 The novel GDD has become possible first in the ESEM and has produced a practically 100% SE collection efficiency not previously possible with the Everhart-Thornley SE detector where the free trajectories of electrons in vacuum cannot all be bent towards the detector.As is further explained below, backscattered electrons can also be detected by the signal-gas interactions, so that various parameters of this generalized gaseous detector must be controlled to separate the BSE component out of the SE image.Therefore, care has been taken to produce nearly pure SE images with these detectors, then called ESD (environmental secondary detector) and GSED (gaseous secondary electron detector).