Or click here to return to our home page. First, one should understand that a SEM is more or less like a vacuum tube. Within a vacuum a heated filament emits electrons.
Electrons then come from the specimen.
The electrons are then detected by a scintillator. The scintillator converts the electrons to photons. The photons are amplified by a photomultiplier tube, which in turn produces an electrical signal that gives an output proportional to the electrons from the specimen. Thus, with proper electronics, the scanned specimen produces an electrical signal that can be converted to an image, the image being based on the electrons scattered or emitted from the specimen surface as it is scanned. Some SEMs, especially older ones, scan the image at the same time as another electron beam scans a video monitor.