 Everhart–Thornley detector

An Everhart–Thornley detector converts emitted electrons into an amplified optical signal in a scanning electron microscope. A positively biased collector attracts low-energy secondary electrons toward a scintillator; their impact produces light carried through a light guide to a photomultiplier.

The measured brightness depends on how many emitted electrons reach the collector, not just on how many leave the surface. Changing specimen tilt or collector bias can therefore change an image without changing composition. Comparing such settings helps identify collection-geometry effects in secondary-electron topographic contrast. ^[ref]