Impedance technique charge modulation

J. van de Lagemaat, N. G. Park, A. J. Frank, I nfluence of electrical potential distribution, charge transport, and recombination on the photopotential and photocurrent conversion efficiency of dye-sensitized nanocrystalline Ti02 solar cells a study by electrical impedance and optical modulation techniques, J. Phys. Chem. B 2000, 104(9), 2044-2052. 

AC impedance technique is also effective to study the passive oxide. The passive oxide may have semiconductive property, so that the AC potential apphcation will induce the charge modulation in the oxide film. For example, when we consider n-type semi-condnctive oxide film rmder positive bias, i.e., nnder reverse bias condition, as shown in Fig. 8, a depression layer is formed in the oxide film. In the depression layer, space charge is extended. 

A consistent picture for dynamics of heterogeneous ET has been emerging in the last 5 years with the development of new experimental approaches. Techniques such as AC impedance, modulated and time-resolved spectroscopy, SECM, and photoelectrochemical methods have extended our knowledge of charge-transfer kinetics to a wide range of time scales. This can be exemplified by comparing impedance analysis, which is limited to k of... 

Differently from other kinds of impedimetric biosensor based on the modulation of the interfacial properties, in this case all the measurements are performed in standard buffer solutions (PBS—Phosphate Buffered Saline o cell culture medium that has similar properties), without the addition of any redox species. This allows avoiding toxicity issues, possible electrochemical interferences and preserves the simplicity and generality of the proposed technique. Thus, in the absence of Faradaic processes, no charge transfer mechanism takes place and the interfacial impedance is simply formed by the series of the double layer capacitance and the solution resistance. For the gold/PBS interface, the double layer capacitance can be estimated multiplying the area of the electrode exposed to the hquid (down to the micro-scale) by the specific interfacial capacitance being 0.1-0.2 pF/pm. ... 

Other Modulation Techniques. Electric field modulated photoluminescence in a liquid junction device was reported in Ref. 75. The results agreed with the dead layer model previously discussed. Quantitative comparison of differentiation of Eq. 1 with respect to the eiectrode potentiai and impedance measurements yieided an agreement between the dead Layer and the space-charge iayer. 

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