Field-induced injection

Under high applied electric fields, electrons can surmount a potential barrier even at very low temperatures. This process is based on field-induced timneling of the charge carriers across potential barrier. The probability for the timneling depends strongly on the height and the width of the potential barrier. 

The field-induced tunneling across a potential barrier can be described using the Fowler-Nordheim equation [79]  

When die electric field-induced luiiiicling currents are analyzed in a log 1/E ) versus / plot, a straight line should be obtained. The height of the potential barrier can be derived from the slope of this straight line using Eq. (9.12). 

However, the values for the current, which are obtained using the Fowler-Nordheim equation with the actual device parameters, are several orders of magnitude [81, 82] higher than the values for the measured current in real devices. 

Besides injection mechanisms, in order to describe the UV characteristics of FEDs, the charge transport mechanisms in the bulk have to be taken into account. 

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Therefore, the following method was suggested and realized (the scheme is shown in Fig. 17). A 1.5 M solution of KCl or NaCl (the effect of preventing BR solubility of these salts is practically the same) was used as a subphase. A platinum electrode was placed in the subphase. A flat metal electrode, with an area of about 70% of the open barriered area, was placed about 1.5-2 mm above the subphase surface. A positive potential of +50 -60 V was applied to this electrode with respect to the platinum one. Then BR solution was injected with a syringe into the water subphase in dark conditions. The system was left in the same conditions for electric field-induced self-assembly of the membrane fragments for 1 hour. After this, the monolayer was compressed to 25 mN/m surface pressure and transferred onto the substrate (porous membrane). The residual salt was washed with water. The water was removed with a nitrogen jet. 

Although Sah etal. (1983) and Gale etal. (1983) have demonstrated that H can be introduced into Si by electron injection into the oxide layer of metal-oxide-silicon devices, there has been no report of hydrogen penetration with an applied bias of opposite polarity. This may suggest electric-field-induced proton migration through the oxide. 

A narrow band of sample material is injected at the head of the channel. A field or gradient is then applied across the face of the channel as shown in the figures. In normal operation (variants will be described in Section 9.11) the field causes the components to migrate to one wall, termed the accumulation wall. Each component quickly reaches (in a process termed relaxation) a steady-state distribution close to that wall. The distribution is exponential as described by Eq. 6.19 and illustrated in Figure 9.6. The mean thickness of the component layer so formed is given by Eq. 6.20, - DJ W, where W (specifically its component U) is the field-induced velocity... 

In the FFF a field or gradient is applied in a direction, perpendicular to the axis of a narrow flow channel. At the same time a solvent is forced steadily through the channel forming a cross-sectional flow profile of parabolic shape. When a polymer sample is injected into the channel, a steady state is soon reached in which the field induced motion and the opposed diffusion are exactly balanced. The continuous size-distribution of the polymer will migrate with a continuous spectrum of velocities and will emerge at the end of the flow channel with a continuous time distribution. When processed through a detector and its associated electronics, the time distribution becomes an elution (retention) spectrum. 

In the case where the current flowing through the sample is injection limited (cf. Sec. 4.3.2), the recombination zone width becomes a complex function of applied field because the field decreasing F2// factor in Eq. (154) adds to the field-dependent mobility of w and often can dominate the electric field-induced changes in the recombination zone (cf. Sec. 5.4). 

The transient polarization may play role in possible mechanisms of EL excitation, we will consider two of those (i) field-induced de-trapping of the charge in the bulk of the film, and (ii) the charge injection via the electrode/polymer interface that is quenched by the polarization counter-field build-up. 

In practice, the sample is injected at the inlet to the channel. The external field is next applied across the face of the channel, as illustrated in Figure 33-16. In the presence of the field, sample components migrate toward the accumulation wall at a velocity determined by the strength of the interaction of the component with the field. Sample components rapidly reach a steady-state concentration distribution near the accumulation wall, as shown in Figure 33-17. The mean thickness of the component layer I is related to the diffusion coefficient of the molecule D and to the field-induced velocity u toward the wall. The faster the component moves in the field, the thinner the layer near the wall. The larger the diffusion coefficient, the thicker the layer. Since the sample components have different values of D and it, the mean layer thickness will vary among components. 

Expression of the therapeutic protein is enhanced by electroporation - the application of a small amount of electricity at the site of injection for a few milliseconds. This high-intensity electric field induces temporary and reversible breakdown of the plasma membrane allowing plasmids and other molecules to gain intracellular access [110]. This plasmid-based PA-inducible transgene regulating... 

Kiguchi, M. et al.. Electric-field-induced charge injection or exhaustion in organic thin film transistor, Phys. Rev. B, 71, 035332, 2005. 

McNeill et al. [113,114] studied the near-field photoluminescence of thin-fihn MEH-PPV induced by a voltage bias applied between the near-field probe and the substrate. The goal was to investigate the field-induced modulation of the local carrier density. The injected carriers recombined giving rise to photoluminescence measured by the NSOM probe. The images under applied bias showed a domain structure similar to those reported by other groups. This indicates that the inhomogeneous polymer structure affects the process both with and without an electric-field-induced carrier injection. 

Traditionally, the term electroconvection is used in at least four different physical contexts, of which three pertain to flows of liquid dielectrics. Thus, it is used to describe the electric field-induced flow of nematic liquid crystals, the flow of liquid dielectrics caused by the action of electric field on the space charge of ions of the appropriate sign injected in a low quantity into a fluid, or the effects of an electric field acting on the surface charge accumulated at the interface between two weakly conducting fluids. The latter process was studied by G. I. Taylor, who in the mid-1960s introduced the leaky dielectric model... 

When a sample is injected at one end of the channel the field drives the particles or molecules to the accumulation wall of the channel (Figure IB). For small particles (say Brownian diffusion is comparable with the field-induced flux, diffuse clouds form for each component in the mixture (Figure 3A). The mean thickness of each cloud depends on the balance of the field force and diffusion, which generally depends on the particle size and other particle properties. These clouds are typically 1-10 pm thick, compared with the channel thickness of 50-500 pm. This relaxation step is usually carried out with the channel flow turned off. 

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