

    NASA Technical Reports Server (NTRS)

    Brandon, Erik J. (Inventor); Smart, Marshall C. (Inventor); West, William C. (Inventor)

    2011-01-01

    Double-layer capacitors capable of operating at extremely low temperatures (e.g., as low as -75.degree. C.) are disclosed. Electrolyte solutions combining a base solvent (e.g., acetonitrile) and a cosolvent are employed to lower the melting point of the base electrolyte. Example cosolvents include methyl formate, ethyl acetate, methyl acetate, propionitrile, butyronitrile, and 1,3-dioxolane. An optimized concentration (e.g., 0.10 M to 0.75 M) of salt, such as tetraethylammonium tetrafluoroborate, is dissolved into the electrolyte solution. In some cases (e.g., 1,3-dioxolane cosolvent) additives, such as 2% by volume triethylamine, may be included in the solvent mixture to prevent polymerization of the solution. Conventional device form factors and structural elements (e.g., porous carbon electrodes and a polyethylene separator) may be employed.

  15. Accretion onto neutron stars with the presence of a double layer

    NASA Technical Reports Server (NTRS)

    Williams, A. C.; Weisskopf, M. C.; Elsner, R. F.; Darbro, W.; Sutherland, P. G.

    1987-01-01

    It is known, from laboratory experiments, that double layers will form in plasmas, usually in the presence of an electric current. It is argued that a double layer may be present in the accretion column of a neutron star in a binary system. It is suggested that the double layer may be the predominant deceleration mechanism for the accreting ions, especially for sources with X-ray luminosities of less than about 10 to the 37th erg/s. Previous models have involved either a collisionless shock or an assumed gradual deceleration of the accreting ions to thermalize the energy of the infalling matter.

  16. Accretion onto neutron stars with the presence of a double layer

    NASA Technical Reports Server (NTRS)

    Williams, A. C.; Weisskopf, M. C.; Elsner, R. F.; Darbro, W.; Sutherland, P. G.

    1986-01-01

    It is known from laboratory experiments that double layers can form in plasmas, usually in the presence of an electric current. It is argued that a double layer may be present in the accretion column of a neutron star in a binary system. It is suggested that the double layer may be the predominant deceleration mechanism for the accreting ions, especially for sources with X-ray luminosities of less than about 10 to the 37th erg/s. Previous models have involved either a collisionless shock or an assumed gradual deceleration of the accreting ions to thermalize the energy of the infalling matter.

  17. Surface morphological, electrical and transport properties of rapidly annealed double layers Ru/Cr Schottky structure on n-type InP

    NASA Astrophysics Data System (ADS)

    Shanthi Latha, K.; Rajagopal Reddy, V.

    2017-02-01

    The electrical and transport properties of a fabricated bilayer Ru/Cr/n-InP Schottky diode (SD) have been investigated at different annealing temperatures. Atomic force microscopy results have showed that the overall surface morphology of the Ru/Cr/n-InP SD is fairly smooth at elevated temperatures. High barrier height is achieved for the diode annealed at 300 °C compared to the as-deposited, annealed at 200 and 400 °C diodes. The series resistance and shunt resistance of the Ru/Cr/n-InP SD are estimated by current-voltage method at different annealing temperatures. The barrier heights and series resistance are also determined by Cheung's and modified Norde functions. The interface state density of the Ru/Cr/n-InP SD is found to be decreased after annealing at 300 °C and then slightly increased upon annealing at 400 °C. The difference between barrier heights obtained from current-voltage and capacitance-voltage is also discussed. Experimental results have showed that the Poole-Frenkel emission is found to be dominant in the lower bias region whereas Schottky emission is dominant in the higher bias region for the Ru/Cr/n-InP SDs irrespective of annealing temperatures.

  18. Surface morphological, electrical and transport properties of rapidly annealed double layers Ru/Cr Schottky structure on n-type InP

    NASA Astrophysics Data System (ADS)

    Shanthi Latha, K.; Rajagopal Reddy, V.

    2017-07-01

    The electrical and transport properties of a fabricated bilayer Ru/Cr/ n-InP Schottky diode (SD) have been investigated at different annealing temperatures. Atomic force microscopy results have showed that the overall surface morphology of the Ru/Cr/ n-InP SD is fairly smooth at elevated temperatures. High barrier height is achieved for the diode annealed at 300 °C compared to the as-deposited, annealed at 200 and 400 °C diodes. The series resistance and shunt resistance of the Ru/Cr/ n-InP SD are estimated by current-voltage method at different annealing temperatures. The barrier heights and series resistance are also determined by Cheung's and modified Norde functions. The interface state density of the Ru/Cr/ n-InP SD is found to be decreased after annealing at 300 °C and then slightly increased upon annealing at 400 °C. The difference between barrier heights obtained from current-voltage and capacitance-voltage is also discussed. Experimental results have showed that the Poole-Frenkel emission is found to be dominant in the lower bias region whereas Schottky emission is dominant in the higher bias region for the Ru/Cr/ n-InP SDs irrespective of annealing temperatures.

  19. Density-functional theory of spherical electric double layers and zeta potentials of colloidal particles in restricted-primitive-model electrolyte solutions.

    PubMed

    Yu, Yang-Xin; Wu, Jianzhong; Gao, Guang-Hua

    2004-04-15

    A density-functional theory is proposed to describe the density profiles of small ions around an isolated colloidal particle in the framework of the restricted primitive model where the small ions have uniform size and the solvent is represented by a dielectric continuum. The excess Helmholtz energy functional is derived from a modified fundamental measure theory for the hard-sphere repulsion and a quadratic functional Taylor expansion for the electrostatic interactions. The theoretical predictions are in good agreement with the results from Monte Carlo simulations and from previous investigations using integral-equation theory for the ionic density profiles and the zeta potentials of spherical particles at a variety of solution conditions. Like the integral-equation approaches, the density-functional theory is able to capture the oscillatory density profiles of small ions and the charge inversion (overcharging) phenomena for particles with elevated charge density. In particular, our density-functional theory predicts the formation of a second counterion layer near the surface of highly charged spherical particle. Conversely, the nonlinear Poisson-Boltzmann theory and its variations are unable to represent the oscillatory behavior of small ion distributions and charge inversion. Finally, our density-functional theory predicts charge inversion even in a 1:1 electrolyte solution as long as the salt concentration is sufficiently high.

  20. Exact Analytic Result of Contact Value for the Density in a Modified Poisson-Boltzmann Theory of an Electrical Double Layer.

    PubMed

    Lou, Ping; Lee, Jin Yong

    2009-04-14

    For a simple modified Poisson-Boltzmann (SMPB) theory, taking into account the finite ionic size, we have derived the exact analytic expression for the contact values of the difference profile of the counterion and co-ion, as well as of the sum (density) and product profiles, near a charged planar electrode that is immersed in a binary symmetric electrolyte. In the zero ionic size or dilute limit, these contact values reduce to the contact values of the Poisson-Boltzmann (PB) theory. The analytic results of the SMPB theory, for the difference, sum, and product profiles were compared with the results of the Monte-Carlo (MC) simulations [ Bhuiyan, L. B.; Outhwaite, C. W.; Henderson, D. J. Electroanal. Chem. 2007, 607, 54 ; Bhuiyan, L. B.; Henderson, D. J. Chem. Phys. 2008, 128, 117101 ], as well as of the PB theory. In general, the analytic expression of the SMPB theory gives better agreement with the MC data than the PB theory does. For the difference profile, as the electrode charge increases, the result of the PB theory departs from the MC data, but the SMPB theory still reproduces the MC data quite well, which indicates the importance of including steric effects in modeling diffuse layer properties. As for the product profile, (i) it drops to zero as the electrode charge approaches infinity; (ii) the speed of the drop increases with the ionic size, and these behaviors are in contrast with the predictions of the PB theory, where the product is identically 1.

  1. Pd/Ni-WO3 anodic double layer gasochromic device

    DOEpatents

    Lee, Se-Hee; Tracy, C. Edwin; Pitts, J. Roland; Liu, Ping

    2004-04-20

    An anodic double layer gasochromic sensor structure for optical detection of hydrogen in improved response time and with improved optical absorption real time constants, comprising: a glass substrate; a tungsten-doped nickel oxide layer coated on the glass substrate; and a palladium layer coated on the tungsten-doped nickel oxide layer.

  2. Capattery double layer capacitor life performance

    NASA Astrophysics Data System (ADS)

    Evans, David A.; Clark, Nancy H.; Baca, W. E.; Miller, John R.; Barker, Thomas B.

    Double layer capacitors (DLCs) have received increased use in computer memory backup applications for consumer products during the past ten years. Their extraordinarily high capacitance density along with their maintenance-free operation makes them particularly suited for these products. These same features also make DLCs very attractive in military type applications. Unfortunately, lifetime performance data has not been reported in the literature for any DLC component. Our objective in this study was to investigate the effects that voltage and temperature have on the properties and performance of single and series-connected DLCs as a function of time. Evans model RE110474, 0.47-farad, 11.0-volt Capatteries were evaluated. These components have a tantalum package, use welded construction, and contain a glass-to-metal seal, all incorporated to circumvent the typical DLC failure modes of electrolyte loss and container corrosion. A five-level, two-factor Central Composite Design was used in the study. Single and series-connected Capatteries rated at 85 C, 11.0-volts operation were subjected to test temperatures between 25 and 95 C, and voltages between 0 and 12.9 volts (9 test conditions). Measured responses included capacitance, equivalent series resistance, and discharge time. Data were analyzed using a regression analysis to obtain response functions relating DLC properties to their voltage, temperature, and test time history. These results are described and should aid system and component engineers in using DLCs in critical applications.

  3. Coronal electron confinement by double layers

    SciTech Connect

    Li, T. C.; Drake, J. F.; Swisdak, M.

    2013-12-01

    In observations of flare-heated electrons in the solar corona, a longstanding problem is the unexplained prolonged lifetime of the electrons compared to their transit time across the source. This suggests confinement. Recent particle-in-cell (PIC) simulations, which explored the transport of pre-accelerated hot electrons through ambient cold plasma, showed that the formation of a highly localized electrostatic potential drop, in the form of a double layer (DL), significantly inhibited the transport of hot electrons. The effectiveness of confinement by a DL is linked to the strength of the DL as defined by its potential drop. In this work, we investigate the scaling of the DL strength with the hot electron temperature by PIC simulations and find a linear scaling. We demonstrate that the strength is limited by the formation of parallel shocks. Based on this, we analytically determine the maximum DL strength, and also find a linear scaling with the hot electron temperature. The DL strength obtained from the analytic calculation is comparable to that from the simulations. At the maximum strength, the DL is capable of confining a significant fraction of hot electrons in the source.

  4. Laboratory evidence for ion-acoustic-type double layers

    NASA Technical Reports Server (NTRS)

    Chan, C.; Cho, M. H.; Hershkowitz, N.; Intrator, T.

    1984-01-01

    The formation of an ion-acoustic-type double layer was observed in the laboratory for the first time. The rarefactive part of a long-wavelength ion-acoustic wave grew in amplitude because of the presence of drifting electrons. The corresponding current limitation led to the formation of the double layer.

  5. Anomalous dc resistivity and double layers in the auroral ionosphere

    SciTech Connect

    Kindel, J.M.; Barnes, C.; Forslund, D.W.

    1980-01-01

    There are at least four candidate instabilities which might account for anomalous dc rereresistivity in the auroral ionosphere. These are: the ion-acoustic instability, the Buneman instability, the ion-cyclotron instability and double layers. Results are reported of computer simulations of these four instabilities which suggest that double layers are most likely to be responsible for sistivity in the auroral zone.

  6. Double layer capacitance of anode/solid-electrolyte interfaces.

    PubMed

    Ge, Xiaoming; Fu, Changjing; Chan, Siew Hwa

    2011-09-07

    The double layer of electrode/electrolyte interfaces plays a fundamental role in determining the performance of solid state electrochemical cells. The double layer capacitance is one of the most-studied descriptors of the double layer. This work examines a case study on lanthanum strontium vanadate (LSV)/yttria-stabilized zirconia (YSZ) interfaces exposed in solid oxide fuel cell anode environment. The apparent double layer capacitance is obtained from impedance spectroscopy. The intrinsic double layer capacitance is evaluated based on Stern's method in conjunction with the Volta potential analysis across LSV/YSZ interfaces. Both the apparent and the intrinsic double layer capacitances exhibit right-skewed volcano patterns, when the interfaces are subjected to anodic biases from 0 to 150 mV. The apparent double layer capacitance is about one order of magnitude larger than the intrinsic double layer capacitance. This discrepancy roots in the inconsistent surface areas that are involved. This analysis of capacitance would provide a more realistic TPB estimate of a working solid-state electrochemical device. This journal is © the Owner Societies 2011

  7. SUPPRESSION OF ENERGETIC ELECTRON TRANSPORT IN FLARES BY DOUBLE LAYERS

    SciTech Connect

    Li, T. C.; Drake, J. F.; Swisdak, M.

    2012-09-20

    During flares and coronal mass ejections, energetic electrons from coronal sources typically have very long lifetimes compared to the transit times across the systems, suggesting confinement in the source region. Particle-in-cell simulations are carried out to explore the mechanisms of energetic electron transport from the corona to the chromosphere and possible confinement. We set up an initial system of pre-accelerated hot electrons in contact with ambient cold electrons along the local magnetic field and let it evolve over time. Suppression of transport by a nonlinear, highly localized electrostatic electric field (in the form of a double layer) is observed after a short phase of free-streaming by hot electrons. The double layer (DL) emerges at the contact of the two electron populations. It is driven by an ion-electron streaming instability due to the drift of the back-streaming return current electrons interacting with the ions. The DL grows over time and supports a significant drop in temperature and hence reduces heat flux between the two regions that is sustained for the duration of the simulation. This study shows that transport suppression begins when the energetic electrons start to propagate away from a coronal acceleration site. It also implies confinement of energetic electrons with kinetic energies less than the electrostatic energy of the DL for the DL lifetime, which is much longer than the electron transit time through the source region.

  8. Discharge rates of porous carbon double layer capacitors

    SciTech Connect

    Eisenmann, E.T.

    1995-10-01

    Double layer capacitors with porous carbon electrodes have very low frequency response limits and correspondingly low charge-discharge rates. Impedance measurements of various commercial double layer capacitors and of carbon electrodes prepared from selected precursor materials were found to yield similar, yet subtly different characteristics. Through modeling with the traditional transmission line equivalent circuit for porous electrodes, a resistive layer can be identified, which forms on carbon films during carbonization and survives the activation procedure. A method for determining the power-to-energy ratio of electrochemical capacitors has been developed. These findings help define new ways for optimizing the properties of double layer capacitors.

  9. Effect of double-sided CaTiO3 buffer layers on the electrical properties of CaCu3Ti4O12 films on Pt /Ti/SiO2/Si substrates

    NASA Astrophysics Data System (ADS)

    Fang, Liang; Shen, Mingrong; Li, Zhenya

    2006-11-01

    The CaCu3Ti4O12 (CCTO) films with single- and double-sided CaTiO3 (CTO) buffer layers were grown on Pt /Ti/SiO2/Si substrates by pulsed laser deposition at 650°C, which was lower than the normal deposition temperature of the CCTO films. The CTO layer was used as seeding layer to improve the crystallization of the CCTO films and could enhance the dielectric properties of the multilayered films. In addition, the multilayered films exhibited low frequency dielectric relaxation and reduced leakage current density, which could be ascribed to the improved interfacial characteristics between the CTO layer and the electrode. The conduction mechanisms of the single layered and multilayered films were also discussed briefly.

  10. Exfoliation of layered double hydroxides for enhanced oxygen evolution catalysis.

    PubMed

    Song, Fang; Hu, Xile

    2014-07-17

    The oxygen evolution reaction is a key reaction in water splitting. The common approach in the development of oxygen evolution catalysts is to search for catalytic materials with new and optimized chemical compositions and structures. Here we report an orthogonal approach to improve the activity of catalysts without alternating their compositions or structures. Specifically, liquid phase exfoliation is applied to enhance the oxygen evolution activity of layered double hydroxides. The exfoliated single-layer nanosheets exhibit significantly higher oxygen evolution activity than the corresponding bulk layered double hydroxides in alkaline conditions. The nanosheets from nickel iron and nickel cobalt layered double hydroxides outperform a commercial iridium dioxide catalyst in both activity and stability. The exfoliation creates more active sites and improves the electronic conductivity. This work demonstrates the promising catalytic activity of single-layered double hydroxides for the oxygen evolution reaction.

  11. Pure double-layer bubbles in quadratic F (R ) gravity

    NASA Astrophysics Data System (ADS)

    Eiroa, Ernesto F.; Figueroa Aguirre, Griselda; Senovilla, José M. M.

    2017-06-01

    We present a class of spherically symmetric spacetimes corresponding to bubbles separating two regions with constant values of the scalar curvature, or equivalently with two different cosmological constants, in quadratic F (R ) theory. The bubbles are obtained by means of the junction formalism, and the matching hypersurface supports in general a thin shell and a gravitational double layer. In particular, we find that pure double layers are possible for appropriate values of the parameters of the model whenever the quadratic coefficient is negative. This is the first example of a pure double layer in a gravitational theory.

  12. Double-peaked sodium layers at high latitudes

    NASA Technical Reports Server (NTRS)

    Von Zahn, U.; Goldberg, R. A.; Stegman, J.; Witt, G.

    1989-01-01

    Na lidar observations indicate that at high latitudes in summer the neutral Na layer frequently attains a double-peaked structure. The main layer with a maximum near 90 km altitude is supplemented by a secondary, narrow layer near 95 km altitude. Results are presented concerning secondary sodium layers. It appears likely that the formation of secondary Na layers observed frequently above the lidar site is not solely a 'sodium phenomenon', but part of a more comprehensive layering process for metal atoms and ions. Na(+)/Na density ratios close to 0.5 near the peaks of both the main and secondary layers are derived.

  13. Double-peaked sodium layers at high latitudes

    NASA Technical Reports Server (NTRS)

    Von Zahn, U.; Goldberg, R. A.; Stegman, J.; Witt, G.

    1989-01-01

    Na lidar observations indicate that at high latitudes in summer the neutral Na layer frequently attains a double-peaked structure. The main layer with a maximum near 90 km altitude is supplemented by a secondary, narrow layer near 95 km altitude. Results are presented concerning secondary sodium layers. It appears likely that the formation of secondary Na layers observed frequently above the lidar site is not solely a 'sodium phenomenon', but part of a more comprehensive layering process for metal atoms and ions. Na(+)/Na density ratios close to 0.5 near the peaks of both the main and secondary layers are derived.

  14. Double sodium layer observation over Beijing, China by lidar

    NASA Astrophysics Data System (ADS)

    Wang, Jihong; Yang, Guotao; Yong, Yang; Song, Shalei; Gong, Shunsheng; Cheng, Xuewu

    2012-07-01

    The sodium layer is usually located between 80-105 km. The double sodium layer (DSL) event observed by sodium lidar (light detection and radar) over Wuhan extend the altitude to about 125km. A secondary sodium layer appeared above the normal sodium layer. However, the exact mechanism responsible for the DSL formation is still unclear, due to lack of DSL events observed. In this paper, we reports a series of double sodium layer events observed by sodium lidar over Beijing, China. About ten DSL events occurred during 2010 and 2011. All DSL events were observed in summer. The SeSL last about several hours and joined the normal sodium layer, which seems its loss mechanism. When the SeSL disappeared, the sporadic sodium layer occurred in the normal sodium layer.

  15. Two-dimensional quasi-double-layers in two-electron-temperature, current-free plasmas

    SciTech Connect

    Merino, Mario; Ahedo, Eduardo

    2013-02-15

    The expansion of a plasma with two disparate electron populations into vacuum and channeled by a divergent magnetic nozzle is analyzed with an axisymmetric model. The purpose is to study the formation and two-dimensional shape of a current-free double-layer in the case when the electric potential steepening can still be treated within the quasineutral approximation. The properties of this quasi-double-layer are investigated in terms of the relative fraction of the high-energy electron population, its radial distribution when injected into the nozzle, and the geometry and intensity of the applied magnetic field. The two-dimensional double layer presents a curved shape, which is dependent on the natural curvature of the equipotential lines in a magnetically expanded plasma and the particular radial distribution of high-energy electrons at injection. The double layer curvature increases the higher the nozzle divergence is, the lower the magnetic strength is, and the more peripherally hot electrons are injected. A central application of the study is the operation of a helicon plasma thruster in space. To this respect, it is shown that the curvature of the double layer does not increment the thrust, it does not modify appreciably the downstream divergence of the plasma beam, but it increases the magnetic-to-pressure thrust ratio. The present study does not attempt to cover current-free double layers involving plasmas with multiple populations of positive ions.

  16. Superior coagulation of graphene oxides on nanoscale layered double hydroxides and layered double oxides.

    PubMed

    Zou, Yidong; Wang, Xiangxue; Chen, Zhongshan; Yao, Wen; Ai, Yuejie; Liu, Yunhai; Hayat, Tasawar; Alsaedi, Ahmed; Alharbi, Njud S; Wang, Xiangke

    2016-12-01

    With the development and application of graphene oxides (GO), the potential toxicity and environmental behavior of GO has become one of the most forefront environmental problems. Herein, a novel nanoscale layered double hydroxides (glycerinum-modified nanocrystallined Mg/Al layered double hydroxides, LDH-Gl), layered double oxides (calcined LDH-Gl, LDO-Gl) and metallic oxide (TiO2) were synthesized and applied as superior coagulants for the efficient removal of GO from aqueous solutions. Coagulation of GO as a function of coagulant contents, pH, ionic strength, GO contents, temperature and co-existing ions were studied and compared, and the results showed that the maximum coagulation capacities of GO were LDO-Gl (448.3 mg g(-1)) > TiO2 (365.7 mg g(-1)) > LDH-Gl (339.1 mg g(-1)) at pH 5.5, which were significantly higher than those of bentonite, Al2O3, CaCl2 or other natural materials due to their stronger reaction active and interfacial effect. The presence of SO3(2-) and HCO3(-) inhibited the coagulation of GO on LDH-Gl and LDO-Gl significantly, while other cations (K(+), Mg(2+), Ca(2+), Ni(2+), Al(3+)) or anion (Cl(-)) had slightly effect on GO coagulation. The interaction mechanism of GO coagulation on LDO-Gl and TiO2 might due to the electrostatic interactions and strong surface complexation, while the main driving force of GO coagulation on LDH-Gl might be attributed to electrostatic interaction and hydrogen bond, which were further evidenced by TEM, SEM, FT-IR and XRD analysis. The results of natural environmental simulation showed that LDO-Gl, TiO2 or other kinds of natural metallic oxides could be superior coagulants for the efficient elimination of GO or other toxic nanomaterials from aqueous solutions in real environmental pollution cleanup.

