ELECTRON-IRRADIATION DAMAGE IN NIO

The electron irradiation behavior of NiO has been systematically investigated in terms of beam energy and flux, crystal orientation, and surface environment, under both UHV (10-10 Torr) and non-UHV (10-7 Torr) conditions. The microscope vacuum was determined to be a major factor in the type of surface damage observed. Under UHV conditions, NiO showed only ballistic surface erosion. Under non-UHV conditions, electron-stimulated reactions occurred in competition with ballistic processes. In this case, the synergistic response of the material to both ionization and ballistic damage mechanisms generally resulted in more complicated surface structural changes and accelerated the erosion process. Reaction of the NiO surface with gaseous species in the microscope resulted in the formation of a Ni3O4 spinel phase. In the presence of reactive carbon, the NiO surface reduced to islands of metallic nickel. Encapsulation by a tenacious, graphitic carbon layer provided protection of the surface from electron irradiation damage. © 1990.