Photocurrent imaging of passive metals

Abstract

The theory of photoelectrochemical imaging using a scanning laser microscope is presented in outline: the idea of a photocurrent transfer function whose parameters might be spatially variable is introduced and a distinction is made between continuous-scan and step-scan methods of rastering the light spot. In the continuous-scan method interesting blurring, streaking and shadowing effects highlight changes over the surface of different parameters of the photocurrent transfer function. Images of passive copper, bismuth, iron and stainless steel show effects of varying thickness of the passive film and charge carrier recombination rate, effects localised at grain boundaries and around inclusions in the metal and effects showing localised corrosion, inhibition and inhibition breakdown.