  17. Enhanced intervalley scattering in artificially stacked double-layer graphene

    NASA Astrophysics Data System (ADS)

    Iqbal, M. Z.; Kelekçi, Özgür; Iqbal, M. W.; Jin, Xiaozhan; Hwang, Chanyong; Eom, Jonghwa

    2014-08-01

    We fabricated artificially stacked double-layer graphene by sequentially transferring graphene grown by chemical vapor deposition. The double-layer graphene was characterized by Raman spectroscopy and transport measurements. A weak localization effect was observed for different charge carrier densities and temperatures. The obtained intervalley scattering rate was unusually high compared to normal Bernal-stacked bilayer or single-layer graphene. The sharp point defects, local deformation, or bending of graphene plane required for intervalley scattering from one Dirac cone to another seemed to be enhanced by the artificially stacked graphene layers.

  18. Quantum electron-acoustic double layers in a magnetoplasma

    SciTech Connect

    Misra, A. P.; Samanta, S.

    2008-12-15

    Using a quantum magnetohydrodynamic (QMHD) model, the existence of small but finite amplitude quantum electron-acoustic double layers (QEADLs) is reported in a magnetized collisionless dense quantum plasma whose constituents are two distinct groups of cold and hot electrons, and the stationary ions forming only the neutralizing background. It is shown that the existence of steady state solutions of these double layers obtained from an extended Korteweg-de Vries (KdV) equation depends parametrically on the ratio of the cold to hot electron unperturbed number density ({delta}), the quantum diffraction parameter (H), the obliqueness parameter (l{sub z}), and the external magnetic field via the normalized electron-cyclotron frequency ({omega}). It is found that the system supports both compressive and rarefactive double layers depending on the parameters {delta} and l{sub z}. The effects of all these parameters on the profiles of the double layers are also examined numerically.

  19. Dust-acoustic double layers - Ion inertial effects

    NASA Technical Reports Server (NTRS)

    Mace, Richard L.; Hellberg, Manfred A.

    1993-01-01

    Space and astrophysical plasmas often comprise a number of massive ion components in addition to a tenuous, negatively charged dust component and an electron component. Stationary electrostatic double layers in a dusty plasma are investigated in a model treating the ion components as Boltzmann-distributed (inertialess) fluids. On comparison with the inertialess theory, one finds considerably reduced double layer existence parameter regimes. Significantly, highly nonlinear double layers are ruled out when ion inertia is incorporated. However, in the restricted parameter regimes in which the inertial theory predicts double layers for small ion/dust mass ratios (about 10 exp -15-10 exp -8) there is good qualitative agreement with inertialess theory. The reasons for these, and other discrepancies and similarities, are discussed.

  20. Morphologies, Preparations and Applications of Layered Double Hydroxide Micro-/Nanostructures

    PubMed Central

    Kuang, Ye; Zhao, Lina; Zhang, Shuai; Zhang, Fazhi; Dong, Mingdong; Xu, Sailong

    2010-01-01

    Layered double hydroxides (LDHs), also well-known as hydrotalcite-like layered clays, have been widely investigated in the fields of catalysts and catalyst support, anion exchanger, electrical and optical functional materials, flame retardants and nanoadditives. This feature article focuses on the progress in micro-/nanostructured LDHs in terms of morphology, and also on the preparations, applications, and perspectives of the LDHs with different morphologies.

  1. Layered double hydroxide stability. 1. Relative stabilities of layered double hydroxides and their simple counterparts

    NASA Technical Reports Server (NTRS)

    Boclair, J. W.; Braterman, P. S.

    1999-01-01

    Solutions containing di- and trivalent metal chlorides [M(II) = Mg2+, Zn2+, Co2+, Ni2+, Mn2+; M(III) = Al3+, Fe3+] were titrated with NaOH to yield hydrotalcite-like layered double hydroxides (LDH), [[M(II)]1-x[M(III)]x(OH)2][Cl]x yH2O, by way of M(III) hydroxide/hydrous oxide intermediates. Analysis of the resultant titration curves yields nominal solubility constants for the LDH. The corresponding LDH stabilities are in the order Mg < Mn < Co approximately Ni < Zn for M(II) and Al < Fe for M(III). The stability of LDH relative to the separate metal hydroxides/hydrous oxides is discussed.

  2. Layered double hydroxide stability. 1. Relative stabilities of layered double hydroxides and their simple counterparts

    NASA Technical Reports Server (NTRS)

    Boclair, J. W.; Braterman, P. S.

    1999-01-01

    Solutions containing di- and trivalent metal chlorides [M(II) = Mg2+, Zn2+, Co2+, Ni2+, Mn2+; M(III) = Al3+, Fe3+] were titrated with NaOH to yield hydrotalcite-like layered double hydroxides (LDH), [[M(II)]1-x[M(III)]x(OH)2][Cl]x yH2O, by way of M(III) hydroxide/hydrous oxide intermediates. Analysis of the resultant titration curves yields nominal solubility constants for the LDH. The corresponding LDH stabilities are in the order Mg < Mn < Co approximately Ni < Zn for M(II) and Al < Fe for M(III). The stability of LDH relative to the separate metal hydroxides/hydrous oxides is discussed.

  3. On The Chaotic Dynamics Of Multiple Double Layers In Plasma

    SciTech Connect

    Ivan, L. M.; Chiriac, S. A.; Aflori, M.; Dimitriu, D. G.

    2007-04-23

    When a multiple double layers structure in plasma is driven far from equilibrium, it passes into a chaotic state, characterized by uncorrelated oscillations of the plasma parameters. Two scenarios of transition to chaos were identified: the Feigenbaum scenario (cascade of period doubling bifurcations) and the intermittency scenario.

  4. Mixed layer development in a double-diffusive, thermohaline system

    SciTech Connect

    Poplawsky, C.J.; Incropera, F.P.; Viskanta, R.

    1981-11-01

    A double-diffusive, thermohaline system has been studied under laboratory conditions involving uniform heating from below. Shadowgraph visualization has been used with temperature and salt concentration measurements to investigate mixing layer development and the onset of diffusion layer instabilities. Such instabilities were observed to occur in two of the experiments and were approximately predicted by an existing stability criterion. 17 refs.

  5. Fabrication of double layer optical tissue phantom by spin coating method: mimicking epidermal and dermal layer

    NASA Astrophysics Data System (ADS)

    Park, Jihoon; Bae, Yunjin; Bae, Youngwoo; Kang, Heesung; Lee, Kyoung-Joung; Jung, Byungjo

    2013-02-01

    Methodologies to fabricate a solid optical tissue phantom (OTP) mimicking epidermal thin-layer have been developed for in vitro human skin experiment. However, there are cumbersome and time-consuming efforts in fabrication process such as a custom-made casting and calculation of solvent volume before curing process. In a previous study, we introduced a new methodology based on spin coating method (SCM) which is utilized to fabricate a thin-layer OTP analogous to epidermal thickness. In this study, a double layer solid OTP which has epidermal and dermal layers was fabricated to mimic the morphological and optical similarity of human tissue. The structural characteristic and optical properties of fabricated double layer OTP were measured using optical coherence tomography and inverse adding doubling algorithms, respectively. It is expected that the new methodology based on the SCM may be usefully used in the fabrication of double layer OTP.

  6. Surface-plasmons lasing in double-graphene-layer structures

    SciTech Connect

    Dubinov, A. A.; Aleshkin, V. Ya.; Ryzhii, V.; Shur, M. S.; Otsuji, T.

    2014-01-28

    We consider the concept of injection terahertz lasers based on double-graphene-layer (double-GL) structures with metal surface-plasmon waveguide and study the conditions of their operation. The laser under consideration exploits the resonant radiative transitions between GLs. This enables the double-GL laser room temperature operation and the possibility of voltage tuning of the emission spectrum. We compare the characteristics of the double-GL lasers with the metal surface-plasmon waveguides with those of such laser with the metal-metal waveguides.

  7. Multilabel Image Annotation Based on Double-Layer PLSA Model

    PubMed Central

    Zhang, Jing; Li, Da; Hu, Weiwei; Chen, Zhihua; Yuan, Yubo

    2014-01-01

    Due to the semantic gap between visual features and semantic concepts, automatic image annotation has become a difficult issue in computer vision recently. We propose a new image multilabel annotation method based on double-layer probabilistic latent semantic analysis (PLSA) in this paper. The new double-layer PLSA model is constructed to bridge the low-level visual features and high-level semantic concepts of images for effective image understanding. The low-level features of images are represented as visual words by Bag-of-Words model; latent semantic topics are obtained by the first layer PLSA from two aspects of visual and texture, respectively. Furthermore, we adopt the second layer PLSA to fuse the visual and texture latent semantic topics and achieve a top-layer latent semantic topic. By the double-layer PLSA, the relationships between visual features and semantic concepts of images are established, and we can predict the labels of new images by their low-level features. Experimental results demonstrate that our automatic image annotation model based on double-layer PLSA can achieve promising performance for labeling and outperform previous methods on standard Corel dataset. PMID:24999490

  8. Interfacial double layer mediated electrochemical growth of thin-walled platinum nanotubes

    NASA Astrophysics Data System (ADS)

    Zhang, Liqiu; Kim, Sang Min; Cho, Sanghyun; Jang, Hee-Jeong; Liu, Lichun; Park, Sungho

    2017-01-01

    This work demonstrates that thin-walled platinum nanotubes can be readily synthesized by controlling the interfacial double layer in alumina nanochannels. The gradient distribution of ions in nanochannels enables the creation of Pt nanotubes with walls as thin as 5 nm at the top end when using a solution containing polyvinylpyrrolidone (PVP) and chloroplatinic acid (H2PtCl6) under the influence of an electric potential in nanochannels. The highly efficient formation of thin-walled Pt nanotubes is a result of the concentration gradient of {{{{PtCl}}}6}2- and a thick double layer, which was caused by the low concentration of Pt precursors and the enhanced surface charge density induced by protonated PVP steric adsorption. This well-controlled synthesis reveals that the interfacial double layer is a useful tool to tailor the structure of nanomaterials in a nanoscale space, and holds promise in the construction of more complex functional nanostructures.

  9. Gas flows through double-layer membrane of thermomolecular pump

    NASA Astrophysics Data System (ADS)

    Oscar, Friedlander; Yuriy, Nikolskiy; Ivan, Voronich

    2014-12-01

    The results of numerical and experimental modeling of the flows in double-layer permeable membranes are presented. One of the layers, the thick one, is the supporting layer in which the perforation diameter is larger than that in the thin layer. Across one or both layers the temperature differences were created. The calculations of the flows inside the perforated channels and additional drag of the channels in the membrane thick layer were carried out with the Stokes equations and with the kinetic boundary conditions across the membrane thin layer. In the experimental research of the thermomolecular pressure difference the thermoelectric effect (the Peltier effect) was used for creating the temperature difference between the membrane layer surfaces.

  10. Topological phases in double layers of bismuthene and antimonene

    NASA Astrophysics Data System (ADS)

    Wang, Xiaoxiong; Bian, Guang; Xu, Caizhi; Wang, Peng; Hu, Huanzhi; Zhou, Weiping; Brown, S. A.; Chiang, T.-C.

    2017-09-01

    Two-dimensional topological insulators show great promise for spintronic applications. Much attention has been placed on single atomic or molecular layers, such as bismuthene. The selections of such materials are, however, limited. To broaden the base of candidate materials with desirable properties for applications, we report herein an exploration of the physics of double layers of bismuthene and antimonene. The electronic structure of a film depends on the number of layers, and it can be modified by epitaxial strain, by changing the effective spin–orbit coupling strength, and by the manner in which the layers are geometrically stacked. First-principles calculations for the double layers reveal a number of phases, including topological insulators, topological semimetals, Dirac semimetals, trivial semimetals, and trivial insulators. Their phase boundaries and the stability of the phases are investigated. The results illustrate a rich pattern of phases that can be realized by tuning lattice strain and effective spin–orbit coupling.

  11. Stable electrolyte for high voltage electrochemical double-layer capacitors

    DOE PAGES

    Ruther, Rose E.; Sun, Che -Nan; Holliday, Adam; ...

    2016-12-28

    A simple electrolyte consisting of NaPF6 salt in 1,2-dimethoxyethane (DME) can extend the voltage window of electric double-layer capacitors (EDLCs) to >3.5 V. DME does not passivate carbon electrodes at very negative potentials (near Na/Na+), extending the practical voltage window by about 1.0 V compared to standard, non-aqueous electrolytes based on acetonitrile. The voltage window is demonstrated in two- and three-electrode cells using a combination of electrochemical impedance spectroscopy (EIS), charge-discharge cycling, and measurements of leakage current. DME-based electrolytes cannot match the high conductivity of acetonitrile solutions, but they can satisfy applications that demand high energy density at moderate power.more » The conductivity of NaPF6 in DME is comparable to commercial lithium-ion battery electrolytes and superior to most ionic liquids. Lastly, factors that limit the voltage window and EDLC energy density are discussed, and strategies to further boost energy density are proposed.« less

  12. Stable electrolyte for high voltage electrochemical double-layer capacitors

    SciTech Connect

    Ruther, Rose E.; Sun, Che -Nan; Holliday, Adam; Cheng, Shiwang; Delnick, Frank M.; Zawodzinski, Thomas A.; Nanda, Jagjit

    2016-12-28

    A simple electrolyte consisting of NaPF6 salt in 1,2-dimethoxyethane (DME) can extend the voltage window of electric double-layer capacitors (EDLCs) to >3.5 V. DME does not passivate carbon electrodes at very negative potentials (near Na/Na+), extending the practical voltage window by about 1.0 V compared to standard, non-aqueous electrolytes based on acetonitrile. The voltage window is demonstrated in two- and three-electrode cells using a combination of electrochemical impedance spectroscopy (EIS), charge-discharge cycling, and measurements of leakage current. DME-based electrolytes cannot match the high conductivity of acetonitrile solutions, but they can satisfy applications that demand high energy density at moderate power. The conductivity of NaPF6 in DME is comparable to commercial lithium-ion battery electrolytes and superior to most ionic liquids. Lastly, factors that limit the voltage window and EDLC energy density are discussed, and strategies to further boost energy density are proposed.

  13. Analytical model of LDMOS with a double step buried oxide layer

    NASA Astrophysics Data System (ADS)

    Yuan, Song; Duan, Baoxing; Cao, Zhen; Guo, Haijun; Yang, Yintang

    2016-09-01

    In this paper, a two-dimensional analytical model is established for the Buried Oxide Double Step Silicon On Insulator structure proposed by the authors. Based on the two-dimensional Poisson equation, the analytic expressions of the surface electric field and potential distributions for the device are achieved. In the BODS (Buried Oxide Double Step Silicon On Insulator) structure, the buried oxide layer thickness changes stepwise along the drift region, and the positive charge in the drift region can be accumulated at the corner of the step. These accumulated charge function as the space charge in the depleted drift region. At the same time, the electric field in the oxide layer also varies with the different drift region thickness. These variations especially the accumulated charge will modulate the surface electric field distribution through the electric field modulation effects, which makes the surface electric field distribution more uniform. As a result, the breakdown voltage of the device is improved by 30% compared with the conventional SOI structure. To verify the accuracy of the analytical model, the device simulation software ISE TCAD is utilized, the analytical values are in good agreement with the simulation results by the simulation software. That means the established two-dimensional analytical model for BODS structure is valid, and it also illustrates the breakdown voltage enhancement by the electric field modulation effect sufficiently. The established analytical models will provide the physical and mathematical basis for further analysis of the new power devices with the patterned buried oxide layer.

  14. Structural and electrical properties of Pb(Zr ,Ti)O3 grown on (0001) GaN using a double PbTiO3/PbO bridge layer

    NASA Astrophysics Data System (ADS)

    Xiao, Bo; Gu, Xing; Izyumskaya, Natalia; Avrutin, Vitaliy; Xie, Jinqiao; Liu, Huiyong; Morkoç, Hadis

    2007-10-01

    Pb(Zr0.52Ti0.48)O3 films were deposited by rf magnetron sputtering on silicon-doped GaN(0001)/c-sapphire with a PbTiO3/PbO oxide bridge layer grown by molecular beam epitaxy. X-ray diffraction data showed the highly (111)-oriented perovskite phase in lead zirconate titanate (PZT) films with PbTiO3/PbO bridge layers, compared to the pyrochlore phase grown directly on GaN. The in-plane epitaxial relationships were found from x-ray pole figures to be PZT[112¯]‖GaN[11¯00] and PZT[11¯0]‖GaN[112¯0]. The polarization-electric field measurements revealed the ferroelectric behavior with remanent polarization of 30-40μC /cm2 and asymmetric hysteresis loops due to the depletion layer formed in GaN under reverse bias which resulted in a high negative coercive electric field (950kV/cm).

  15. Electrochemical double-layer capacitors based on functionalized graphene

    NASA Astrophysics Data System (ADS)

    Pope, Michael Allan

    Graphene is a promising electrode material for electrochemical double-layer capacitors (EDLCs) used for energy storage due to its high electrical conductivity and theoretical specific surface area. However, the intrinsic capacitance of graphene is known to be low and governed by the electronic side of the interface. Furthermore, graphene tends to aggregate and stack together when processed into thick electrode films. This significantly lowers the ion-accessible specific surface area (SSA). Maximizing both the SSA and the intrinsic capacitance are the main problems addressed in this thesis in an effort to improve the specific capacitance and energy density of EDLCs. In contrast to pristine graphene, functionalized graphene produced by the thermal exfoliation of graphite oxide contains residual functional groups and lattice defects. To study how these properties affect the double-layer capacitance, a model electrode system capable of measuring the intrinsic electrochemical properties of functionalized graphene was developed. To prevent artifacts and uncertainties related to measurements on porous electrodes, the functionalized graphene sheets (FGSs) were assembled as densely tiled monolayers using a Langmuir-Blodgett technique. In this way, charging can be studied in a well-defined 2D geometry. The possibility of measuring and isolating the intrinsic electrochemical properties of FGS monolayers was first demonstrated by comparing capacitance and redox probe measurements carried out on coatings deposited on passivated gold and single crystal graphite substrates. This monolayer system was then used to follow the double-layer capacitance of the FGS/electrolyte interface as the structure and chemistry of graphene was varied by thermal treatments ranging from 300 °C to 2100 °C. Elemental analysis and Raman spectroscopy were used to determine the resulting chemical and structural transformation upon heat treatment. It was demonstrated that intrinsically defective

  16. Double layer -- a particle accelerator in the magnetosphere

    SciTech Connect

    Fu, Xiangrong

    2015-07-16

    Slides present the material under the following topics: Introduction (What is a double layer (DL)? Why is it important? Key unsolved problems); Theory -- time-independent solutions of 1D Vlasov--Poisson system; Particle-in-cell simulations (Current-driven DLs); and Electron acceleration by DL (Betatron acceleration). Key problems include the generation mechanism, stability, and electron acceleration. In summary, recent observations by Van Allen Probes show large number of DLs in the outer radiation belt, associated with enhanced flux of relativistic electrons. Simulations show that ion acoustic double layers can be generated by field-aligned currents. Thermal electrons can gain energy via betatron acceleration in a dipole magnetic field.

  17. Validity of the "thin" and "thick" double-layer assumptions to model streaming currents in porous media

    NASA Astrophysics Data System (ADS)

    Leinov, E.; Jackson, M.

    2012-12-01

    Measurements of the streaming potential component of the spontaneous potential have been used to characterize groundwater flow and subsurface hydraulic properties in numerous studies. Streaming potentials in porous media arise from the electrical double layer which forms at solid-fluid interfaces. The solid surfaces typically become electrically charged, in which case an excess of counter-charge accumulates in the adjacent fluid. If the fluid is induced to flow by an external pressure gradient, then some of the excess charge within the diffuse part of the double layer is transported with the flow, giving rise to a streaming current. Divergence of the streaming current density establishes an electrical potential, termed the streaming potential. Within the diffuse layer, the Poisson-Boltzmann equation is typically used to describe the variation in electrical potential with distance from the solid surface. In many subsurface settings, it is reasonable to assume that the thickness of the diffuse layer is small compared to the pore radius. This is the so-called 'thin double layer assumption', which has been invoked by numerous authors to model streaming potentials in porous media. However, a number of recent papers have proposed a different approach, in which the thickness of the diffuse layer is assumed to be large compared to the pore radius. This is the so-called 'thick double layer assumption' in which the excess charge density within the pore is assumed to be constant and independent of distance from the solid surface. The advantage of both the 'thin' and 'thick' double layer assumptions is that calculation of the streaming current is greatly simplified. However, perhaps surprisingly, the conditions for which these assumptions are valid have not been determined quantitatively, yet they have a significant impact on the interpretation of streaming potential measurements in natural systems. We use a simple capillary tubes to model investigate the validity of the thin

  18. Double-layered cell transfer technology for bone regeneration.

    PubMed

    Akazawa, Keiko; Iwasaki, Kengo; Nagata, Mizuki; Yokoyama, Naoki; Ayame, Hirohito; Yamaki, Kazumasa; Tanaka, Yuichi; Honda, Izumi; Morioka, Chikako; Kimura, Tsuyoshi; Komaki, Motohiro; Kishida, Akio; Izumi, Yuichi; Morita, Ikuo

    2016-09-14

    For cell-based medicine, to mimic in vivo cellular localization, various tissue engineering approaches have been studied to obtain a desirable arrangement of cells on scaffold materials. We have developed a novel method of cell manipulation called "cell transfer technology", enabling the transfer of cultured cells onto scaffold materials, and controlling cell topology. Here we show that using this technique, two different cell types can be transferred onto a scaffold surface as stable double layers or in patterned arrangements. Various combinations of adherent cells were transferred to a scaffold, amniotic membrane, in overlapping bilayers (double-layered cell transfer), and transferred cells showed stability upon deformations of the material including folding and trimming. Transplantation of mesenchymal stem cells from periodontal ligaments (PDLSC) and osteoblasts, using double-layered cell transfer significantly enhanced bone formation, when compared to single cell type transplantation. Our findings suggest that this double-layer cell transfer is useful to produce a cell transplantation material that can bear two cell layers. Moreover, the transplantation of an amniotic membrane with PDLSCs/osteoblasts by cell transfer technology has therapeutic potential for bone defects. We conclude that cell transfer technology provides a novel and unique cell transplantation method for bone regeneration.

