VERY-LOW ENERGY MICROSCOPY IN COMMERCIAL SEMS

Minimum necessary adaptations are described that are sufficient for ob taining very low energy electron micrographs (VLEEMs) from commerciall y available routine scanning electron micrographs (SEMs) with the elec trons accelerated to an energy of the order of tens of keV. A cathode lens inserted into the specimen chamber enables one to decelerate elec trons in front of the specimen surface to a desired low landing energy , which can be freely varied even down to zero. When a potential sligh tly more negative than the accelerating voltage is applied, a scanning mirror electron microscopy mode can be effected. The achievable point resolution at very low energies proves to be not too dependent on the objective lens parameters, so that the physical limit of aberrations of the homogeneous field of the cathode lens is nearly attainable. The detection efficiency for the standard Everhart-Thornley secondary ele ctron detector is discussed, and results for the routine Tesla BS 340 SEM are presented.