Everhart-Thomley detector

The most traditional secondary electron detector is the Everhart Thomley detector (Fig. 7.10). The low energy secondary electrons are easily attracted and deflected by the field produced by the collector (polarised grid at a voltage of+200V). This potential is sufficient to curve the trajectories of these electrons and guarantee a significant collection angle. The detector receives electrons even from object points not visible to it. 

SEM can be equipped with various detector systems like scintillator detectors (e.g., Everhart-Thomley detector) and solid state detectors. The standard setup contains a backscattered electron detector and a secondary electron detector. Since BSEs are deflected out of the specimen, the detector is mounted at the exit point of the electron beam. The collector system for SE and BSE are shown in Fig. 1. 

Secondary electrons are most frequently used for image formation and can be detected by a scintillator-photomultiplier combination (Everhart-Thomley detector. Fig. 80). A large fraction of slow SE is attracted by a positively biased grid... 

HRSEM images of STA-7 were taken using a JEOL JSM-7000F (FE SEM). Images of silicalite-2 and zeolite A were taken on a JEOL JSM-7401F (cold-FE SEM) using the Everhart-Thomley (E-T) secondary electron detector. Samples were not coated but placed on a conductive surface. 

Figure 7.10 Everhart Thomley type secondary electron detector (taken from F. Maurice, L. Meny and R. Ttxier, Microanalyse et microscopie electronique a balayage, 1978, with the permission of EDP Sciences, Les Ulis).

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