  19. Double-layered cell transfer technology for bone regeneration

    PubMed Central

    Akazawa, Keiko; Iwasaki, Kengo; Nagata, Mizuki; Yokoyama, Naoki; Ayame, Hirohito; Yamaki, Kazumasa; Tanaka, Yuichi; Honda, Izumi; Morioka, Chikako; Kimura, Tsuyoshi; Komaki, Motohiro; Kishida, Akio; Izumi, Yuichi; Morita, Ikuo

    2016-01-01

    For cell-based medicine, to mimic in vivo cellular localization, various tissue engineering approaches have been studied to obtain a desirable arrangement of cells on scaffold materials. We have developed a novel method of cell manipulation called “cell transfer technology”, enabling the transfer of cultured cells onto scaffold materials, and controlling cell topology. Here we show that using this technique, two different cell types can be transferred onto a scaffold surface as stable double layers or in patterned arrangements. Various combinations of adherent cells were transferred to a scaffold, amniotic membrane, in overlapping bilayers (double-layered cell transfer), and transferred cells showed stability upon deformations of the material including folding and trimming. Transplantation of mesenchymal stem cells from periodontal ligaments (PDLSC) and osteoblasts, using double-layered cell transfer significantly enhanced bone formation, when compared to single cell type transplantation. Our findings suggest that this double-layer cell transfer is useful to produce a cell transplantation material that can bear two cell layers. Moreover, the transplantation of an amniotic membrane with PDLSCs/osteoblasts by cell transfer technology has therapeutic potential for bone defects. We conclude that cell transfer technology provides a novel and unique cell transplantation method for bone regeneration. PMID:27624174

  20. Does the plasma radiate near a Double Layer?

    NASA Astrophysics Data System (ADS)

    Pottelette, Raymond; Berthomier, Matthieu; Pickett, Jolene

    2016-04-01

    Earth is an intense radio source in the kilometer wavelength range. Being a direct consequence of the parallel acceleration processes taking place in the Earth's auroral region, the radiation contains fundamental information on the characteristic spatial and temporal scales of the turbulent accelerating layer. It is now widely assumed that the cyclotron maser instability leads to Auroral Kilometric Radiation (AKR) generation. It has been suggested from the FAST measurements that the AKR results from a so-called horseshoe electron distribution. This distribution is generated when a localized parallel electric field - called Double Layer (DL) - accelerates earthward the electrons that propagate into an increasing magnetic field. The magnetic moment of the electrons is conserved so that their pitch angle is increased. This results in the creation of a horseshoe-like shape for the electron distribution exhibiting large positive velocity gradients in the direction perpendicular to B, thereby providing free energy for the AKR generation which takes place at the local electron gyrofrequency. In these circumstances, the radiation is generated far away (several thousand kilometers) from a DL, because the parallel accelerated electrons need to travel a long distance before forming a horseshoe distribution. From an experimental point of view, it is not an easy task to highlight the presence of DLs, because they are moving transient structures so that high time resolution measurements are needed. A detailed analysis suggests that these large-amplitude parallel electric fields are located inside sharp density gradients at the interface separating the cold, dense ionospheric plasma from the hot, tenuous magnetospheric plasma. We present some FAST observations which illustrate the generation of elementary radiation events in the neighborhood of a DL. The events occur 10 to 20% above the local electron gyrofrequency in association with the presence of nonlinear coherent structures

  1. Two-dimensional double layer in plasma in a diverging magnetic field

    NASA Astrophysics Data System (ADS)

    Saha, S. K.; Raychaudhuri, S.; Chowdhury, S.; Janaki, M. S.; Hui, A. K.

    2012-09-01

    Plasma created by an inductive RF discharge is allowed to expand along a diverging magnetic field. Measurement of the axial plasma potential profile reveals the formation of an electric double layer near the throat of the expansion chamber. An accelerated ion beam has been detected in the downstream region, confirming the presence of the double layer. The 2-D nature of the ion energy distribution function of the downstream plasma has been studied by a movable ion energy analyser, which shows that the beam radius increases along the axial distance. The 2-D structure of the plasma potential has been studied by a movable emissive probe. The existence of a secondary lobe in the contour plot of plasma equipotential is a new observation. It is also an interesting observation that the most diverging magnetic field line not intercepting the junction of the discharge tube and the expansion chamber has an electric field aligned with it.

  2. Coulomb Drag and Magnetotransport in Graphene Double Layers

    NASA Astrophysics Data System (ADS)

    Tutuc, Emanuel

    2013-03-01

    Graphene double layers, a set of two closely spaced graphene monolayers seperated by an ultra-thin dielectric, represent an interesting electron system to explore correlated electron states. We discuss the fabrication of such samples using a layer-by-layer transfer approach, the electron transport in individual layers at zero and in a high magnetic field, and Coulomb drag measurements. Coulomb drag, probed by flowing a drive current in one layer, and measuring the voltage drop in the opposite layer provides a direct measurement of the electron-electron scattering between the two layers, and can be used to probe the electron system ground state. Coulomb drag in graphene, measured as a function of both layer densities and temperature reveals two distinct regimes: (i) diffusive drag at elevated temperatures, above 50 K, and (ii) mesoscopic fluctuations-dominated drag at low temperatures. A second topic discussed here is a technique that allows a direct measurement of the Fermi energy in an electron system with an accuracy independent of the sample size, using a graphene double layer heterostructure. The underlying principle of the technique is that an interlayer bias applied to bring the top layer to the charge neutrality point is equal to the Fermi energy of the bottom layer, which in effect renders the top graphene layer a resistively detected Kelvin probe. We illustrate this method by measuring the Fermi velocity, Landau level spacing, and Landau level broadening in monolayer graphene. Work done in collaboration with S. Kim, I. Jo, J. Nah, D. Dillen, K. Lee, B. Fallahazad, Z. Yao, and S. K. Banerjee. We thank ONR, NRI, and NSF for support.

  3. Study of the anode plasma double layer: optogalvanic detectors

    SciTech Connect

    Gurlui, S.; Dimitriu, D.; Strat, M.; Strat, Georgeta

    2006-01-15

    The experimental and theoretical results show that the anode double layer (DL) is a very sensitive plasma formation suitable for fine optogalvanic studies. The obtained results demonstrate that the parameters of the oscillations sustained by a DL (frequency, amplitude) can be used as optogalvanic detectors.

  4. Double layer formation at the interface of complex plasmas

    SciTech Connect

    Yaroshenko, V. V.; Thoma, M. H.; Thomas, H. M.; Morfill, G. E.

    2008-08-15

    Necessary conditions are formulated for the generation of a double layer at the interface of a complex plasma and a particle-free electron-ion plasma in a weakly collisional discharge. Examples are calculated for realistic observed complex plasmas, and it is shown that situations of both ''smooth'' transitions and 'sharp' transitions can exist. The model can explain the abrupt boundaries observed.

  5. The Role of Superthermal Electrons in the Formation of Double Layers and their Application in Space Plasmas

    NASA Astrophysics Data System (ADS)

    Singh, N.

    2014-12-01

    It is now widely recognized that superthermal electrons commonly exist with the thermal population in most space plasmas. When plasmas consisting of such electron population expand, double layers (DLs) naturally forma due to charge separation; the more mobile superthermal electrons march ahead of the thermal population, leaving a positive charge behind and generating electric fields. Under certain conditions such fields evolve into thin double layers or shocks. The double layers accelerate ions. Such double-layer formation was first invoked to explain expansion of laser produced plasmas. Since then it has been studied in laboratory experiments, and applied to (i) polar wind acceleration,(ii) the existence of low-altitude double layers in the auroral acceleration, (iii) a possible mechanism for the origination of the solar wind, (iv) the helicon double layer thrusters, and (v) the deceleration of electrons after their acceleration in solar flare events. The role of superthermal-electron driven double layers, also known as the low-altitude auroral double layers in the upward current region, in the upward acceleration of ionospheric ions is well-known. In the auroral application the upward moving superthermal electrons consist of backscattered downgoing primary energetic electrons as well as the secondary electrons. Similarly we suggest that such double layers might play roles in the acceleration of ions in the solar wind across the coronal transition region, where the superthermal electrons are supplied by magnetic reconnection events. We will present a unified theoretical view of the superthermal electron-driven double layers and their applications. We will summarize theoretical, experimental, simulation and observational results highlighting the common threads running through the various existing studies.

  6. Megavolt parallel potentials arising from double-layer streams in the Earth's outer radiation belt.

    PubMed

    Mozer, F S; Bale, S D; Bonnell, J W; Chaston, C C; Roth, I; Wygant, J

    2013-12-06

    Huge numbers of double layers carrying electric fields parallel to the local magnetic field line have been observed on the Van Allen probes in connection with in situ relativistic electron acceleration in the Earth's outer radiation belt. For one case with adequate high time resolution data, 7000 double layers were observed in an interval of 1 min to produce a 230,000 V net parallel potential drop crossing the spacecraft. Lower resolution data show that this event lasted for 6 min and that more than 1,000,000 volts of net parallel potential crossed the spacecraft during this time. A double layer traverses the length of a magnetic field line in about 15 s and the orbital motion of the spacecraft perpendicular to the magnetic field was about 700 km during this 6 min interval. Thus, the instantaneous parallel potential along a single magnetic field line was the order of tens of kilovolts. Electrons on the field line might experience many such potential steps in their lifetimes to accelerate them to energies where they serve as the seed population for relativistic acceleration by coherent, large amplitude whistler mode waves. Because the double-layer speed of 3100  km/s is the order of the electron acoustic speed (and not the ion acoustic speed) of a 25 eV plasma, the double layers may result from a new electron acoustic mode. Acceleration mechanisms involving double layers may also be important in planetary radiation belts such as Jupiter, Saturn, Uranus, and Neptune, in the solar corona during flares, and in astrophysical objects.

  7. Megavolt Parallel Potentials Arising from Double-Layer Streams in the Earth's Outer Radiation Belt

    NASA Astrophysics Data System (ADS)

    Mozer, F. S.; Bale, S. D.; Bonnell, J. W.; Chaston, C. C.; Roth, I.; Wygant, J.

    2013-12-01

    Huge numbers of double layers carrying electric fields parallel to the local magnetic field line have been observed on the Van Allen probes in connection with in situ relativistic electron acceleration in the Earth’s outer radiation belt. For one case with adequate high time resolution data, 7000 double layers were observed in an interval of 1 min to produce a 230 000 V net parallel potential drop crossing the spacecraft. Lower resolution data show that this event lasted for 6 min and that more than 1 000 000 volts of net parallel potential crossed the spacecraft during this time. A double layer traverses the length of a magnetic field line in about 15 s and the orbital motion of the spacecraft perpendicular to the magnetic field was about 700 km during this 6 min interval. Thus, the instantaneous parallel potential along a single magnetic field line was the order of tens of kilovolts. Electrons on the field line might experience many such potential steps in their lifetimes to accelerate them to energies where they serve as the seed population for relativistic acceleration by coherent, large amplitude whistler mode waves. Because the double-layer speed of 3100km/s is the order of the electron acoustic speed (and not the ion acoustic speed) of a 25 eV plasma, the double layers may result from a new electron acoustic mode. Acceleration mechanisms involving double layers may also be important in planetary radiation belts such as Jupiter, Saturn, Uranus, and Neptune, in the solar corona during flares, and in astrophysical objects.

  8. Anomalous Coulomb drag in bilayer graphene double layers

    NASA Astrophysics Data System (ADS)

    Liu, Xiaomeng; Taniguchi, Takashi; Watanabe, Kenji; Kim, Philip

    Bilayer graphene double-layer structure consists of two layers of bilayer graphene separated by atomically thin hexagonal boron nitride (hBN). With a perfect Fermi surface nesting and strong electron-electron interaction (ECoulomb > Ekinetic), such systems offer exciting platforms to study interaction driven phenomena, such as Coulomb drag and exciton condensation. We fabricate ultra-clean encapsulated bilayer graphene double layers with dry pick-up method. Room temperature drag measurement on our devices shows the sign of drag agree with the typical Fermi liquid behavior. However, at lower temperatures, the sign of drag reversed, indicating a new drag mechanism emerges and dominates. We measure this with different geometry, temperature, bias and gating to investigate the origin of such effect and discuss the implication of the drag sign changes.

  9. Bound States in the Continuum in double layer structures

    PubMed Central

    Li, LiangSheng; Yin, Hongcheng

    2016-01-01

    We have theoretically investigated the reflectivity spectrums of single- and double-layer photonic crystal slabs and the dielectric multilayer stack. It is shown that light can be perfectly confined in a single-layer photonic crystal slab at a given incident angle by changing the thickness, permittivity or hole radius of the structure. With a tunable double-layer photonic crystal slab, we demonstrate that the occurrence of tunable bound states in the continuum is dependent on the spacing between two slabs. Moreover, by analytically investigating the Drude lossless multilayer stack model, the spacing dependence of bound states in the continuum is characterized as the phase matching condition that illuminates these states can occur at any nonzero incident angles by adjusting the spacing. PMID:27245435

  10. Double-sensor method for detection of oscillating electric field.

    PubMed

    Ohkuma, Yasunori; Ikeyama, Taeko; Nogi, Yasuyuki

    2011-04-01

    An electric-field sensor consisting of thin copper plates is designed to measure an oscillating electric field produced by charge separations on a plasma column. The sensor installed in a vacuum region around plasma detects charges induced by the electric field on the copper plates. The value of the induced charges depends not only on the strength of the electric field, but also on the design of the sensor. To obtain the correct strength of the electric field, a correction factor arising from the design of the sensor must be known. The factor is calculated numerically using Laplace's equation and compared with a value measured using a uniform electric field in the frequency range of 10-500 kHz. When an external circuit is connected to the sensor to measure the induced charges, the electric field around the sensor is disturbed. Therefore, a double-sensor method for excluding a disturbed component in the measured electric field is proposed. The reliability of the double-sensor method is confirmed by measuring dipole-like and quadrupole-like electric fields. © 2011 American Institute of Physics

  11. Highly transparent low resistance Ga doped ZnO/Cu grid double layers prepared at room temperature

    NASA Astrophysics Data System (ADS)

    Jang, Cholho; Zhizhen, Ye; Jianguo, Lü

    2015-12-01

    Ga doped ZnO (GZO)/Cu grid double layer structures were prepared at room temperature (RT). We have studied the electrical and optical characteristics of the GZO/Cu grid double layer as a function of the Cu grid spacing distance. The optical transmittance and sheet resistance of the GZO/Cu grid double layer are higher than that of the GZO/Cu film double layer regardless of the Cu grid spacing distance and increase as the Cu grid spacing distance increases. The calculated values for the transmittance and sheet resistance of the GZO/Cu grid double layer well follow the trend of the experimentally observed transmittance and sheet resistance ones. For the GZO/Cu grid double layer with a Cu grid spacing distance of 1 mm, the highest figure of merit (ΦTC = 6.19 × 10-3 Ω-1) was obtained. In this case, the transmittance, resistivity and filling factor (FF) of the GZO/Cu grid double layer are 83.74%, 1.10 × 10-4 Ω·cm and 0.173, respectively. Project supported by the Key Project of the National Natural Science Foundation of China (No. 91333203), the Program for Innovative Research Team in University of Ministry of Education of China (No. IRT13037), the National Natural Science Foundation of China (No. 51172204), and the Zhejiang Provincial Department of Science and Technology of China (No. 2010R50020).

  12. A hybrid Mg-Al layered double hydroxide/graphene nanostructure obtained via hydrothermal synthesis

    NASA Astrophysics Data System (ADS)

    Zhao, Xiaodong; Cao, Jian-Ping; Zhao, Jun; Hu, Guo-Hua; Dang, Zhi-Min

    2014-06-01

    A hybrid Mg-Al layered double hydroxide/graphene (LDH-GR) material nanostructure has been fabricated by employing the hydrothermal treatment at 140 °C for 10 h. Graphene oxide is simultaneously reduced to graphene during the hydrothermal treatment. The LDH and LDH-GR have high degree of crystallinity and assembled layer structure, which is attributed to electrostatic interaction mechanism. The obtained hybrid nanostructure materials can be used as flame retardant or conductor of electricity and heat due to the combination of different properties arising from graphene and LDH.

  13. Ordered poly(p-phenylene)/layered double hydroxide ultrathin films with blue luminescence by layer-by-layer assembly.

    PubMed

    Yan, Dongpeng; Lu, Jun; Wei, Min; Han, Jingbin; Ma, Jing; Li, Feng; Evans, David G; Duan, Xue

    2009-01-01

    Lavender layers: A poly(p-phenylene) anionic derivate and exfoliated Mg-Al layered double hydroxide monolayers were assembled into ultrathin films with well-defined blue fluorescence (see picture; the numbers indicate the number of bilayers), long-range order, and high photostability. These films work as multiple quantum-well structures for valence electrons.

  14. Experimental investigation of current free double layers in helicon plasmas

    SciTech Connect

    Sahu, B. B.; Tarey, R. D.; Ganguli, A.

    2014-02-15

    The paper presents investigations of current free double layer (CFDL) that forms in helicon plasmas. In contrast to the other work reporting on the same subject, in the present investigations the double layer (DL) forms in a mirror-like magnetic field topology. The RF compensated Langmuir probe measurements show multiple DLs, which are in connection with, the abrupt fall of densities along with potential drop of about 24 V and 18 V. The DLs strengths (e ΔV{sub p})/(k T{sub e}) are about 9.5 and 6, and the corresponding widths are about 6 and 5 D lengths. The potential drop is nearly equal to the thermal anisotropies between the two plasma regions forming the DL, which is present in the plateau region of mirror, unlike the earlier studies on the DL formation in the region of strong gradients in the magnetic field. Also, it presents a qualitative discussion on the mechanism of DL formation.

  15. Theory of current-free double layers in plasmas

    NASA Astrophysics Data System (ADS)

    Goswami, K. S.; Saharia, K.; Schamel, H.

    2008-06-01

    The existence of current-free double layers in unmagnetized plasma is studied by means of the quasipotential method applied to the Vlasov-Poisson system. Crucial for its existence are trapped particle populations that are characterized by notches (dips) in the velocity distribution functions at resonant velocity becoming flat at large amplitude limit. The potential drop across the double layer, or its amplitude ψ, can be arbitrarily strong covering the whole range 0<ψ <∞. Both the small and large amplitude limit are worked out explicitly, inclusively effective kinetic temperatures and pressures. It is, hence, the effective electron (ion) temperature increase (decrease) with increasing potential, caused by the trapped particles, which is responsible for the existence of this two-parameter family of solutions.

  16. Provenance graph query method based on double layer index structure

    NASA Astrophysics Data System (ADS)

    Cai, Qing Qiu; Cui, Hong Gang; Tang, Hao

    2017-08-01

    Order to solve the problem that the efficiency of the existing source map is low and the resource occupancy rate is high, considering the relationship between the origin information and the data itself and the internal structure of the origin information, a method of provenance graph query based on double layer index structure is proposed. Firstly, we propose a two layer index structure based on the global index of the dictionary table and the local index based on the bitmap. The global index is used to query the server nodes stored in the source map. The local index is used to query the global index. Finally, based on the double-level index structure, a method of starting map query is designed. The experimental results show that the proposed method not only improves the efficiency of query and reduces the waste of memory resources.

  17. Magnetohydrodynamic effects on a charged colloidal sphere with arbitrary double-layer thickness

    NASA Astrophysics Data System (ADS)

    Hsieh, Tzu H.; Keh, Huan J.

    2010-10-01

    An analytical study is presented for the magnetohydrodynamic (MHD) effects on a translating and rotating colloidal sphere in an arbitrary electrolyte solution prescribed with a general flow field and a uniform magnetic field at a steady state. The electric double layer surrounding the charged particle may have an arbitrary thickness relative to the particle radius. Through the use of a simple perturbation method, the Stokes equations modified with an electric force term, including the Lorentz force contribution, are dealt by using a generalized reciprocal theorem. Using the equilibrium double-layer potential distribution from solving the linearized Poisson-Boltzmann equation, we obtain closed-form formulas for the translational and angular velocities of the spherical particle induced by the MHD effects to the leading order. It is found that the MHD effects on the particle movement associated with the translation and rotation of the particle and the ambient fluid are monotonically increasing functions of κa, where κ is the Debye screening parameter and a is the particle radius. Any pure rotational Stokes flow of the electrolyte solution in the presence of the magnetic field exerts no MHD effect on the particle directly in the case of a very thick double layer (κa →0). The MHD effect caused by the pure straining flow of the electrolyte solution can drive the particle to rotate, but it makes no contribution to the translation of the particle.

  18. Magnetohydrodynamic effects on a charged colloidal sphere with arbitrary double-layer thickness.

    PubMed

    Hsieh, Tzu H; Keh, Huan J

    2010-10-07

    An analytical study is presented for the magnetohydrodynamic (MHD) effects on a translating and rotating colloidal sphere in an arbitrary electrolyte solution prescribed with a general flow field and a uniform magnetic field at a steady state. The electric double layer surrounding the charged particle may have an arbitrary thickness relative to the particle radius. Through the use of a simple perturbation method, the Stokes equations modified with an electric force term, including the Lorentz force contribution, are dealt by using a generalized reciprocal theorem. Using the equilibrium double-layer potential distribution from solving the linearized Poisson-Boltzmann equation, we obtain closed-form formulas for the translational and angular velocities of the spherical particle induced by the MHD effects to the leading order. It is found that the MHD effects on the particle movement associated with the translation and rotation of the particle and the ambient fluid are monotonically increasing functions of κa, where κ is the Debye screening parameter and a is the particle radius. Any pure rotational Stokes flow of the electrolyte solution in the presence of the magnetic field exerts no MHD effect on the particle directly in the case of a very thick double layer (κa→0). The MHD effect caused by the pure straining flow of the electrolyte solution can drive the particle to rotate, but it makes no contribution to the translation of the particle.

  19. Electrical-assisted double side incremental forming and processes thereof

    SciTech Connect

    Roth, John; Cao, Jian

    2014-06-03

    A process for forming a sheet metal component using an electric current passing through the component is provided. The process can include providing a double side incremental forming machine, the machine operable to perform a plurality of double side incremental deformations on the sheet metal component and also apply an electric direct current to the sheet metal component during at least part of the forming. The direct current can be applied before or after the forming has started and/or be terminated before or after the forming has stopped. The direct current can be applied to any portion of the sheet metal. The electrical assistance can reduce the magnitude of force required to produce a given amount of deformation, increase the amount of deformation exhibited before failure and/or reduce any springback typically exhibited by the sheet metal component.

  20. Completed double layer boundary element method for periodic suspensions

    NASA Astrophysics Data System (ADS)

    Fan, X.-J.; Phan-Thien, N.; Zheng, R.

    In this paper, a traction-based boundary element method is formulated and implemented for periodic suspensions. Hydrodynamic interaction of particles at infinity is handled by O'Brien's method (1979), which is suitably modified for the adjoint double layer using the mean field values of the traction and the background flow. After a deflation of the extreme eigenvalue -1 of the adjoint double layer operator, an iterative solution strategy is implemented, which solves for the traction field on the surfaces of a group of near-by particles sequentially. Ewald's summation technique is employed, by expressing the adjoint double layer kernel in two sums, one converges rapidly in real space, and the other, in the reciprocal Fourier space. The implementation is tested on a periodic suspension of spheres and spheroids in simple and elongated face-centred cubic arrays, and proved to be very accurate when compared to established results. New results for the intrinsic viscosities of periodic suspensions of cubes and spheroids from moderate to high volume fractions are reported. Based on the numerical data for suspensions of spheroids, a simple modification of the constitutive equation of Hinch and Leal (1972), which was derived for dilute suspension of spheroids, is reported, allowing the constitutive equation to reasonably fit the numerical data at moderate to high concentrations.

