Scanning Microscopy


The electric/magnetic quadrupole detector allow's efficient detection of secondary electrons in low voltage scanning electron microscopy without introducing disturbing aberrations. The original detector of this type was built in 1986; it has now been equipped with scintillator-photomultiplier assemblies on both positive electrodes. Their signals, A and B, can be combined to A+B or A-B, thus enhancing or suppressing different types of contrast. The aberration disc produced by the present design of detector was estimated to have a diameter of 10 nm. Experimentally, no deterioration of image resolution was observed. The collection efficiency was predicted to be 26% and can be better than 65% with an optimized collector size. For experimental determination, the detector was first calibrated by reflecting the primary beam of known current towards the scintillators. The detected proportion of secondary electrons was subsequently determined from the detected signal. The efficiency was found to be 20% which is in agreement with the theoretical value.

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