Thomley-Everhart secondary

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).

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. 

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. 

FIGURE 21>22 Diagram ol Everhart-Thomley secondary electron delector. Paths of secondary electrons (SE) and backscattered electrons (BE are shown. The scintillator is a phosphor that emits light when struck by energetic particles such as electrons, gamma rays, or radioactive particles. 

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... 

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