  1. Generation of Weak Double Layers and Low-Frequency Electrostatic Waves in the Solar Wind

    NASA Astrophysics Data System (ADS)

    Lakhina, G. S.; Singh, S. V.

    2015-10-01

    We propose that the mechanism for the generation of weak double layers (WDLs) and low-frequency coherent electrostatic waves, observed by Wind in the solar wind at 1 AU, might be slow and fast ion-acoustic solitons and double layers. The solar wind plasma is modelled as a fluid of hot protons and hot α particles streaming with respect to protons, and suprathermal electrons having a κ-distribution. The fast ion-acoustic mode is similar to the ion-acoustic mode of a proton-electron plasma and can support only positive-potential solitons. The slow ion-acoustic mode is a new mode that occurs due to the presence of α particles. This mode can support both positive and negative solitons and double layers. The slow ion-acoustic mode can exist even when the relative streaming, U0, between α particles and protons is zero, provided that the α temperature, Ti, is not exactly equal to four times the proton temperature, Tp. An increase of the κ-index leads to an increase in the critical Mach number, maximum Mach number, and the maximum amplitude of both slow and fast ion-acoustic solitons. The slow ion-acoustic double layer can explain the amplitudes and widths, but not the shapes, of the observed WDLs in the solar wind at 1 AU by Wind spacecraft. The Fourier transform of the slow ion-acoustic solitons/double layers would produce broadband low-frequency electrostatic waves having main peaks between 0.35 kHz to 1.6 kHz, with an electric field in the range of E = (0.01 - 0.7) mV m^{-1}, in excellent agreement with the observed low-frequency electrostatic wave activity in the solar wind at 1 AU.

  2. Simulation of double layers in a model auroral circuit with nonlinear impedance

    NASA Technical Reports Server (NTRS)

    Smith, R. A.

    1986-01-01

    A reduced circuit description of the U-shaped potential structure of a discrete auroral arc, consisting of the flank transmission line plus parallel-electric-field region, is used to provide the boundary condition for one-dimensional simulations of the double-layer evolution. The model yields asymptotic scalings of the double-layer potential, as a function of an anomalous transport coefficient alpha and of the perpendicular length scale l(a) of the arc. The arc potential phi(DL) scales approximately linearly with alpha, and for alpha fixed phi (DL) about l(a) to the z power. Using parameters appropriate to the auroral zone acceleration region, potentials of phi (DPL) 10 kV scale to projected ionospheric dimensions of about 1 km, with power flows of the order of magnitude of substorm dissipation rates.

  3. Resistivity due to weak double layers - A model for auroral arc thickness

    NASA Technical Reports Server (NTRS)

    Prakash, Manju; Lysak, Robert L.

    1992-01-01

    We have calculated the resistivity due to a sequence of fluctuating weak double layers aligned parallel to the ambient magnetic field line. The average response of an electron drifting through a 1D randomly oriented array of WDLs is studied using a test particle approach. The average is taken over the randomly fluctuating values of the electric field associated with the double layers. Based on our calculations, we estimate that a 350 eV electron energy the thickness of the visual auroral arc is about 2.5 km and that of the auroral fine structure as about 250 m when mapped down to the ionosphere. The significance of our calculations is discussed in the context of magnetosphere-ionosphere coupling.

  4. Simulation of double layers in a model auroral circuit with nonlinear impedance

    NASA Technical Reports Server (NTRS)

    Smith, R. A.

    1986-01-01

    A reduced circuit description of the U-shaped potential structure of a discrete auroral arc, consisting of the flank transmission line plus parallel-electric-field region, is used to provide the boundary condition for one-dimensional simulations of the double-layer evolution. The model yields asymptotic scalings of the double-layer potential, as a function of an anomalous transport coefficient alpha and of the perpendicular length scale l(a) of the arc. The arc potential phi(DL) scales approximately linearly with alpha, and for alpha fixed phi (DL) about l(a) to the z power. Using parameters appropriate to the auroral zone acceleration region, potentials of phi (DPL) 10 kV scale to projected ionospheric dimensions of about 1 km, with power flows of the order of magnitude of substorm dissipation rates.

  5. Electrochemical Double Layered Capacitor Development and Implementation System

    NASA Astrophysics Data System (ADS)

    Strunk, Gavin P.

    Electrochemical Double Layered Capacitors (EDLC's) are becoming a more popular topic of research for hybrid power systems, especially vehicles. They are known for their high power density, high cycle life, low internal resistance, and wider operating temperature compared to batteries. They are rarely used as a standalone power source; however, because of their lack of energy density compared to batteries and fuel cells. Researchers are now discovering the benefits of using them in hybrid systems. The increased complexity of a hybrid power source presents many challenges. A major drawback of this complexity is the lack of design tools to assist a designer in translating a simulation all the way to a full scale implementation. A full spectrum of tools was designed to assist designers at all stages of implementation including: single cell testing, a multi-cell management system, and a full scale vehicle data acquisition system to monitor performance. First, the full scale vehicle data acquisition is described. The system is isolated from the electric shuttle bus it was tested on to allow the system to be ported to other vehicles and applications. This was done to modularize the system to characterize a wide variety of full scale applications. Next, a single cell test system was designed that allows the designer to characterize cell specifications, as well as, test control and safety systems in a controlled environment. The goal is to ensure safety systems can be thoroughly tested to ensure robustness as the bank is scaled up. This system also includes simulation models that provide examples of using the simulation to predict the behavior of a cell and the test system to validate the results of the simulation. This information is then used by the designer to more effectively design sensor ranges for the bank. Finally, a multi-cell EDLC management system was designed to implement a bank. It incorporates 12 series EDLC cells per control module, and the modular design

  6. Skin explosion of double-layer conductors in fast-rising high magnetic fields

    SciTech Connect

    Chaikovsky, S. A. Datsko, I. M.; Labetskaya, N. A.; Ratakhin, N. A.

    2014-04-15

    An experiment has been performed to study the electrical explosion of thick cylindrical conductors using the MIG pulsed power generator capable of producing a peak current of 2.5 MA within 100 ns rise time. The experimental goal was to compare the skin explosion of a solid conductor with that of a double-layer conductor whose outer layer had a lower conductivity than the inner one. It has been shown that in magnetic fields of peak induction up to 300 T and average induction rise rate 3 × 10{sup 9} T/s, the double-layer structure of a conductor makes it possible to achieve higher magnetic induction at the conductor surface before it explodes. This can be accounted for, in particular, by the reduction of the ratio of the Joule heat density to the energy density of the magnetic field at the surface of a double-layer conductor due to redistribution of the current density over the conductor cross section.

  7. Skin explosion of double-layer conductors in fast-rising high magnetic fields

    NASA Astrophysics Data System (ADS)

    Chaikovsky, S. A.; Oreshkin, V. I.; Datsko, I. M.; Labetskaya, N. A.; Ratakhin, N. A.

    2014-04-01

    An experiment has been performed to study the electrical explosion of thick cylindrical conductors using the MIG pulsed power generator capable of producing a peak current of 2.5 MA within 100 ns rise time. The experimental goal was to compare the skin explosion of a solid conductor with that of a double-layer conductor whose outer layer had a lower conductivity than the inner one. It has been shown that in magnetic fields of peak induction up to 300 T and average induction rise rate 3 × 109 T/s, the double-layer structure of a conductor makes it possible to achieve higher magnetic induction at the conductor surface before it explodes. This can be accounted for, in particular, by the reduction of the ratio of the Joule heat density to the energy density of the magnetic field at the surface of a double-layer conductor due to redistribution of the current density over the conductor cross section.

  8. Double Charged Surface Layers in Lead Halide Perovskite Crystals.

    PubMed

    Sarmah, Smritakshi P; Burlakov, Victor M; Yengel, Emre; Murali, Banavoth; Alarousu, Erkki; El-Zohry, Ahmed M; Yang, Chen; Alias, Mohd S; Zhumekenov, Ayan A; Saidaminov, Makhsud I; Cho, Namchul; Wehbe, Nimer; Mitra, Somak; Ajia, Idris; Dey, Sukumar; Mansour, Ahmed E; Abdelsamie, Maged; Amassian, Aram; Roqan, Iman S; Ooi, Boon S; Goriely, Alain; Bakr, Osman M; Mohammed, Omar F

    2017-03-08

    Understanding defect chemistry, particularly ion migration, and its significant effect on the surface's optical and electronic properties is one of the major challenges impeding the development of hybrid perovskite-based devices. Here, using both experimental and theoretical approaches, we demonstrated that the surface layers of the perovskite crystals may acquire a high concentration of positively charged vacancies with the complementary negatively charged halide ions pushed to the surface. This charge separation near the surface generates an electric field that can induce an increase of optical band gap in the surface layers relative to the bulk. We found that the charge separation, electric field, and the amplitude of shift in the bandgap strongly depend on the halides and organic moieties of perovskite crystals. Our findings reveal the peculiarity of surface effects that are currently limiting the applications of perovskite crystals and more importantly explain their origins, thus enabling viable surface passivation strategies to remediate them.

  9. Study for double-layered AZO/ATO transparent conducting thin film

    NASA Astrophysics Data System (ADS)

    Cao, Miaomiao; Li, Yudong; Yang, Jing; Chen, Yigang

    2013-03-01

    The purpose of this study is to provide transparent conductive composite films, used for such as dye-sensitized solar cells (DSSCs). In this work, transparent conductive oxide films with double-layer structure, ATO(antimony doped tin oxide)films covered on AZO(aluminum doped zinc oxide)films, were prepared on glass substrates by RF magnetron sputtering method. Subsequently the films were post-annealed at different temperature. The structure, surface morphology, optical and electrical properties of the films were investigated as a function of annealing temperature. Our results indicate that the composite films can maintain good electrical and optical properties at a temperature higher than 450°C compared to that of single-layer film.

  10. The Double Jones Birefringence in Magneto-electric Medium

    PubMed Central

    Mahmood, Waqas; Zhao, Qing

    2015-01-01

    In this paper, the Maxwell’s equations for a tensorial magneto-electric (ME) medium are solved, which is an extension to the work on the uniaxial anisotropic nonmagnetic medium. The coefficients of the dielectric permittivity, magnetic permeability, and of the magneto-electric effect are considered as tensors. The polarization is shown lying in the plane of two perpendicular independent vectors, and the relationship for the transverse polarization is given. The propagation of an electromagnetic wave through a ME medium gives rise to double Jones birefringence. Besides, the condition for an independent phenomenon of D’yakonov surface wave in a magneto-isotropic but with magneto-electric medium is given, which is measurable experimentally when the incident angle is . Lastly, it is shown that the parameter for the magneto-electric effect plays a role in the damping of the wave. PMID:26354609

  11. The Double Jones Birefringence in Magneto-electric Medium

    NASA Astrophysics Data System (ADS)

    Mahmood, Waqas; Zhao, Qing

    2015-09-01

    In this paper, the Maxwell’s equations for a tensorial magneto-electric (ME) medium are solved, which is an extension to the work on the uniaxial anisotropic nonmagnetic medium. The coefficients of the dielectric permittivity, magnetic permeability, and of the magneto-electric effect are considered as tensors. The polarization is shown lying in the plane of two perpendicular independent vectors, and the relationship for the transverse polarization is given. The propagation of an electromagnetic wave through a ME medium gives rise to double Jones birefringence. Besides, the condition for an independent phenomenon of D’yakonov surface wave in a magneto-isotropic but with magneto-electric medium is given, which is measurable experimentally when the incident angle is . Lastly, it is shown that the parameter for the magneto-electric effect plays a role in the damping of the wave.

  12. Cation ordering and superstructures in natural layered double hydroxides.

    PubMed

    Krivovichev, Sergey V; Yakovenchuk, Victor N; Zolotarev, Andrey A; Ivanyuk, Gregory N; Pakhomovsky, Yakov A

    2010-01-01

    Layered double hydroxides (LDHs) constitute an important group of materials with many applications ranging from catalysis and absorption to carriers for drug delivery, DNA intercalation and carbon dioxide sequestration. The structures of LDHs are based upon double brucite-like hydroxide layers [M(2+)(n)M(3+)(m)(OH)(2(m+n)](m+), where M(2+) = Mg(2+), Fe(2+), Mn(2+), Zn(2+), etc.; M(3+) = Al(3+), Fe(3+), Cr(3+), Mn(3+), etc. Structural features of LDHs such as cation ordering, charge distribution and polytypism have an immediate influence upon their properties. However, all the structural studies on synthetic LDHs deal with powder samples that prevent elucidation of such fine details of structure architecture as formation of superstructures due to cation ordering. In contrast to synthetic materials, natural LDHs are known to form single crystals accessible to single-crystal X-ray diffraction analysis, which provides a unique possibility to investigate 3D cation ordering in LDHs that results in formation of complex superstructures, where 2D cation order is combined with a specific order of layer stacking (polytypism). Therefore LDH minerals provide an indispensable source of structural information for modeling of structures and processes happening in LDHs at the molecular and nanoscale levels.

  13. Double dipole RET investigation for 32 nm metal layers

    NASA Astrophysics Data System (ADS)

    Babcock, Carl; Zou, Yi; Dunn, Derren; Baum, Zachary; Zhao, Zengqin; Matthew, Itty; LaCour, Pat

    2008-10-01

    For 32 nm test chips, aggressive resolution enhancement technology (RET) was required for 1x metal layers to enable printing minimum pitches before availability of the final 32 nm exposure tool. Using a currently installed immersion scanner with 1.2 numerical aperture (NA) for early 32 nm test chips, one of the RET strategies capable of resolving the minimum pitch with acceptable process latitude was dipole illumination. To avoid restricting the use of minimum pitch to a single orientation, we developed a double-expose/single-develop process using horizontal and vertical dipole illumination. To enable this RET, we developed algorithms to decompose general layouts, including random logic, interconnect test patterns, and SRAM designs, into two mask layers: a first exposure (E1) of predominantly vertical features, to be patterned with horizontal dipole illumination; and, a second exposure (E2) of predominantly horizontal features, to be patterned with vertical dipole illumination. We wrote this algorithm into our OPC program, which then applies sub-resolution assist features (SRAFs) separately to the E1 and E2 masks, coordinating the two to avoid problems with overlapping exposures. This was followed by two-mask OPC, using E1 and E2 as mask layers and the original layout (single layer) as the target layer. In this paper, we describe some of the issues with decomposing layout by orientation, issues that arise in SRAF application and OPC, and some approaches we examined to address these issues.

  14. Decoupling of double-tearing resonant layers by sheared flows

    NASA Astrophysics Data System (ADS)

    Abbott, Stephen; Germaschewski, Kai

    2015-11-01

    Double-tearing modes consist of two resonant, reconnecting layers of the same mode number coupled together by an ideal MHD outer region. Linearly this interaction can result in faster growth as the two layers drive each other. Nonlinearly it may lead to explosive releases of energy, and is a possible driver for off-axis sawtooth crashes in advanced tokamaks. Recent work has shown that differential rotation effects, such as equilibrium sheared flows or diamagnetic drifts, can decouple the DTM layers leaving two drifting, single tearing modes. These isolated tearing layers are slower growing and easier to stabilize. Understanding and producing this decoupling is thus an important element of preventing disruptive DTM activity. In this work we present progress on developing an analytic theory of DTM decoupling. We show that the application of equilibrium sheared flows mixes the symmetric and antisymmetric DTM eigenmode solutions, reducing the growth rate. This representation predicts a linear relationship between the growth rate and the amplitude of differential sheared flow needed to decouple the layers, which we confirm with linear MHD simulations. Through numerical scaling studies we examine the relationship between mode decoupling and the slab-kink mode underlying DTM growth.

  15. Near infrared organic photodetector utilizing a double electron blocking layer.

    PubMed

    Shafian, Shafidah; Hwang, Heewon; Kim, Kyungkon

    2016-10-31

    A near infrared organic photodiode (OPD) utilizing a double electron blocking layer (EBL) fabricated by the sequential deposition of molybdenum (VI) oxide (MoO3) and poly(3,4ethylenedioxythiophene):poly(styrene-sulfonate) (PEDOT:PSS) is reported. The double EBL improves the on/off current ratio of OPD up to 1.36 x 104 at -1V, which is one order of magnitude higher than PEDOT:PSS single EBL (2.45 x 103) and three orders of magnitude higher than that of MoO3 single EBL (7.86). The detectivity at near infrared (800 nm) at -1V is 4.90 x 1011 Jones, which is 2.83 times higher than the PEDOT:PSS single EBL and 2 magnitudes higher compared to the MoO3 single EBL.

  16. Substituted Quaternary Ammonium Salts Improve Low-Temperature Performance of Double-Layer Capacitors

    NASA Technical Reports Server (NTRS)

    Brandon, Erik J.; Smart, Marshall C.; West, William C.

    2011-01-01

    Double-layer capacitors are unique energy storage devices, capable of supporting large current pulses as well as a very high number of charging and discharging cycles. The performance of doublelayer capacitors is highly dependent on the nature of the electrolyte system used. Many applications, including for electric and fuel cell vehicles, back-up diesel generators, wind generator pitch control back-up power systems, environmental and structural distributed sensors, and spacecraft avionics, can potentially benefit from the use of double-layer capacitors with lower equivalent series resistances (ESRs) over wider temperature limits. Higher ESRs result in decreased power output, which is a particular problem at lower temperatures. Commercially available cells are typically rated for operation down to only 40 C. Previous briefs [for example, Low Temperature Supercapacitors (NPO-44386), NASA Tech Briefs, Vol. 32, No. 7 (July 2008), p. 32, and Supercapacitor Electrolyte Solvents With Liquid Range Below 80 C (NPO-44855), NASA Tech Briefs, Vol. 34, No. 1 (January 2010), p. 44] discussed the use of electrolytes that employed low-melting-point co-solvents to depress the freezing point of traditional acetonitrile-based electrolytes. Using these modified electrolyte formulations can extend the low-temperature operational limit of double-layer capacitors beyond that of commercially available cells. This previous work has shown that although the measured capacitance is relatively insensitive to temperature, the ESR can rise rapidly at low temperatures, due to decreased electrolyte conductance within the pores of the high surface- area carbon electrodes. Most of these advanced electrolyte systems featured tetraethylammonium tetrafluoroborate (TEATFB) as the salt. More recent work at JPL indicates the use of the asymmetric quaternary ammonium salt triethylmethylammonium tetrafluoroborate (TEMATFB) or spiro-(l,l')-bipyrrolidium tetrafluoroborate (SBPBF4) in a 1:1 by volume solvent

  17. Cellular Uptake Behavior of Fluorescein: Intercalated Layered Double Hydroxide

    NASA Astrophysics Data System (ADS)

    Tanaka, Miyuki; Aisawa, Sumio; Hirahara, Hidetoshi; Narita, Eiichi; Yin, Shu; Sato, Tsugio

    2012-06-01

    In order to define the ability of layered double hydroxide (LDH) as materials for drug delivery, fluorescein (Fluo) anion intercalated LDH (Fluo/LDH) was synthesized by hydrothermal treatment and observed the cellular uptake of the Fluo/LDH for mammalian cell (L929). The synthesized Fluo/LDH showed a LDH structure, high fluorescence and low cytotoxicity. According to the fluorescence, confocal and TEM images of cells, the Fluo/LDH seemed to be internalized into the L929 cell by cellular endocytosis and dissolved inside the cell to exhibit the fluorescence of cellular cytoplasm.

  18. Multi-ion Double Layers in a Magnetized Plasma

    NASA Astrophysics Data System (ADS)

    Shahmansouri, M.; Alinejad, H.; Tribeche, M.

    2015-11-01

    A theoretical investigation is carried out to study the existence, formation and basic properties of ion acoustic (IA) double layers (DLs) in a magnetized bi-ion plasma consisting of warm/cold ions and Boltzmann distributed electrons. Based on the reductive perturbation technique, an extended Korteweg de-Vries (KdV) equation is derived. The propagation of two possible modes (fast and slow), and their evolution are investigated. The effects of obliqueness, magnitude of the magnetic field, ion concentration, polarity of ions, and ion temperature on the IA DL profile are analyzed, and then the ranges of parameters for which the IA DLs exist are investigated in details.

  19. Langmuir probe measurements of double-layers in a pulsed discharge

    NASA Technical Reports Server (NTRS)

    Levine, J. S.; Crawford, F. W.

    1980-01-01

    Langmuir probe measurements were carried out which confirm the occurrence of double-layers in an argon positive column. Pulsing the discharge current permitted probe measurements to be performed in the presence of the double-layer. Supplementary evidence, obtained from DC and pulsed discharges, indicated that the double-layers formed in the two modes of operation were similar. The double-layers observed were weak and stable; their relation to other classes of double-layers are discussed, and directions for future work are suggested.

  20. Laser acceleration of monoenergetic protons via a double layer emerging from an ultra-thin foil

    NASA Astrophysics Data System (ADS)

    Eliasson, Bengt; Liu, Chuan S.; Shao, Xi; Sagdeev, Roald; Shukla, Padma K.; Dudnikova, Galina; Liu, T. C.

    2009-11-01

    Theoretical and numerical studies are presented of the acceleration of monoenergetic protons in a double layer formed by the laser irradiation of an ultra-thin film. The ponderomotive force of the laser light pushes the electrons forward, and the induced space charge electric field pulls the ions and makes the thin foil accelerate as a whole. A stable double layer is formed, in which the ions are trapped by the combined electric field and inertial force in the accelerated frame, together with the electrons that are trapped in the well of the ponderomotive and ion electric field. The trapped ions reach monoenergetic energies up to 100 MeV and beyond, making them suitable for cancer treatment. We present an analytic theory for the laser-accelerated ion energy as a function of the laser intensity, foil thickness and the plasma number density. The underlying physics of the trapped and untrapped ions and of the stabilization of the Rayleigh-Taylor instability are discussed.

  1. Influence of localised double suction on a turbulent boundary layer

    NASA Astrophysics Data System (ADS)

    Oyewola, O.; Djenidi, L.; Antonia, R. A.

    2007-07-01

    The effects of localised suction applied through a pair of porous wall strips on a turbulent boundary layer have been quantified through the measurements of mean velocity and Reynolds stresses. The results indicate that the use of second strip extends the pseudo-relaminarisation zone but also reduces the overshoot in the longitudinal and normal r.m.s. velocities. While the minimum r.m.s. occurs at x/δo=3.0 (one strip) and x/δo=12 (two strips), the reduction observed for the latter case is larger. Relative to no suction, the turbulence level is modified by suction and the effect is enhanced with double suction. This increased effectiveness reflects the fact that the second strip acts on a boundary layer whose near-wall active motion has been seriously weakened by the first strip.

