By implementing a scanning near-field optical microscope into the specimen
chamber of a scanning electron microscope, cathodoluminescence can be local
ly detected in the optical near-field. The achievable spatial resolution in
this set-up is only limited by the size of the aperture in a coated fibre
probe and its separation from the sample, rather than by the energy dissipa
tion volume of the primary electrons and diffusion processes of excess carr
iers inside the specimen, We demonstrate how electronically active defects
in polycrystalline diamond can be distinguished and localized with sub-wave
length lateral resolution by spectral filtering of the cathodoluminescence
signal.