Acrylamide based proton conducting polymer gel electrolyte for electric double layer capacitors

A new class of polymer gel electrolyte (PGE) was synthesized using acrylamide as host polymer and LiClO₄ as dopant. The polymer gel was subjected to electrochemical AC impedance analysis and thermal analysis. The polymer has conductivity in the order of 10⁻³ S cm⁻¹ at ambient temperature. Thermogravimetric analysis (TGA) revealed the effect of dopant on host polymer matrix. A supercapacitor was fabricated using acrylamide based polymer gel electrolyte with activated carbon as electrode material and it was subjected to various electrochemical techniques like cyclic voltammetry, electrochemical AC impedance analysis and galvanostatic charge–discharge tests at various current densities. From cyclic voltammetry a specific capacitance of 28 F/g was obtained at a scan rate of 10 mV/s. The capacitor had good self-discharge behavior and good cycle life of more than 10,000 cycles. The coulombic efficiency was more than 95%. These results indicate that this acrylamide-based polymer gel electrolyte doped with LiClO₄ is a potential electrolyte for electric double-layer capacitors (EDLCs).     

Performance of C/C electric double layer capacitors with coal-based active carbon electrodes

Coal-based active carbon was prepared and used as electrodes of electric double-layer capacitors (EDLCs). The performance of EDLCs using active carbon electrodes with different pore structure was studied, including cyclic voltammetry, galvanostatic charge-discharge, and electrochemical impedance spectroscopy. With an increase of sodium hydrate/coal ratio, the pore structure of active carbon is greatly improved, resulting in larger double-layer capacitance. The capacitance of asymmetric EDLC is up to 65.98 F/g. Moreover, it is found that different pore structure of active carbon is necessary for positive and negative electrodes. Asymmetric EDLC not only exhibits high capacitance but also shows excellent charge-discharge performance, suggesting that it is very suitable and promising to design electrode materials for supercapacitors.     

Performance of double layer electrolyte cells Part I: Model behavior

The present work reports on the estimated performance of double layer electrolyte based cells, including one yttria stabilized zirconia (YSZ) electron blocking layer. In order to evaluate the impact of the relative magnitude of the materials properties on the cell performance, a range of electrical properties has been considered, taking YSZ as reference. At constant temperature, the open circuit voltage, the oxygen permeability and the oxygen partial pressure profiles in such two layer electrolyte cells are related to the materials ionic and electronic transport properties, layers thickness and overall cell oxygen partial pressure boundary conditions. The effectiveness of the electron blocking characteristics of YSZ layers is demonstrated for a variety of materials, but consideration of the exact electrical properties (the n-type but also the p-type and ionic conductivities) of the second electrolyte layer is shown to be a fundamental requirement for proper design of such cells.     

InAs/AlAs quantum dots with InGaAs insertion layer: dependence of the indium composition and the thickness

We have systematically studied the effect of an In_xGa_1−xAs insertion layer (IL) on the optical and structural properties of InAs quantum dot (QD) structures. A high density of 9.6×10¹⁰ cm⁻² of InAs QDs with an In_0.3Ga_0.7As IL has been achieved on a GaAs (1 0 0) substrate by metal organic chemical vapor deposition. A photoluminescence line width of 25 meV from these QDs has been obtained. We attribute the high density and high uniformity of these QDs to the use of the IL. Our results show that the InGaAs IL is useful for obtaining high-quality InAs QD structures for devices with a 1.3 μm operation.     

Elementary processes at semiconductor/electrolyte interfaces: perspectives and limits of electron spectroscopy

Semiconductor device properties based on electrolyte contacts or modified by electrochemical reactions are dominated by the electronic structure of the interface. Electron spectroscopy as e.g. photoemission is the most appropriate surface science techniques to investigate elementary processes at semiconductor/electrolyte interfaces. For such investigations a specific experimental set-up (SoLiAS) has been built-up which allows performing model experiments as well as surface analysis after emersion under different experimental conditions. The experimental approach is presented by a number of experiments performed during the last years with GaAs as substrate material. Model experiments by adsorption and coadsorption of electrolyte species give information on fundamental aspects of semiconductor/electrolyte interactions. Emersion experiments give information on a final composition and the related electronic structure of electrodes after electrochemical reactions. The use of frozen electrolytes will help to bridge the gap between these two approaches. With the combination of the experimental procedures one may expect a detailed analysis of electrolyte (modified) interfaces covering chemical composition, electronic structure of surfaces/interfaces as well as surface/interface potentials.     