  2. Buckling instability of circular double-layered graphene sheets.

    PubMed

    Natsuki, Toshiaki; Shi, Jin-Xing; Ni, Qing-Qing

    2012-04-04

    In this paper, we study the buckling properties of circular double-layered graphene sheets (DLGSs), using plate theory. The two graphene layers are modeled as two individual sheets whose interactions are determined by the Lennard-Jones potential of the carbon-carbon bond. An analytical solution of coupled governing equations is proposed for predicting the buckling properties of circular DLGSs. Using the present theoretical approach, the influences of boundary conditions, plate sizes, and buckling-mode shapes on the buckling behaviors are investigated in detail. The buckling stability is significantly affected by the buckling-mode shapes. As a result of van der Waals interactions, the buckling stress of circular DLGSs is much larger for the anti-phase mode than for the in-phase mode.

  3. Structural characterisation of a layered double hydroxide nanosheet

    NASA Astrophysics Data System (ADS)

    Funnell, Nicholas P.; Wang, Qiang; Connor, Leigh; Tucker, Matthew G.; O'Hare, Dermot; Goodwin, Andrew L.

    2014-06-01

    We report the atomic-scale structure of a Zn2Al-borate layered double hydroxide (LDH) nanosheet, as determined by reverse Monte Carlo (RMC) modelling of X-ray total scattering data. This study involves the extension of the RMC method to enable structural refinement of two-dimensional nanomaterials. The refined LDH models show the intra-layer geometry in this highly-exfoliated phase to be consistent with that observed in crystalline analogues, with the reciprocal-space scattering data suggesting a disordered arrangement of the Zn2+ and Al3+ cations within the nanosheet. The approach we develop is generalisable and so offers a method of characterising the structures of arbitrary nanosheet phases, including systems that support complex forms of disorder within the nanosheets themselves.We report the atomic-scale structure of a Zn2Al-borate layered double hydroxide (LDH) nanosheet, as determined by reverse Monte Carlo (RMC) modelling of X-ray total scattering data. This study involves the extension of the RMC method to enable structural refinement of two-dimensional nanomaterials. The refined LDH models show the intra-layer geometry in this highly-exfoliated phase to be consistent with that observed in crystalline analogues, with the reciprocal-space scattering data suggesting a disordered arrangement of the Zn2+ and Al3+ cations within the nanosheet. The approach we develop is generalisable and so offers a method of characterising the structures of arbitrary nanosheet phases, including systems that support complex forms of disorder within the nanosheets themselves. Electronic supplementary information (ESI) available. See DOI: 10.1039/c4nr01265h

  4. Intracavity double diode structures with GaInP barrier layers for thermophotonic cooling

    NASA Astrophysics Data System (ADS)

    Tiira, Jonna; Radevici, Ivan; Haggren, Tuomas; Hakkarainen, Teemu; Kivisaari, Pyry; Lyytikäinen, Jari; Aho, Arto; Tukiainen, Antti; Guina, Mircea; Oksanen, Jani

    2017-02-01

    Optical cooling of semiconductors has recently been demonstrated both for optically pumped CdS nanobelts and for electrically injected GaInAsSb LEDs at very low powers. To enable cooling at larger power and to understand and overcome the main obstacles in optical cooling of conventional semiconductor structures, we study thermophotonic (TPX) heat transport in cavity coupled light emitters. Our structures consist of a double heterojunction (DHJ) LED with a GaAs active layer and a corresponding DHJ or a p-n-homojunction photodiode, enclosed within a single semiconductor cavity to eliminate the light extraction challenges. Our presently studied double diode structures (DDS) use GaInP barriers around the GaAs active layer instead of the AlGaAs barriers used in our previous structures. We characterize our updated double diode structures by four point probe IV- measurements and measure how the material modifications affect the recombination parameters and coupling quantum efficiencies in the structures. The coupling quantum efficiency of the new devices with InGaP barrier layers is found to be approximately 10 % larger than for the structures with AlGaAs barriers at the point of maximum efficiency.

  5. Low Temperature Double-layer Capacitors with Improved Energy Density: An Overview of Recent Development Efforts

    NASA Technical Reports Server (NTRS)

    Brandon, Erik J.; West, William C.; Smart, Marshall C.; Korenblit, Yair; Kajdos, Adam; Kvit, Alexander; Jagiello, Jacek; Yushin, Gleb

    2012-01-01

    Electrochemical double-layer capacitors are finding increased use in a wide range of energy storage applications, particularly where high pulse power capabilities are required. Double-layer capacitors store charge at a liquid/solid interface, making them ideal for low temperature power applications, due to the facile kinetic processes associated with the rearrangement of the electrochemical double-layer at these temperatures. Potential low temperature applications include hybrid and electric vehicles, operations in polar regions, high altitude aircraft and aerospace avionics, and distributed environmental and structural health monitoring. State-of-the-art capacitors can typically operate to -40 C, with a subsequent degradation in power performance below room temperature. However, recent efforts focused on advanced electrolyte and electrode systems can enable operation to temperatures as low as -70 C, with capacities similar to room temperature values accompanied by reasonably low equivalent series resistances. This presentation will provide an overview of recent development efforts to extend and improve the wide temperature performance of these devices.

  6. Low Temperature Double-layer Capacitors with Improved Energy Density: An Overview of Recent Development Efforts

    NASA Technical Reports Server (NTRS)

    Brandon, Erik J.; West, William C.; Smart, Marshall C.; Korenblit, Yair; Kajdos, Adam; Kvit, Alexander; Jagiello, Jacek; Yushin, Gleb

    2012-01-01

    Electrochemical double-layer capacitors are finding increased use in a wide range of energy storage applications, particularly where high pulse power capabilities are required. Double-layer capacitors store charge at a liquid/solid interface, making them ideal for low temperature power applications, due to the facile kinetic processes associated with the rearrangement of the electrochemical double-layer at these temperatures. Potential low temperature applications include hybrid and electric vehicles, operations in polar regions, high altitude aircraft and aerospace avionics, and distributed environmental and structural health monitoring. State-of-the-art capacitors can typically operate to -40 C, with a subsequent degradation in power performance below room temperature. However, recent efforts focused on advanced electrolyte and electrode systems can enable operation to temperatures as low as -70 C, with capacities similar to room temperature values accompanied by reasonably low equivalent series resistances. This presentation will provide an overview of recent development efforts to extend and improve the wide temperature performance of these devices.

  7. Physical properties of fixed-charge layer double hydroxides

    NASA Astrophysics Data System (ADS)

    Hines, D. R.; Solin, S. A.; Costantino, Umberto; Nocchetti, Morena

    2000-05-01

    The physical properties of a series of layer double hydroxides (LDH) of the form [(CO3)0.195(1-x)Cl0.39x(H2O)y]:[Zn0.61Al0.39(OH)2], 0<=x<=1, 0<=y<=(0.4+0.2x) have been studied. The hydration dynamics of these materials indicate that the guest layer water molecules form a hydration ring which defines the height of the solvated, nested Cl anion. The water molecules can tilt around their C2v axis such that the height of the solvated Cl ion is a function of the number of molecules forming the hydration ring. The composition dependence of the basal spacing, determined from x-ray-diffraction powder patterns measured as a function of humidity and temperature for these materials, is a function of both the Cl concentration (x) and the number of guest layer water molecules (y). Distinct basal spacing curves are observed for fully hydrated, partially hydrated, and dehydrated materials. At x=1 the Cl end-member material exhibits a change in stacking sequence from a 3R polytype to a 2H polytype upon dehydration. The dehydrated form of this material also exhibits a (3×3)R30° superlattice ordering of the Cl ions. Due to the nesting of the Cl ion and the active nature of the water molecules, the basal spacing vs x curve for the dehydrated materials is the only curve that can be fit by the discrete finite layer rigidity model. The interlayer rigidity parameter for LDH materials has been determined to be p=4.84+/-0.06 indicating that these materials are stiffer than class-II layered solids but not as stiff as class-III layered solids.

  8. Biodiesel synthesis using calcined layered double hydroxide catalysts

    SciTech Connect

    Schumaker, J. Link; Crofcheck, Czarena; TAckett, S. Adam; Santillan-Jimenez, Eduardo; Morgan, Tonya; Ji, Yaying; Crocker, Mark; Toops, Todd J

    2008-01-01

    The catalytic properties of calcined Li-Al, Mg-Al and Mg-Fe layered double hydroxides (LDHs) were examined in two transesterification reactions, namely, the reaction of glyceryl tributyrate with methanol, and the reaction of soybean oil with methanol. While the Li-Al catalysts showed high activity in these reactions at the reflux temperature of methanol, the Mg-Fe and Mg-Al catalysts exhibited much lower methyl ester yields. CO2 TPD measurements revealed the presence of sites of weak, medium and strong basicity on both Mg-Al and Li-Al catalysts, the latter showing higher concentrations of medium and strong base sites; by implication, these are the main sites active in transesterification catalyzed by calcined Li-Al LDHs. Maximum activity was observed for the Li-Al catalysts when a calcination temperature of 450-500 aC was applied, corresponding to decomposition of the layered double hydroxide to the mixed oxide without formation of crystalline lithium aluminate phases.

  9. Partial double-layered patella in a nondysplasic adolescent.

    PubMed

    García-Mata, Serafín; Hidalgo-Ovejero, Angel

    2016-11-01

    Double-layered patella (DLP) is a rare patella-formation abnormality reported in association with multiple epiphyseal dysplasia. DLP is one of the five types of bipartite patella, caused by a coronal septum that divides the patella into anterior and posterior segments. Although the double layer of bone has been reported as complete, it may also manifest as partial, as in our case. A 13-year-old male patient attended A&E after accidentally falling and sustaining a direct injury to his left knee, with pain in the anterior surface of the right patella. He was diagnosed with an incomplete vertical fracture of the left patella. An axial view radiography indicated an external partial DLP. No bone dysplasia was found. Computed tomographic scan and MRI showed partial DLP and bone marrow oedema because of the injury in the femoral condyle, but no fracture. The reason for highlighting this type of patella abnormality is to present the case of a patient without bone dysplasia, either partial or incomplete, that has not been reported previously. We also wish to emphasize the importance of not confusing it with a fracture in standard radiographies.

  10. Synthesis of Water-Dispersible Single-Layer CoAl-Carbonate Layered Double Hydroxide.

    PubMed

    Li, Haiping; Tran, Thanh-Nhan; Lee, Byong-Jun; Zhang, Chunfei; Park, Jong-Deok; Kang, Tong-Hyun; Yu, Jong-Sung

    2017-06-21

    Despite extensive study on single-layer layered double hydroxides (SL-LDHs) with NO3(-) counterions, SL-LDHs with CO3(2-) counterions (CO3(2-) SL-LDHs) have never been prepared before. Herein, a CoAl-CO3(2-) SL-LDH which stays stable in water and powdery state is first synthesized using ethylene glycol as a reaction medium. The SL-LDH, with thickness of ∼0.85 nm, is composed of one Co(Al)O6 layer sandwiched between two CO3(2-) layers. The SL-LDH powder shows high specific surface area (∼289 m(2)/g) and excellent electrocatalytic oxygen evolution efficiency. This work provides the first simple way to prepare CO3(2-) SL-LDHs and will open an avenue for synthesizing other SL-LDHs.

  11. Inducing electric polarization in ultrathin insulating layers

    NASA Astrophysics Data System (ADS)

    Martinez-Castro, Jose; Piantek, Marten; Persson, Mats; Serrate, David; Hirjibehedin, Cyrus F.

    Studies of ultrathin polar oxide films have attracted the interest of researchers for a long time due to their different properties compared to bulk materials. However they present several challenges such as the difficulty in the stabilization of the polar surfaces and the limited success in tailoring their properties. Moreover, recently developed Van der Waals materials have shown that the stacking of 2D-layers trigger new collective states thanks to the interaction between layers. Similarly, interface phenomena emerge in polar oxides, like induced ferroelectricity. This represents a promising way for the creation of new materials with customized properties that differ from those of the isolated layers. Here we present a new approach for the fabrication and study of atomically thin insulating films. We show that the properties of insulating polar layers of sodium chloride (NaCl) can be engineered when they are placed on top of a charge modulated template of copper nitride (Cu2N). STM studies carried out in ultra-high vacuum and at low temperatures over NaCl/Cu2N/Cu(001) show that we are able to build up and stabilize interfaces of polar surface at the limit of one atomic layer showing new properties not present before at the atomic scale.

  12. Synthesis and characterization of lawsone-lntercalated Zn-Al-layered double hydroxides.

    PubMed

    Yasin, Yamin; Ismail, Nur Mushirah; Hussein, Mohd Zobir; Aminudin, Norhaniza

    2011-06-01

    A drug-inorganic nanostructured material involving pharmaceutically active compound lawsone intercalated Zn-Al layered double hydroxides (Law-LDHs) with Zn/AI = 4 has been assembled by co-precipitation and ion exchange methods. Powder X-ray diffraction (XRD) and Fourier transform infrared spectra (FTIR) analysis indicate a successful intercalation of lawsone between the layers of layered double hydroxides. It suggests that layered double hydroxides may have application as the basis of a drug delivery system.

  13. Role of barrier layer on dielectric function of graphene double layer system at finite temperature

    NASA Astrophysics Data System (ADS)

    Patel, Digish K.; Ambavale, Sagar K.; Prajapati, Ketan; Sharma, A. C.

    2016-05-01

    We have theoretically investigated the static dielectric function of graphene double layer system (GDLS) at finite temperatures within the random phase approximation. GDLS has been suspended on a substrate and barrier layer of three different materials; h-BN, Al2O3 and HfO2 has been introduced between two graphene sheets of GDLS. We have reported dependence of the overall dielectric function of GDLS on interlayer distance and the effect of the dielectric environment at finite temperatures. Results show close relation between changing environment and behavior of dielectric constant of GDLS.

  14. Characteristics of Double Tropopause Layers Observed During TORERO

    NASA Astrophysics Data System (ADS)

    Haggerty, J. A.; Mahoney, M. J.; Campos, T. L.; Pierce, B.; Volkamer, R. M.

    2012-12-01

    The existence of double tropopauses is indicated in data collected during the Tropical Ocean tRoposphere Exchange of Reactive halogen species and Oxygenated VOC (TORERO) experiment in January - February 2012. Airborne remote and in situ measurements from the NSF/NCAR Gulfstream V place tropopause heights at ~12-13 km and ~16-17 km during oceanic flights westward and southward from Antofagasta, Chile. Coastal radiosonde profiles confirm the locations of these tropopause layers. Various measurements define and characterize the transition layer between the upper troposphere and lower stratosphere. The Microwave Temperature Profiler (MTP), a scanning radiometer which measures emitted radiation at three frequencies, provides temperature vertical structure over a layer several kilometers above and below the aircraft with vertical resolution sufficient to resolve the tropopause. Tropopause height as determined from the temperature profile is based on the cold point and lapse rate transitions. In situ measurements of trace gases such as ozone, carbon monoxide, and water vapor also provide distinct signatures at the tropopause, although the aircraft did not always reach sufficient altitudes to detect the second tropopause. Model profiles of temperature and trace gases were also generated by the Real-time Air Quality Modeling System (RAQMS) during TORERO. RAQMS is a global meteorological, chemical and aerosol assimilation/forecasting system that assimilates real-time stratospheric ozone retrievals from the Microwave Limb Sounder (MLS), total column ozone from the Ozone Monitoring Instrument (OMI), and aerosol optical depth (AOD) from the Moderate Resolution Imaging Spectroradiometer (MODIS). In this paper, observations of the TORERO double tropopause features as defined by temperature and trace gas profiles are presented and compared to model-defined tropopause properties.

  15. Forming mechanism of the bipolar resistance switching in double-layer memristive nanodevices.

    PubMed

    Lee, S B; Yoo, H K; Kim, K; Lee, J S; Kim, Y S; Sinn, S; Lee, D; Kang, B S; Kahng, B; Noh, T W

    2012-08-10

    To initiate resistance switching phenomena, it is usually necessary to apply a strong electric field to a sample. This forming process poses very serious obstacles in real nanodevice applications. In unipolar resistance switching (URS), it is well known that the forming originates from soft dielectric breakdown. However, the forming in bipolar resistance switching (BRS) is poorly understood. In this study, we investigated the forming processes in Pt/Ta₂O₅/TaOx/Pt and Pt/TaOx/Pt nanodevices, which showed BRS and URS, respectively. By comparing the double- and single-layer systems, we were able to observe differences in the BRS and URS forming processes. Using computer simulations based on an 'interface-modified random circuit breaker network model', we could explain most of our experimental observations. This success suggests that the BRS forming in our Pt/Ta₂O₅/TaOx/Pt double-layer system can occur via two processes, i.e., polarity-dependent resistance switching in the Ta₂O₅ layer and soft dielectric breakdown in the TaOx layer. This forming mechanism can be used to improve the performance of BRS devices. For example, we could improve the endurance properties of Pt/Ta₂O₅/TaOx/Pt cells by using a small forming voltage.

  16. Electric circuit model for strained-layer epitaxy

    NASA Astrophysics Data System (ADS)

    Kujofsa, Tedi; Ayers, John E.

    2016-11-01

    For the design and analysis of a strained-layer semiconductor device structure, the equilibrium strain profile may be determined numerically by energy minimization but this method is computationally intense and non-intuitive. Here we present an electric circuit model approach for the equilibrium analysis of an epitaxial stack, in which each sublayer may be represented by an analogous configuration involving a current source, a resistor, a voltage source, and an ideal diode. The resulting node voltages in the analogous electric circuit correspond to the equilibrium strains in the original epitaxial structure. This new approach enables analysis using widely accessible circuit simulators, and an intuitive understanding of electric circuits may be translated to the relaxation of strained-layer structures. In this paper, we describe the mathematical foundation of the electrical circuit model and demonstrate its application to epitaxial layers of Si1-x Ge x grown on a Si (001) substrate.

  17. Double injection, resonant-tunneling recombination, and current-voltage characteristics in double-graphene-layer structures

    SciTech Connect

    Ryzhii, M.; Ryzhii, V.; Otsuji, T.; Maltsev, P. P.; Leiman, V. G.; Ryabova, N.; Mitin, V.

    2014-01-14

    We evaluate the effect of the recombination associated with interlayer transitions in ungated and gated double-graphene-layer (GL) structures on the injection of electrons and holes. Using the proposed model, we derive analytical expressions for the spatial distributions of the electron and hole Fermi energies and the energy gap between the Dirac points in GLs as well as their dependences on the bias and gate voltages. The current-voltage characteristics are calculated as well. The model is based on hydrodynamic equations for the electron and hole transports in GLs under the self-consistent electric field. It is shown that in undoped double-GL structures with weak scattering of electrons and holes on disorder, the Fermi energies and the energy gap are virtually constant across the main portions of GLs, although their values strongly depend on the voltages and recombination parameters. In contrast, the electron and hole scattering on disorder lead to substantial nonuniformities. The resonant inter-GL tunneling enables N-shaped current-voltage characteristics provided that GLs are sufficiently short. The width of the current maxima is much larger than the broadening of the tunneling resonance. In the double-GL structures with relatively long GLs, the N-shaped characteristics transform into the Z-shaped characteristics. The obtained results are in line with the experimental observations [Britnell et al., Nat. Commun. 4, 1794–1799 (2013)] and might be useful for design and optimization of different devices based on double-GL structures, including field-effect transistors and terahertz lasers.

  18. The Unique Characteristics of Double Layered Ejecta Craters on Mars

    NASA Astrophysics Data System (ADS)

    Mouginis-Mark, P. J.; Boyce, J. M.

    2004-12-01

    THEMIS VIS images reveal several unique characteristics of double layered ejecta (DLE) craters on Mars that suggest a strikingly different mode of formation from single layered ejecta (SLE) or multi-layered ejecta (MLE) craters. DLE craters are typically 15 to 25 km in diameter and differ from the other types of Martian craters in the following ways: (1) DLE craters lack secondary craters; (2) ejecta layers of DLE craters lack distal ramparts; (3) flow features within the outer layer of DLE craters suggest a very low emplacement velocity; and (4) radial striations exist only within DLE ejecta, and that these striations cross both the inner and outer ejecta layers. The interior morphology of DLE is also less complex than SLE or MLE layered ejecta craters; DLE craters lack wall terraces and, where present, have only simple central peaks. Previous morphologic analyses of DLE craters proposed that they might have formed in the volatile-rich sediments that are believed to infill areas such as Utopia, Arcadia and Acidalia Planitiae. But our inspection of the THEMIS VIS data set confirms the Viking-based results of Barlow and Perez (JGR-Planets, vol. 108 (E8), doi 10.1029/2002JE002036, 2003) that DLE craters are not uniquely located in the northern plains. We find that DLE craters with nearly identical morphologies also occur within the highlands of Mars, including Hesperia Planum, Icaria Planum, Arabia Terra, Noachis Terra, and Terra Sirenum. A few examples of DLE craters are found at a range of elevations between -5.8 km to +2.7 km relative to the MOLA datum, and within two latitudes belts between 23° to 52° N, and between 29° to 46° S. Thus some other mode of formation apart from impact into volatile-rich sediments of the northern plains needs to be identified. Through our on-going characterization of DLE craters with THEMIS VIS data, we hope to identify the attributes of these craters to help identify their unique mode of formation.

  19. Double Layers: Potential Formation and Related Nonlinear Phenomena in Plasmas: Proceedings of the 5th Symposium

    NASA Astrophysics Data System (ADS)

    Iizuka, S.

    1998-02-01

    The Table of Contents for the book is as follows: * PREFACE * INTERNATIONAL SCIENTIFIC COMMITTEE * LOCAL ORGANIZING COMMITTEE AT TOHOKU UNIVERSITY * CHAPTER 1: DOUBLE LAYERS, SHEATHS, AND POTENTIAL STRUCTURES * 1.1 Double Layers * On Fluid Models of Stationary, Acoustic Double Layers (Invited) * Particle Simulation of Double Layer (Invited) * Space-Time Dependence of Non-Steady Double Layers * The Role of Low Energy Electrons for the Generation of Anode Double Layers in Glow Discharges * Arbitrary Amplitude Ion-Acoustic Double Layers in a Dusty Plasma * 1.2 Sheaths * Bounded Plasma Edge Physics as Observed from Simulations in 1D and 2D (Invited) * Control of RF Sheath Structure in RF Diode Discharge * Observation of Density Gradients with Fine Structures and Low Frequency Wave Excitation at the Plasma-Sheath Boundary * Double Sheath Associated with an Electron Emission to a Plasma Containing Negative Ions * Sheath Edge and Floating Potential for Multi-Species Plasmas Including Dust Particles * 1.3 Potential Structures and Oscillations * Potential Structure Formed at a Constriction of a DC He Positive Column and its Coupling with Ionization Wave * Potential Structure in a New RF Magnetron Device with a Hollow Electrode * Potential Disruption in a RF Afterglow Electronegative Plasma * Potential Oscillation in a Strongly Asymmetry RF Discharge Containing Negative Ions * Effects of External Potential Control on Coulomb Dust Behavior * Potential Structure of Carbon Arc Discharge for High-Yield Fullerenes Formation * Control of Axial and Radial Potential Profiles in Tandem Mirrors (Invited) * CHAPTER 2: FIELD-ALIGNED ELECTRIC FIELDS AND RELATED PARTICLE ACCELERATIONS * 2.1 Field-Aligned Potential Formation * Formation of Large Potential Difference in a Plasma Flow along Converging Magnetic Field Lines (Invited) * Presheath Formation in front of an Oblique End-Plate in a Magnetized Sheet Plasma * Plasma Potential Formation Due to ECRH in a Magnetic Well * Electrostatic

  20. Study of carrier blocking property of poly-linalyl acetate thin layer by electric-field-induced optical second-harmonic generation measurement

    NASA Astrophysics Data System (ADS)

    Taguchi, Dai; Manaka, Takaaki; Iwamoto, Mitsumasa; Anderson, Liam J.; Jacob, Mohan V.

