Stored charge

Dielectric Constant. Capacitance, C, refers to the abiHty of two conductors to store charge, in the presence of a potential difference, V ... 

A capacitor, previously called a condenser, stores electrical energy based on the relationship between voltage (V) and stored charge (Q) in coulombs as shown in the equation C = QU. One farad of capacitance is a coulomb per volt of stored charge. The voltage limit of a capacitor is determined by the breakdown potential of the dielectric material. 

Fig. 2. Stored charge (as calculated from conductivity changes) as a function of irradiation time. Concentration of the silver sol 2.5 x 10 M. J rate of charging the microelectrode (i.e. rate of radical generation divided by Faraday s equivalent)...

On a larger scale, it is possible to store charge in gold nanoparticles. Chen described 1.8 nm diameter nanoparticles coated with a layer of alkylthiols,... 

Fig. 10.8 aZTT Figure of Merit ( Eb,=CVbr/A, in gC/cmz) and leakage currents (measured at a stored charge of 7. iC/cm2, current density measured in A/cm2) as a function of position on the substrate. 

When discharging, the upper and lower switches are both closed so that the stored charge from the capacitor is now delivered to the patient. The inductor acts to modify the current waveform delivered as described below. 

The capacitance (C) can be defined as the ability to retain or store charge. The impedance of a capacitor is given by the following equation ... 

These carboxylate ions are weaker counterions than CP and Pp, so that the corresponding dendrimers tend to ionize more easily and to give clearer signals in MALDI-TOF mass spectra. As to the electrochemical properties, their cyclic voltammetries show a reversible metal centered oxidation and two reversible ligand-centered reduction processes at potential values very similar to those of the corresponding dendrimers with CP counterions. Therefore, the [Ru(tpy)2]2+ complexes are electrochemically equivalent and can efficiently store charges. 

For the third-generation dendrimer 26 the first reduction wave is symmetrically bell-shaped and the peak current is proportional to the scan rate (for v < 400 V/s), demonstrating that 26 is adsorbed on the electrode surface. From the area under the peak and the dendrimer area, a bilayer is estimated to be deposited onto the electrode. Upon increasing scan rate (v > 104 V/s), only a fraction of the units are reduced during the forward scan because only part of the fullerene moieties are close enough to the surface to allow direct electron transfer. On the other hand, at lower scan rates, all the fullerene redox sites are accessible and thus they can store charges. 

An electrified interface can be considered a system capable of storing charge, considering that it is a region where charges are accumulated or depleted relative to the bulk of the electrolyte. However, the ability to store charge is the characteristic... 

The Differential Capacity Due to the Space Charge. When capacity measurements are carried out on a semiconductoi/electrolyte interface, one must not forget that the space-charge region inside the semiconductor has the ability to store charge. The contribution of this region to the differential capacity of the interface can... 

The interphase between an electrolyte solution and an electrode has become known as the electrical double layer. It was recognized early that the interphase behaves like a capacitor in its ability to store charge. Helmholtz therefore proposed a simple electrostatic model of the interphase based on charge separation across a constant distance as illustrated in Figure 2.12. This parallel-plate capacitor model survives principally in the use of the term double layer to describe a situation that is quite obviously far more complex. Helmholtz was unable to account for the experimentally observed potential dependence and ionic strength dependence of the capacitance. For an ideal capacitor, Q = CV, and the capacitance C is not a function of V. 

It is instructive to compare this to the capacitance of a plate capacitor o A/d. Here, A is the cross-sectional area and d is the separation between the two plates. We see that the electric double layer behaves like a plate capacitor, in which the distance between the plates is given by the Debye length The capacity of a double layer — that is the ability to store charge — rises with increasing salt concentration because the Debye length decreases. 

The ability of a C-I-S structure to store charge is measured by its capacitance Cp (per area) which is given by (J3)... 

As may be noted, water vapor speeds up device response to hydrogen. Figure lib gives V-p (where V-pn is the turn on voltage for transport down the channel created by the stored charge) versus time for a MOSFET based on the Pd/Si02/Si structure. These data are for an exposure to 180 ppm H2 in air at 150°C. In this case, both response and recovery behavior are shown. Figure 12 clearly shows that Pd/SiC>2/... 

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