PbO films on lead electrodes

The primary purpose of the studies described in the previous section was the characterisation of the optical properties of the photoactive layer. Often, however, a reliable in-situ method of following film growth is required. As 

The growth of PbO films on lead in H2S04 has been discussed in the previous section, where it was shown that the tetragonal modification of the oxide is formed. The corrosion of lead in sulphuric acid is more rapid at elevated temperatures and a systematic study of the rate of oxide growth as a function of temperature has been made by photocurrent spectroscopy [17]. 

Results obtained for the oxide film on bismuth illustrate this approach [29]. The oxide grows by the field-assisted migration of ions and Fig. 12 shows that the forward sweep of a cyclic voltammogram exhibits the plateau currrent characteristic of this mechanism. On the reverse sweep, where the field is insufficient to sustain further film growth, the current falls to zero until the potential is reached at which the film is reduced. The figure also shows the photocurrent observed under the same conditions when the electrode is illuminated. On the forward sweep, the photocurrent rises as the film thickens, but on the reverse sweep it falls and then changes sign before the reduction potential is reached. 

The photoemission process involves the excitation of electrons from the metal electrode into the oxide overlayer and the threshold energy therefore 

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