    2014-02-01

    By using electric-field-induced optical second-harmonic generation (EFISHG) measurement, we studied the carrier-blocking property of poly-linalyl acetate (PLA) thin layers sandwiched in indium-zinc-oxide (IZO)/PLA/C60/Al double-layer diodes. Results showed that the PLA layer totally blocks electrons crossing the C60 layer, and also blocks holes entering from the IZO layer. The EFISHG measurement effectively substantiates the hole-blocking electron-blocking property of the PLA layer sandwiched in double layer diodes.

  1. On the dielectric response of complex layered oxides: Mica-type silicates and layered double hydroxides

    NASA Astrophysics Data System (ADS)

    Mehrotra, Vivek; Giannelis, Emmanuel P.

    1992-08-01

    The dielectric properties of mica-type silicates and layered double hydroxides have been studied in the pristine and various intercalated forms in the frequency range 101-107 Hz. A relaxation peak has been observed for the pristine silicate, whereas the pristine layered double hydroxide exhibits an anomalous low-frequency dispersion. The dielectric response is rationalized in terms of structural ordering and fluctuation of charge carriers as well as models invoking fractal time processes and fractal structure. The response is also related to the structure and mobility of the intercalated water molecules. In both pristine hosts, the predominant conduction mechanism is proton hopping between sites generated by a network of intercalated water molecules. Silicate intercalated with the insulating form of polyaniline exhibits an almost frequency-independent response. In the case of conducting polyaniline intercalated silicate, where polarons are the majority charge carriers, an anomalous low-frequency dispersion is observed and the response is typical of a metal-insulator composite. Finally, impedance measurements have been used to calculate the spatial disorder and/or surface irregularity of the host layers, expressed by the fractal dimension ds. The changes observed in ds upon intercalation of high-charge ions are correlated to the stacking disorder of the host layers.

  2. Tunable bandgap in few-layer black phosphorus by electrical field

    NASA Astrophysics Data System (ADS)

    Li, Dong; Xu, Jin-Rong; Ba, Kun; Xuan, Ningning; Chen, Mingyuan; Sun, Zhengzong; Zhang, Yu-Zhong; Zhang, Zengxing

    2017-09-01

    Dynamically engineering bandgap in semiconductors may enable a flexible design and optimization of electronics and optoelectronics. Layered black phosphorus is a 2D semiconductor with a direct bandgap and promising device characteristics. Theoretical studies indicate that the bandgap in black phosphorus can be tuned by electrical field. Here, through designing a double-gated field-effect transistor device configuration, we experimentally demonstrate that the bandgap in few-layer black phosphorus can be dynamically continually tuned by perpendicular electrical field. With an electrical displacement field of 1 V nm-1, the detailed study indicates that the bandgap can reduce around 100 meV. The finding here should be helpful on the flexible design and optimization of black phosphorus electronics and optoelectronics, and may open up some other new possible applications.

  3. Hybrid and biohybrid layered double hydroxides for electrochemical analysis.

    PubMed

    Mousty, Christine; Prévot, Vanessa

    2013-04-01

    Layered double hydroxides (LDH) are lamellar materials that have been extensively used as electrode modifiers. Nanostructured organic-inorganic materials can be designed by intercalation of organic or metallic complexes within the interlayer space of these materials or by the formation of composite materials based on biopolymers (alginate or chitosan) or biomolecules, such as enzymes. These hybrid or biohybrid materials have interesting properties applicable in electroanalytical devices. From an exhaustive review of the literature, the relevance of these hybrid and biohybrid LDH materials as electrode materials for electrochemical detection of species with an environmental or health impact is evaluated. The analytical characteristics (sensitivity and detection limit) of LDH-based amperometric sensors or biosensors are scrutinized.

  4. Double-layer shocks in a magnetized quantum plasma

    SciTech Connect

    Misra, A. P.; Samanta, S.

    2010-09-15

    The formation of small but finite amplitude electrostatic shocks in the propagation of quantum ion-acoustic waves obliquely to an external magnetic field is reported in a quantum electron-positron-ion plasma. Such shocks are seen to have double-layer (DL) structures composed of the compressive and accompanying rarefactive slow-wave fronts. Existence of such DL shocks depends critically on the quantum coupling parameter H associated with the Bohm potential and the positron to electron density ratio {delta}. The profiles may, however, steepen initially and reach a steady state with a number of solitary waves in front of the shocks. Such novel DL shocks could be a good candidate for particle acceleration in intense laser-solid density plasma interaction experiments as well as in compact astrophysical objects, e.g., magnetized white dwarfs.

  5. Biological evaluation of layered double hydroxides as efficient drug vehicles.

    PubMed

    Li, Yan; Liu, Dan; Ai, Hanhua; Chang, Qing; Liu, Dandan; Xia, Ying; Liu, Shuwen; Peng, Nanfang; Xi, Zhuge; Yang, Xu

    2010-03-12

    Recently there has been a rapid expansion of the development of bioinorganic hybrid systems for safe drug delivery. Layered double hydroxides (LDH), a variety of available inorganic matrix, possess great promise for this purpose. In this study, an oxidative stress biomarker system, including measurement of reactive oxygen species, glutathione content, endogenous nitric oxide, carbonyl content in proteins, DNA strand breaks and DNA-protein crosslinks, was designed to evaluate the biocompatibility of different concentrations of nano-Zn/Al-LDH with a Hela cell line. The drug delivery activity of the LDH-folic-acid complex was also assessed. The resulting data clearly demonstrated that nano-LDH could be applied as a relatively safe drug vehicle with good delivery activity, but with the caveat that the effects of high dosages observed here should not be ignored when attempting to maximize therapeutic activity by increasing LDH concentration.

  6. Layered double hydroxides: an attractive material for electrochemical biosensor design.

    PubMed

    Shan, Dan; Cosnier, Serge; Mousty, Christine

    2003-08-01

    Electrochemical biosensors for phenol determination were developed based on the immobilization of polyphenol oxidase (PPO) within two different clay matrixes, one anionic (layered double hydroxide, LDH) and the other cationic (Laponite). The biosensor based on the enzyme immobilized in [Zn-Al-Cl] LDH shows greater sensitivity (7807 mA M(-1) cm(-2)) and maximum current (492 microA cm(-2)). Biosensor characteristics, such as Michaelis-Menten constant, recycling constant, activation energy, and permeability highlight the advantages of LDH matrixes to immobilize PPO. It appears that LDH provides a favorable environment to PPO activity. The best PPO/[Zn-Al-Cl] configuration was used to determine five different phenol derivatives reaching extremely sensitive detection limits (< or = 1 nM).

  7. Layered Double Hydroxide-Based Nanocarriers for Drug Delivery

    PubMed Central

    Bi, Xue; Zhang, Hui; Dou, Liguang

    2014-01-01

    Biocompatible clay materials have attracted particular attention as the efficient drug delivery systems (DDS). In this article, we review developments in the use of layered double hydroxides (LDHs) for controlled drug release and delivery. We show how advances in the ability to synthesize intercalated structures have a significant influence on the development of new applications of these materials. We also show how modification and/or functionalization can lead to new biotechnological and biomedical applications. This review highlights the most recent progresses in research on LDH-based controlled drug delivery systems, focusing mainly on: (i) DDS with cardiovascular drugs as guests; (ii) DDS with anti-inflammatory drugs as guests; and (iii) DDS with anti-cancer drugs as guests. Finally, future prospects for LDH-based drug carriers are also discussed. PMID:24940733

  8. Terahertz wave generation and detection in double-graphene layered van der Waals heterostructures

    NASA Astrophysics Data System (ADS)

    Yadav, Deepika; Boubanga Tombet, Stephane; Watanabe, Takayuki; Arnold, Stevanus; Ryzhii, Victor; Otsuji, Taiichi

    2016-12-01

    We report on the first experimental observation of terahertz emission and detection in a double graphene layered (GL) heterostructure which comprises a thin hexagonal-boron nitride tunnel-barrier layer sandwiched between two separately contacted GLs. Inter-GL population inversion is induced by electrically biasing the structure. Resonant tunneling and negative differential resistance is expected when the two graphene band structures are perfectly aligned. However, in the case of small misalignments we demonstrate that the photon-absorption/emission-assisted non-resonant- and resonant-tunneling causes all excess charges in the n-type GL to recombine with the holes in the p-type GL giving rise to an increased measured dc current. This work highlights a novel strategy for the realization of efficient voltage-tunable terahertz emitters and detectors.

  9. Electric Field Double Probe Measurements for Ionospheric Space Plasma Experiments

    NASA Technical Reports Server (NTRS)

    Pfaff, R.

    1999-01-01

    Double probes represent a well-proven technique for gathering high quality DC and AC electric field measurements in a variety of space plasma regimes including the magnetosphere, ionosphere, and mesosphere. Such experiments have been successfully flown on a variety of spacecraft including sounding rockets and satellites. Typical instrument designs involve a series of trades, depending on the science objectives, type of platform (e.g., spinning or 3-axis stabilized), expected plasma regime where the measurements will be made, available telemetry, budget, etc. In general, ionospheric DC electric field instruments that achieve accuracies of 0.1 mV/m or better, place spherical sensors at large distances (10m or more) from the spacecraft body in order to extend well beyond the spacecraft wake and sheath and to achieve large signal-to-noise ratios for DC and long wavelength measurements. Additional sets of sensors inboard of the primary, outermost sensors provide useful additional information, both for diagnostics of the plasma contact potentials, which particularly enhance the DC electric field measurements on non-spinning spacecraft, and for wavelength and phase velocity measurements that use the spaced receiver or "interferometer" technique. Accurate attitude knowledge enables B times V contributions to be subtracted from the measured potentials, and permits the measured components to be rotated into meaningful geophysical reference frames. We review the measurement technique for both DC and wave electric field measurements in the ionosphere discussing recent advances involving high resolution burst memories, multiple baseline double probes, new sensor surface materials, biasing techniques, and other considerations.

  10. Layered double oxide (LDO) particle containing photoreactive hybrid layers with tunable superhydrophobic and photocatalytic properties

    NASA Astrophysics Data System (ADS)

    Deák, Ágota; Janovák, László; Csapó, Edit; Ungor, Ditta; Pálinkó, István; Puskás, Sándor; Ördög, Tibor; Ricza, Tamás; Dékány, Imre

    2016-12-01

    Inorganic/organic hybrid layers have been prepared having superhydrophobic as well as photoreactive properties. The hybrid thin films with micro- and nanosized dual-scale surface roughness consist of ∼25 μm layered double oxide (LDO) photocatalyst particles and low surface energy poly(perfluorodecyl acrylate) [p(PFDAc)] fluoropolymer binder material. The application of [p(PFDAc)] resulted in the decrease in the surface free energy of the hydrophilic LDO. The structured surface LDO with ∼12% ZnO phase content were synthesized from layer double hydroxide (LDH) spheres. The determined excitation wavelength and the calculated band gap energy values were 386 nm and 3.23 eV, respectively. The hybrid thin films were prepared by a simple spray-coating method, which is a low-cost, fast and scalable film-forming technique. The surface roughness and also the wetting properties of the two-component hybrid layers proved to be finely adjustable by the LDO:fluoropolymer ratio. It was found that at 80-90 wt% LDO content, the thin films with a surface free energy value of ∼12 mJ/m2 displayed superhydrophobic behaviour (Θ > 150°) with satisfactory photocatalytic properties. This means special photoreactive surfaces with superhydrophobic properties instead of the conventional superhydropilic photocatalyst layers. According to the benzoic acid photodegradation test experiments of benzoic acid, the hybrid layers with 80-90 wt% LDO content photooxidized 22-24% of the initial test molecule concentration (0.17 g/L) under UV-A (λmax = 365 nm) illumination.

  11. THE n-DISTRIBUTION OF ELECTRONS AND DOUBLE LAYERS IN THE ELECTRON-BEAM-RETURN-CURRENT SYSTEM OF SOLAR FLARES

    SciTech Connect

    Karlicky, Marian

    2012-05-01

    We investigate processes in the electron-beam-return-current system in the impulsive phase of solar flares to answer a question about the formation of the n-electron distribution detected in this phase of solar flares. An evolution of the electron-beam-return-current system with an initial local density depression is studied using a three-dimensional electromagnetic particle-in-cell model. In the system the strong double layer is formed. Its electric field potential increases with the electron beam flux. In this electric field potential, the electrons of background plasma are strongly accelerated and propagate in the return-current direction. The high-energy part of their distribution at the high-potential side of the strong double layer resembles that of the n-distribution. Thus, the detection of the n-distributions, where a form of the high-energy part of the distribution is the most important, can indicate the presence of strong double layers in solar flares. The similarity between processes in solar flare loops and those in the downward current region of the terrestrial aurora, where the double layers were observed by FAST satellite, supports this idea.

  12. Eddy turbulence, the double mesopause, and the double layer of atomic oxygen

    NASA Astrophysics Data System (ADS)

    Vlasov, M. N.; Kelley, M. C.

    2012-01-01

    In this study, we consider the impact of eddy turbulence on temperature and atomic oxygen distribution when the peak of the temperature occurs in the upper mesosphere. A previous paper (Vlasov and Kelley, 2010) considered the simultaneous impact of eddy turbulence on temperature and atomic oxygen density and showed that eddy turbulence provides an effective mechanism to explain the cold summer and warm winter mesopause observed at high latitudes. Also, the prevalent role of eddy turbulence in this case removes the strong contradiction between seasonal variations of the O density distribution and the impact of upward/downward motion corresponding to adiabatic cooling/heating of oxygen atoms. Classically, there is a single minimum in the temperature profile marking the location of the mesopause. But often, a local maximum in the temperature is observed in the height range of 85-100 km, creating the appearance of a double mesopause (Bills and Gardner, 1993; Yu and She, 1995; Gusev et al., 2006). Our results show that the relative temperature maximum in the upper mesosphere (and thus the double mesopause) can result from heating by eddy turbulence. According to our model, there is a close connection between the extra temperature peak in the mesosphere and the oxygen atom density distribution. The main feature of the O density height profile produced by eddy turbulence in our model is a double peak instead of a single peak of O density. A rocket experiment called TOMEX confirms these results (Hecht et al., 2004). Applying our model to the results of the TOMEX rocket campaign gives good agreement with both the temperature and oxygen profiles observed. Climatology of the midlatitude mesopause and green line emission shows that the double mesopause and the double layers of the green line emission, corresponding to the double O density height profile, are mainly observed in spring and fall (Yu and She, 1995; Liu and Shepherd, 2006). Further observations of the oxygen atom

  13. Vorticity Transport in a Two Layer, Double Gyre Ocean Basin

    NASA Astrophysics Data System (ADS)

    Kaiser, Bryan; Clayson, Carol Anne; Jayne, Steve

    2016-11-01

    The double gyre ocean circulations predicted by strongly frictional, barotropic, linearized ocean models qualitatively agree with the patterns of large scale gyres in the world ocean. However, nonlinear ocean models featuring less intense eddy diffusion parameterization can converge to an infinite number of statistically stationary circulations, depending on the parameterization of dissipation of energy and vorticity. Patterns of vorticity flux and dissipation in a barotropic ocean have been examined previous studies; in this work the inclusion of the first baroclinic mode is examined. The first vertical mode permits the model to be split into two layers, the top approximating the thermocline and the bottom approximating the abyssal circulation. The separation into two layers not only adds realism and but also removes the nonphysical direct restraint of the upper ocean by bottom friction. Steady state circulations for various boundary conditions, sources and sinks of vorticity, and Reynolds numbers are simulated using a parallel pseudo-spectral quasi-geostrophic flow solver and mechanisms of vorticity flux and dissipation are discussed.

  14. Plasmons in spatially separated double-layer graphene nanoribbons

    NASA Astrophysics Data System (ADS)

    Bagheri, Mehran; Bahrami, Mousa

    2014-05-01

    Motivated by innovative progresses in designing multi-layer graphene nanostructured materials in the laboratory, we theoretically investigate the Dirac plasmon modes of a spatially separated double-layer graphene nanoribbon system, made up of a vertically offset armchair and metallic graphene nanoribbon pair. We find striking features of the collective excitations in this novel Coulomb correlated system, where both nanoribbons are supposed to be either intrinsic (undoped/ungated) or extrinsic (doped/gated). In the former, it is shown the low-energy acoustical and the high-energy optical plasmon modes are tunable only by the inter-ribbon charge separation. In the later, the aforementioned plasmon branches are modified by the added doping factor. As a result, our model could be useful to examine the existence of a linear Landau-undamped low-energy acoustical plasmon mode tuned via the inter-ribbon charge separation as well as doping. This study might also be utilized for devising novel quantum optical waveguides based on the Coulomb coupled graphene nanoribbons.

  15. Layered double hydroxides as anion- and cation-exchanging materials

    NASA Astrophysics Data System (ADS)

    Richardson, Mickey Charles

    2007-12-01

    Layered double hydroxides (LDH) have been principally known as anion-exchanging, clay-like materials for several decades, and continues to be the main driving force for current and future research. The chemical interactions of LDH, with transition metallocyanides, have been a popular topic of investigation for many years, partly due to the use of powder x-ray diffraction and infrared spectroscopy as the main characterization tools. Each transition metallocyanide has a characteristic infrared stretching frequency that can be easily observed, and their respective sizes can be observed while intercalated within the interlayer of the LDH. The ability of LDH to incorporate metal cations or any ions/molecules/complexes, that have a postive charge, have not been previously investigated, mainly due to the chemical and physical nature of LDH. The possibility of cationic incorporation with LDH would most likely occur by surface adsorption, lattice metal replacement, or by intercalation into the LDH interlayers. Although infrared spectroscopy finds it main use through the identification of the anions incorporated with LDH, it can also be used to study and identify the various active and inactive bending and stretching modes that the metal hydroxide layers have.

  16. Plasmons in spatially separated double-layer graphene nanoribbons

    SciTech Connect

    Bagheri, Mehran; Bahrami, Mousa

    2014-05-07

    Motivated by innovative progresses in designing multi-layer graphene nanostructured materials in the laboratory, we theoretically investigate the Dirac plasmon modes of a spatially separated double-layer graphene nanoribbon system, made up of a vertically offset armchair and metallic graphene nanoribbon pair. We find striking features of the collective excitations in this novel Coulomb correlated system, where both nanoribbons are supposed to be either intrinsic (undoped/ungated) or extrinsic (doped/gated). In the former, it is shown the low-energy acoustical and the high-energy optical plasmon modes are tunable only by the inter-ribbon charge separation. In the later, the aforementioned plasmon branches are modified by the added doping factor. As a result, our model could be useful to examine the existence of a linear Landau-undamped low-energy acoustical plasmon mode tuned via the inter-ribbon charge separation as well as doping. This study might also be utilized for devising novel quantum optical waveguides based on the Coulomb coupled graphene nanoribbons.

  17. Anisotropic hybrid excitation modes in monolayer and double-layer phosphorene on polar substrates

    NASA Astrophysics Data System (ADS)

    Saberi-Pouya, S.; Vazifehshenas, T.; Salavati-fard, T.; Farmanbar, M.

    2017-09-01

    We investigate the anisotropic hybrid surface optical (SO) phonon-plasmon dispersion relations in monolayer and double-layer phosphorene systems located on the polar substrates, such as SiO2, h -BN, and Al2O3 . We calculate these hybrid modes by using the dynamical dielectric function in the random phase approximation in which the electron-electron interaction and long-range electric field generated by the substrate SO phonons via Fröhlich interaction are taken into account. In the long-wavelength limit, we obtain some analytical expressions for the hybrid SO phonon-plasmon dispersion relations which agree with those obtained from the loss function. Our results indicate a strong anisotropy in SO phonon-plasmon modes, which are stronger along the light-mass direction in our heterostructures. Furthermore, we find that the type of substrate has a significant effect on the dispersion relations of the coupled modes. Importantly, the hybrid excitations are apparently sensitive to the misalignment and separation between layers in double-layer phosphorene.

  18. Propagation characteristics of ion-acoustic double layer in multicomponent inhomogeneous auroral zone plasma

    NASA Astrophysics Data System (ADS)

    Kaur, Harvinder; Gill, Tarsem Singh; Bala, Parveen

    2017-08-01

    In the present investigation, ion-acoustic double layers in an inhomogeneous plasma consisting of Maxwellian and non-thermal distributions of electrons are studied. We have derived a modified Korteweg-de Vries (mKdV) equation for ion-acoustic double layers propagating in a collisionless inhomogeneous plasma. It is observed that the non-thermal parameters affect the amplitude and width of the double layer which further depend on the density.

  19. On the generation of double layers from ion- and electron-acoustic instabilities

    SciTech Connect

    Fu, Xiangrong Cowee, Misa M.; Winske, Dan; Gary, S. Peter

    2016-03-15

    A plasma double layer (DL) is a nonlinear electrostatic structure that carries a uni-polar electric field parallel to the background magnetic field due to local charge separation. Past studies showed that DLs observed in space plasmas are mostly associated with the ion acoustic instability. Recent Van Allen Probes observations of parallel electric field structures traveling much faster than the ion acoustic speed have motivated a computational study to test the hypothesis that a new type of DLs—electron acoustic DLs—generated from the electron acoustic instability are responsible for these electric fields. Nonlinear particle-in-cell simulations yield negative results, i.e., the hypothetical electron acoustic DLs cannot be formed in a way similar to ion acoustic DLs. Linear theory analysis and the simulations show that the frequencies of electron acoustic waves are too high for ions to respond and maintain charge separation required by DLs. However, our results do show that local density perturbations in a two-electron-component plasma can result in unipolar-like electric field structures that propagate at the electron thermal speed, suggesting another potential explanation for the observations.

  20. On the generation of double layers from ion- and electron-acoustic instabilities

    NASA Astrophysics Data System (ADS)

    Fu, Xiangrong; Cowee, Misa M.; Gary, S. Peter; Winske, Dan

    2016-03-01

    A plasma double layer (DL) is a nonlinear electrostatic structure that carries a uni-polar electric field parallel to the background magnetic field due to local charge separation. Past studies showed that DLs observed in space plasmas are mostly associated with the ion acoustic instability. Recent Van Allen Probes observations of parallel electric field structures traveling much faster than the ion acoustic speed have motivated a computational study to test the hypothesis that a new type of DLs—electron acoustic DLs—generated from the electron acoustic instability are responsible for these electric fields. Nonlinear particle-in-cell simulations yield negative results, i.e., the hypothetical electron acoustic DLs cannot be formed in a way similar to ion acoustic DLs. Linear theory analysis and the simulations show that the frequencies of electron acoustic waves are too high for ions to respond and maintain charge separation required by DLs. However, our results do show that local density perturbations in a two-electron-component plasma can result in unipolar-like electric field structures that propagate at the electron thermal speed, suggesting another potential explanation for the observations.

