Charge transfer, interfacial

Figure 12. Energy diagram of a semiconductor/electrolyte interface showing photogeneration and loss mechanisms (via surface recombination and interfacial charge transfer for minority charge carriers). The surface concentration of minority...

This means that the PMC signal will, apart from the generation rate of minority carriers and a proportionality constant, be determined by the interfacial charge transfer rate constant kr and the interfacial charge recombination rate sr... 

Let us now investigate the case of a semiconductor with a relatively slow interfacial charge transfer. In this case the surface concentration of minority carriers is high and we can neglect the second term (which does not contain Ps). For higher values of electrode potential, the term L Qxp(-AUqfkT) can also be neglected. 

The interfacial charge-transfer rate constant can be determined when the PMC signal and the photocurrent are measured simultaneously. When the interfacial charge transfer is, on the other hand, very large and Aps negligible, the PMC value becomes... 

Figure 13. Numerically calculated PMC potential curves from transport equations (14)—(17) without simplifications for different interfacial reaction rate constants for minority carriers (holes in n-type semiconductor) (a) PMC peak in depletion region. Bulk lifetime 10" s, combined interfacial rate constants (sr = sr + kr) inserted in drawing. Dark points, calculation from analytical formula (18). (b) PMC peak in accumulation region. Bulk lifetime 10 5s. The combined interfacial charge-transfer and recombination rate ranges from 10 (1), 100 (2), 103 (3), 3 x 103 (4), 104 (5), 3 x 104 (6) to 106 (7) cm s"1. The flatband potential is indicated.

Figure 15. Effect of interfacial rate constants on PMC behavior and on the photocurrent (/0 = 1 cm-2), (a) Fast interfacial charge-transferrate, and (b) low interfacial charge-transfer rate.

Figure 16 shows such PMC peaks in the depletion region for electrodes of Si,9 WSez8 and ZnO.12 They all appear near the onset of anodic photocurrents. They have different shapes, which, however, can easily be explained with the assumption of potential-dependent interfacial charge-transfer and charge recombination rates. 

In studies on Pt dotted silicon electrodes, PMC measurements revealed that tiny Pt dots increased the interfacial charge transfer compared with bare silicon surfaces in contact with aqueous electrolytes. However, during an aging effect, the thickness of the oxide layer between the silicon and the platinum dots gradually increased so that the kinetic advantage again decreased with time.11... 

Experimental evidence with very different semiconductors has shown that at semiconductor interfaces where limited surface recombination and a modest interfacial charge-transfer rate for charge carriers generate a peak... 

As outlined at the beginning of this chapter, combined photocurrent and microwave conductivity measurements supply the information needed to determine three relevant potential-dependent quantities the surface concentration of excess minority carriers (Aps), the interfacial recombination rate (sr), and the interfacial charge-transfer rate ( r). By inserting the... 

With electrochemically studied semiconductor samples, the evaluation of t [relation (39)] would be more straightforward. AU could be increased in a well-defined way, so that the suppression of surface recombination could be expected. Provided the Debye length of the material is known, the interfacial charge-transfer rate and the surface recombination... 

Interfacial Charge Transfer Reactions in Colloidal Dispersions and Their Application to Water Cleavage by Visible Light Gratzel, M. 15... 

Derivatized semiconductor photoelectrodes offer a way to design photosensitive interfaces for effecting virtually any redox process. Manipulation of interfacial charge transfer processes has been demonstrated using hydrolytically unstable redox... 

An electric current flowing through an ITIFS splits into nonfaradaic (charging or capacity) and faradic current contributions. The latter contribution comprises the effects of both the transport of reactants to or from the interface, and the interfacial charge transfer, the rate of which is a function of the interfacial potential difference. By applying a transient electrochemical technique, these two effects can be resolved... 

Many of the electrochemical techniques described in this book fulfill all of these criteria. By using an external potential to drive a charge transfer process (electron or ion transfer), mass transport (typically by diffusion) is well-defined and calculable, and the current provides a direct measurement of the interfacial reaction rate [8]. However, there is a whole class of spontaneous reactions, which do not involve net interfacial charge transfer, where these criteria are more difficult to implement. For this type of process, hydro-dynamic techniques become important, where mass transport is controlled by convection as well as diffusion. 

The oscillations observed with artificial membranes, such as thick liquid membranes, lipid-doped filter, or bilayer lipid membranes indicate that the oscillation can occur even in the absence of the channel protein. The oscillations at artificial membranes are expected to provide fundamental information useful in elucidating the oscillation processes in living membrane systems. Since the oscillations may be attributed to the coupling occurring among interfacial charge transfer, interfacial adsorption, mass transfer, and chemical reactions, the processes are presumed to be simpler than the oscillation in biomembranes. Even in artificial oscillation systems, elementary reactions for the oscillation which have been verified experimentally are very few. 

Theoretical insight into the interfacial charge transfer at ITIES and detection mechanism of this type of sensor were considered [61-63], In case of ionophore assisted transport for a cation I the formation of ion-ionophore complexes in the organic (membrane) phase is expected, which can be described with the appropriate complex formation constant, /3ILnI. 

Kamat, P.V., Interfacial charge transfer processes in colloidal semiconductor systems, Prog. React. Kinet., 19,277,1994. 

The investigation of possible utilization of EISA-manufactured layers in electronic applications has started relatively recently, but the already performed studies demonstrate a very high potential of mesoporous films for technologies using interfacial and bulk charge transport. The advantages of the EISA-prepared layers become especially evident when the interfacial charge transfer from the species attached to the interface plays the key role in system performance. 

T.W. Hamann, F. Gstrein, B.S. Brunschwig, N.S. Lewis, Measurement of the driving force dependence of interfacial charge transfer rate constants in response to pH changes at n-ZnO/ H20 interfacies, Chem. Phys. 326 (2006) 15-23. 

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