Materials modification by electronic excitation

Abstract

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

The treatment of electronic excitations in atomistic models of radiation damage in metals

“…Fleischer et al [12] have shown that the extent of radiation damage in dielectrics correlates better with the rate of ionization by the PKA than with its rate of energy loss, again lending support to the Coulomb explosion model. Itoh and Stoneham [13] point to evidence from work on dichalcogenides that shows track formation does not occur for electrical conductivity exceeding 10 5 Ω −1 cm −1 .…”

An ab initio study of the effect of charge localization on oxygen defect formation and migration energies in magnesium oxide

“…There has been a recent revival of interest in attempting to understand and include these effects, with notable progress in metallic materials (Duffy & Rutherford 2007;Duffy et al 2008;Race et al 2009). Electronic excitations in insulating materials are more complex than those in metals as the band gap results in a range of additional processes including the trapping and self-trapping of electrons, holes and excitons (Itoh & Stoneham 2001). The trapping of electrons and holes at defects (Chen & Abraham 1990; vacancies and interstitials) in ionic crystals is particularly relevant to radiation damage, as the trapped carriers will effectively change the net defect charge and this will have a strong effect on defect migration energies, and hence the microstructure evolution.…”

Activation spectroscopy of electronically induced defects in solid Ne

“…The basis for the physics of their formation is a concentration of the electronic excitation energy within a volume about that of a unit cell followed by the energy release. These defects were actively studied on a variety of materials [2][3][4]. Atomic cryocrystals with their simple lattice and well-known electronic structure are especially suitable for these studies due to small binding energies in conjunction with a strong exciton-phonon interaction.…”