  1. On the generation of double layers from ion- and electron-acoustic instabilities

    DOE PAGES

    Fu, Xiangrong; Cowee, Misa M.; Gary, Stephen Peter; ...

    2016-03-17

    A plasma double layer (DL) is a nonlinear electrostatic structure that carries a uni-polar electric field parallel to the background magnetic field due to local charge separation. Past studies showed that DLs observed in space plasmas are mostly associated with the ion acoustic instability. Recent Van Allen Probes observations of parallel electric fields traveling much faster than the ion acoustic speed have motivated a computational study to test the hypothesis that a new type of DLs – electron acoustic DLs – generated from the electron acoustic instability are responsible for these electric fields. Nonlinear particle-in-cell simulations yield negative results, i.e.more » the hypothetical electron acoustic DLs cannot be formed in a way similar to ion acoustic DLs. We find that linear theory analysis and the simulations show that the frequencies of electron acoustic waves are too high for ions to respond and maintain charge separation required by DLs. However, our results do show that local density perturbations in a two-electron-component plasma can result in unipolar-like electric fields that propagate at the electron thermal speed, suggesting another potential explanation for the observations.« less

  2. A mechanism for weak double layers and coherent low-frequency electrostatic wave activity in the solar wind

    NASA Astrophysics Data System (ADS)

    Singh Lakhina, Gurbax; Singh, Satyavir

    2016-07-01

    A mechanism for the weak double layers and coherent low-frequency electrostatic wave activity observed by Wind spacecraft in the solar wind at 1 AU is proposed in terms of ion-acoustic solitons and double layers. The solar wind plasma is modelled by a three component plasma consisting of fluid hot protons, hot alpha particles streaming with respect to protons, and suprathermal electrons having κ- distribution. This system supports two types of, slow and fast, ion-acoustic solitary waves. The fast ion-acoustic mode is similar to the ion-acoustic mode of proton-electron plasma, and can support only positive potential solitons. The slow ion-acoustic mode is a new mode that occurs due to the presence of alpha particles. This mode can support both positive and negative solitons and double layers. An increase of the κ- index leads to an increase in the critical Mach number, maximum Mach number and the maximum amplitude of both slow and fast ion-acoustic solitons. The slow ion-acoustic double layer can explain the amplitudes and widths, but not shapes, of the weak double layers (WDLs) observed in the solar wind at 1 AU by Wind spacecraft. The Fourier transform of the slow ion-acoustic solitons/double layers would produce broadband low-frequency electrostatic waves having main peaks between 0.35 kHz to 1.6 kHz, with electric field in the range of E = (0.01 - 0.7 ) mV/m, in excellent agreement with the observed low-frequency electrostatic wave activity in the solar wind at 1 AU.

  3. Large-scale simulations of layered double hydroxide nanocomposite materials

    NASA Astrophysics Data System (ADS)

    Thyveetil, Mary-Ann

    Layered double hydroxides (LDHs) have the ability to intercalate a multitude of anionic species. Atomistic simulation techniques such as molecular dynamics have provided considerable insight into the behaviour of these materials. We review these techniques and recent algorithmic advances which considerably improve the performance of MD applications. In particular, we discuss how the advent of high performance computing and computational grids has allowed us to explore large scale models with considerable ease. Our simulations have been heavily reliant on computational resources on the UK's NGS (National Grid Service), the US TeraGrid and the Distributed European Infrastructure for Supercomputing Applications (DEISA). In order to utilise computational grids we rely on grid middleware to launch, computationally steer and visualise our simulations. We have integrated the RealityGrid steering library into the Large-scale Atomic/Molecular Massively Parallel Simulator (LAMMPS) 1 . which has enabled us to perform re mote computational steering and visualisation of molecular dynamics simulations on grid infrastruc tures. We also use the Application Hosting Environment (AHE) 2 in order to launch simulations on remote supercomputing resources and we show that data transfer rates between local clusters and super- computing resources can be considerably enhanced by using optically switched networks. We perform large scale molecular dynamics simulations of MgiAl-LDHs intercalated with either chloride ions or a mixture of DNA and chloride ions. The systems exhibit undulatory modes, which are suppressed in smaller scale simulations, caused by the collective thermal motion of atoms in the LDH layers. Thermal undulations provide elastic properties of the system including the bending modulus, Young's moduli and Poisson's ratios. To explore the interaction between LDHs and DNA. we use molecular dynamics techniques to per form simulations of double stranded, linear and plasmid DNA up

  4. Energy distribution of elastically scattered electrons from double layer samples

    NASA Astrophysics Data System (ADS)

    Tőkési, K.; Varga, D.

    2016-02-01

    We present a theoretical description of the spectra of electrons elastically scattered from thin double layered Au-C samples. The analysis is based on the Monte Carlo simulation of the recoil and Doppler effects in reflection and transmission geometries of the scattering at a fixed angle of 44.3 ° and a primary energy of 40 keV. The relativistic correction is taken into account. Besides the experimentally measurable energy distributions the simulations give many partial distributions separately, depending on the number of elastic scatterings (single, and multiple scatterings of different types). Furthermore, we present detailed analytical calculations for the main parameters of the single scattering, taking into account both the ideal scattering geometry, i.e. infinitesimally small angular range, and the effect of the real, finite angular range used in the measurements. We show our results for intensity ratios, peak shifts and broadenings for four cases of measurement geometries and layer thicknesses. While in the peak intensity ratios of gold and carbon for transmission geometries were found to be in good agreement with the results of the single scattering model, especially large deviations were obtained in reflection geometries. The separation of the peaks, depending on the geometry and the thickness, generally smaller, and the peak width generally larger than it can be expected from the nominal values of the primary energy, scattering angle, and mean kinetic energy of the atoms. We also show that the peaks are asymmetric even for the case of the single scattering due to the finite solid angle. Finally, we present a qualitative comparison with the experimental data. We find our resulting energy distribution of elastically scattered electrons to be in good agreement with recent measurements.

  5. Transport spectroscopy in bilayer graphene using double layer heterostructures

    NASA Astrophysics Data System (ADS)

    Lee, Kayoung; Jung, Jeil; Fallahazad, Babak; Tutuc, Emanuel

    2017-09-01

    We provide a comprehensive study of the chemical potential of bilayer graphene in a wide range of carrier density, at zero and high magnetic (B)-fields, and at different transverse electric (E)-fields, using high quality double bilayer graphene heterostructures. Using a direct thermodynamic transport spectroscopic technique, we probe the chemical potential as a function of carrier density in six samples. The data clearly reveal the non-parabolicity and electron-hole asymmetry of energy-momentum dispersion in bilayer graphene. The tight-binding hopping amplitudes, t 0, t 1, and t 4, renormalized by electron-electron interaction are extracted from the chemical potential versus density dependence. A diverse set of electron-electron interaction driven phenomena were also clearly discerned at zero and high B-fields. We measure the gaps at integer fillings with orbital index N  =  0, 1, and discuss about the dependence of the N  =  0, 1 quantum Hall phases on the carrier density (or filling factor), E-field, and B-field.

  6. Illustrating the processability of magnetic layered double hydroxides: layer-by-layer assembly of magnetic ultrathin films.

    PubMed

    Coronado, E; Martí-Gastaldo, C; Navarro-Moratalla, E; Ribera, A; Tatay, S

    2013-05-20

    We report the preparation of single-layer layered double hydroxide (LDH) two-dimensional (2D) nanosheets by exfoliation of highly crystalline NiAl-NO3 LDH. Next, these unilamellar moieties have been incorporated layer-by-layer (LbL) into a poly(sodium 4-styrenesulfonate)/LDH nanosheet multilayer ultrathin film (UTF). Fourier transform infrared spectroscopy (FT-IR), ultraviolet-visible light (UV-vis), and X-ray diffraction (XRD) profiles have been used to follow the uniform growth of the UTF. The use of a magnetic LDH as the cationic component of the multilayered architecture enables study of the resulting magnetic properties of the UTFs. Our magnetic data show the appearance of spontaneous magnetization at ∼5 K, thus confirming the effective transfer of the magnetic properties of the bulk LDH to the self-assembled film that displays glassy-like ferromagnetic behavior. The high number of bilayers accessible-more than 80-opens the door for the preparation of more-complex hybrid multifunctional materials that combine magnetism with the physical properties provided by other exfoliable layered inorganic hosts.

  7. [Sorption of nitrobenzene to anionic surfactant modified layered double hydroxides].

    PubMed

    Xia, Yan; Zhu, Run-Liang; Tao, Qi; Liu, Han-Yang

    2013-01-01

    Sodium dodecyl sulfate (SDS) modified MgAl layered double hydroxides (LDHs) were synthesized at different surfactant concentrations (0.5-2.0 TAEC) by the co-precipitation method. The LDH-DS samples obtained were characterized by powder X-ray diffraction and FT-IR spectroscopy. The results showed that SDS was successfully intercalated into the interlayer of the LDH, and the basal spacing was expanded from 0.80 nm to 3.98 nm. The intercalated SDS was considered consistent with a paraffin bilayers arrangement. The sorption of nitrobenzene on LDH-DS was examined, and the results showed that linear model could fit the sorption isotherms well (R2 > 0.99), which implied a partitioning sorption process. The sorption coefficient of nitrobenzene (K(d)) on LDH-DS was positively related to the DS - loading amount, but the organic carbon content normalized sorption coefficient of nitrobenzene (K(oc)) was shown to remain relatively constant. The sorption thermodynamics results showed that the sorption of nitrobenzene on LDH-DS was an endothermic process, and the increase of entropy was the driving force for the sorption process.

  8. Novel synthesis of layered double hydroxides (LDHs) from zinc hydroxide

    NASA Astrophysics Data System (ADS)

    Meng, Zilin; Zhang, Yihe; Zhang, Qian; Chen, Xue; Liu, Leipeng; Komarneni, Sridhar; Lv, Fengzhu

    2017-02-01

    The most common synthesis methods for layered double hydroxides (LDHs) are co-precipitation and reconstruction, which can have some limitations for application. Here, we report a novel synthesis method for LDHs. We use zinc hydroxide as the precursor to synthesize LDHs phase through a simple transformation process of zinc hydroxide phase. For this transformation process, aluminum can enter into zinc hydroxide and replace zinc quickly to transform it into LDH by creating positive charges in the zinc hydroxide solid phase. The mechanism of LDH formation was through Al3+ reaction first with zinc hydroxide followed by recrystallization of the original structure of zinc hydroxide. Thus, the new process of LDH formation involves a reaction of Al to substitute for Zn and recrystallization leading to LDH and the final pH influences the crystallization of LDHs by this process. In addition, Cr3+ was employed as a trivalent cation for LDH formation to react with zinc hydroxide, which also led to LDH structure.

  9. Immobilization of individual nanotubes in graphitic layers for electrical characterization

    NASA Astrophysics Data System (ADS)

    Roy, Debmalya; Tiwari, Neeru; Mukhopadhyay, K.; Saxena, A. K.

    2014-03-01

    A simple route is followed to produce an abundance of individual carbon nanotubes (CNTs) immobilized in graphitic layers to counter the challenge of locating individual CNTs and restrict the lateral displacement of CNTs due to the high electrostatic force exerted by a scanning tunnelling microscope tip for electrical characterization. Graphitic layers are selected for the embedding matrix as graphite and the nanotubes have a similar work function and hence would not perturb the electrical configuration of the nanotube. Solvent mediated exfoliation of graphite layers to insert the nanotubes was preferred over oxidative expansion, as oxidation could perturb the electrical configuration of graphite. During the exfoliation of graphite the optimized amount of nanotubes was introduced into the medium such that an individual nanotube could be immobilized in few-layer graphene followed by precipitation and centrifugation. The dose and the time of sonication were optimized to ensure that damage to the walls of the nanotubes is minimized, although the ultrasonication causes scissoring of the nanotube length. This procedure for immobilizing nanotubes in graphitic layers would be equally applicable for functionalized CNTs as well. The capability of embedding individual nanotubes into a similar work function material in an organic solvent, which could then be transferred onto a substrate by simple drop casting or spin coating methods, has an added advantage in sample preparation for the STM characterization of CNTs.

  10. Layered double hydroxide nanoparticles in gene and drug delivery.

    PubMed

    Ladewig, Katharina; Xu, Zhi Ping; Lu, Gao Qing Max

    2009-09-01

    Layered double hydroxides (LDHs) have been known for many decades as catalyst and ceramic precursors, traps for anionic pollutants, catalysts and additives for polymers, but their successful synthesis on the nanometer scale a few years ago opened up a whole new field for their application in nanomedicine. The delivery of drugs and other therapeutic/bioactive molecules (e.g., peptides, proteins, nucleic acids) to mammalian cells is an area of research that is of tremendous importance to medicine and provides manifold applications for any new developments in the area of nanotechnology. Among the many different nanoparticles that have been shown to facilitate gene and/or drug delivery, LDH nanoparticles have attracted particular attention owing to their many desirable properties. This review aims to report recent progress in gene and drug delivery using LDH nanoparticles. It summarizes the advantages and disadvantages of using LDH nanoparticles as carriers for nucleic acids and drugs against the general background of bottlenecks that are encountered by cellular delivery systems. It describes further the models that have been proposed for the internalization of LDH nanoparticles into cells so far and discusses the intracellular fate of the particles and their cargo. The authors offer some remarks on how this field of research will progress in the near future and which challenges need to be overcome before LDH nanoparticles can be used in a clinical setting.

  11. Lubrication approximation in completed double layer boundary element method

    NASA Astrophysics Data System (ADS)

    Nasseri, S.; Phan-Thien, N.; Fan, X.-J.

    This paper reports on the results of the numerical simulation of the motion of solid spherical particles in shear Stokes flows. Using the completed double layer boundary element method (CDLBEM) via distributed computing under Parallel Virtual Machine (PVM), the effective viscosity of suspension has been calculated for a finite number of spheres in a cubic array, or in a random configuration. In the simulation presented here, the short range interactions via lubrication forces are also taken into account, via the range completer in the formulation, whenever the gap between two neighbouring particles is closer than a critical gap. The results for particles in a simple cubic array agree with the results of Nunan and Keller (1984) and Stoksian Dynamics of Brady etal. (1988). To evaluate the lubrication forces between particles in a random configuration, a critical gap of 0.2 of particle's radius is suggested and the results are tested against the experimental data of Thomas (1965) and empirical equation of Krieger-Dougherty (Krieger, 1972). Finally, the quasi-steady trajectories are obtained for time-varying configuration of 125 particles.

  12. Dislocated double-layer metal gratings: an efficient unidirectional coupler.

    PubMed

    Liu, Tianran; Shen, Yang; Shin, Wonseok; Zhu, Qiangzhong; Fan, Shanhui; Jin, Chongjun

    2014-07-09

    We propose theoretically and demonstrate experimentally a dislocated double-layer metal grating structure, which operates as a unidirectional coupler capable of launching surface plasmon polaritons in a desired direction under normal illumination. The structure consists of a slanted dielectric grating sandwiched between two gold gratings. The upper gold grating has a nonzero lateral relative displacement with respect to the lower one. Numerical simulations show that a grating structure with 7 periods can convert 49% of normally incident light into surface plasmons with a contrast ratio of 78 between the powers of the surface plasmons launched in two opposite directions. We explain the unidirectional coupling phenomenon by the dislocation-induced interference of the diffracted waves from the upper and lower gold gratings. Furthermore, we developed a simple and cost-effective technique to fabricate the structure via tilted two-beam interference lithography and subsequent shadow deposition of gold. The experimental results demonstrate a coupling efficiency of 36% and a contrast ratio of 43. The relatively simple periodic nature of our structure lends itself to large-scale low-cost fabrication and simple theoretical analysis. Also, unlike the previous unidirectional couplers based on aperiodic structures, the design parameters of our unidirectional coupler can be determined analytically. Therefore, this structure can be an important component for surface-plasmon-based nanophotonic circuits by providing an efficient interface between free-space and surface plasmon waves.

  13. Immobilization of individual nanotubes in graphitic layers for electrical characterization.

    PubMed

    Roy, Debmalya; Tiwari, Neeru; Mukhopadhyay, K; Saxena, A K

    2014-03-21

    A simple route is followed to produce an abundance of individual carbon nanotubes (CNTs) immobilized in graphitic layers to counter the challenge of locating individual CNTs and restrict the lateral displacement of CNTs due to the high electrostatic force exerted by a scanning tunnelling microscope tip for electrical characterization. Graphitic layers are selected for the embedding matrix as graphite and the nanotubes have a similar work function and hence would not perturb the electrical configuration of the nanotube. Solvent mediated exfoliation of graphite layers to insert the nanotubes was preferred over oxidative expansion, as oxidation could perturb the electrical configuration of graphite. During the exfoliation of graphite the optimized amount of nanotubes was introduced into the medium such that an individual nanotube could be immobilized in few-layer graphene followed by precipitation and centrifugation. The dose and the time of sonication were optimized to ensure that damage to the walls of the nanotubes is minimized, although the ultrasonication causes scissoring of the nanotube length. This procedure for immobilizing nanotubes in graphitic layers would be equally applicable for functionalized CNTs as well. The capability of embedding individual nanotubes into a similar work function material in an organic solvent, which could then be transferred onto a substrate by simple drop casting or spin coating methods, has an added advantage in sample preparation for the STM characterization of CNTs.

  14. Junction conditions in quadratic gravity: thin shells and double layers

    NASA Astrophysics Data System (ADS)

    Reina, Borja; Senovilla, José M. M.; Vera, Raül

    2016-05-01

    The junction conditions for the most general gravitational theory with a Lagrangian containing terms quadratic in the curvature are derived. We include the cases with a possible concentration of matter on the joining hypersurface—termed as thin shells, domain walls or braneworlds in the literature—as well as the proper matching conditions where only finite jumps of the energy-momentum tensor are allowed. In the latter case we prove that the matching conditions are more demanding than in general relativity. In the former case, we show that generically the shells/domain walls are of a new kind because they possess, in addition to the standard energy-momentum tensor, a double layer energy-momentum contribution which actually induces an external energy flux vector and an external scalar pressure/tension on the shell. We prove that all these contributions are necessary to make the entire energy-momentum tensor divergence-free, and we present the field equations satisfied by these energy-momentum quantities. The consequences of all these results are briefly analyzed.

  15. Methotrexate intercalated ZnAl-layered double hydroxide

    NASA Astrophysics Data System (ADS)

    Chakraborty, Manjusha; Dasgupta, Sudip; Soundrapandian, Chidambaram; Chakraborty, Jui; Ghosh, Swapankumar; Mitra, Manoj K.; Basu, Debabrata

    2011-09-01

    The anticancerous drug methotrexate (MTX) has been intercalated into an ZnAl-layered double hydroxide (LDH) using an anion exchange technique to produce LDH-MTX hybrids having particle sizes in the range of 100-300 nm. X-ray diffraction studies revealed increases in the basal spacings of ZnAl-LDH-MTX hybrid on MTX intercalation. This was corroborated by the transmission electron micrographs, which showed an increase in average interlayer spacing from 8.9 Å in pristine LDH to 21.3 Å in LDH-MTX hybrid. Thermogravimetric analyses showed an increase in the decomposition temperature for the MTX molecule in the LDH-MTX hybrid indicating enhanced thermal stability of the drug molecule in the LDH nanovehicle. The cumulative release profile of MTX from ZnAl-LDH-MTX hybrids in phosphate buffer saline (PBS) at pH 7.4 was successfully sustained for 48 h following Rigter-Peppas model release kinetics via diffusion.

  16. Bionanocomposites based on layered double hydroxides as drug delivery systems

    NASA Astrophysics Data System (ADS)

    Aranda, Pilar; Alcântara, Ana C. S.; Ribeiro, Ligia N. M.; Darder, Margarita; Ruiz-Hitzky, Eduardo

    2012-10-01

    The present work introduces new biohybrid materials involving layered double hydroxides (LDH) and biopolymers to produce bionanocomposites, able to act as effective drug delivery systems (DDS). Ibuprofen (IBU) and 5-aminosalicylic acid (5-ASA) have been chosen as model drugs, being intercalated in a Mg-Al LDH matrix. On the one side, the LDHIBU intercalation compound prepared by ion-exchange reaction was blended with the biopolymers zein, a highly hydrophobic protein, and alginate, a polysaccharide widely applied for encapsulating drugs. On the other side, the LDH- 5-ASA intercalation compound prepared by co-precipitation was assembled to the polysaccharides chitosan and pectin, which show mucoadhesive properties and resistance to acid pH values, respectively. Characterization of the intercalation compounds and the resulting bionanocomposites was carried out by means of different experimental techniques: X-ray diffraction, infrared spectroscopy, chemical and thermal analysis, as well as optical and scanning electron microscopies. Data on the swelling behavior and drug release under different pH conditions are also reported.

  17. Ion-cyclotron turbulence and diagonal double layers in a magnetospheric plasma

    NASA Technical Reports Server (NTRS)

    Liperovskiy, V. A.; Pudovkin, M. I.; Skuridin, G. A.; Shalimov, S. L.

    1981-01-01

    A survey of current concepts regarding electrostatic ion-cyclotron turbulence (theory and experiment), and regarding inclined double potential layers in the magnetospheric plasma is presented. Anomalous resistance governed by electrostatic ion-cyclotron turbulence, and one-dimensional and two-dimensional models of double electrostatic layers in the magnetospheric plasma are examined.

  18. Double-layer structure in polar mesospheric clouds observed from SOFIE/AIM

    NASA Astrophysics Data System (ADS)

    Gao, Haiyang; Shepherd, Gordon G.; Tang, Yuanhe; Bu, Lingbing; Wang, Zhen

    2017-02-01

    Double-layer structures in polar mesospheric clouds (PMCs) are observed by using Solar Occultation for Ice Experiment (SOFIE) data between 2007 and 2014. We find 816 and 301 events of double-layer structure with percentages of 10.32 and 7.25 % compared to total PMC events, and the mean distances between two peaks are 3.06 and 2.73 km for the Northern Hemisphere (NH) and Southern Hemisphere (SH) respectively. Double-layer PMCs almost always have less mean ice water content (IWC) than daily IWC during the core of the season, but they are close to each other at the beginning and the end. The result by averaging over all events shows that the particle concentration has obvious double peaks, while the particle radius exhibits an unexpected monotonic increase with decreasing altitude. By further analysis of the background temperature and water vapour residual profiles, we conclude that the lower layer is a reproduced one formed at the bottom of the upper layer. 56.00 and 47.51 % of all double-layer events for the NH and SH respectively have temperature enhancements larger than 2 K locating between their double peaks. The longitudinal anti-correlation between the gravity waves' (GWs') potential energies and occurrence frequencies of double-layer PMCs suggests that the double-layer PMCs tend to form in an environment where the GWs have weaker intensities.

