25 research outputs found
Consequences of anisotropy in electrical charge storage: application to the characterization by the mirror method of TiO2 rutile
This article is devoted first to anisotropic distributions of stored electric
charges in isotropic materials, second to charge trapping and induced
electrostatic potential in anisotropic dielectrics. On the one hand, we examine
the case of anisotropic trapped charge distributions in linear homogeneous
isotropic (LHI) insulators, obtained after an electron irradiation in a
scanning electron microscope. This injection leads to the formation of a mirror
image
Modelization of flow electrification in a polymer melt
Flow electrification of polymer melts is an important side effect of polymer
processing. The studies dealing with this phenomenon are seldom and most of the
scientific work has been focused on flow electrification of aqueous and
insulating Newtonian liquids. From that prior art it is well established that
the flow electrification in Newtonian liquids is a consequence of the formation
of an ionic double layer. Convection of this layer induces the electrification
of the liquid at the outlet of the pipe. In those models, the key parameters
governing the flow electrification are thus the intrinsic electrical properties
of the polymer and the flow characteristics. In this work, we reconsider the
assumptions made previously and we propose a new approach to modelise the flow
electrification in the particular case of non-Newtonian polymer materials in
laminar flow conditions. We establish that, a key parameter for the
electrification quantification in the polymer melt is the shape of the velocity
profile. Additionally, in some cases, we show that a slip velocity at the
polymer/die wall interface must be considered to describe accurately the
electrification. As a consequence, we deduce that the slip velocity at the
interface can be calculated by measuring the electrification: this work gives
an alternative manner to measure the slip velocity during polymer flow
Electron Beam Charging of Insulators with Surface Layer and Leakage Currents
International audienceThe electron beam induced selfconsistent charge transport in layered insulators is described by means of an electron-hole fight-drift model FDM and an iterative computer simulation. Ballistic secondary electrons and holes, their attenuation and drift, as well as their recombination, trapping, and detrapping are included. Thermal and field-enhanced detrapping are described by the Poole-Frenkel effect. Furthermore, an additional surface layer with a modified electric surface conductivity is included which describes the surface leakage currents and will lead to particular charge incorporation at the interface between the surface layer and the bulk substrate
Electron beam charging of insulators: A self-consistent flight-drift model
International audienceElectron beam irradiation and the self-consistent charge transport in bulk insulating samples are described by means of a new flight-drift model and an iterative computer simulation. Ballistic secondary electron and hole transport is followed by electron and hole drifts, their possible recombination and/or trapping in shallow and deep traps. The trap capture cross sections are the Poole-Frenkel-type temperature and field dependent. As a main result the spatial distributions of currents j(x,t), charges, the field F(x,t) and the potential slope V(x,t) are obtained in a self-consistent procedure as well as the time-dependent secondary electron emission rate sigma(t) and the surface potential V0(t) For bulk insulating samples the time-dependent distributions approach the final stationary state with j(x,t)=const=0 and sigma=1. Especially for low electron beam energies E0=4 keV the incorporation of mainly positive charges can be controlled by the potential VG of a vacuum grid in front of the target surface. For high beam energies E0=10, 20, and 30 keV high negative surface potentials V0=−4, −14, and −24 kV are obtained, respectively. Besides open nonconductive samples also positive ion-covered samples and targets with a conducting and grounded layer (metal or carbon) on the surface have been considered as used in environmental scanning electron microscopy and common SEM in order to prevent charging. Indeed, the potential distributions V(x) are considerably small in magnitude and do not affect the incident electron beam neither by retarding field effects in front of the surface nor within the bulk insulating sample. Thus the spatial scattering and excitation distributions are almost not affected
Switching of magnetization by non-linear resonance studied in single nanoparticles
Magnetization reversal in magnetic particles is one of the fundamental issues
in magnetic data storage. Technological improvements require the understanding
of dynamical magnetization reversal processes at nanosecond time scales. New
strategies are needed to overcome current limitations. For example, the problem
of thermal stability of the magnetization state (superparamagnetic limit) can
be pushed down to smaller particle sizes by increasing the magnetic anisotropy.
High fields are then needed to reverse the magnetization that are difficult to
achieve in current devices. Here we propose a new method to overcome this
limitation. A constant applied field, well below the switching field, combined
with a radio-frequency (RF) field pulse can reverse the magnetization of a
nanoparticle. The efficiency of this method is demonstrated on a 20 nm cobalt
particle by using the micro-SQUID technique. Other applications of this method
might be nucleation or depinning of domain walls.Comment: 11 pages, 5 figure
Interpretation of the human skin biotribological behaviour after tape stripping
The present study deals with the modification of the human skin biotribological behaviour after tape stripping. The tape-stripping procedure consists in the sequential application and removal of adhesive tapes on the skin surface in order to remove stratum corneum (SC) layers, which electrically charges the skin surface. The skin electric charges generated by tape stripping highly change the skin friction behaviour by increasing the adhesion component of the skin friction coefficient. It has been proposed to rewrite the friction adhesion component as the sum of two terms: the first classical adhesion term depending on the intrinsic shear strength, Ï„0, and the second term depending on the electric shear strength, Ï„elec. The experimental results allowed to estimate a numerical value of the electric shear strength Ï„elec. Moreover, a plan capacitor model with a dielectric material inside was used to modelize the experimental system. This physical model permitted to evaluate the friction electric force and the electric shear strength values to calculate the skin friction coefficient after the tape stripping. The comparison between the experimental and the theoretical value of the skin friction coefficient after the tape stripping has shown the importance of the electric charges on skin biotribological behaviour. The static electric charges produced by tape stripping on the skin surface are probably able to highly modify the interaction of formulations with the skin surface and their spreading properties. This phenomenon, generally overlooked, should be taken into consideration as it could be involved in alteration of drug absorption
Boundary Lubrication by Pure Crystalline Zinc Orthophosphate Powder in Oil
International audienc
Dépôt de couches minces de YIG par ablation laser femtoseconde
National audienc