Photochemistry on a polarisable semi-conductor: what do we understand today?

The continued development of ferroelectric materials into more and more consumer led applications has been at the forefront of recent ferroelectric material research. It is, however, possible to view a ferroelectric as a wide band gap semi-conductor that can sustain a surface charge density. This charge density arises from the movement of ions in the crystal lattice and the need to compensate for this charge. When viewing ferroelectrics as polarisable semi-conductors a large number of new interactions are possible. One such is the use of super band gap illumination to generate electron–hole pairs. These photogenerated carriers can then perform local electrochemistry. What is most interesting for ferroelectric materials is that the REDOX chemistry can be chosen by selectively modifying the domain structure of the ferroelectric—we can perform oxidation and reduction on the surface of the same material at spatially separate locations, or use the material to drive photoexcited carriers apart. This means we can separate the REDOX products or produce patterns of photogenerated material in places we have predetermined. This review aims to introduce the background research that has led to the current understanding as well a highlight some of the current areas that require further development.