85,746 research outputs found
Universal reduction of pressure between charged surfaces by long-wavelength surface charge modulation
We predict theoretically that long-wavelength surface charge modulations
universally reduce the pressure between the charged surfaces with counterions
compared with the case of uniformly charged surfaces with the same average
surface charge density. The physical origin of this effect is the fact that
surface charge modulations always lead to enhanced counterion localization near
the surfaces, and hence, fewer charges at the midplane. We confirm the last
prediction with Monte Carlo simulations.Comment: 8 pages 1 figure, Europhys. Lett., in pres
Interfacial transport with mobile surface charges and consequences for ionic transport in carbon nanotubes
In this paper, we explore the effect of a finite surface charge mobility on
the interfacial transport: conductance, streaming currents, electro- and
diffusio-osmotic flows. We first show that the surface charge mobility modifies
the hydrodynamic boundary condition for the fluid, which introduces a
supplementary term depending on the applied electric field. In particular, the
resulting slip length is found to decrease inversely with the surface charge.
We then derive expressions for the various transport mobilities, high-lighting
that the surface charge mobility merely moderates the amplification effect of
interfacial slippage, to the noticeable exception of diffusio-osmosis and
surface conductance. Our calculations, obtained within Poisson-Boltzmann
framework, highlight the importance of non-linear electrostatic contributions
to predict the small concentration/large charge limiting regimes for the
transport mobilities. We discuss these predictions in the context of recent
electrokinetic experiments with carbon nanotubes
Surface-charge-induced freezing of colloidal suspensions
Using grand-canonical Monte Carlo simulations we investigate the impact of
charged walls on the crystallization properties of charged colloidal
suspensions confined between these walls. The investigations are based on an
effective model focussing on the colloids alone. Our results demonstrate that
the fluid-wall interaction stemming from charged walls has a crucial impact on
the fluid's high-density behavior as compared to the case of uncharged walls.
In particular, based on an analysis of in-plane bond order parameters we find
surface-charge-induced freezing and melting transitions
Quantitative measurement of the surface charge density
We present a method of measuring the charge density on dielectric surfaces.
Similar to electrostatic force microscopy we record the electrostatic
interaction between the probe and the sample surface, but at large tip-sample
distances. For calibration we use a pyroelectric sample which allows us to
alter the surface charge density by a known amount via a controlled temperature
change. For proof of principle we determined the surface charge density under
ambient conditions of ferroelectric lithium niobate
On the validity of the âthinâ and âthickâ double-layer assumptions when calculating streaming currents in porous media
We find that the thin double layer assumption, in which the thickness of the electrical diffuse layer is assumed small compared to the radius of curvature of a pore or throat, is valid in a capillary tubes model so long as the capillary radius is >200 times the double layer thickness, while the thick double layer assumption, in which the diffuse layer is assumed to extend across the entire pore or throat, is valid so long as the capillary radius is >6 times smaller than the double layer thickness. At low surface charge density (0.5 M) the validity criteria are less stringent. Our results suggest that the thin double layer assumption is valid in sandstones at low specific surface charge (<10 mC· m -2), but may not be valid in sandstones of moderate- to small pore-throat size at higher surface charge if the brine concentration is low (<0.001 M). The thick double layer assumption is likely to be valid in mudstones at low brine concentration (<0.1 M) and surface charge (<10 mC· m -2), but at higher surface charge, it is likely to be valid only at low brine concentration (<0.003 M). Consequently, neither assumption may be valid in mudstones saturated with natural brines. Copyright © 2012 Matthew D. Jackson and Eli Leinov
Study and analysis of surface charge collection and emission spectrum of plasma ashing process
This research presents an important observation on the total surface charge collection using quantox wafers through the measurement of surface voltage (Vs) on wafer surface with contactless Kelvin Probe for changes in parameters during plasma ashing. In this report, it is covered on the plasma characteristics and performance using the optical emission spectroscopy (OES) measurement, the study on how processing condition change can impact the total surface charge collection and also the uniformity of the charges on the wafer surface, using the quantox measurement. In this study, 3 different types of ashers are tested with varying 5 processing parameters, which where the process time, pressure, gas flow, power and temperature. It is seen that changes in the condition of these parameters do impact on the total surface charge collection and also the uniformity of the charges on the wafer surface. Based on the processing conditions, it is observed that Inductively-Coupled Plasma (ICP) asher model is better in terms of total surface charge collection and uniformity compared to Barrel asher model, which has lower total charge collection but with higher non-uniformity due to the machine chamber configuration. On the other hand, Helical Resonator Plasma (HRP) asher model contributes to higher total surface charge collection with the lesser uniformity, which could potential contribute to plasma induced damage (PID)
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