Investigation of trapped charges profile for an irradiated insulated material

The process of examining and analysing insulating materials using a scanning electron microscope usually accompanied by an important phenomenon called the mirror effect or charging effects. Such effects arise due to the ability of insulators to trapping charges at the sample surface for a period. The accumulation of charges leads to creating an electric potential that may be strong enough to deflect incident electrons in the same way a convex mirror scatters light. The created potential depends mainly on the charge amount, charges accumulation profile and the way by which the charges arranging themselves. Present work aims at exploring the influences of the charges distribution profile and their arrangements. In order to achieve such a goal, the sample-surface potential has theoretically formulated to include various shapes of the accumulated charges. Thereafter, the correspondence expression of the mirror plot curve is defined to link the geometrical distribution of charges. The resultant formula for the surface potential and mirror plot showed that the point charge approximation is a special case of the presented model. The formula of mirror-plot curve has put forward to be a detection tool for the actual build-up form that the electrons accumulating might take on the insulator surface. Simulation results have shown that the presented procedure could be adopted to search for the optimum distribution profile that may meet an experimental data. It is found that the most probable profile that accumulated electrons might form is the semi-hemispheric one. The surface of this profile is generally an ellipsoid of a variant axis rather a flat one. Results also reveal that, all the multipole-moment types could be formed for any shape of accumulation, but their weightiness progressively decreases whenever the pole-number increases. Furthermore, the configurations that trapped electrons arrange themselves within each distribution profile can be traced with the variation of scanning potential.