AVS 45th International Symposium
    Applied Surface Science Division Monday Sessions
       Session AS-MoA

Invited Paper AS-MoA3
Problems in Surface Characterization of Oxides and Insulators

Monday, November 2, 1998, 2:40 pm, Room 307

Session: Oxides and Insulators - Surface Characterization and Applications
Presenter: J. Cazaux, University of Reims, France
Correspondent: Click to Email
Most of the oxides are insulators in which charging effects and radiation damage effects often coexist when they are investigated with incident particles. In electron irradiated insulators, charge phenomena result from a competition between the secondary electron emission which contributes to a positive charging and the trapping of incident electrons which tends the specimen to be negatively charged. The initial charge distribution (and the electric field it induces) may be estimated but self regulation processes rapidly take place. The final state equilibrium is difficult to predict because it is a function of the nature and of the density of trapping centers that may pre-exist or that are induced by the irradiation and then negative charging may be observed at primary beam energies where a positive charging is expected from the total yield approach. Various specific mechanisms may be involved in the chemical change of irradiated insulators and most of them are electric field dependent. There is first the migration of the mobile species driven by the electric field build-up. There is also the dissociation of some electron/hole pairs generated by the transport of energetic (photo) electrons. The third cause of damage results from the ionization of core electrons followed by (intra or inter atomic) Auger transitions.Each transition finally leaves the excited atom with two electrons missing and the lack of conduction electrons (in insulators) prevents the initial charge of this atom or of its surroundings to be quickly restored. Halogen ions change sign while O@super-2@ ions become neutral and they may be desorbed into the vacuum when they are located close to the surface. Examples of microscopic (Electric image effects and Schottky barrier lowering) and macroscopic (electric field function) calculations will be given. These calculations are supported by a significant number of recent experimental results. Practical consequences to minimize these effects or to take benefit of them (nanolithography ; controlled surface modifications) will be suggested