Sequential deposition of polydisperse particles with double layer interactions: An integral-equation theory

Adsorption of charged colloidal particles to oppositely charged surfaces is usually an irreversible process. The interaction between a pair of particles can be modeled with an exponentially decaying potential originating from double layer interactions. This work explored the effect of the Debye length on monolayer structures using the integral-equation theory which was successfully developed based on a binary-mixture approximation to include the effect of particle size polydispersity. The theoretical results from the integral equations with a Percus-Yevick closure showed that upon increasing the Debye length, the radial distribution functions, g(r), as well as the structure factor, S(k), decreased, in good agreement with simulation results. When the effect of size distributions was investigated, the prominent peak of the radial distribution function increased non-linearly with the product κσ_av, which followed the same trend as was reported for the case of the jamming coverage of the monolayer film.     

Off-centre charge model of the planar electric double layer for asymmetric 2:1/1:2 valencies

ABSTRACT

Grand canonical Monte Carlo simulation results are reported for the structure and capacitance of a planar electric double layer containing off-centre charged rigid sphere cations and centrally charged rigid sphere anions. The ion species are assigned asymmetric valencies, +2:?1 and +1:?2, respectively, and set in a continuum dielectric medium (solvent) characterised by a single relative permittivity. An off-centre charged ion is obtained by displacing the ionic charge from the centre of the sphere towards its surface, and the physical double layer model is completed by placing the ionic system next to a uniformly charged, non-penetrable, non-polarizable planar electrode. Structural results such as electrode-ion singlet distribution functions, ionic charge density and orientation profiles are complemented by differential capacitance results at electrolyte concentrations of 0.2?mol/dm³ and 1?mol/dm³, respectively, and for various displacements of the cationic charge centre. The effect of asymmetry due to off-centre cations and valency asymmetry on the double layer properties is maximum for divalent counterions and when the cation charge is closest to the hard sphere surface.     

Desorption of polymers: role of the stagnant layer

The desorption of polymers is studied theoretically and with Monte Carlo simulations. Two regimes can be distinguished: in one regime the detachment of the polymer from the surface is the slowest process, and in the other it is the diffusion of the polymer away from the surface. In both regimes the desorption rate depends on the thickness H of the stagnant layer, i.e. the layer in which the polymer movement is dominated by diffusion. In the diffusion-limited regime the desorption rate scales as H ^{? 2}, as expected for diffusive processes. In the detachment-limited regime the desorption rate scales as H ^{? 1}. The importance of the thickness of the stagnant layer in the detachment-limited regime is due to the fact that the polymer, after it has detached, will most likely readsorb soon after: the probability that the polymer does not readsorb, but crosses the stagnant layer, is inversely proportional to the thickness of the stagnant layer.     

First-principle study on the electronic structure and magnetic properties in Fe/MgO/Fe magnetic tunnel junction with Mg insertion layer

The effect of a Mg insertion layer between the Fe electrode and the MgO barrier layer on the electronic structure and magnetic properties of Fe/MgO/Fe magnetic tunnel junction has been studied by first-principle method. Two models of (a) Fe(1 0 0)/MgO(1 0 0)/Fe(1 0 0) and (b) Fe(1 0 0)/Mg/MgO(1 0 0)/Mg/Fe(1 0 0) were established. Our calculation results show that the Mg insertion layer has enhanced both the spin polarization and the magnetic moment of its adjacent Fe layer. The results have been discussed in terms of the variation in the DOS features and charge transfer with the Mg insertion layer.     

Capacitance characteristics of metal-oxide-semiconductor capacitors with a single layer of embedded nickel nanoparticles for the application of nonvolatile memory

This paper reports that metal-oxide-semiconductor (MOS) capacitors with a single layer of Ni nanoparticles were successfully fabricated by using electron-beam evaporation and rapid thermal annealing for application to nonvolatile memory. Experimental scanning electron microscopy images showed that Ni nanoparticles of about 5~nm in diameter were clearly embedded in the SiO₂ layer on p-type Si (100). Capacitance--voltage measurements of the MOS capacitor show large flat-band voltage shifts of 1.8~V, which indicate the presence of charge storage in the nickel nanoparticles. In addition, the charge-retention characteristics of MOS capacitors with Ni nanoparticles were investigated by using capacitance--time measurements. The results showed that there was a decay of the capacitance embedded with Ni nanoparticles for an electron charge after 10$^{4}$~s. But only a slight decay of the capacitance originating from hole charging was observed. The present results indicate that this technique is promising for the efficient formation or insertion of metal nanoparticles inside MOS structures.     

