The electrochemical impedance of one-equivalent electrode processes at dark semiconductor|redox electrodes involving charge transfer through surface states. 1. Theory

Journal of Physical Chemistry B

Volumn 103, Issue 1, 1999, Pages 122-129

  Hens, Z ^a  

^a GHENT UNIVERSITY   (Belgium)

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EID: 0000842283     PISSN: 15206106     EISSN: None     Source Type: Journal    
DOI: 10.1021/jp982766f     Document Type: Article

References (38)

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26. It is assumed that the surface states mediating the charge transfer are not induced by the electrode process itself.
27. This means that the semiconductor surface is a surface of equal potential.
28. According to the electrochemical sign convention, cathodic currents are taken as negative, anodic currents as positive.
29. 22 or reactions involving changes of the structure of the Helmholtz-layer apart from the filling or unfilling of surface states are excluded.
30. Sinusoidally varying quantities derived from a given quantity a are written as ã exp(iωt).
31. In what follows, neither the dependence of the small signal variables on the pulsation ω nor the fact that, when taking a partial derivative, all other independent variables remain constant is indicated explicitly.
32. It is assumed that the cathodic and anodic current density depend only on the concentration of oxidizing and reducing agent at the interface, respectively.
33. The magnitude of the electric field at the interface might influence these rate constants causing a dependence of the current densities at the semiconductor side on the potential drop across the Helmholtz layer and vice versa. The assumption made considers this to be a minor effect only.
34. Hole excitation from the valence band to the surface state is not accounted for in this expression.
35. sc and the occupancy of the surface states θ are kept constant in this partial derivative. The final result, obtained by calculating the partial derivatives explicitely, is nevertheless the same for both.
36. It is assumed that all injected holes either recombine at the semiconductor surface or are captured by the reaction product (reverse reaction). This is justified if parallel recombination mechanisms (band to band recombination, recombination in the space-charge layer,...) and other hole consuming reactions (anodic dissolution) are negligible as compared to these two processes.
37. This quantity should not be confused with the surface concentration of valence-band holes, see ref 15.
38. H is equal to zero such that no diffusion impedance appears in the electrochemical impedance, cfr. ref 16.