Anodic saturation current

Our experimental techniques have been described extensively in earlier papers (2, 13). The gamma ray irradiations were carried out in a 50,000-curie source located at the bottom of a pool. The photoionization experiments were carried out by krypton and argon resonance lamps of high purity. The krypton resonance lamp was provided with a CaF2 window which transmits only the 1236 A. (10 e.v.) line while the radiation from the argon resonance lamp passed through a thin ( 0.3 mm.) LiF window. In the latter case, the resonance lines at 1067 and 1048 A. are transmitted. The intensity of 1048-A. line was about 75% of that of the 1067-A. line. The number of ions produced in both the radiolysis and photoionization experiments was determined by measuring the saturation current across two electrodes. In the radiolysis, the outer wall of a cylindrical stainless steel reaction vessel served as a cathode while a centrally located rod was used as anode. The photoionization apparatus was provided with two parallel plate nickel electrodes which were located at equal distances from the window of the resonance lamp. 

Since holes are consumed at the surface during the anodic dissolution, the n-type samples show increasing differences between the measured and the calculated capacities with increasing rate of dissolution, i. e., with increasing anodic polarization. In this case d-c potential curves also show deviations from the initial exponential slope. At higher anodic potentials a saturation current occurs. Illumination compensates for or decreases the influence of the anodic current on the concentration cf holes. Fig. 11 shows schematically the influence of anodic dissolution and illumination. For p-type Ge the same effects occur, when electrons are consumed by the electrode reaction, i. e., in the cathodic region. 

The data of Efimov and Erusalimchik (5) shown in Fig.l give an example of the different current-voltage characteristics obtained with various resistivity n- and p-type germanium electrodes made anode in 0.1 N HC1. Brattain and Garrett (4) and others (7-10), however, found much lower saturation current densities by one to two orders of magnitude with n-type germanium made anode in similar electrolytes. Similar curves for n-type silicon would show saturation current densities in the order of microamperes per square centimeter. 

The equilibrium hole concentration can be increased by raising the temperature of the semiconductor. Uhlir (7) found that the temperature variation of the saturation current density across the barrier between anodic n-type germanium and 10% potassium hydroxide solution is quite like that of a p-n junction. About a tenfold increase in the saturation current density is obtained for each 30° C rise in temperature as shown in Fig. 2. 

The Reichmann derivation is of special interest because the final current equation (Eq. 7.68) describes the complete valence band process at an n-type electrode for anodic as well as for cathodic polarization. Eq. (7.68) looks rather complex because it contains two saturation currents, /o and jy. The general issue of this equation becomes clearer when the dark current is also considered. Setting /o = 0 one obtains from Eq. (7.68)... 

Concerning the current-potential curve as measured with an n-type electrode, one can observe that the saturation current-potential curve is not only determined by the light intensity but also by the doping of the n-type Ge electrode. As illustrated in Fig. 8.3, the anodic dark current measured with an n-type electrode, also depends on the doping. It increased with the resistivity of the n-type material which means that it... 

I hc number of electrons ejected from a pholoemissive surface is directly proportional to the radiant power of the beam that strikes that surface. As the voltage applied across the two electrodes of the lube is increased, the fraction of the emiiicd electrons that reaches the anode rapidly increases when the saturation voltage is achieved, essentially all of Ihe electrons are collected at Ihe anode. The current then becomes independent of voltage and directly proportional to the radiant power. Phototubes are usually operated at a voltage of about 90 V. which is well within the saturation region. 

As described above, the self-assembly of Cys promotes the electron transfer between SOD and the Au electrode. This Cys-promoted rapid and direct electron transfer of SOD and its relevance to the redox reaction of the copper complex moiety in SOD formed a strong basis for the development of a SOD-based third-generation biosensor for 02 because the copper complex moiety has been well documented as the active site for the catalytic dismutation of O2 [128]. Figure 10-39 shows CVs at the bare Au, Cys/Au and SOD/Cys/ Au electrodes in PBS (O2 saturated) containing 0.002 unit of XOD and 50 pM xanthine, i.e. in the presence of O2. Both cathodic and anodic peak currents corresponding to the redox reaction of the SOD confined on the electrode are significantly increased, compared with those in the absence of O2 (Fig. 10-36a) [133—135]. Such a redox response was not... 

In liquid SO2 and CsAsFg as supporting electrolyte the oxidation of saturated hydrocarbons could be studied up to potentials of 6.0 V vs see by using platinum ultramicroelectrodes. Irreversible voltammetric waves were found for the compounds methane to n-octane that were studied The anodic peak currents suggest n-values around 2 a bulk electrolysis consumed 2 faradays per mole of alkane. The primary products in dilute solutions (1-10 mM) were shorter chain hydrocarbons. Electrolysis of more concentrated solutions led, via reaction of the oxidation products with starting material, to longer-chain hydrocarbons. 

As mentioned above, the anodic charging currents and cathodic discharging currents at FiePcZn in aqueous Ce "/" " solution were found to be independent of the electrolyte concentration and could therefore not be analyzed by Equation (10.10), although /m did show a saturation behavior comparable to PcZn. 

The saturation concentration of FeCl2 in water is equal to 4.25 mol 1". Calculate the anodic limiting current density for iron dissolution from a rotating disk electrode in a binary electrolyte of 2.0 mol 1 FeCl2 at a rotation rate of 200 rpm. The temperature... 

Anodic currents at n-type specimen and cathodic currents at p-type specimen are controlled by diffusion and thermal generation of minority carriers. The height of these so-called "saturation currents" is given by... 

Electrochemistry is an analytical tool that can be used to determine redox potentials of an analyte as well as the fate of a molecule upon addition or removal of electrons. Of particular importance to photochemists is the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO). Cyclic voltammetry is one of the most commonly used electrochemical techniques and is based on the change in potential as a linear function of time. An electrochemical reaction is reversible if = 1 and AEp = 59/n mV, where ip is the anodic peak current, ip is the cathodic peak current, and A p (AE), = A p — Ep ") is the potential peak separation for the anodic ( ), ) and cathodic Ep ) peaks. The oxidation or reduction potential for a reversible electrochemical process is given by 1/2 = Ep + Ep jl and is recorded vs. a reference electrode. All electrochemical data provided herein are converted to V vs. saturated calomel electrode (SCE) to make the comparison more facile. A reversible redox couple implies that the complex undergoes facile electron transfer with the electrode and that no chemical reaction follows the electrochemical step. 

---