Electrons, Ions and Cathodoluminescence in the Environmental SEM

Abstract “Secondary” or ‘low energy’ electron emission in the environmental SEM is a complex summation of surface and near surface interactions of electron and ions, fields developed within the sample and conventional electron-sample interactions. Little is understood about the first two aspects and recent data has illustrated limitations on our understanding of cathodoluminescence. The recently described Charge Contrast Imaging (CCI) has drawn attention to the fact that the role of ions in the environmental SEM have been largely ignored. Generally the positive ions have been regarded to provide charge cancellation at the specimen surface but otherwise to have little effect. This view has persisted in the face of evidence that even without gas amplification effects, charge neutral conditions are obtained at the sample surface with a chamber gas pressure of 0.1 torr2, a pressure far lower than normal operating conditions for the ESEM (1 -2 0 torr).