Determination of redox properties of semiconducting materials

Wojciech Macyk 

Jagiellonian University, Faculty of Chemistry, Ingardena 3, Kraków 30-060, Poland

Abstract

Chemical and electrochemical surface processes attract a growing attention due to their possible practical applications. In particular, semiconducting materials and their modifications are used as catalysts and photocatalysts, electrodes, (bio)sensors etc. One of the crucial feature of an appropriate semiconductor suitable for a given purpose is the position of valence and conduction band edges at the energy (or potential) scale. For instance, the redox properties of photogenerated holes and electrons determine the activity of a photocatalyst. Therefore determination of redox potentials of semiconducting materials is very important. This knowledge helps to select the proper material and to elucidate mechanisms of processes taking place at the surface.

Although the energy bandgap can be relatively easily estimated from reflectance spectra of semiconductors, the measurement of band edge potentials is more difficult. One of the methods is based on capacity measurements. From the Mott-Schottky plot (the space charge capacity vs. electrode potential) it is possible to determine the so called flatband potential. The capacitance method is useful for semiconductor electrodes but not for suspensions. A number of other methods based on spectroscopic determinations, modulation spectroscopy, photocurrent, and photovoltage measurements have also been developed. In this presentation selected methods will be presented. Simple photoelectrochemical and spectroelectrochemical methods suitable for flatband potential measurements for semiconducting powders and transparent films will be discussed in detail.

 

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Presentation: Keynote lecture at SMCBS'2005 Workshop, by Wojciech Macyk
See On-line Journal of SMCBS'2005 Workshop

Submitted: 2005-09-02 11:42
Revised:   2009-06-07 00:44