Diamond is a wide band-gap semiconductor with many unique physical properties that make it an attractive technological material. One such property is the negative electron affinity (NEA) behavior of the surface when properly terminated with hydrogen or a thin metal layer. The NEA diamond surface exhibits an unusually large secondary electron (SE) yield which is desirable for applications in cold cathode electron emitters of flat panel displays. Examination of NEA diamond surfaces by scanning electron microscopy (SEM) has indicated that a unique mechanism appears to be responsible for the SE contrast in which sub-surface microstructural information is contained. This paper provides a brief interpretation of the origin of SE contrast from the NEA diamond surface.The electron affinity of a semiconductor surface, χ, is defined by the position of the vacuum energy level, E0, relative to the conduction band minimum, Ec (Fig. la). If χ>0, excited conduction band electrons must migrate to the surface and arrive with sufficient kinetic energy to overcome the surface energy barrier in order to escape into vacuum.
