Double layers above the aurora

Two different kinds of double layers were found in association with auroral precipitation. One of these is the so-called electrostatic shock, which is oriented at an oblique angle to the magnetic field in such a way that the perpendicular electric field is much larger than the parallel electric field. This type of double layer is often found at the edges of regions of upflowing ion beams and the direction of the electric fields in the shock points toward the ion beam. The potential drop through the shock can be several kV and is comparable to the total potential needed to produce auroral acceleration. Instabilities associated with the shock may generate obliquely propagating Alfven waves, which may accelerate electrons to produce flickering auroras. The flickering aurora provides evidence that the electrostatic shock may have large temporal fluctuations. The other kind of double layer is the small-amplitude double layer found in regions of upward flowing in beams, often in association with electrostatic ion cyclotron waves. The parallel and perpendicular electric fields in these structures are comparable in magnitude. The associated potentials are a few eV. Since many such double layers are found in regions of upward flowing ion beams, the combined potential drop through a set of these double layers can be substantial

Electric double layer structure close to the three-phase contact line in an electrolyte wetting a solid substrate

The electric double layer structure in an electrolyte close to a solid substrate near the three-phase contact line is approximated by considering the linearized Poisson-Boltzmann equation in a wedge geometry. The mathematical approach complements the semi-analytical solutions reported in the literature by providing easily available characteristic information on the double layer structure. In particular, the model contains a length scale that quantifies the distance from the fluid-fluid interface over which this boundary influences the electric double layer. The analysis is based on an approximation for the equipotential lines. Excellent agreement between the model predictions and numerical results is achieved for a significant range of contact angles. The length scale quantifying the influence of the fluid-fluid interface is proportional to the Debye length and depends on the wall contact angle. It is shown that for contact angles approaching 90{\deg} there is a finite range of boundary influence.Comment: 6 pages, 9 figures; http://link.aps.org/doi/10.1103/PhysRevE.86.02260

Simultaneous control of thermoelectric properties in p-type and n-type materials by electric double-layer gating : New design for thermoelectric device

We report novel design for thermoelectric device which can control thermoelectric properties of p-type and n-type materials simultaneously by electric double-layer gating. Here, p-type Cu2O and n-type ZnO were used as positive and negative electrodes of the electric double-layer capacitor structure. When the gate voltage was applied between two electrodes, the holes and electrons were accumulated on the surface of Cu2O and ZnO, respectively. The thermopower was measured by applying thermal gradient along the accumulated layer on the electrodes. We demonstrate here that the accumulated layers are worked as a p-n pair of the thermoelectric device.Comment: 10 pages, 4 figures. Accepted in Applied physics expres

Screening of electrostatic potential in a composite fermion system

Screening of the electric field of a test charge by monolayer and double-layer composite fermion systems is considered. It is shown that the electric field of the test charge is partly screened at distances much large then the magnetic length. The value of screening as a function of the distance depends considerably on the filling factor. The effect of variation of the value of screening in the double-layer system upon a transition to a state described by the Halperin wave function is determined.Comment: 5 pages, 2 eps figures include

Electric double layer composed of an antagonistic salt in an aqueous mixture: Local charge separation and surface phase transition

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. % while the cations are expelled from it. We then vary the surface charge density $\sigma$ on the wall. For $\sigma>0$ the anions remain accumulated, but for $\sigma<0$ the cations are attracted to the wall with increasing $|\sigma|$. Furthermore, the electric potential drop $\Psi(\sigma)$ is nonmonotonic when the solvent interaction parameter $\chi(T)$ exceeds a critical value $\chi_c$ 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 $\sigma$ and common $\Psi$. In equilibrium such two layer regions can coexist. The steric effect due to finite ion sizes is crucial in these phenomena.Comment: 8 Pages, 8 Figs, accepted for Phys. Rev. Let