Showing papers by "Boris I Shklovskii published in 2010"
TL;DR: In this article, Li et al. showed that the Coulomb correlations between individual electrons within a 2DEG can lead to a negative thermodynamic density of states, which is known as Coulomb capacitance.
Abstract: In electronic devices where a two-dimensional electron gas (2DEG) comprises one or both sides of a plane capacitor, the resulting capacitance $C$ can be larger than the ``geometric capacitance'' ${C}_{g}$ determined by the physical separation $d$ between electrodes. This larger capacitance is known to result from the Coulomb correlations between individual electrons within the low-density 2DEG, which lead to a negative thermodynamic density of states. Experiments on such systems generally operate in the regime where the average spacing between electrons ${n}^{\ensuremath{-}1/2}$ in the 2DEG is smaller than $d$ and these experiments observe $Cg{C}_{g}$ by only a few percent. A recent experiment [L. Li, C. Richter, S. Paetel, T. Kopp, J. Mannhart, and R. Ashoori, arXiv:1006.2847 (unpublished)], however, has observed $C$ larger than ${C}_{g}$ by almost 40% while operating in the regime $n{d}^{2}⪡1$. In this paper we argue that at $n{d}^{2}⪡1$ correlations between the electronic charge of opposite electrodes become important. We develop a theory of the capacitance for the full range of $n{d}^{2}$. We show that, in the absence of disorder, the capacitance can be $4d/a$ times larger than the geometric value, where $a⪡d$ is the electron Bohr radius. Our results compare favorably with the experiment of Li et al. [arXiv:1006.2847 (unpublished)] without the use of adjustable parameters.
54 citations
TL;DR: It is shown that at small voltages the capacitance of the double layer is limited only by the weak dipole-dipole repulsion between bound ions, and is therefore very large.
Abstract: The capacitance of the double layer formed at a metal/ionic-conductor interface can be remarkably large, so that the apparent width of the double layer is as small as 0.3 A. Mean-field theories fail to explain such large capacitance. We propose an alternate theory of the ionic double layer which allows for the binding of discrete ions to their image charges in the metal. We show that at small voltages the capacitance of the double layer is limited only by the weak dipole-dipole repulsion between bound ions, and is therefore very large. At large voltages the depletion of bound ions from one of the capacitor electrodes triggers a collapse of the capacitance to the mean-field value.
51 citations
TL;DR: In this article, the authors used Monte Carlo simulations to examine the simplest model of a room-temperature ionic liquid (RTIL), called the restricted primitive model, at a metal surface and found that at moderately low temperatures the capacitance of the metal-RTIL interface is so large that the effective thickness of the electrostatic double layer is up to three times smaller than the ion radius.
Abstract: We use Monte Carlo simulations to examine the simplest model of a room-temperature ionic liquid (RTIL), called the "restricted primitive model," at a metal surface. We find that at moderately low temperatures the capacitance of the metal-RTIL interface is so large that the effective thickness of the electrostatic double layer is up to three times smaller than the ion radius. To interpret these results we suggest an approach which is based on the interaction between discrete ions and their image charges in the metal surface and which therefore goes beyond the mean-field approximation. When a voltage is applied across the interface, the strong image attraction causes counterions to condense onto the metal surface to form compact ion-image dipoles. These dipoles repel each other to form a correlated liquid. When the surface density of these dipoles is low, the insertion of an additional dipole does not require much energy. This leads to a large capacitance C that decreases monotonically with voltage V, producing a "bell-shaped" curve C(V). We also consider what happens when the electrode is made from a semimetal rather than a perfect metal. In this case, the finite screening radius of the electrode shifts the reflection plane for image charges to the interior of the electrode, and we arrive at a "camel-shaped" C(V). These predictions seem to be in qualitative agreement with experiment.
37 citations
TL;DR: It is argued that the proposed "one-component plasma" model should work well for strongly asymmetric ion liquids and also suggest an improved theory of pseudocapacitance.
Abstract: Mean-field theories claim that the capacitance of the double layer formed at a metal/ionic conductor interface cannot be larger than that of the Helmholtz capacitor, whose width is equal to the radius of an ion. However, in some experiments the apparent width of the double layer capacitor is substantially smaller. We propose an alternate non-mean-field theory of the ionic double layer to explain such large capacitance values. Our theory allows for the binding of discrete ions to their image charges in the metal, which results in the formation of interface dipoles. We focus primarily on the case where only small cations are mobile and other ions form an oppositely charged background. In this case, at small temperature and zero applied voltage dipoles form a correlated liquid on both contacts. We show that at small voltages the capacitance of the double layer is determined by the transfer of dipoles from one electrode to the other and is therefore limited only by the weak dipole-dipole repulsion between bound ions so that the capacitance is very large. At large voltages the depletion of bound ions from one of the capacitor electrodes triggers a collapse of the capacitance to the much smaller mean-field value, as seen in experimental data. We test our analytical predictions with a Monte Carlo simulation and find good agreement. We further argue that our "one-component plasma" model should work well for strongly asymmetric ion liquids. We believe that this work also suggests an improved theory of pseudocapacitance.
21 citations