Scanning laser photoelectrochemical studies of oxide films on metals

Kucernak, Anthony Robert John (1991) Scanning laser photoelectrochemical studies of oxide films on metals. University of Southampton, Doctoral Thesis.

Abstract

A scanning laser microscope has been built and used to create images based on the photoelectrochemical response of a surface. This technique has been given the name SCALPEM: Scanning Laser PhotoElectro-

chemical Microscopy. Oxide films on copper, iron and AISI 304L stainless steel under aqueous solutions have been studied. Localised deviations have been followed over various experiments as a function of applied potential, light intensity, detection method, solution composition, laser spot scan speed, illumination wavelength, exposure time to solution. These deviations have been attributed to variation of particular local properties.

The photocurrent developed by these samples depended on whether or not intensity modulated illumination was used. For the case in which the scanning laser spot is not intensity modulated, a theory has been presented to explain contrast variations within images. This theory relates contrast variations to modifications in the parameters affecting the photocurrent frequency response: the low and high frequency generation parameters, and the time constant for carrier recombination. The theory has been used to explain experimental results in which changes in contrast have arisen due to changes in the spot scan speed, variations in the sign of photocurrent, and the occurrence of film thickening or alteration process.

The applicability of this technique to the study of corrosion has been shown in a number of experiments. The precursor steps to pit initiation on stainless steel at managnese sulphide inclusions have been imaged as has the effect of benzotriazole (a commercial corrosion inhibitor) on the corrosion of copper in sodium solution,

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