Field-assisted diffusion

Narayanan et al. conducted a theoretical analysis on the cell parameters that determined this maximum shuttling current. By assuming that the mass transport of the redox couple [R]/[0] is mainly realized by means of diffusion—which is reasonable because the low concentration of [R]/[0] at the additive level makes the field-assisted migration negligible—they applied the finite linear diffusion... 

The preceding equation shows that the transit time dispersion under weak field conditions is controlled by conventional diffusion, whereas at strong fields, the main contribution to Ate arises from the field-assisted diffusion term. A crossover from Atj to Atj occurs in the field dependence of the transit time dispersion that corresponds to the crossover from Atj E to Atj E in the dependence of the transit time dispersion on the transit time. It is worth noting that all parameters describing the contribution of the preceding equation are defined by independent measurements, while the contribution of the field-induced diffusion depends on the value of the effective release time, which is poorly known and can be very different in different disordered materials. 

In parallel processes, c.g., field-assisted diffusion and sliding, the bond between the surface and the adatom is never completely broken. Field-assisted diffusion of an adatom on the surface occurs due to the presence of the intense, inhomogeneous electric field between the probe tip and the surface, which gives rise to a potential gradient. 

Nanocrystalline systems display a number of unusual features that are not fully understood at present. In particular, further work is needed to clarify the relationship between carrier transport, trapping, inter-particle tunnelling and electron-electrolyte interactions in three dimensional nan-oporous systems. The photocurrent response of nanocrystalline electrodes is nonlinear, and the measured properties such as electron lifetime and diffusion coefficient are intensity dependent quantities. Intensity dependent trap occupation may provide an explanation for this behaviour, and methods for distinguishing between trapped and mobile electrons, for example optically, are needed. Most models of electron transport make a priori assumptions that diffusion dominates because the internal electric fields are small. However, field assisted electron transport may also contribute to the measured photocurrent response, and this question needs to be addressed in future work. 

In organic cells, however, the steps involved in the generation of photo-current are (1) light absorption, (2) exciton creation, (3) exciton diffusion, (4) exciton dissociation in the bulk or at the surface, (5) field-assisted carrier separation, (6) carrier transport, and (7) carrier delivery to external circuit. Assuming that only the excitons which reach the junction interface produce free carriers, if the blocking contact is illuminated [65],... 

The above observations have been interpreted within the framework of two distinct models, one involving trapping/detrapping of the photogenerated electrons [345, 346] and the other based on electron diffusion (or field-assisted diffusion) not attenuated by electron localization [347, 348]. The millisecond transit times also mean that the transit times are very long compared with equilibration of majority carriers in a bulk semiconductor or electron-hole pair separation within the depletion layer of a flat electrode. The slow transport is rationalized by a weak driving force and by invoking percolation effects [338]. 

The inward motion of anions is assumed to be the dominant ionic transport across the oxide. The ionic movement is field-assisted drifting and is the rate-limiting process. The diffusion of ions at room temperature is considered to be too slow to account for the oxide growth rates. The current density is written as... 

Kever et al. [10] have proposed that the main reason for the switching is the field-assisted diffusion of Cu-ions into the oxide layer that is commonly found at the Cu(TCNQ)/metal interface in devices with aluminium top-contacts, leading to the formation of conductive filaments through the oxide. We have... 

In addition, the strong fields at the surface and interface at elevated temperatures may lead to field-assisted diffusion of mobile ion species such as protons and alkali ions, and strong illumination will require a new quasistatic equilibration, accompanied possibly by photodesorption (or adsorption), which might require long-time relaxation back to the dark equilibrium. 

In this work, DC electric field-assisted ion exchange was carried out to enhance the sodium-potassium inter-diffusion and improve the mechanical performance of borosilicafe glass. Elecfric fields with intensity varying between 100 V cm and 3000 V cm were applied in both direct and inverted polarizations. Four point bending test and the Vickers indentation method were used to characterize the mechanical properties. Energy dispersion x-ray spectroscopy was carried out to determine the potassium concentration within the surface layers of the samples. 

Sviridov SI, Eliseeva NP. Field-assisted diffusion of potassium ions in sodium silicate glass. Glass Physics and Chemistry. 2006 32(6) 604-ll. DOI 10.1134/... 

This mechanism is consistent with the hypothesis that in the second stage dissolution kinetics is dependent on diffusion within the concentration boundary layer. It is conceivable that in the first stage field assisted dissolution may be the controlling step. In this stage formation of Ti(OH)4 or of hydroxy-cations, e.g. Ti(OH)3, has different effects on titanium transport. While Ti(OH)4 does not react with organic molecules, Ti(OH)3 can form organometallic complexes which may be transported systemically. 

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