Injection current

The most commonly applied indirect method of measuring soil resistivity using the four-electrode arrangement of Fig. 3-14 is described further in Section 24.3.1. The measured quantities are the injected current, /, between the electrodes A and B, and the voltage, t/, between the electrodes C and D. The specific soil resistivity follows from Eq. (24-41). For the usual measuring arrangement with equally spaced electrodes a = b,ii follows from Eq. (24-41) ... 

Figure 12-1. A comparison of theoretical and experimental injection currents into typically lOOnin thick films of conjugated polymers sandwiched between an ITO anode and an Al cathode. Open symbols refer to calculated j(F) characteristics. A is the zero field injection barrier (Ref. [21]).

Figure 12-4. Dependence of die injection current on the zero Held barrier height A lor variable widths of the density of hopping states (Rel. 2I ).

For typical polymer LED device parameters, currenl is space charge limited if the energy barrier to injection is less than about 0.3-0.4 eV and contact limited if it is laiger than that. Injection currents have a component due to thermionic emission and a component due to tunneling. Both thermionic emission and tunneling... 

Elaborating upon these ideas Arkhipov et itl. calculated the dependence of the injection current on electric field temperature of the DOS and strength of intersite coupling. 

Figure 12-6. Representation of the calculated injection currents on u In j vs Fln scale, appropriate for testing thermionic injection following Ridiardson-Schollky theory.

Although the problems associated with septum injectors can be eliminated by using stop-flow septumless injection, currently the most widely used devices in commercial chromatographs are the microvolume sampling valves (Fig. 8.3) which enable samples to be introduced reproducibly into pressurised columns without significant interruption of the mobile phase flow. The sample is loaded at atmospheric pressure into an external loop in the valve and introduced into the mobile phase by an appropriate rotation of the valve. The volume of sample introduced, ranging from 2 piL to over 100 /iL, may be varied by changing... 

S. J. Radautsan, Transient Injection Current in Solids, Stinitza, Kishinev, 1983. 

Fig. 21.2. Two-microelectrode current-clamp technique used to observe, in single Ascaris body muscle cells in a body-flap preparation, the response to a controlled pulsed application of levamisole. One micropipette, to measure membrane potential, and another micropipette, to inject current, are inserted inside the area of the muscle cell known as the bag region. Levamisole is applied in a time- and pressure-controlled manner from a microcatheter placed over the bag region of the muscle. A second microcatheter is used to apply additional chemical agents (Martin, 1982).

Fig. 21.3. Two-micropipette current-clamp recording and effect of maintained application of 30 pM levamisole, which produces a 15 mV depolarization (upward movement of trace). The downward transients are the result of injected current pulses used to measure membrane conductance. The trace gets narrower as the input conductance increases from 2.35 pS to 4.35 pS as the levamisole ion channels open. The peak amplitude of the membrane potential response and change in input conductance are used as an assay of the number and activity of the levamisole ion channel receptors present in the muscle cell membrane. The response was fully reversible on washing (not shown).

As a first example, let us consider a metallic thermistor inserted in fig. 3, whose resistance is, in a first approximation, expressed as R(T)=Ro(l+aT). R(T) is the resistance of a PTC thermistor at a given temperature T, Ro is the resistance at To, and I represents a suitable DC (or AC current), while A is the constant gain of a low noise amplifier, operating in a suitable bandwidth. Let us suppose that the injected current I does not induce, through the heating process, a detectable change of the resistance value. 

For the p-type substrate a significant number of electrons are collected at the backside, as shown in the top part of Fig. 3.2. This is true not only for the illuminated p-type electrode but also if the electrode is kept in the dark, which indicates that electrons are injected during the tetravalent dissolution reaction. In the regime of oscillations the electron injection current is found to oscillate, too [CalO]. 

This fast removal of Si-F species can be ascribed to the weakening of the Si backbonds induced by the strong polarizing effect of F [Ubl], The weak back-bonds are then attacked by HF or H20. This reaction scheme for the dissolution process is supported by quantum-chemical calculations [Trl]. The observed dissolution valence of two for Jelectron injection current and Si-F bond density [Be22] are experimental findings that are in support of the divalent dissolution mechanism, as shown in Fig. 4.3 [Lei, Ge7, Ho6]. 

The steady-state current for an n-type Si electrode in the dark anodized at 0.5 V positive of OCP in 1M NH4F shows a strong dependence on pH. While it is about 5 pA cm-2 for pH 2-6, it peaks at pH = 7 with values above 10 pA cnT2, followed by a decrease to about 1 pA cm 2 for pH >8 [H06]. As shown in Fig. 4.11, the dark current of an n-type silicon electrode in 3% HF increases significantly with increasing DOC. This chemically-induced electron injection current is about one order of magnitude larger than the one observed for low DOC. A similar dependence of reverse current on DOC has also been observed in pure water. Atomic force microscopy (AFM) inspections of the electrode showed an atomically flat... 

Electron injection has been observed during the chemical dissolution of an oxide film in HF [Mai, Ozl, Bi5]. The injected electrons are easily detected if the anodized electrode is n-type and kept in the dark. Independently of oxide thickness and whether the oxide is thermally grown or formed by anodization, injected electrons are only observed during the dissolution of the last few monolayers adjacent to the silicon interface. The electron injection current transient depends on dissolution rate respectively HF concentration, however, the exchanged charge per area is always in the order of 0.6 mC cm-2. This is shown in Fig. 4.14 for an n-type silicon electrode illuminated with chopped light. The transient injection current is clearly visible in the dark phases. 

For p-type electrodes, the cathodic current is carried at low overvoltages by the minority carriers (electrons) in the conduction band and is controlled at high overvoltages by the limiting current of electron diffusion the anodic current is carried by the mtqority carriers (holes) in the valence band and the concentration of interfacial holes increases with increasing anodic overvoltage until the Fermi level is pinned in the valence band at the electrode interface, where the anodic current finally becomes an electron injection current into the electrode. 

Fig. 10-24. Electron levels and polarization curves for a redox reaction of cathodic holes both at an n-type and at a p-type electrode of the same semiconductor in the dark curve (1) = polarization curve of cathodic hole injection in n -type electrode curve (2)= polarization curve of cathodic hole injection in p-type electrode (equivalent to a curve representing cathodic hole injection current as a i mction of quasi-Fermi level of interfodal holes in n-type electrode) = cathodic hole injection current N = polarization of cathodic hole ixu ection at potential nECi) of n-type electrode, P = polarization of cathodic hole iqjection at potential pE(.i) of p-type electrode.

Boundary layer models take a similar approach but attempt to extend the parameterization of gas exchange to individual micrometeorological processes including transfer of heat (solar radiation effects including the cool skin), momentum (friction, waves, bubble injection, current shear), and other effects such as rainfall and chemical enhancements arising from reaction with water. 

Akuetey G, Hirsch J (1991) Contact-injected currents in polyvinylcarbazole. Phil Mag B 63 389... 

Despite poor MOS channel mobility and high pinch-off resistance, this device demonstrated breakdown voltage of 4,580V and specific on-resistance of 387 mDcm which is only 4% of the theoretical limit of Si for such voltage range. It has also demonstrated excellent dynamic characteristics, showing almost no dependence of turnoff and turn-on times on injected current [41]. 

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