High-field model

Figure 1.2 Illustration of the high-field model (a) adjacent lattice planes in the oxide and (b) effect of the E-field on the activation energy W (source Ref. [20]).

Lohrengel [12] proposed an extension of the high-field model where the concentration of defects varies with the electric field strength. When the concentration reaches a constant value, the high-field equations may be valid. D Alkaine et al. [13] developed a model where migration is the main type of transport, applied for both stationary [13,14] and potentiodynamic [14,15] conditions of film growth. In this case, it was assumed that the movement of ions inside the film presents characteristics similar to their movement in solution and that the potential gradient across the film obeys a linear relationship. 

Many insulating (Al, Si) or semiconducting (Fe, Pt) films grow according to the high field model. Then, the formation potential mainly determines the film thickness d ... 

Passivation with Participation of the Electrolyte The high field model of oxide growth excludes a contribution from metal ions in the electrolyte. In some cases, however, a precipitation of oxide from the electrolyte can contribute to passivation. 

Fig. 14 Passive film growth on Cr following application of a potential step from (a) 0.0 to 0.4 V and (b) 0.4 to 0.8 V. Full line is film thickness calculated from QCM frequency response (with widely spaced dots indicating uncertainty, 2or). The predictions of the interface and high-field models (explained in main text) are also indicated by the line-styles marked IFM and HFM, respectively. Electrodes Crfilm on Au supported on 10-MHz AT quartz crystal. Solution ...

Other models have also been proposed the point defect model, which is a modified version of the high field model (Lin et al., 1981 Chao et al., 1981) and the place exchange model (Lanyon and Trap-nell, 1955 Sato and Cohen, 1964 Conway and Angerstein-Kozlowska, 1981). 

Figure 6 shows the field dependence of hole mobiUty for TAPC-doped bisphenol A polycarbonate at various temperatures (37). The mobilities decrease with increasing field at low fields. At high fields, a log oc relationship is observed. The experimental results can be reproduced by Monte Carlo simulation, shown by soHd lines in Figure 6. The model predicts that the high field mobiUty follows the following equation (37) where d = a/kT (p is the width of the Gaussian distribution density of states), Z is a parameter that characterizes the degree of positional disorder, E is the electric field, is a prefactor mobihty, and Cis an empirical constant given as 2.9 X lO " (cm/V). ...

The general influence of covalency can be qualitatively explained in a very basic MO scheme. For example, we may consider the p-oxo Fe(III) dimers that are encountered in inorganic complexes and nonheme iron proteins, such as ribonucleotide reductase. In spite of a half-filled crystal-field model), the ferric high-spin ions show quadrupole splittings as large as 2.45 mm s < 0, 5 = 0.53 mm s 4.2-77 K) [61, 62]. This is explained... 

Figure 1 shows the proton spectrum of our model compound, recorded at a frequency of 200 MHz (though high fields are invaluable for solving the structures of complex biomolecules, we have found that instruments operating at 200-300 MHz are often in fact better when we are dealing with small molecules). 

Figure 3a shows the mean-field predictions for the polymer phase diagram for a range of values for Ep/Ec and B/Ec. The corresponding simulation results are shown in Fig. 3b. As can be seen from the figure, the mean-field theory captures the essential features of the polymer phase diagram and provides even fair quantitative agreement with the numerical results. A qualitative flaw of the mean-field model is that it fails to reproduce the crossing of the melting curves at 0 = 0.73. It is likely that this discrepancy is due to the neglect of the concentration dependence of XeS Improved estimates for Xeff at high densities can be obtained from series expansions based on the lattice-cluster theory [68,69].

Schmidt (1976) has given a classical model for the field dependence of quasi-free electron mobility that predicts p(E) in the high-field limit. At any... 

The relative and absolute stereochemistry of antimitotic macrolide archazolid A and B, originally isolated in the early nineties, has been determined on the basis of extensive high-field NMR studies, molecular modelling and chemical derivatization <06OL4751>. The proposed structures have yet to be confirmed by total synthesis. 

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