Specific solutions of the generalized Korteweg-de Vries equation with possible physical applications

Solutions for a type of generalized Korteweg-de Vries equation which should have physical impact will be determined here. These types of solutions should have applications in the study of intrinsic localized modes optical waveguide arrays and fluid dynamics. It is shown that trigonometric and hyperbolic solutions can be obtained by matching powers and coefficients of the independent terms in the equation after the assumed solution has been substituted. As well, solutions to the equation in terms of more complicated Jacobe elliptic functions are determined.     

双层h-BN/Graphene结构稳定性及其掺杂特性的第一性原理研究

采用基于密度泛函理论的第一性原理计算方法研究了双层h-BN/Graphene的稳定性及其掺杂特性.研究发现,双层h-BN/Graphene能带结构在K点处有一个小的带隙,在费米能处有类Graphene的线性色散关系.通过施加应变和掺杂来调节带隙,发现掺杂后费米能级附近引入的新能级,主要是N原子的贡献,掺杂后的Na原子和N,C之间存在电荷转移,材料转变为金属性.电荷的转移、载流子密度的增加,在电子元器件中有重要的应用前景.     

Cathode of the fuel cell with polymer electrolyte (nafion): active layer and estimated degree of platinum utilization

It is hypothesized that a fractal nafion film is formed on the pore surface of the platinum carrier grain in the process of manufacturing the catalyst ink that form the active layer. This film is capable of increasing significantly the degree of platinum utilization. The process of nafion penetration into pores of the carrier grain is simulated on a computer. The factors that allow a high degree of platinum utilization to be obtained are established. The results of computer calculations are in agreement with experimental estimates of the degree of platinum utilization.     

Modelling the voltammetric study of intercalation in a host structure: application to lithium intercalation in RuO2

Intercalation process kinetics have been studied theoretically for the case of potential sweep voltammetry. The influence of the thickness (or the particle radius) of the “host” material and the potential sweep rate has been determined between the limits of thin film diffusion and semi-infinite diffusion for a reversible process. Experimental data have been obtained with the cell: RuO₂/LiClO₄-PEO/Li. The theoretical results have been used to calculate the diffusion coefficient of lithium in the “host” structure RuO₂ at 80°C, giving an approximate value of 1.6 × 10^?11 cm² s^?1     

The role of multiple damaged layers at the Si/SiO2 interface on the dielectric breakdown of MOS capacitors

Oxide breakdown in metal-oxide-semiconductor (MOS) devices in the nanometer scale is simulated as a cluster growth depending process in which the local electric field is a function of a randomly varying local dielectric permissivity. Effects of MOS device bias polarity, film thickness and non-uniform defect distributions through the entire oxide film on the breakdown are studied. The slope of the Weibull distribution increases with the oxide thickness in agreement with experimental results.     

InAs nanostructures on InP (001) substrate with the insertion of a superthin AlAs layer

An AlAs layer of two or three monolayers was inserted beneath the strained InAs layer in the fabrication of InAs nanostructure on the In_0.53Ga_0.47As and In_0.52Al_0.48As buffer layer lattice-matched to InP(001) substrate using molecular beam epitaxy. The effects of AlAs insertion on the InAs nanostructures were investigated and discussed.      

The role of the interfacial SiOx layer in SnO2/n-Si photocells

It is proposed that the charge transport across the SiO _x layer at the interface SnO₂/Si proceeds by a hopping mechanism. During heat treatment of the photovoltaic cells, in air, chemical reactions occur with O₂/H₂O, which lead to a drastic reduction of the density of hopping sites near the Si conduction band edge. The SiO _x hopping sites of energy near the valence band edge are less affected by these chemical reactions. Thus, photogenerated holes can still pass the barrier while the dark current flow is strongly inhibited.     

The role of the indirect tunneling processes and asymmetry in couplings in orbital Kondo transport through double quantum dots

A system of two quantum dots attached to external electrodes is considered theoretically in the orbital Kondo regime. In general, the double dot system is coupled via both Coulomb interaction and direct hopping. Moreover, the indirect hopping processes between the dots (through the leads) are also taken into account. To investigate the system's electronic properties we apply the slave-boson mean field (SBMF) technique. With the help of the SBMF approach the local density of states for both dots and the transmission (as well as linear and differential conductance) is calculated. We show that Dicke- and Fano-like line shapes may emerge in the transport characteristics of the double dot system. Moreover, we observed that these modified Kondo resonances are very susceptible to the change of the indirect coupling's strength. We have also shown that the Kondo temperature becomes suppressed with increasing asymmetry in the dot-lead couplings when there is no indirect coupling. Moreover, when the indirect coupling is turned on the Kondo temperature becomes suppressed. By allowing a relative sign of the nondiagonal elements of the coupling matrix with left and right electrodes, we extend our investigations to become more generic. Finally, we have also included the level renormalization effects due to indirect tunneling, which are mostly neglected.