Abstract:
This work investigates the generation and detection of gaseous scintillation signals produced in
variable pressure scanning electron microscopy through electron-gas molecule excitation reactions.
Here a gaseous scintillation detection GSD system is developed to efficiently detect photons
produced via excitation reactions in electron cascades. Images acquired using GSD are compared to
those obtained using conventional gaseous secondary electron detection GSED and demonstrate
that images rich in secondary electron SE contrast can be achieved using the gaseous scintillation
signal. A theoretical model, based on existing Townsend theories, is developed. It describes the
production and amplification of photon signals generated by cascading SEs, high energy
backscattered electrons, and primary beam electrons. Photon amplification the total number of
photons produced per sample emissive electron is then investigated and compared to conventional
electronic amplification over a wide range of microscope operating parameters, scintillating imaging
gases, and photon collection geometries. These studies revealed that argon gas exhibited the largest
GSD gain, followed by nitrogen then water vapor, exactly opposite to the trend observed for
electron amplification data. It was also found that detected scintillation signals exhibit larger SE
signal-to-background levels compared to those of conventional electronic signals detected via
GSED. Finally, dragging the electron cascade towards the light pipe assemblage of GSD systems,
or electrostatic focusing, dramatically increases the collection efficiency of photons.
