Materials modi®cation by electronic excitation

Electronic excitation by lasers or electron beams can modify the properties of materials. The changes are not just due to heat, nor do they result from the well-known collision dynamics of much radiation damage. Everyday examples of modi®cation by electronic excitation include photography, and photochromics (such as sunglasses) which change colour. In the last few years it has become clear that excitation can offer novel types of modi®cation, with better-controlled changes. The ®eld has evolved through a mix of basic science, of new laser and electron beam tools, and of new needs from microelectronics, photonics and nanotechnology. Underlying this development are some common themes which integrate the basic science and its applications. These include especially the ideas of energy localisation and charge localisation. There are detailed comparisons of experiment and theory for halides, but there is a wealth of information for other materials. From this, we identify ways to connect understanding to technological needs, like selective removal of material, controlled changes, altering the balance between process steps, and possibilities of quantum control. The ®eld is reviewed in full in our recent book [N. Itoh, A.M. Stoneham, Materials Modi®cation by Electronic Excitation, Cambridge University Press, Cambridge, 2000]. # 2000 Elsevier Science B.V. All rights reserved.