  19. Evidence of current free double layer in high density helicon discharge

    SciTech Connect

    Ganguli, A.; Sahu, B. B.; Tarey, R. D.

    2013-01-15

    This paper investigates the formation of double layer (DL) in helicon plasmas. In the experiment, argon plasma production is using the excitation of m = -1 helicon mode with magnetic mirror field with high mirror ratio of {approx}1:1.7. We have specifically used the radio frequency compensated Langmuir probe (LP) to measure the relevant plasma parameters simultaneously so as to investigate the details about the plasma production. The DL, which consists of both warm and bulk populations towards higher potential region and only dense bulk plasmas towards the lower potential region downstream the antenna, is present in the transition region. LP measurements also show an abrupt fall of density along with a potential drop of about 20 V and (e {Delta}V{sub p}/k T{sub e}) Almost-Equal-To 12 within a few cm. The potential drop is equal to the difference of the electron temperatures between the two plasma regions forming the DL, which is present in the plateau region of mirror, unlike in several prior studies on the DL formation in the region of strong gradients in the magnetic field. The DL is strong, current-free, electric double-layer with estimated thickness of about 10 Debye lengths.

  20. Surface-charging behavior of Zn-Cr layered double hydroxide.

    PubMed

    Rojas Delgado, R; Arandigoyen Vidaurre, M; De Pauli, C P; Ulibarri, M A; Avena, M J

    2004-12-15

    A Zn-Cr layered double hydroxide (LDH) having the formula Zn(2)Cr(OH)(6)Cl(0.7)(CO(3))(0.15)2.1H(2)O was synthesized and characterized by powder X-ray diffraction, infrared spectroscopy, acid-base potentiometric titration, mass titration, electrophoretic mobility, and modeling of the electrical double layer. Adsorption of alizarin was also performed in order to show some particular features of the HDL. Net hydroxyl adsorption, which increases with increasing pH and decreasing supporting electrolyte concentration, takes place above pH 5. The electrophoretic mobility of the particles was always positive and it decreased when the pH was higher than 9. An isoelectric point of 12 could be estimated by extrapolating the data. The modified MUSIC model was used to estimate deprotonation constants of surface groups and different adsorption models were compared. Good fit of hydroxyl adsorption and electrophoresis could be achieved by considering both OH(-)/Cl(-) exchange at structural sites and proton desorption from surface hydroxyl groups. The modeling, in agreement with alizarin adsorption, indicates that most of the structural positive charge of the LDH is screened at the surface by exchanged anions and negatively charged surface groups. It also suggests that only structural charge sites initially neutralized by chloride ions are active for anion exchange. The remaining sites are blocked by carbonate and do not participate in the exchange.

  1. Weak dust-acoustic double-layers in a polarized dusty plasma

    NASA Astrophysics Data System (ADS)

    Messekher, Abderrahim; Tribeche, Mouloud

    2017-03-01

    The problem of small amplitude dust-acoustic double-layers in a polarized dusty plasma is addressed. Our results show that in such a plasma double-layers structures, the amplitude and nature of which depend sensitively on the plasma parameters, can exist. In particular, it may be noted that as the polarization parameter R increases, the domain of the allowable Mach numbers M enlarges and small values of M are more involved. An increase of R leads to a monotonic decrease of the dust-acoustic double-layers amplitude before levelling-off at a constant value. An increase of M provides qualitatively the same results by with a net shift of the R-values towards lower values. We have then investigated the threshold R_{cr} for the possible onset of rarefactive dust-acoustic double-layers and concluded that only compressive double-layers are admitted.

  2. Weak dust-acoustic double-layers in a polarized dusty plasma

    NASA Astrophysics Data System (ADS)

    Messekher, Abderrahim; Tribeche, Mouloud

    2017-08-01

    The problem of small amplitude dust-acoustic double-layers in a polarized dusty plasma is addressed. Our results show that in such a plasma double-layers structures, the amplitude and nature of which depend sensitively on the plasma parameters, can exist. In particular, it may be noted that as the polarization parameter R increases, the domain of the allowable Mach numbers M enlarges and small values of M are more involved. An increase of R leads to a monotonic decrease of the dust-acoustic double-layers amplitude before levelling-off at a constant value. An increase of M provides qualitatively the same results by with a net shift of the R-values towards lower values. We have then investigated the threshold R_{ {cr}} for the possible onset of rarefactive dust-acoustic double-layers and concluded that only compressive double-layers are admitted.

  3. Laser Induced Fluorescence Studies of Electrostatic Double Layers in an Expanding Helicon Plasma

    NASA Astrophysics Data System (ADS)

    Carr, Jerry, Jr.

    We report the first evidence of a laboratory double layer (DL) collapsing in the presence of an instability studied by Chakraborty Thakur et al. 1 with the use of time resolved laser induced fluorescence (LIF) studies. Higher time resolution studies then provided the first statistically validated proof of the correlation between the ion acoustic instability and a DL. Time-frequency analysis in the form of time resolved cross power spectra and continuous wavelet transforms were used to provide insight into beam formation. The implications of this work is that in the creation of strong DLs in expanding plasmas for plasma propulsion or other applications may be self-limited through instability growth. Over the past decade, experimental and theoretical studies have demonstrated the formation of stable, electrostatic, current-free double layers (CFDLs) in plasmas with a strong density gradient; typically a result of a divergent magnetic field. In this work, we present evidence for the formation of multiple double layers within a single divergent magnetic field structure. Downstream of the divergent magnetic field, multiple accelerated ion populations are observed through laser induced fluorescence measurements of the ion velocity distribution function. The formation of the multiple double layer structure is a strong function of the neutral gas pressure in the experiment. The similarity of the accelerated ion populations observed in these laboratory experiments to ion populations observed in reconnection outflow regions in the magnetosphere and in numerical simulations is also described. If ion energization during magnetic reconnection also results solely from acceleration in electric fields, these observations imply a prediction that the ion heating, i.e., the broadening of ion velocity distribution functions, reported in magnetic reconnection experiments is more accurately described by a superposition of differently accelerated ion populations. Therefore, the ion

  4. Electric and Magnetic Tuning Between the Trivial and Topological Phases in InAs/GaSb Double Quantum Wells.

    PubMed

    Qu, Fanming; Beukman, Arjan J A; Nadj-Perge, Stevan; Wimmer, Michael; Nguyen, Binh-Minh; Yi, Wei; Thorp, Jacob; Sokolich, Marko; Kiselev, Andrey A; Manfra, Michael J; Marcus, Charles M; Kouwenhoven, Leo P

    2015-07-17

    Among the theoretically predicted two-dimensional topological insulators, InAs/GaSb double quantum wells (DQWs) have a unique double-layered structure with electron and hole gases separated in two layers, which enables tuning of the band alignment via electric and magnetic fields. However, the rich trivial-topological phase diagram has yet to be experimentally explored. We present an in situ and continuous tuning between the trivial and topological insulating phases in InAs/GaSb DQWs through electrical dual gating. Furthermore, we show that an in-plane magnetic field shifts the electron and hole bands relatively to each other in momentum space, functioning as a powerful tool to discriminate between the topologically distinct states.

  5. Highly Efficient Organic Solar Cells Consisting of Double Bulk Heterojunction Layers.

    PubMed

    Huang, Jiang; Wang, Hanyu; Yan, Kangrong; Zhang, Xiaohua; Chen, Hongzheng; Li, Chang-Zhi; Yu, Junsheng

    2017-03-15

    An organic solar cell (OSCs) containing double bulk heterojunction (BHJ) layers, namely, double-BHJ OSCs is constructed via stamp transferring of low bandgap BHJ atop of mediate bandgap active layers. Such devices allow a large gain in photocurrent to be obtained due to enhanced photoharvest, without suffering much from the fill factor drop usually seen in thick-layer-based devices. Overall, double-BHJ OSC with optimal ≈50 nm near-infrared PDPP3T:PC71 BM layer atop of ≈200 nm PTB7-Th:PC71 BM BHJ results in high power conversion efficiencies over 12%.

  6. Layered double hydroxide stability. 2. Formation of Cr(III)-containing layered double hydroxides directly from solution

    NASA Technical Reports Server (NTRS)

    Boclair, J. W.; Braterman, P. S.; Jiang, J.; Lou, S.; Yarberry, F.

    1999-01-01

    Solutions containing divalent metal [M(II) = Mg2+, Zn2+, Co2+, Ni2+, Mn2+] chlorides and CrCl3 6H2O were titrated with NaOH to yield, for M(II) = Zn, Co, and Ni, hydrotalcite-like layered double hydroxides (LDHs), [[M(II)]1-z[Cr(III)]z(OH)2][Cl]z yH2O, in a single step, without intermediate formation of chromium hydroxide. Analysis of the resultant titration curves yields solubility constants for these compounds. These are in the order Zn < Ni approximately Co, with a clear preference for formation of the phase with z = 1/3. With Mg2+ as chloride, titration gives a mixture of Cr(OH)3 and Mg(OH)2, but the metal sulfates give Mg2Cr(OH)6 1/2(SO4) by a two-step process. Titrimetric and spectroscopic evidence suggests short-range cation order in the one-step LDH systems.

  7. Layered double hydroxide stability. 2. Formation of Cr(III)-containing layered double hydroxides directly from solution

    NASA Technical Reports Server (NTRS)

    Boclair, J. W.; Braterman, P. S.; Jiang, J.; Lou, S.; Yarberry, F.

    1999-01-01

    Solutions containing divalent metal [M(II) = Mg2+, Zn2+, Co2+, Ni2+, Mn2+] chlorides and CrCl3 6H2O were titrated with NaOH to yield, for M(II) = Zn, Co, and Ni, hydrotalcite-like layered double hydroxides (LDHs), [[M(II)]1-z[Cr(III)]z(OH)2][Cl]z yH2O, in a single step, without intermediate formation of chromium hydroxide. Analysis of the resultant titration curves yields solubility constants for these compounds. These are in the order Zn < Ni approximately Co, with a clear preference for formation of the phase with z = 1/3. With Mg2+ as chloride, titration gives a mixture of Cr(OH)3 and Mg(OH)2, but the metal sulfates give Mg2Cr(OH)6 1/2(SO4) by a two-step process. Titrimetric and spectroscopic evidence suggests short-range cation order in the one-step LDH systems.

  8. Large Scale Synthesis of NiCo Layered Double Hydroxides for Superior Asymmetric Electrochemical Capacitor

    NASA Astrophysics Data System (ADS)

    Li, Ruchun; Hu, Zhaoxia; Shao, Xiaofeng; Cheng, Pengpeng; Li, Shoushou; Yu, Wendan; Lin, Worong; Yuan, Dingsheng

    2016-01-01

    We report a new environmentally-friendly synthetic strategy for large-scale preparation of 16 nm-ultrathin NiCo based layered double hydroxides (LDH). The Ni50Co50-LDH electrode exhibited excellent specific capacitance of 1537 F g‑1 at 0.5 A g‑1 and 1181 F g‑1 even at current density as high as 10 A g‑1, which 50% cobalt doped enhances the electrical conductivity and porous and ultrathin structure is helpful with electrolyte diffusion to improve the material utilization. An asymmetric ultracapacitor was assembled with the N-doped graphitic ordered mesoporous carbon as negative electrode and the NiCo LDH as positive electrode. The device achieves a high energy density of 33.7 Wh kg‑1 (at power density of 551 W kg‑1) with a 1.5 V operating voltage.

  9. The aerocapacitor: An electrochemical double-layer energy-storage device

    SciTech Connect

    Mayer, S.T.; Pekala, R.W.; Kaschmitter, J.L.

    1997-10-01

    The authors have applied unique types of carbon foams developed at Lawrence Livermore National Laboratory (LLNL) to make an {open_quotes}aerocapacitor{close_quotes}. The aerocapacitor is a high power-density, high energy-density, electrochemical double-layer capacitor which uses carbon aerogels as electrodes. These electrodes possess very high surface area per unit volume and are electrically continuous in both the carbon and electrolyte phase on a 10 nm scale. Aerogel surface areas range from 100 to 700 m{sup 2}/cc (as measured by BET analysis), with bulk densities of 0.3 to 1.0 g/cc. This morphology permits stored energy to be released rapidly, resulting in high power densities (7.5 kW/kg). Materials parameterization has been performed, and device capacitances of several tens of Farads per gram and per cm{sup 3} of aerogel have been achieved.

  10. Large Scale Synthesis of NiCo Layered Double Hydroxides for Superior Asymmetric Electrochemical Capacitor

    PubMed Central

    Li, Ruchun; Hu, Zhaoxia; Shao, Xiaofeng; Cheng, Pengpeng; Li, Shoushou; Yu, Wendan; Lin, Worong; Yuan, Dingsheng

    2016-01-01

    We report a new environmentally-friendly synthetic strategy for large-scale preparation of 16 nm-ultrathin NiCo based layered double hydroxides (LDH). The Ni50Co50-LDH electrode exhibited excellent specific capacitance of 1537 F g−1 at 0.5 A g−1 and 1181 F g−1 even at current density as high as 10 A g−1, which 50% cobalt doped enhances the electrical conductivity and porous and ultrathin structure is helpful with electrolyte diffusion to improve the material utilization. An asymmetric ultracapacitor was assembled with the N-doped graphitic ordered mesoporous carbon as negative electrode and the NiCo LDH as positive electrode. The device achieves a high energy density of 33.7 Wh kg−1 (at power density of 551 W kg−1) with a 1.5 V operating voltage. PMID:26754281

  11. Limitations and strengths of uniformly charged double-layer theory: physical significance of capacitance anomalies.

    PubMed

    Partenskii, Michael B; Jordan, Peter C

    2008-06-01

    Theoretical studies of electrical double layers typically consider the response of ionic conductors to the field of uniform charge-density distributions sigma ("sigma -control"). Many such analyses predict apparent anomalies of differential capacitance, C , including divergences and negative values. To clarify misconceptions regarding these predictions, we critically reexamine some theoretical approaches dealing with the admissible sign of C . We examine the anomalies' origin and stress its relation to the artificiality of sigma-control. We show that calculations based on sigma-control can illuminate the nature of instabilities and phase transitions under the physically attainable conditions of potential control, where applied voltage phi rather than sigma is fixed. For illustration, we discuss the physical nature of the "ultimate anomaly," negative integral capacitance predicted by some recent analyses. We also show that sigma-control anomalies can explain some experimentally observed features of C(phi) .

  12. Double-Layer Mediated Electromechanical Response of Amyloid Fibrils in Liquid Environment

    PubMed Central

    Nikiforov, M.P.; Thompson, G.L.; Reukov, V.V.; Jesse, S.; Guo, S.; Rodriguez, B.J.; Seal, K.; Vertegel, A.A.; Kalinin, S.V.

    2010-01-01

    Harnessing electrical bias-induced mechanical motion on the nanometer and molecular scale is a critical step towards understanding the fundamental mechanisms of redox processes and implementation of molecular electromechanical machines. Probing these phenomena in biomolecular systems requires electromechanical measurements be performed in liquid environments. Here we demonstrate the use of band excitation piezoresponse force microscopy for probing electromechanical coupling in amyloid fibrils. The approaches for separating the elastic and electromechanical contributions based on functional fits and multivariate statistical analysis are presented. We demonstrate that in the bulk of the fibril the electromechanical response is dominated by double-layer effects (consistent with shear piezoelectricity of biomolecules), while a number of electromechanically active hot spots possibly related to structural defects are observed. PMID:20088597

  13. Double-layer mediated electromechanical response of amyloid fibrils in liquid environment.

    PubMed

    Nikiforov, M P; Thompson, G L; Reukov, V V; Jesse, S; Guo, S; Rodriguez, B J; Seal, K; Vertegel, A A; Kalinin, S V

    2010-02-23

    Harnessing electrical bias-induced mechanical motion on the nanometer and molecular scale is a critical step toward understanding the fundamental mechanisms of redox processes and implementation of molecular electromechanical machines. Probing these phenomena in biomolecular systems requires electromechanical measurements be performed in liquid environments. Here we demonstrate the use of band excitation piezoresponse force microscopy for probing electromechanical coupling in amyloid fibrils. The approaches for separating the elastic and electromechanical contributions based on functional fits and multivariate statistical analysis are presented. We demonstrate that in the bulk of the fibril the electromechanical response is dominated by double-layer effects (consistent with shear piezoelectricity of biomolecules), while a number of electromechanically active hot spots possibly related to structural defects are observed.

  14. Semi-analytical model for quasi-double-layer surface electrode ion traps

    NASA Astrophysics Data System (ADS)

    Zhang, Jian; Chen, Shuming; Wang, Yaohua

    2016-11-01

    To realize scale quantum processors, the surface-electrode ion trap is an effective scaling approach, including single-layer, double-layer, and quasi-double-layer traps. To calculate critical trap parameters such as the trap center and trap depth, the finite element method (FEM) simulation was widely used, however, it is always time consuming. Moreover, the FEM simulation is also incapable of exhibiting the direct relationship between the geometry dimension and these parameters. To eliminate the problems above, House and Madsen et al. have respectively provided analytic models for single-layer traps and double-layer traps. In this paper, we propose a semi-analytical model for quasi-double-layer traps. This model can be applied to calculate the important parameters above of the ion trap in the trap design process. With this model, we can quickly and precisely find the optimum geometry design for trap electrodes in various cases.

  15. Double layer field shaping systems for toroidal plasmas

    DOEpatents

    Ohyabu, Nobuyoshi

    1982-01-01

    Methods and apparatus for plasma generation, confinement and control such as Tokamak plasma systems are described having a two layer field shaping coil system comprising an inner coil layer close to the plasma and an outer coil layer to minimize the current in the inner coil layer.

  16. Some aspects of double layer formation in a plasma constrained by a magnetic mirror

    NASA Technical Reports Server (NTRS)

    Lennartsson, W.

    1987-01-01

    The shift from wave-generated anomalous resistivity toward the more large-scale effects of magnetic confinement of current carrying plasmas was inspired by the more extensive data on auroral particle distribution functions that were made available, data that may often seem consistent with a dissipation-free acceleration of auroral electrons over an extended altitude range. Efforts to interpret these data have brought new vigor to the concept that a smooth and static electric field can be self-consistently generated by suitable pitch angle anisotropies among the high altitude particle populations, different for electrons and ions, and that such an electric field is both necessary and sufficient to maintain the plasma in a quasi-neutral steady state. Certain aspects of this concept are reviewed and criticized, both from a general theoretical standpoint and from the standpoint of what is known about the magnetospheric environment. It is argued that this concept has flaws and that the actual physical problem is considerably more complicated, requiring a more complex electric field, possibly including double layer structures.

  17. Enhanced power conversion efficiency of dye-sensitized solar cells using nanoparticle/nanotube double layered film.

    PubMed

    Sun, Kyung Chul; Yun, Sung Hoon; Yoon, Chang Hyun; Ko, Hwan Ho; Yi, Sung; Jeong, Sung Hoon

    2013-12-01

    To enhance the power conversion efficiency of dye-sensitized solar cell, a new type of double layered photoanode was prepared using TiO2 nanoparticle in under layer and TiO2 nanotube in upper layer. TiO2 nanotubes were synthesized by hydrothermal polymerization. The morphology and the properties were investigated and characterized by Field Emission-Scanning Electron Microscopy (FE-SEM), Field Emission-Transmission Electron Microscopy (FE-TEM), Wide Angle X-ray Diffraction (WAXD), Thermogravimetric analysis (TGA) and, Brunauer-Emmett-Teller test (BET). The light-to-electricity conversion efficiency was improved with the double-layered TiO2 film, which in turn, significantly increases the power conversion efficiency of dye-sensitized solar cells (DSSCs). This is due to large dye adsorption of light-scatters as well as TiO2 main layer. Moreover, rapid electron transport and light-havesting efficiency contributed to high conversion efficiency. The power conversion efficiency of an optimized cell (photoanode consisting of 13-15 microm main-layer and TNT over-layer) was 8.06% under simulated Air mass 1.5 (AM 1.5) global sunlight (1 Sun, 100 mW/cm2).

  18. Interplay between Depletion and Double-Layer Forces Acting between Charged Particles in Solutions of Like-Charged Polyelectrolytes

    NASA Astrophysics Data System (ADS)

    Moazzami-Gudarzi, Mohsen; Kremer, Tomislav; Valmacco, Valentina; Maroni, Plinio; Borkovec, Michal; Trefalt, Gregor

    2016-08-01

    Direct force measurements between negatively charged silica particles in the presence of a like-charged strong polyelectrolyte were carried out with an atomic force microscope. The force profiles can be quantitatively interpreted as a superposition of depletion and double-layer forces. The depletion forces are modeled with a damped oscillatory profile, while the double-layer forces with the mean-field Poisson-Boltzmann theory for a strongly asymmetric electrolyte, whereby an effective valence must be assigned to the polyelectrolyte. This effective valence is substantially smaller than the bare valence due to ion condensation effects. The unusual aspect of the electrical double layer in these systems is the exclusion of the like-charged polyelectrolyte from the vicinity of the surface, leading to a strongly nonexponential diffuse ionic layer that is dominated by counterions and has a well-defined thickness. As the oscillatory depletion force sets in right after this layer, this condition can be used to predict the phase of the oscillatory depletion force.

  19. A theory study of the multiplication characteristics of InP/InGaAs avalanche photodiodes with double multiplication layers and double charge layers

    NASA Astrophysics Data System (ADS)

    Liu, Guipeng; Chen, Wenjie; Liu, Linsheng; Jin, Peng; Tian, Yonghui; Yang, Jianhong

    2016-09-01

    An In0.53Ga0.47As/InP avalanche photodiodes (APD) structure with double multiplication layers and double charge layers has been proposed. The calculated results with considering the dead space effect show that a thin 2nd multiplication layer will reduce the excess noise factor F in this structure for a fixed mean gain . And its performances will reach the best when the 2nd multiplication layer is 0.01 μm, which will reduce the excess noise factor 7% compared to a conventional APD for =10. The effects of 1st and 2nd charge layers on the APD have also been studied in this paper.

  20. Inter-layer edge tunneling and transport properties in separately contacted double-layer quantum-Hall systems

    NASA Astrophysics Data System (ADS)

    Yoshioka, Daijiro

    1998-01-01

    A theory of transport in the quantum-Hall regime is developed for separately contacted double-layer electron systems. Inter-layer tunneling provides a channel for equilibration of the distribution functions in the two layers at the edge states. Resistances and transresistances for various configurations of the electrodes are calculated as functions of the inter-layer tunneling amplitude. Induced current in one of the layer by a current in the other is also calculated. It is shown that reflection at the leads causes change in the results for some electrode configurations. The results obtained in this work is consistent with recent experiments.